CiteULike: Tag motor

Direct observation of kinesin stepping by optical trapping interferometry

Karel Svoboda — 2007-06-02T13:48:17-00:00

Nature, Vol. 365, No. 6448. (21 October 1993), pp. 721-727.

Do biological motors move with regular steps? To address this question, we constructed instrumentation with the spatial and temporal sensitivity to resolve movement on a molecular scale. We deposited silica beads carrying single molecules of the motor protein kinesin on microtubules using optical tweezers and analysed their motion under controlled loads by interferometry. We find that kinesin moves with 8-nm steps.

Probing the kinesin reaction cycle with a 2D optical force clamp

Steven Block — 2006-03-08T19:58:36-00:00

Proceedings of the National Academy of Sciences of the United States of America, Vol. 100, No. 5. (4 March 2003), pp. 2351-2356.

With every step it takes, the kinesin motor undergoes a mechanochemical reaction cycle that includes the hydrolysis of one ATP molecule, ADP/Pi release, plus an unknown number of additional transitions. Kinesin velocity depends on both the magnitude and the direction of the applied load. Using specialized apparatus, we subjected single kinesin molecules to forces in differing directions. Sideways and forward loads up to 8 pN exert only a weak effect, whereas comparable forces applied in the backward direction lead to stall. This strong directional bias suggests that the primary working stroke is closely aligned with the microtubule axis. Sideways loads slow the motor asymmetrically, but only at higher ATP levels, revealing the presence of additional, load-dependent transitions late in the cycle. Fluctuation analysis shows that the cycle contains at least four transitions, and confirms that hydrolysis remains tightly coupled to stepping. Together, our findings pose challenges for models of kinesin motion.

Individual dimers of the mitotic kinesin motor Eg5 step processively and support substantial loads in vitro

Megan Valentine — 2006-05-03T01:04:17-00:00

Nature Cell Biology, Vol. 8, No. 5. (02 April 2006), pp. 470-476.

Eg5kinesin Eg5, a member of the kinesin superfamily of microtubule-based motors, is essential for bipolar spindle assembly and maintenance during mitosis, yet little is known about the mechanisms by which it accomplishes these tasks. Here, we used an automated optical trapping apparatus in conjunction with a novel motility assay that employed chemically modified surfaces to probe the mechanochemistry of Eg5. Individual dimers, formed by a recombinant human construct Eg5–513–5His, stepped processively along microtubules in 8-nm increments, with short run lengths averaging approximately eight steps. By varying the applied load (with a force clamp) and the ATP concentration, we found that the velocity of Eg5 was slower and less sensitive to external load than that of conventional kinesin, possibly reflecting the distinct demands of spindle assembly as compared with vesicle transport. The Eg5–513–5His velocity data were described by a minimal, three-state model where a force-dependent transition follows nucleotide binding.

Kinesin Walks Hand-Over-Hand

Ahmet Yildiz — 2006-05-11T18:09:25-00:00

Science, Vol. 303, No. 5658. (30 January 2004), pp. 676-678.

Kinesin is a processive motor that takes 8.3-nm center-of-mass steps along microtubules for each adenosine triphosphate hydrolyzed. Whether kinesin moves by a "hand-over-hand" or an "inchworm" model has been controversial. We have labeled a single head of the kinesin dimer with a Cy3 fluorophore and localized the position of the dye to within 2 nm before and after a step. We observed that single kinesin heads take steps of 17.3 +/- 3.3 nm. A kinetic analysis of the dwell times between steps shows that the 17-nm steps alternate with 0-nm steps. These results strongly support a hand-over-hand mechanism, and not an inchworm mechanism. In addition, our results suggest that kinesin is bound by both heads to the microtubule while it waits for adenosine triphosphate in between steps. 10.1126/science.1093753

Nucleotide-Dependent Single- to Double-Headed Binding of Kinesin

Kenji Kawaguchi — 2007-06-01T20:42:49-00:00

Science, Vol. 291, No. 5504. (26 January 2001), pp. 667-669.

