CiteULike: ljaeger's library [54 articles]

Separating brain regions involved in internally guided and visual feedback control of moving effectors: An event-related fMRI study

Kenji Ogawa — 2008-08-11T11:08:15-00:00

NeuroImage, Vol. 32, No. 4. (1 October 2006), pp. 1760-1770.

Online visual information of moving effectors plays important roles in visually guided movements. The present study used event-related functional resonance imaging to temporally separate neural activity associated with internally guided and visual feedback control of moving effectors. Using a cursor controlled by a computer mouse, participants traced curved lines on a screen. During this movement, vision of the moving cursor was occluded after tracing had begun and then was restored after variable intervals. The results showed that when visual feedback was unavailable, bilateral activation was significantly greater in the basal ganglia, thalamus, premotor cortex and mesial motor areas, peaking at the presupplementary motor area (pre-SMA). In contrast, when visual feedback was available, significantly greater activation was observed bilaterally in the posterior parietal cortex (PPC) and cerebellum and in the middle and inferior frontal gyri and occipito-temporal cortex in the right hemisphere. Pre-SMA activity was significantly negatively correlated with tracing error when visual feedback was unavailable. In contrast, right PPC activation showed a significant positive correlation with tracing error after visual feedback became available. These findings suggest that the pre-SMA is involved in internally guided movements in the absence of visual feedback, and that the PPC is related to visual feedback control by evaluating online visuomotor error. The current study clarifies the different functional roles of fronto-parietal and cerebellum circuits subserving visually guided movements regarding visual feedback control of effectors.

Fitts' law as the outcome of a dynamic noise filtering model of motor control

Gerard van Galen — 2008-08-05T09:05:24-00:00

Human Movement Science, Vol. 14, No. 4-5. (November 1995), pp. 539-571.

Studies into the real-time evolution of goal-directed movements have been strongly dominated by the view that movement time and other kinematic features are a direct reflection of on-line computational processes. Well-known examples of this position try to explain the logarithmic relation between the movement time of aiming movements and their demanded endpoint accuracy, as described by Fitts in 1954, by the use of centrally controlled servomechanisms and submovements. In the present article it is doubted whether such a strict cognitive approach can provide real understanding of the kinematics of aiming movements. An alternative, noise filtering model of motor control is presented proposing that the psychomotor system is an inherently noisy mechanical system for which spatial demands should be formulated in terms of a desired signal-to-noise ratio between goal-related propulsion of the limb (signal) and stochastic error (noise). Adequate movements would, from this point of view, result from the optimization between the application of muscle forces to the limb system and the noise reducing effects of biomechanical properties, such as stiffness, viscosity, or friction due to surface contact. At a theoretical level, the present approach is exemplified in a simulation model which takes into account the stochastic nature of the motor unit recruitment process and the noise filtering properties of a biomechanical limb. Empirical data acquired in a simulation study, as well as published data on eye-ball control during looking tasks and data on axial pen pressure control in graphic tasks, lend support to the view that adaptive control of muscular co-contraction is a relevant degree of freedom for the control of spatial accuracy.

Short-term learning of a visually guided power-grip task is associated with dynamic changes in EEG oscillatory activity

C Kranczioch — 2008-07-14T12:01:48-00:00

Clinical Neurophysiology, Vol. 119, No. 6. (June 2008), pp. 1419-1430.

Objective Performing a motor task after a period of training has been associated with reduced cortical activity and changes in oscillatory brain activity. Little is known about whether learning also affects the neural network associated with motor preparation and post movement processes. Here we investigate how short-term motor learning affects oscillatory brain activity during the preparation, execution, and post-movement stage of a force-feedback task.Methods Participants performed a visually guided power-grip tracking task. EEG was recorded from 64 scalp electrodes. Power and coherence data for the early and late stages of the task were compared.Results Performance improved with practice. During the preparation for the task alpha power was reduced for late experimental blocks. A movement execution-related decrease in beta power was attenuated with increasing task practice. A post-movement increase in alpha and lower beta activity was observed that decreased with learning. Coherence analysis revealed changes in cortico-cortical coupling with regard to the stage of the visuomotor task and with regard to learning. Learning was variably associated with increased coherence between contralateral and/or ipsilateral frontal and parietal, fronto-central, and occipital brain regions.Conclusions Practice of a visuomotor power-grip task is associated with various changes in the activity of a widespread cortical network. These changes might promote visuomotor learning.Significance This study provides important new evidence for and sheds new light on the complex nature of the brain processes underlying visuomotor integration and short-term learning.

Neural Basis for the Processes That Underlie Visually Guided and Internally Guided Force Control in Humans

David Vaillancourt — 2008-07-14T11:58:09-00:00

J Neurophysiol, Vol. 90, No. 5. (1 November 2003), pp. 3330-3340.

Despite an intricate understanding of the neural mechanisms underlying visual and motor systems, it is not completely understood in which brain regions humans transfer visual information into motor commands. Furthermore, in the absence of visual information, the retrieval process for motor memory information remains unclear. We report an investigation where visuomotor and motor memory processes were separated from only visual and only motor activation. Subjects produced precision grip force during a functional MRI (fMRI) study that included four conditions: rest, grip force with visual feedback, grip force without visual feedback, and visual feedback only. Statistical and subtractive logic analyses segregated the functional process maps. There were three important observations. First, along with the well-established parietal and premotor cortical network, the anterior prefrontal cortex, putamen, ventral thalamus, lateral cerebellum, intermediate cerebellum, and the dentate nucleus were directly involved in the visuomotor transformation process. This activation occurred despite controlling for the visual input and motor output. Second, a detailed topographic orientation of visuomotor to motor/sensory activity was mapped for the premotor cortex, parietal cortex, and the cerebellum. Third, the retrieval of motor memory information was isolated in the dorsolateral prefrontal cortex, ventral prefrontal cortex, and anterior cingulate. The motor memory process did not extend to the supplementary motor area (SMA) and the basal ganglia. These findings provide evidence in humans for a model where a distributed network extends over cortical and subcortical regions to control the visuomotor transformation process used during visually guided tasks. In contrast, a localized network in the prefrontal cortex retrieves force output from memory during internally guided actions. 10.1152/jn.00394.2003

Cortical activity in precision- versus power-grip tasks: an fMRI study.

HH Ehrsson — 2007-05-17T16:21:11-00:00

J Neurophysiol, Vol. 83, No. 1. (January 2000), pp. 528-536.