The motility of kinesin motors is explained by a "hand-over-hand" model in which two heads of kinesin alternately repeat single-headed and double-headed binding with a microtubule. To investigate the binding mode of kinesin at the key nucleotide states during adenosine 5'-triphosphate (ATP) hydrolysis, we measured the mechanical properties of a single kinesin-microtubule complex by applying an external load with optical tweezers. Both the unbinding force and the elastic modulus in solutions containing AMP-PNP (an ATP analog) were twice the value of those in nucleotide-free solution or in the presence of both AMP-PNP and adenosine 5'-diphosphate. Thus, kinesin binds through two heads in the former and one head in the latter two states, which supports a major prediction of the hand-over-hand model.

Mechanics of the kinesin step

NJ Carter — 2005-05-18T18:48:51-00:00

Nature, Vol. 435, No. 7040., pp. 308-312.

Kinesin is a molecular walking machine that organizes cells by hauling packets of components directionally along microtubules. The physical mechanism that impels directional stepping is uncertain. We show here that, under very high backward loads, the intrinsic directional bias in kinesin stepping can be reversed such that the motor walks sustainedly backwards in a previously undescribed mode of ATP-dependent backward processivity. We find that both forward and backward 8-nm steps occur on the microsecond timescale and that both occur without mechanical substeps on this timescale. The data suggest an underlying mechanism in which, once ATP has bound to the microtubule-attached head, the other head undergoes a diffusional search for its next site, the outcome of which can be biased by an applied load.

Association between visual perceptual deficits and motor deficits in children with developmental coordination disorder.

H Van Waelvelde — 2006-03-22T16:09:21-00:00

Dev Med Child Neurol, Vol. 46, No. 10. (October 2004), pp. 661-666.

This study explored the relation between a motor-free visual perceptual deficit, different visual-motor integration deficits, and different motor skills in children with developmental coordination disorder (DCD). Thirty-six children (22 males), aged 9 or 10 years, with DCD and a control group (n=36), matched for age and sex, were assessed with the Movement Assessment Battery for Children (MABC), a ball-catching test, a jumping test, a timed response task to a visual moving stimulus, and the Beery-Buktenica Developmental Test of Visual-Motor Integration, incorporating copying, visual discrimination, and tracing tasks. Children with DCD performed significantly worse than the control group on all measures. The visual discrimination task did not correlate significantly with any of the motor tasks. The visual timing task correlated significantly with the ball-catching test in the DCD group. The copying test was significantly correlated with the MABC in the DCD group. The association between visual-perceptual deficits and motor tasks was shown to be task specific.

Motor, cognitive, and behavioural disorders in children born very preterm.

LA Foulder-Hughes — 2006-03-22T15:31:35-00:00

Dev Med Child Neurol, Vol. 45, No. 2. (February 2003), pp. 97-103.

Children born preterm have been shown to exhibit poor motor function and behaviour that is associated with school failure in the presence of average intelligence. A geographically determined cohort of two-hundred and eighty preterm children (151 males, 129 females) born before 32 weeks' gestation and attending mainstream schools were examined at 7 to 8 years of age together with 210 (112 males, 98 females) age- and sex-matched control participants were tested for motor, cognitive, and behavioural problems. Tests applied were the Movement Assessment Battery for Children (MABC), Clinical Observations of Motor and Postural Skills (COMPS), Developmental Test of Visual-Motor Integration (VMI), Wechsler Intelligence Scale for Children, and Connors' Teacher Rating Scale for attention-deficit-hyperactivity disorder (ADHD). Control children scored significantly better than the preterm group on all motor, cognitive, and behavioural measures. The lowest birthweight and most preterm individuals tended to score the lowest. Motor impairment was diagnosed in 86 (30.7%) of the preterm group and 14 (6.7%) of the control children using the MABC; 97 (42.7%) and 18 (10.2%) using the COMPS; and 68 (24.3%) and 17 (8.1%) respectively using the VMI. Each test of motor function identified different children with disability, although 23 preterm children were identified as having motor disability by all three tests. Preterm children were more likely to have signs of inattention and impulsivity and have a diagnosis of ADHD. Minor motor disabilities persist in survivors of preterm birth despite improvements in care and are not confined to the smallest or most preterm infants. They may exist independently of cognitive and behavioural deficits, although they often co-exist. The condition is heterogeneous and may require more than one test to identify all children with potential learning problems.

Clinical value of the Beery visual-motor integration supplemental tests of visual perception and motor coordination.

MT Kulp — 2006-03-22T15:28:56-00:00

Optom Vis Sci, Vol. 80, No. 4. (April 2003), pp. 312-315.

PURPOSE: Children may perform poorly on a test of visual-motor integration due to deficits in one or more of the following: visual analysis/visual spatial ability, motor coordination, visual conceptualization, or visual-motor integration. The VMI Supplemental Developmental Test of Visual Perception (VP) and VMI Supplemental Developmental Test of Motor Coordination (MC) were developed to help differentiate between such difficulties after administration of the Beery-Buktenica Developmental Test of Visual-Motor Integration (VMI). However, the clinical value of the VMI supplemental tests has not been reported. METHOD: The VMI, VP, and MC were administered to 193 children (mean age = 8.77 years). RESULTS: Multiple linear regression revealed that the supplemental tests were significantly related to the VMI (VP: beta = 0.212 +/- 0.044, p < 0.001; MC: beta = 0.422 +/- 0.299, p < 0.001) but explained only 36.2% of the variance in the VMI. Poor performance was defined as a score >1 SD below the mean for study population norms and below the 16th percentile for published norms. Using study population norms, 35 children did poorly on the VMI, 20% of whom scored poorly on VP, 14.3% of whom scored poorly on MC, 17.1% of whom scored poorly on both supplemental tests, and 48.6% of whom scored within normal on both supplemental tests. Using the published norms, 40 children scored poorly on the VMI. Twenty-eight children scored poorly on VP, 39% of whom scored within normal on the VMI. Fifty-six children scored poorly on MC, 54% of whom scored within normal on the VMI. CONCLUSION: There was a significant amount of variance in performance on the VMI that was not explained by performance on the tests of VP or MC alone. Each area should be individually assessed during the visual perceptual examination of children, regardless of performance on the VMI. Even children who perform within normal limits on the VMI may show a deficit in VP or MC.

The contribution of motor skills and playfulness to the play performance of preschoolers.

CD Morrison — 2005-08-09T18:33:32-00:00

Am J Occup Ther, Vol. 45, No. 8. (August 1991), pp. 687-694.

Consideration of a child's motor proficiency, intrinsic motivation, internal locus of control, and freedom to suspend many of the constraints of objective reality were proposed to provide a more comprehensive assessment of play than would an assessment of play performance alone. For empirical validation of this conceptual model of play, 29 subjects (15 nondisabled children and 14 children with juvenile rheumatoid arthritis) between the ages of 4 years 6 months and 6 years 6 months were given four assessments: (a) the Preschool Play Scale (Bledsoe & Shepherd, 1982, Knox, 1974); (b) the Bruininks-Oseretsky Test of Motor Proficiency (Bruininks, 1978); (c) the Preschool and Primary Internal-External Locus of Control Scale (Nowicki & Duke, 1974); and (d) tests of associative fluency (Wallach & Koogan, 1965; Ward, 1968). Multiple regression procedures revealed that, when considered together, scores on the Bruininks-Oseretsky Test of Motor Proficiency, tests of associative fluency, and the Preschool and Primary Internal-External Locus of Control Scale predicted scores on the Preschool Play Scale, thereby supporting the usefulness of the proposed theoretical model. Further, there was no significant difference in the mean scores of the two groups on the Preschool Play Scale. Although this finding may be an artifact of the small sample size, it also may support the authors' belief that children with motor impairments are able to compensate for their limitations by developing areas of relative strength that allow them to play normally. When this belief was further tested with Pearson product-moment correlations and Fisher's Z transformations, it was found that correlations between the test scores of the nondisabled children were not significantly different from those of the children with juvenile rheumatoid arthritis. Clearly, further research is needed.