Most manual grips can be divided in precision and power grips on the basis of phylogenetic and functional considerations. We used functional magnetic resonance imaging to compare human brain activity during force production by the right hand when subjects used a precision grip and a power grip. During the precision-grip task, subjects applied fine grip forces between the tips of the index finger and the thumb. During the power-grip task, subjects squeezed a cylindrical object using all digits in a palmar opposition grasp. The activity recorded in the primary sensory and motor cortex contralateral to the operating hand was higher when the power grip was applied than when subjects applied force with a precision grip. In contrast, the activity in the ipsilateral ventral premotor area, the rostral cingulate motor area, and at several locations in the posterior parietal and prefrontal cortices was stronger while making the precision grip than during the power grip. The power grip was associated predominately with contralateral left-sided activity, whereas the precision-grip task involved extensive activations in both hemispheres. Thus our findings indicate that in addition to the primary motor cortex, premotor and parietal areas are important for control of fingertip forces during precision grip. Moreover, the ipsilateral hemisphere appears to be strongly engaged in the control of precision-grip tasks performed with the right hand.

An fMRI Study of the Role of the Medial Temporal Lobe in Implicit and Explicit Sequence Learning

Haline Schendan — 2008-05-22T07:03:00-00:00

Neuron, Vol. 37, No. 6. (27 March 2003), pp. 1013-1025.

fMRI was used to investigate the neural substrates supporting implicit and explicit sequence learning, focusing especially upon the role of the medial temporal lobe. Participants performed a serial reaction time task (SRTT). For implicit learning, they were naive about a repeating pattern, whereas for explicit learning, participants memorized another repeating sequence. fMRI analyses comparing repeating versus random sequence blocks demonstrated activation of frontal, parietal, cingulate, and striatal regions implicated in previous SRTT studies. Importantly, mediotemporal lobe regions were active in both explicit and implicit SRTT learning. Moreover, the results provide evidence of a role for the hippocampus and related cortices in the formation of higher order associations under both implicit and explicit learning conditions, regardless of conscious awareness of sequence knowledge.

Role of the posterior parietal cortex in updating reaching movements to a visual target.

M Desmurget — 2007-04-14T00:43:22-00:00

Nat Neurosci, Vol. 2, No. 6. (June 1999), pp. 563-567.

The exact role of posterior parietal cortex (PPC) in visually directed reaching is unknown. We propose that, by building an internal representation of instantaneous hand location, PPC computes a dynamic motor error used by motor centers to correct the ongoing trajectory. With unseen right hands, five subjects pointed to visual targets that either remained stationary or moved during saccadic eye movements. Transcranial magnetic stimulation (TMS) was applied over the left PPC during target presentation. Stimulation disrupted path corrections that normally occur in response to target jumps, but had no effect on those directed at stationary targets. Furthermore, left-hand movement corrections were not blocked, ruling out visual or oculomotor effects of stimulation.

Parietal cortex: from sight to action

Giacomo Rizzolatti — 2008-05-14T12:15:00-00:00

Current Opinion in Neurobiology, Vol. 7, No. 4. (August 1997), pp. 562-567.

Recent findings have altered radically our thinking about the functional role of the parietal cortex. According to this view, the parietal lobe consists of a multiplicity of areas with specific connections to the frontal lobe. These areas, together with the frontal areas to which they are connected, mediate distinct sensorimotor transformations related to the control of hand, arm, eye or head movements. Space perception is not unitary, but derives from the joint activity of the fronto-parietal circuits that control actions requiring space computation.

Grasping objects: the cortical mechanisms of visuomotor transformation

M Jeannerod — 2008-05-14T10:55:32-00:00

Trends in Neurosciences, Vol. 18, No. 7. (July 1995), pp. 314-320.

Grasping requires coding of the object's intrinsic properties (size and shape), and the transformation of these properties into a pattern of distal (finger and wrist) movements. Computational models address this behavior through the interaction of perceptual and motor schemas. In monkeys, the transformation of an object's intrinsic properties into specific grips takes place in a circuit that is formed by the inferior parietal lobule and the inferior premotor area (area F5). Neurons in both these areas code size, shape and orientation of objects, and specific types of grip that are necessary to grasp them. Grasping movements are coded more globally in the inferior parietal lobule, whereas they are more segmented in area F5. In humans, neuropsychological studies of patients with lesions to the parietal lobule confirm that primitive shape characteristics of an object for grasping are analyzed in the parietal lobe, and also demonstrate that this [`]pragmatic' analysis of objects is separated from the [`]semantic' analysis performed in the temporal lobe.

Brain Activation Related to the Representations of External Space and Body Scheme in Visuomotor Control

BM de Jong — 2008-05-13T13:29:47-00:00

NeuroImage, Vol. 14, No. 5. (November 2001), pp. 1128-1135.

Regional cerebral blood flow was assessed during reaching movements with either target or finger selection. Measurements were performed with positron emission tomography in normal subjects. We thus identified two patterns of cerebral activation representing parietal command functions based on either external space or body scheme information. Directing the right-hand index finger toward one target dot in an array of five was related to activations distributed over dorsal extrastriate visual cortex (putative area V3A), along the parieto-occipital sulcus (putative V6/V6A) and the posterior intraparietal sulcus (IPS). Right-hemisphere dominance was present at the occipital extension of posterior IPS. Positioning one right-hand finger of five on the middle target dot was related with anterior IPS activation, extending over the marginal gyrus of the left inferior parietal lobe. The latter indicated a parietal role in prehension, independent of the shape of the target reached for. In both conditions of the reaching task, instructions for movement were auditorily given by random numbers 1 to 5, thus excluding visual cueing. The observed lateralization of movement-related parietal functions helps to explain neurological symptoms such as ideomotor apraxia and spatial hemineglect.

Functional properties and interaction of the anterior and posterior intraparietal areas in humans

Elisa Shikata — 2008-05-13T13:28:10-00:00

European Journal of Neuroscience, Vol. 17, No. 5. (2003), pp. 1105-1110.

Abstract In the monkey the lateral bank of the anterior part of the intraparietal sulcus (area AIP), contains neurons that are involved in visually guided, object-related hand movements. It has also been shown that neurons in the caudal part of the intraparietal sulcus (area CIP) preferentially respond to 3D surface orientation. According to these results, it has been hypothesized that neurons in area CIP primarily encode the 3D features of an object and forwards this information to area AIP. AIP then utilizes this information for appropriate hand actions towards the object. Based on analogies to these primate studies, recent neuroimaging studies have suggested human homologues of areas AIP and CIP, however, the functional interaction between these areas remains unclear. Our event related fMRI study was designed to address specifically the question, how CIP and AIP interact in the process of adjustment of hand orientation towards objects. Volunteers were asked to perform three tasks: discrimination of surface orientation, imaging of visually guided hand movements and execution of visually guided hand movements. Our data show that the human AIP was activated both during discrimination of surface orientation and during the subsequent spatial adjustment of the thumb and index finger position towards the surface orientation. In contrast, human CIP was activated by the surface orientation but not by spatial adjustment of finger position. These data clearly indicate that the function of human CIP is more involved in coding 3D features of the objects, whereas human AIP is more involved in visually guided hand movements, similar to its role in the monkey.

Human medial intraparietal cortex subserves visuomotor coordinate transformation

Christian Grefkes — 2008-04-29T02:37:45-00:00

NeuroImage, Vol. 23, No. 4. (December 2004), pp. 1494-1506.

In the macaque, the posterior parietal cortex (PPC) integrates multimodal sensory information for planning and coordinating complex movements. In particular, the areas around the intraparietal sulcus (IPS) serve as an interface between the sensory and motor systems to allow for coordinated movements in space. Because recent imaging studies suggest a comparable functional and anatomical organization of human and monkey IPS, we hypothesized that in humans, as in macaques, the medial intraparietal cortex (area MIP) subserves visuomotor transformations. To test this hypothesis, changes of neural activity were measured using functional magnetic resonance imaging (fMRI) while healthy subjects performed a joystick paradigm similar to the ones previously employed in macaques for studying area MIP. As hypothesized, visuomotor coordinate transformation subserving goal-directed hand movements activated superior parietal cortex with the local maximum of increased neural activity lying in the medial wall of IPS. Compared to the respective visuomotor control conditions, goal-directed hand movements under predominantly proprioceptive control activated a more anterior part of medial IPS, whereas posterior medial IPS was more responsive to visually guided hand movements. Contrasting the two coordinate transformation conditions, changing the modality of movement guidance (visual/proprioceptive) did not significantly alter the BOLD signal within IPS but demonstrated differential recruitment of modality specific areas such as V5/MT and sensorimotor cortex/area 5, respectively. The data suggest that the human medial intraparietal cortex subserves visuomotor transformation processes to control goal-directed hand movements independently from the modality-specific processing of visual or proprioceptive information.

Activity in the parietal area during visuomotor learning with optical rotation.

Kentaro Inoue — 2008-05-13T09:05:34-00:00

Cognitive Neuroscience and Neuropsychology, Vol. 8, No. 18. (1997), pp. 3979-3983.

A Blueprint for Movement: Functional and Anatomical Representations in the Human Motor System

Michel Rijntjes — 2008-05-07T08:47:47-00:00

J. Neurosci., Vol. 19, No. 18. (15 September 1999), pp. 8043-8048.

Despite a clear somatotopic organization of the motor cortex, a movement can be learned with one extremity and performed with another. This suggests that there exists a limb-independent coding for movements. To dissociate brain regions coding for movement parameters from those relevant to the chosen effector, subjects wrote their signature with their dominant index finger and ipsilateral big toe, and we determined those areas activated by both conditions using functional magnetic resonance imaging. The results show that movement parameters for this highly trained movement are stored in secondary sensorimotor cortices of the extremity with which it is usually performed, i.e., the dominant hand, including dorsal and ventral lateral premotor cortices. These areas can be accessed by the foot and are therefore functionally independent from the primary representation of the effector. Thus, somatotopy in secondary structures in the human motor system seems to be defined functionally, and not on the basis of anatomical representations.

Motor learning in man: A review of functional and clinical studies

Ulrike Halsband — 2006-08-24T15:37:13-00:00

Journal of Physiology-Paris, Vol. 99, No. 4-6. (June 2006), pp. 414-424.

This chapter reviews results of clinical and functional imaging studies which investigated the time-course of cortical and subcortical activation during the acquisition of motor a skill.During the early phases of learning by trial and error, activation in prefrontal areas, especially in the dorsolateral prefrontal cortex, is has been reported. The role of these areas is presumably related to explicit working memory and the establishment of a novel association between visual cues and motor commands. Furthermore, motor associated areas of the right hemisphere and distributed cerebellar areas reveal strong activation during the early motor learning. Activation in superior-posterior parietal cortex presumably arises from visuospatial processes, while sensory feedback is coded in the anterior-inferior parietal cortex and the neocerebellar structures.With practice, motor associated areas of the left-hemisphere reveal increased activity. This shift to the left hemisphere has been observed regardless of the hand used during training, indicating a left-hemispheric dominance in the storage of visuomotor skills. Concerning frontal areas, learned actions of sequential character are represented in the caudal part of the supplementary motor area (SMA proper), whereas the lateral premotor cortex appears to be responsible for the coding of the association between visuo-spatial information and motor commands.Functional imaging studies which investigated the activation patterns of motor learning under implicit conditions identified for the first, a motor circuit which includes lateral premotor cortex and SMA proper of the left hemisphere and primary motor cortex, for the second, a cognitive loop which consists of basal ganglia structures of the right hemisphere. Finally, activity patterns of intermanual transfer are discussed. After right-handed training, activity in motor associated areas maintains during performance of the mirror version, but is increased during the performance of the original-oriented version with the left hand. In contrary, increased activity during the mirror reversed action, but not during the original-oriented performance of the untrained right hand is observed after left-handed training.These results indicate the transfer of acquired right-handed information which reflects the mirror symmetry of the body, whereas spatial information is mainly transferred after left-handed training. Taken together, a combined approach of clinical lesion studies and functional imaging is a promising tool for identifying the cerebral regions involved in the process of motor learning and provides insight into the mechanisms underlying the generalisation of actions.

Motor cortex activation is related to force of squeezing

Steven Cramer — 2008-03-18T14:14:29-00:00

Human Brain Mapping, Vol. 16, No. 4. (2002), pp. 197-205.

Primate studies have demonstrated that motor cortex neurons show increased activity with increased force of movement. In humans, this relationship has received little study during a power grip such as squeezing, and has previously only been evaluated across a narrow range of forces. Functional MRI was performed in eight healthy subjects who alternated between rest and right hand squeezing at one of three force levels. During scanning, motor performances were recorded using a dynamometer. At each force level, activation volume was measured within left sensorimotor cortex, right sensorimotor cortex, and a midline supplementary motor area. In left sensorimotor cortex, % signal change was also assessed. The range of force generated across the three force levels varied from 4.9 N to 276 N. In left sensorimotor cortex, activation volume increased significantly with greater force. The % signal change also increased with greater force and correlated closely with activation volume. In supplementary motor area, activation volume increased significantly with increasing force, but with greater intersubject variability. In right sensorimotor cortex, a trend for larger activation volumes with greater force did not reach significance. The laterality index, an expression of the relative degree of contralateral vs. ipsilateral sensorimotor cortex activation, did not change across the three force levels. Increased force of squeezing is associated with increased contralateral sensorimotor cortex and supplementary motor area activation. This relationship was found across the full spectrum of forces that the human hand is capable of generating. Use of a valid, reliable method for assessing motor behavior during functional MRI may be important to clinical applications. Hum. Brain Mapping 16:197-205, 2002. © 2002 Wiley-Liss, Inc.