A fast communication aid for non-verbal subjects with severe motor handicaps.

VA Pollak — 2005-08-16T06:11:10-00:00

J Med Eng Technol, Vol. 13, No. 1-2. (r 1989), pp. 23-27.

A computer-based communication system for non-verbal persons with severely deficient coordination of the upper extremities is described. The device doubles as an environmental control unit. Modular design is chosen throughout. Commercially available subunits are used to reduce cost. Input is by a 3 x 3 keyboard, when the user has some command over his hands. Otherwise a binary 'autoscan' access mode is used, which is controlled by repeated closures of a single binary switch. Output is in written form on a display or acoustical by synthesized speech. Hard-copy output can also be provided. Remote communication is possible by modem or by synthesized speech. Speed of message generation is increased by establishing a vocabulary, which contains, in addition to signs and letters of the alphabet, whole words and stereotyped phrases. The data blocks of the latter are accessed by a single input cycle similar to that used for the selection of isolated letters, symbols, etc.

New possibilities for enhanced keyboard input for the handicapped.

M Soede — 2005-08-16T06:11:06-00:00

J Med Eng Technol, Vol. 13, No. 1-2. (r 1989), pp. 34-36.

Motor- and speech-impaired people can have severe problems with communication. If speech is hampered, the use of computerized communication devices can be a solution. Key entry limitations due to motor impairments may result in very low communication speeds--less than three words a minute is not unusual. The research described here deals with speed enhancement on the basis of redundancy in language. Two uses are explored: prediction and automatic decoding in the case of keyboards with a small number of keys. Prediction means that characters, words and (parts of) sentences are predicted on the basis of text which is already typed in. A prototype system is being designed which combines the features of the PAL prediction system from Dundee and the WRITE-keyboard from Boston. Decoding refers to two-step selection systems with a small number of keys in which the second selection is done automatically by a computer program. Keystroke savings of 40 to 50% are possible.

Customised text entry devices for motor-impaired users.

SH Levine — 2005-08-16T06:11:01-00:00

Appl Ergon, Vol. 21, No. 1. (March 1990), pp. 55-62.

The standard QWERTY keyboard is the principal text entry device for word processing and computer-based communications. For many motor-impaired individuals, and in particular those without intelligible speech, the low text entry rates they can typically achieve is a major problem. For some, the QWERTY design is completely inappropriate. Alternative designs that can appreciably increase these rates would greatly enhance their ability to communicate. This paper considers and compares several approaches to the design of text entry devices for motor-impaired users. A general method for customising (i e, optimising) these designs is employed, and consideration is given to designs requiring significantly fewer input switches than the 26 or more keys required by QWERTY. Use is made of language statistics in the design procedure, and the increased availability of inexpensive, powerful computers is directly exploited.

Motor and functional skills of children with developmental coordination disorder: A pilot investigation of measurement issues

S Rodger — 2004-12-28T17:27:06-00:00

Human Movement Science, Vol. 22, No. 4. (November 2003), pp. 461-478.

This paper reports on the motor and functional outcomes of 20 children with developmental coordination disorder (DCD) aged 4–8 years consecutively referred to a pediatric physiotherapy service. Children with a Movement ABC (M-ABC) score less than the 15th percentile, and with no concurrent medical, sensory, physical, intellectual or neurological impairments, were recruited. The Motor Assessment Outcomes Model (MAOM) [Coster and Haley, Infants and Young Children 4 (1992) 11] provided the theoretical base for measurement selection, and preliminary findings at the activities and participation levels of the model are reported in this article. Children with DCD performed at the lower end of the normal range on the Peabody Developmental Motor Scales (fine motor total score) (M ¼ 85:65, SD¼12.23). Performance on the Visual Motor Integration Test (VMI) standard scores was within the average range (M ¼ 96:15, SD¼10.69). Videotaped observations of the children’s writing and cutting indicated that 29% were left-handed and that a large proportion of all children (31%) utilized unusual pencil grasp patterns and immature prehension of scissors. Measurement at the q Based on conference presentation at Developmental Coordination Disorder (DCD), V Banff, Alberta, Canada, 14–16 May 2002. * Corresponding author. Tel.: +61-7-3365-1664; fax: +61-7-3365-1622. E-mail address: s.rodger@mailbox.uq.edu.au (S. Rodger).