Lateralization of the posterior parietal cortex for internal monitoring of self- versus externally generated movements.

Kenji Ogawa — 2008-03-18T13:41:38-00:00

Journal of Cognitive Neuroscience, Vol. 19, No. 11. (2007), pp. 1827-1835.

Imaging the premotor areas

Nathalie Picard — 2008-03-11T13:27:51-00:00

Current Opinion in Neurobiology, Vol. 11, No. 6. (1 December 2001), pp. 663-672.

Recent imaging studies of motor function provide new insights into the organization of the premotor areas of the frontal lobe. The pre-supplementary motor area and the rostral portion of the dorsal premotor cortex, the `pre-PMd', are, in many respects, more like prefrontal areas than motor areas. Recent data also suggest the existence of separate functional divisions in the rostral cingulate zone.

Strengthening horizontal cortical connections following skill learning

MS Rioult-Pedotti — 2008-02-29T13:00:53-00:00

Nature Neuroscience, Vol. 1 (1998), pp. 230-234.

Learning a new motor skill requires an alteration in the spatiotemporal pattern of muscle activation. Motor areas of cerebral neocortex are thought to be involved in this type of learning, possibly by functional reorganization of cortical connections. Here we show that skill learning is accompanied by changes in the strength of connections within adult rat primary motor cortex (M1). Rats were trained for three or five days in a skilled reaching task with one forelimb, after which slices of motor cortex were examined to determine the effect of training on the strength of horizontal intracortical connections in layer II/III. The amplitude of field potentials in the forelimb region contralateral to the trained limb was significantly increased relative to the opposite 'untrained' hemisphere. No differences were seen in the hindlimb region. Moreover, the amount of long-term potentiation (LTP) that could be induced in trained M1 was less than in controls, suggesting that the effect of training was at least partly due to LTP-like mechanisms. These data represent the first direct evidence that plasticity of intracortical connections is associated with learning a new motor skill.

Combining spatial extent and peak intensity to test for activations in functional imaging.

JB Poline — 2007-03-18T16:12:03-00:00

Neuroimage, Vol. 5, No. 2. (February 1997), pp. 83-96.

Within the framework of statistical mapping, there are up to now only two tests used to assess the regional significance in functional images. One is based on the magnitude of the foci and tends to detect high intensity signals, while the second is based on the spatial extent of regions defined by a simple thresholding of the statistical map, a test that is more sensitive to extended signals. The aim of this paper is to combine the two tests into a single test that is more sensitive to a wider range of signals. This combined test is based on an analytical approximation of the distribution of these two parameters (size and height) and is applied in the context of statistical maps. The risk of error in noise-only 2D or 3D volumes is assessed under a wide range of experimental conditions obtained by varying both the resolution of the map and the threshold at which clusters are defined. In addition, we have investigated this new test on simulated signals, and applied it to an experimental PET dataset. The experimental risk of error is close to the predicted one, and the overall sensitivity increases when analyzing a volume containing different types of signals.

Sleep-Related Consolidation of a Visuomotor Skill: Brain Mechanisms as Assessed by Functional Magnetic Resonance Imaging

Pierre Maquet — 2008-02-29T12:50:49-00:00

J. Neurosci., Vol. 23, No. 4. (15 February 2003), pp. 1432-1440.

Subjects were trained on a pursuit task in which the target trajectory was predictable only on the horizontal axis. Half of them were sleep deprived on the first post-training night (n = 13). Three days later, functional magnetic resonance imaging revealed task-related increases in brain responses to the learned trajectory, as compared with a new trajectory. In the sleeping group (n = 12) as compared with the sleep-deprived group, subjects' performance was improved, and their brain activity was greater in the superior temporal sulcus (STS). Increased functional connectivity was observed between the STS and the cerebellum and between the supplementary eye field and the frontal eye field. These differences indicate sleep-related plastic changes during motor skill learning in areas involved in smooth pursuit eye movements.

Brain activity correlates differentially with increasing temporal complexity of rhythms during initialisation, synchronisation, and continuation phases of paced finger tapping.

PA Lewis — 2008-02-29T12:47:27-00:00

Neuropsychologia, Vol. 42, No. 10. (2004), pp. 1301-1312.

Activity in parts of the human motor system has been shown to correlate with the complexity of performed motor sequences in terms of the number of limbs moved, number of movements, and number of trajectories. Here, we searched for activity correlating with temporal complexity, in terms of the number of different intervals produced in the sequence, using an overlearned tapping task. Our task was divided into three phases: movement selection and initiation (initiate), synchronisation of finger tapping with an external auditory cue (synchronise), and continued tapping in absence of the auditory pacer (continue). Comparisons between synchronisation and continuation showed a pattern in keeping with prior neuroimaging studies of paced finger tapping. Thus, activation of bilateral SMA and basal ganglia was greater in continuation tapping than in synchronisation tapping. Parametric analysis revealed activity correlating with temporal complexity during initiate in bilateral supplementary and pre-supplementary motor cortex (SMA and preSMA), rostral dorsal premotor cortex (PMC), basal ganglia, and dorsolateral prefrontal cortex (DLPFC), among other areas. During synchronise, correlated activity was observed in bilateral SMA, more caudal dorsal and ventral PMC, right DLPFC and right primary motor cortex. No correlated activity was observed during continue at P<0.01 (corrected, cluster level), though left angular gyrus was active at P<0.05. We suggest that the preSMA and rostral dorsal PMC activities during initiate may be associated with selection of timing parameters, while activation in centromedial prefrontal cortex during both initiate and synchronise may be associated with temporal error monitoring or correction. The absence of activity significantly correlated with temporal complexity during continue suggests that, once an overlearned timed movement sequence has been selected and initiated, there is no further adjustment of the timing control processes related to its continued production in absence of external cues.

Anatomy of motor learning. II. Subcortical structures and learning by trial and error.

M Jueptner — 2005-10-07T12:14:17-00:00

J Neurophysiol, Vol. 77, No. 3. (March 1997), pp. 1325-1337.

We used positron emission tomography to study motor learning by trial and error. Subjects learned sequences of eight finger movements. Tones generated by a computer told the subjects whether any particular move was correct or incorrect. A control condition was used in which the subjects generated moves, but there was no feedback to indicate success or failure, and so on learning occurred. In this condition (free selection) the subjects were required to make a finger movement on each trial and to vary the movements randomly over trials. The subjects had a free choice of which finger to move on any one trial. On this task there was no systematic change in responses over trials and no change in the response times. Two other conditions were included. In one the subjects repetitively moved the same finger on all trials and in a baseline condition the subjects heard the pacing tones and auditory feedback but made no movements. Comparing new learning with the free selection task, there was a small activation in the right prefrontal cortex. This may reflect the fact that in new learning, but not free selection, the subject rehearse past moves and adapt their responses accordingly. The caudate nucleus was strongly activated during new learning. It is suggested that this activity may be related either to mental rehearsal or to reinforcement of the movements as a consequence of the outcomes. The putamen was activated anteriorly on the free selection task and more posteriorly when the subjects repetitively made the same movement. It is suggested that the differences in the location of the peak activation in the striatum may represent the operation of different corticostriatal loops. The cerebellar nuclei (bilaterally) and vermis were more active in the new learning condition than during the performance of the free selection task. There was no difference in the activation of the cerebellum when the free selection task was compared with repetitive performance of the same movement. We tentatively suggest that the basal ganglia may be involved in the specification of movement on the basis of memory of either the movements or the outcomes, but that the cerebellum may be more directly involved in changes in the parameters of movement execution.

Distinct contribution of the cortico-striatal and cortico-cerebellar systems to motor skill learning

Julien Doyon — 2007-11-30T16:09:04-00:00

Neuropsychologia, Vol. 41, No. 3. (2003), pp. 252-262.

This review paper focuses on studies in healthy human subjects that examined the functional neuroanatomy and cerebral plasticity associated with the learning, consolidation and retention phases of motor skilled behaviors using modern brain imaging techniques. Evidence in support of a recent model proposed by Doyon and Ungerleider [Functional Anatomy of Motor Skill Learning. In: Squire LR, Schacter DL, editors. Neuropsychology of Memory. New York: Guilford Press, 2002.] is also discussed. The latter suggests that experience-dependent changes in the brain depend not only on the stage of learning, but also on whether subjects are required to learn a new sequence of movements (motor sequence learning) or learn to adapt to environmental perturbations (motor adaptation). This model proposes that the cortico-striatal and cortico-cerebellar systems contribute differentially to motor sequence learning and motor adaptation, respectively, and that this is most apparent during the slow learning phase (i.e. automatization) when subjects achieve asymptotic performance, as well as during reactivation of the new skilled behavior in the retention phase.

Functional Anatomy of Visuomotor Skill Learning in Human Subjects Examined with Positron Emission Tomography

Julien Doyon — 2008-02-29T12:26:11-00:00

European Journal of Neuroscience, Vol. 8, No. 4. (1996), pp. 637-648.

Abstract The present study was designed to examine patterns of regional cerebral blood flow (CBF) associated with the learning of a repeated visuomotor sequence both in the early and late phases of the acquisition process. In addition, changes in blood flow related to the implicit versus explicit aspects of learning such a skill were investigated. Fourteen normal control subjects were scanned while performing the task (i) in both early and advanced learning stages of the visuomotor sequence; (ii) after having acquired explicit knowledge of the sequences; and (iii) in two control conditions (perceptual and random sequence). Subtraction of the random condition from the highly learned condition revealed specific areas of activity in the right ventral striatum and dentate nucleus of the cerebellum. Blood flow changes in the right hemisphere were also seen in the medial posterior parietal and prestriate regions, as well as in the anterior cingulate cortex. Finally, once the subjects had acquired explicit knowledge of the embedded sequence that was presented in the highly learned condition, increased CBF activity was observed only in the mid-ventrolateral frontal area in the right hemisphere. These findings confirm that both the striatum and the cerebellum are involved in the implicit acquisition of a visuomotor skill, especially in the advanced stages of the learning process, and furthermore that the ventrolateral prefrontal cortex contributes preferentially to the declarative aspect of this task.

Role of the striatum, cerebellum and frontal lobes in the automatization of a repeated visuomotor sequence of movements

Julien Doyon — 2008-02-29T12:22:58-00:00

Neuropsychologia, Vol. 36, No. 7. (1 June 1998), pp. 625-641.

Recently, Doyon et al. [20] demonstrated that lesions to both the striatum and to the cerebellum in humans produce a similar deficit in the learning of a repeated visuomotor sequence, which occurs late in the acquisition process. We now report the results of two experiments that were designed to examine whether this impairment was due to a lack of automatization of the repeating sequence of finger movements by using a dual-task paradigm and by testing for long-term retention of this skill. In Experiment 1, the performance of groups of patients with Parkinson's disease, or with damage to the cerebellum or to the frontal lobes, was compared to that of matched control subjects on the Repeated Sequence Test (primary task) and the Brooks' Matrices Test (secondary task). These two tests were administered concomitantly in both early and late learning phases of the visuomotor sequence. Overall, the groups did not differ in their ability to execute the primary task. By contrast, in accordance with the predictions, patients in Stages 2-3 of Parkinson's disease or with a cerebellar lesion failed to reveal the expected increase in performance on the secondary task seen with learning, suggesting that the latter groups of patients did not have access to the same level of residual cognitive resources to complete the matrices compared to controls. In Experiment 2, the same groups of patients and control subjects were retested again 10-18 months later. They were given four blocks of 100 trials each of the repeating sequence task, followed by a questionnaire and a self-generation task that measured their declarative knowledge of that sequence. The results revealed a long-term retention impairment only in patients who changed from Stage I to Stage II of the disease (suggesting further striatal degeneration) during the one-year interval, or who had a cerebellar lesion. By contrast, performance of the three clinical groups did not differ from controls on declarative memory tests. These findings suggest that both the striatum and the cerebellum participate to the automatization process during the late (slow) learning stage of a sequence of finger movements and that these structures also play a role in the neuronal mechanism subserving long-term retention of such a motor sequence behavior.

Rapid Plasticity of Human Cortical Movement Representation Induced by Practice

Joseph Classen — 2008-02-29T12:14:59-00:00

J Neurophysiol, Vol. 79, No. 2. (1 February 1998), pp. 1117-1123.