Stimulating music increases motor coordination in patients afflicted with Morbus Parkinson

Gunther Bernatzky — 2005-10-13T14:24:13-00:00

Neuroscience Letters, Vol. 361, No. 1-3. (6 May 2004), pp. 4-8.

The present study measured the short-term effect of special stimulating music on motor coordination in Parkinson patients. Eleven patients with a dominant akinetic Parkinson syndrome as well as ten healthy persons (age-matched control group) participated in this study. In the Parkinson group, the measurement of fine motor coordination with the ‘Vienna Test System’ showed an improvement in two (aiming, line tracking) of the four subtests after listening to the music. The patients improved their performance with the right arm significantly in the subtest aiming-error-time. No statistical differences were found in the other two subtests (steadiness, tapping) in both groups. There was also no improvement in frequency of tapping movement on the power-force-working-plate. Accordingly, music effects more the precision of a movement than the speediness. The measurements on the power-force-working-plate showed a significant improvement in two of five measured parameters: contact time, variability coefficient for total step and impact maximum changed significantly. This study gives evidence that specific music can improve the precision of arm and finger movements.

Humans integrate visual and haptic information in a statistically optimal fashion.

MO Ernst — 2005-02-18T14:19:28-00:00

Nature, Vol. 415, No. 6870. (24 January 2002), pp. 429-433.

When a person looks at an object while exploring it with their hand, vision and touch both provide information for estimating the properties of the object. Vision frequently dominates the integrated visual-haptic percept, for example when judging size, shape or position, but in some circumstances the percept is clearly affected by haptics. Here we propose that a general principle, which minimizes variance in the final estimate, determines the degree to which vision or haptics dominates. This principle is realized by using maximum-likelihood estimation to combine the inputs. To investigate cue combination quantitatively, we first measured the variances associated with visual and haptic estimation of height. We then used these measurements to construct a maximum-likelihood integrator. This model behaved very similarly to humans in a visual-haptic task. Thus, the nervous system seems to combine visual and haptic information in a fashion that is similar to a maximum-likelihood integrator. Visual dominance occurs when the variance associated with visual estimation is lower than that associated with haptic estimation.

Parallel computations for controlling an arm.

G Hinton — 2006-03-13T18:08:07-00:00

J Mot Behav, Vol. 16, No. 2. (June 1984), pp. 171-194.

In order to control a reaching movement of the arm and body, several different computational problems must be solved. Some parallel methods that could be implemented in networks of neuron-like processors are described. Each method solves a different part of the overall task. First, a method is described for finding the torques necessary to follow a desired trajectory. The methods is more economical and more versatile than table look-up and requires very few sequential steps. Then a way of generating an internal representation of a desired trajectory is described. This method shows the trajectory one piece at a time by applying a large set of heuristic rules to a "motion blackboard" that represents the static and dynamic parameters of the state of the body at the current point in the trajectory. The computations are simplified by expressing the positions, orientations, and motions of parts of the body in terms of a single, non-accelerating, world-based frame of reference, rather than in terms of the joint-angles or an egocentric frame based on the body itself.

Human hand moves proactively to the external stimulus: an evolutional strategy for minimizing transient error.