Temporal autocorrelation in univariate linear modeling of FMRI data.

MW Woolrich — 2006-04-16T16:03:45-00:00

Neuroimage, Vol. 14, No. 6. (December 2001), pp. 1370-1386.

In functional magnetic resonance imaging statistical analysis there are problems with accounting for temporal autocorrelations when assessing change within voxels. Techniques to date have utilized temporal filtering strategies to either shape these autocorrelations or remove them. Shaping, or "coloring," attempts to negate the effects of not accurately knowing the intrinsic autocorrelations by imposing known autocorrelation via temporal filtering. Removing the autocorrelation, or "prewhitening," gives the best linear unbiased estimator, assuming that the autocorrelation is accurately known. For single-event designs, the efficiency of the estimator is considerably higher for prewhitening compared with coloring. However, it has been suggested that sufficiently accurate estimates of the autocorrelation are currently not available to give prewhitening acceptable bias. To overcome this, we consider different ways to estimate the autocorrelation for use in prewhitening. After high-pass filtering is performed, a Tukey taper (set to smooth the spectral density more than would normally be used in spectral density estimation) performs best. Importantly, estimation is further improved by using nonlinear spatial filtering to smooth the estimated autocorrelation, but only within tissue type. Using this approach when prewhitening reduced bias to close to zero at probability levels as low as 1 x 10(-5).

The Time Course of Changes during Motor Sequence Learning: A Whole-Brain fMRI Study

Ivan Toni — 2007-04-04T16:22:27-00:00

NeuroImage, Vol. 8, No. 1. (July 1998), pp. 50-61.

There is a discrepancy between the results of imaging studies in which subjects learn motor sequences. Some experiments have shown decreases in the activation of some areas as learning increased, whereas others have reported learning-related increases as learning progressed. We have exploited fMRI to measure changes in blood oxygen level-dependent (BOLD) signal throughout the course of learning. T2*-weighted echo-planar images were acquired over the whole brain for 40 min while the subjects learned a sequence eight moves long by trial and error. The movements were visually paced every 3.2 s and visual feedback was provided to the subjects. A baseline period followed each activation period. The effect due to the experimental conditions was modeled using a square-wave function, time locked to their occurrence. Changes over time in the difference between activation and baseline signal were modeled using a set of polynomial basis functions. This allowed us to take into account linear as well as nonlinear changes over time. Low-frequency changes over time common to both activation and baseline conditions (and thus not learning related) were modeled and removed. Linear and nonlinear changes of BOLD signal over time were found in prefrontal, premotor, and parietal cortex and in neostriatal and cerebellar areas. Single-unit recordings in nonhuman primates during the learning of motor tasks have clearly shown increased activity early in learning, followed by a decrease as learning progressed. Both phenomena can be observed at the population level in the present study.

Transition of Brain Activation from Frontal to Parietal Areas in Visuomotor Sequence Learning

Katsuyuki Sakai — 2008-02-28T09:07:04-00:00

J. Neurosci., Vol. 18, No. 5. (1 March 1998), pp. 1827-1840.

We studied the neural correlates of visuomotor sequence learning using functional magnetic resonance imaging (fMRI). In the test condition, subjects learned, by trial and error, the correct order of pressing two buttons consecutively for 10 pairs of buttons (2 x 10 task); in the control condition, they pressed buttons in any order. Comparison between the test condition and the control condition revealed four brain areas specifically related to learning: the dorsolateral prefrontal cortex (DLPFC), the presupplementary motor area (pre-SMA), the precuneus, and the intraparietal sulcus (IPS). We found that the time course of activation during learning was different between these areas. To normalize the individual differences in the speed of learning, we classified the performance of each subject into three learning stages: early, intermediate, and advanced stages. Both the relative increase of signal intensity and the number of activated pixels within the four areas showed significant changes across the learning stages, with different time courses. The two frontal areas, DLPFC and pre-SMA, were activated in the earlier stages of learning, whereas the two parietal areas, precuneus and IPS, were activated in the later stages. Specifically, DLPFC, pre-SMA, precuneus, and IPS were most highly activated in the early stage, in both the early and intermediate stages, in the intermediate stage, and in both the intermediate and advanced stages, respectively. The results suggest that the acquisition of visuomotor sequences requires frontal activation, whereas the retrieval of visuomotor sequences requires parietal activation, which might reflect the transition from the declarative stage to the procedural stage.

Parietal cortex and movement

MFS Rushworth — 2008-02-28T09:02:21-00:00

Experimental Brain Research, Vol. 117, No. 2. (November 1997), pp. 292-310.

Recording studies in the parietal cortex have demonstrated single-unit activity in relation to sensory stimulation and during movement. We have performed three experiments to assess the effect of selective parietal lesions on sensory motor transformations. Animals were trained on two reaching tasks: reaching in the light to visual targets and reaching in the dark to targets defined by arm position. The third task assessed non-standard, non-spatial stimulus response mapping; in the conditional motor task animals were trained to either pull or turn a joystick on presentation of either a red or a blue square. We made two different lesions in the parietal cortex in two groups of monkeys. Three animals received bilateral lesions of areas 5, 7b and MIP, which have direct connections with the premotor and motor cortices. The three other animals subsequently received bilateral lesions in areas 7a, 7ab and LIP. Both groups were still able to select between movements arbitrarily associated with non-spatial cues in the conditional motor task. Removal of areas 7a, 7ab and LIP caused marked inaccuracy in reaching in the light to visual targets but had no effect on reaching in the dark. Removal of areas 5, 7b and MIP caused misreaching in the dark but had little effect on reaching in the light. The results suggest that the two divisions of the parietal cortex organize limb movements in distinct spatial coordinate systems. Area 7a/7ab/LIP is essential for spatial coordination of visual motor transformations. Area 5/7b/MIP is essential for the spatial coordination of arm movements in relation to proprioceptive and efference copy information. Neither part of the parietal lobe appears to be important for the non-standard, non-spatial transformations of response selection.

Dynamic Cortical and Subcortical Networks in Learning and Delayed Recall of Timed Motor Sequences

Virginia Penhune — 2007-01-29T21:08:31-00:00

J. Neurosci., Vol. 22, No. 4. (15 February 2002), pp. 1397-1406.

We used positron emission tomography to examine learning and retention of timed motor sequences. Subjects were scanned during learning (LRN) and baseline (ISO) on 3 d: day 1, after 5 d of practice (day 5) and after a 4 week delay (recall). Blood flow was compared across days of learning and between the LRN and ISO conditions. Overall, significant changes in activity were seen across days for the LRN condition, but not the ISO baseline. Day 1 results revealed extensive activation in the cerebellar cortex, particularly lobules III/IV and VI. Day 5 results showed increased activity in the basal ganglia (BG) and frontal lobe, with no significant cerebellar activity. At recall, significantly greater activity was seen in M1, premotor, and parietal cortex. Blood flow in the cerebellum decreased significantly between day 1 and recall. These results reveal a dynamic network of motor structures that are differentially active during different phases of learning and delayed recall. For the first time our findings show that recall of motor sequences in humans is mediated by a predominantly cortical network. Based on these results, we suggest that during early learning cerebellar mechanisms are involved in adjusting movement kinematics according to sensory input to produce accurate motor output. Thereafter, the cerebellar mechanisms required for early learning are no longer called into play. During late learning, the BG may be involved in automatization. At delayed recall, movement parameters appear to be encoded in a distributed representation mediated by M1, premotor, and parietal cortex.

Roles of Cerebellar Cortex and Nuclei in Motor Learning: Contradictions or Clues?

Michael Mauk — 2008-02-28T08:47:52-00:00

Neuron, Vol. 18 (1997), pp. 343-346.

The cerebellum, with its relatively simple and regular synaptic organization, has yielded much about its contribution to brain function and its internal information processing. A central theme that has emerged is the cerebellum's role in the adaptation or learning of movements. Ideas about cerebellar-mediated motor learning began in the 1960s, most notably with the seminal theory proposed by [12]. The basic tenets of this theory are supported by numerous studies. In particular, analysis of two forms of motor learning, adaptation of the vestibulo-ocular reflex (VOR) and Pavlovian eyelid conditioning (EC), has revealed much about cerebellar contributions to motor learning and the cerebellar information processing involved.

Neurophysiological investigation of the basis of the fMRI signal.

NK Logothetis — 2005-09-29T20:08:57-00:00

Nature, Vol. 412, No. 6843. (12 July 2001), pp. 150-157.

Functional magnetic resonance imaging (fMRI) is widely used to study the operational organization of the human brain, but the exact relationship between the measured fMRI signal and the underlying neural activity is unclear. Here we present simultaneous intracortical recordings of neural signals and fMRI responses. We compared local field potentials (LFPs), single- and multi-unit spiking activity with highly spatio-temporally resolved blood-oxygen-level-dependent (BOLD) fMRI responses from the visual cortex of monkeys. The largest magnitude changes were observed in LFPs, which at recording sites characterized by transient responses were the only signal that significantly correlated with the haemodynamic response. Linear systems analysis on a trial-by-trial basis showed that the impulse response of the neurovascular system is both animal- and site-specific, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses. These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output.

Functional MRI evidence for adult motor cortex plasticity during motor skill learning.

A Karni — 2006-08-31T19:17:01-00:00

Nature, Vol. 377, No. 6545. (14 September 1995), pp. 155-158.

Performance of complex motor tasks, such as rapid sequences of finger movements, can be improved in terms of speed and accuracy over several weeks by daily practice sessions. This improvement does not generalize to a matched sequence of identical component movements, nor to the contralateral hand. Here we report a study of the neural changes underlying this learning using functional magnetic resonance imaging (MRI) of local blood oxygenation level-dependent (BOLD) signals evoked in primary motor cortex (M1). Before training, a comparable extent of M1 was activated by both sequences. However, two ordering effects were observed: repeating a sequence within a brief time window initially resulted in a smaller area of activation (habituation), but later in larger area of activation (enhancement), suggesting a switch in M1 processing mode within the first session (fast learning). By week 4 of training, concurrent with asymptotic performance, the extent of cortex activated by the practised sequence enlarged compared with the unpractised sequence, irrespective of order (slow learning). These changes persisted for several months. The results suggest a slowly evolving, long-term, experience-dependent reorganization of the adult M1, which may underlie the acquisition and retention of the motor skill.

Imaging Brain Plasticity during Motor Skill Learning

Leslie Ungerleider — 2008-02-28T08:25:10-00:00

Neurobiology of Learning and Memory, Vol. 78, No. 3. (November 2002), pp. 553-564.

The search for the neural substrates mediating the incremental acquisition of skilled motor behaviors has been the focus of a large body of animal and human studies in the past decade. Much less is known, however, with regard to the dynamic neural changes that occur in the motor system during the different phases of learning. In this paper, we review recent findings, mainly from our own work using fMRI, which suggest that: (i) the learning of sequential finger movements produces a slowly evolving reorganization within primary motor cortex (M1) over the course of weeks and (ii) this change in M1 follows more dynamic, rapid changes in the cerebellum, striatum, and other motor-related cortical areas over the course of days. We also briefly review neurophysiological and psychophysical evidence for the consolidation of motor skills, and we propose a working hypothesis of its underlying neural substrate in motor sequence learning.

Anatomy of Motor Learning. I. Frontal Cortex and Attention to Action

M Jueptner — 2008-02-28T08:20:02-00:00

J Neurophysiol, Vol. 77, No. 3. (1 March 1997), pp. 1313-1324.

A global optimisation method for robust affine registration of brain images

Mark Jenkinson — 2008-02-28T08:15:50-00:00

Medical Image Analysis, Vol. 5, No. 2. (June 2001), pp. 143-156.

Registration is an important component of medical image analysis and for analysing large amounts of data it is desirable to have fully automatic registration methods. Many different automatic registration methods have been proposed to date, and almost all share a common mathematical framework -- one of optimising a cost function. To date little attention has been focused on the optimisation method itself, even though the success of most registration methods hinges on the quality of this optimisation. This paper examines the assumptions underlying the problem of registration for brain images using inter-modal voxel similarity measures. It is demonstrated that the use of local optimisation methods together with the standard multi-resolution approach is not sufficient to reliably find the global minimum. To address this problem, a global optimisation method is proposed that is specifically tailored to this form of registration. A full discussion of all the necessary implementation details is included as this is an important part of any practical method. Furthermore, results are presented for inter-modal, inter-subject registration experiments that show that the proposed method is more reliable at finding the global minimum than several of the currently available registration packages in common usage.

Improved Optimization for the Robust and Accurate Linear Registration and Motion Correction of Brain Images

Mark Jenkinson — 2006-10-30T06:56:47-00:00

NeuroImage, Vol. 17, No. 2. (October 2002), pp. 825-841.

Linear registration and motion correction are important components of structural and functional brain image analysis. Most modern methods optimize some intensity-based cost function to determine the best registration. To date, little attention has been focused on the optimization method itself, even though the success of most registration methods hinges on the quality of this optimization. This paper examines the optimization process in detail and demonstrates that the commonly used multiresolution local optimization methods can, and do, get trapped in local minima. To address this problem, two approaches are taken: (1) to apodize the cost function and (2) to employ a novel hybrid global-local optimization method. This new optimization method is specifically designed for registering whole brain images. It substantially reduces the likelihood of producing misregistrations due to being trapped by local minima. The increased robustness of the method, compared to other commonly used methods, is demonstrated by a consistency test. In addition, the accuracy of the registration is demonstrated by a series of experiments with motion correction. These motion correction experiments also investigate how the results are affected by different cost functions and interpolation methods.

Motor sequence learning: a study with positron emission tomography

Ih Jenkins — 2007-04-04T14:37:53-00:00

J. Neurosci., Vol. 14, No. 6. (1 June 1994), pp. 3775-3790.

Attention and stimulus characteristics determine the locus of motor- sequence encoding. A PET study

E Hazeltine — 2008-02-28T08:04:31-00:00

Brain, Vol. 120, No. 1. (1 January 1997), pp. 123-140.

10.1093/brain/120.1.123

Functional anatomy of human procedural learning determined with regional cerebral blood flow and PET

ST Grafton — 2008-02-28T08:02:42-00:00

J. Neurosci., Vol. 12, No. 7. (1 July 1992), pp. 2542-2548.

Prefrontal lesions impair the implicit and explicit learning of sequences on visuomotor tasks

Gomez — 2008-02-28T08:00:42-00:00

Experimental Brain Research, Vol. 142, No. 4. (1 February 2002), pp. 529-538.

Objective: (1) To verify whether the prefrontal cortex (PFC) is specifically involved in visuomotor sequence learning as opposed to other forms of motor learning and (2) to establish the role of executive functions in visuomotor sequence learning. Background: Visuomotor skill learning depends on the integrity of the premotor and parietal cortex; the prefrontal cortex, however, is essential when the learning of a sequence is required. Methods: We studied 25 patients with PFC lesions and 86 controls matched for age and educational level. Participants performed: (1) a Pursuit Tracking Task (PTT), composed of a random tracking task (perceptual learning) and a pattern tracking task (explicit motor sequence learning with learning indicated by the decrease in mean root square error across trial blocks), (2) a 12-item sequence version of a serial reaction time task (SRTT) with specific implicit motor sequence learning indicated by the rebound increase in response time when comparing the last sequence block with the next random block, and (3) a neuropsychological battery that assessed executive functions. Results: PFC patients were impaired in sequence learning on the pattern tracking task of the PTT and on the SRTT as compared to controls, but performed normally on the PTT random tracking task. Learning on the PTT did not correlate with learning on the SRTT. PTT performance correlated with planning functions while SRTT performance correlated with working memory capacity. Conclusions: The PFC is specifically involved in explicit and implicit motor sequence learning. Different PFC regions may be selectively involved in such learning depending on the cognitive demands of the sequential task.

Patterns of regional brain activation associated with different forms of motor learning

Maria-Felice Ghilardi — 2008-02-28T07:53:11-00:00

Brain Research, Vol. 871, No. 1. (14 July 2000), pp. 127-145.

To examine the variations in regional cerebral blood flow during execution and learning of reaching movements, we employed a family of kinematically and dynamically controlled motor tasks in which cognitive, mnemonic and executive features of performance were differentiated and characterized quantitatively. During 15O-labeled water positron emission tomography (PET) scans, twelve right-handed subjects moved their dominant hand on a digitizing tablet from a central location to equidistant targets displayed with a cursor on a computer screen in synchrony with a tone. In the preceding week, all subjects practiced three motor tasks: 1) movements to a predictable sequence of targets; 2) learning of new visuomotor transformations in which screen cursor motion was rotated by 30[degree sign]-60[degree sign]; 3) learning new target sequences by trial and error, by using previously acquired routines in a task placing heavy load on spatial working memory. The control condition was observing screen and audio displays. Subtraction images were analyzed with Statistical Parametric Mapping to identify significant brain activation foci. Execution of predictable sequences was characterized by a modest decrease in movement time and spatial error. The underlying pattern of activation involved primary motor and sensory areas, cerebellum, basal ganglia. Adaptation to a rotated reference frame, a form of procedural learning, was associated with decrease in the imposed directional bias. This task was associated with activation in the right posterior parietal cortex. New sequences were learned explicitly. Significant activation was found in dorsolateral prefrontal and anterior cingulate cortices. In this study, we have introduced a series of flexible motor tasks with similar kinematic characteristics and different spatial attributes. These tasks can be used to assess specific aspects of motor learning with imaging in health and disease.

Assessing the significance of focal activations using their spatial extent

KJ Friston — 2008-02-25T19:17:52-00:00

Human Brain Mapping, Vol. 1, No. 3. (1993), pp. 210-220.

Current approaches to detecting significantly activated regions of cerebral tissue use statistical parametric maps, which are thresholded to render the probability of one or more activated regions of one voxel, or larger, suitably small (e. g., 0.05). We present an approximate analysis giving the probability that one or more activated regions of a specified volume, or larger, could have occurred by chance. These results mean that detecting significant activations no longer depends on a fixed (and high) threshold, but can be effected at any (lower) threshold, in terms of the spatial extent of the activated region. The substantial improvement in sensitivity that ensues is illustrated using a power analysis and a simulated phantom activation study. © 1994 Wiley-Liss, Inc.

Improved Assessment of Significant Activation in Functional Magnetic Resonance Imaging (fMRI): Use of a Cluster-Size Threshold

Steven Forman — 2008-02-28T07:49:15-00:00

Magnetic Resonance in Medicine, Vol. 33, No. 5. (1995), pp. 636-647.

The typical functional magnetic resonance (fMRI) study presents a formidable problem of multiple statistical comparisons (i.e, > 10,000 in a 128 x 128 image). To protect against false positives, investigators have typically relied on decreasing the per pixel false positive probability. This approach incurs an inevitable loss of power to detect statistically significant activity. An alternative approach, which relies on the assumption that areas of true neural activity will tend to stimulate signal changes over contiguous pixels, is presented. If one knows the probability distribution of such cluster sizes as a function of per pixel false positive probability, one can use cluster-size thresholds independently to reject false positives. Both Monte Carlo simulations and fMRI studies of human subjects have been used to verify that this approach can improve statistical power by as much as fivefold over techniques that rely solely on adjusting per pixel false positive probabilities.