F Ishida — 2005-04-07T15:30:10-00:00

Phys Rev Lett, Vol. 93, No. 16. (15 October 2004)

We investigated particularly the proactive nature of the visual-motor system by steady and transient experiments of a hand-tracking task, and confirmed that the hand motion precedes on the average the target motion in steady runs within a finite frequency range of the sinusoidal target motion. The question why and how much the hand motion should precede was answered by frequency-jump experiments. The results implied that the positive phase shift of the hand motion represents the proactive nature of the visual-motor control system which is adaptationally developed for each person to minimize the transient error of the hand motion when the target motion changes unexpectedly.

Real-time imaging of fluorescent flagellar filaments.

L Turner — 2007-04-07T19:22:03-00:00

J Bacteriol, Vol. 182, No. 10. (May 2000), pp. 2793-2801.

Bacteria swim by rotating flagellar filaments that are several micrometers long, but only about 20 nm in diameter. The filaments can exist in different polymorphic forms, having distinct values of curvature and twist. Rotation rates are on the order of 100 Hz. In the past, the motion of individual filaments has been visualized by dark-field or differential-interference-contrast microscopy, methods hampered by intense scattering from the cell body or shallow depth of field, respectively. We have found a simple procedure for fluorescently labeling cells and filaments that allows recording their motion in real time with an inexpensive video camera and an ordinary fluorescence microscope with mercury-arc or strobed laser illumination. We report our initial findings with cells of Escherichia coli. Tumbles (events that enable swimming cells to alter course) are remarkably varied. Not every filament on a cell needs to change its direction of rotation: different filaments can change directions at different times, and a tumble can result from the change in direction of only one. Polymorphic transformations tend to occur in the sequence normal, semicoiled, curly 1, with changes in the direction of movement of the cell body correlated with transformations to the semicoiled form.

On Torque and Tumbling in Swimming Escherichia coli

Nicholas Darnton — 2007-10-09T13:37:11-00:00

J. Bacteriol., Vol. 189, No. 5. (1 March 2007), pp. 1756-1764.

Bacteria swim by rotating long thin helical filaments, each driven at its base by a reversible rotary motor. When the motors of peritrichous cells turn counterclockwise (CCW), their filaments form bundles that drive the cells forward. We imaged fluorescently labeled cells of Escherichia coli with a high-speed charge-coupled-device camera (500 frames/s) and measured swimming speeds, rotation rates of cell bodies, and rotation rates of flagellar bundles. Using cells stuck to glass, we studied individual filaments, stopping their rotation by exposing the cells to high-intensity light. From these measurements we calculated approximate values for bundle torque and thrust and body torque and drag, and we estimated the filament stiffness. For both immobilized and swimming cells, the motor torque, as estimated using resistive force theory, was significantly lower than the motor torque reported previously. Also, a bundle of several flagella produced little more torque than a single flagellum produced. Motors driving individual filaments frequently changed directions of rotation. Usually, but not always, this led to a change in the handedness of the filament, which went through a sequence of polymorphic transformations, from normal to semicoiled to curly 1 and then, when the motor again spun CCW, back to normal. Motor reversals were necessary, although not always sufficient, to cause changes in filament chirality. Polymorphic transformations among helices having the same handedness occurred without changes in the sign of the applied torque. 10.1128/JB.01501-06

Multiple motor learning experiences enhance motor adaptability.

RD Seidler — 2005-11-11T14:38:19-00:00

J Cogn Neurosci, Vol. 16, No. 1. (b 2004), pp. 65-73.

Traditional motor learning theory emphasizes that skill learning is specific to the context and task performed. Recent data suggest, however, that subjects exposed to a variety of motor learning paradigms may be able to acquire general, transferable knowledge about skill learning processes. I tested this idea by having subjects learn five different motor tasks, three that were similar to each other and two that were not related. A group of experimental subjects first performed a joystick-aiming task requiring adaptation to three different visuomotor rotations, with a return to the null conditions between each exposure. They then performed the same joystick-aiming task but had to adapt to a change in display gain instead of rotation. Lastly, the subjects used the joystick-aiming task to learn a repeating sequence of movements. Two groups of control subjects performed the same number of trials, but learned only the gain change or the movement sequence. Experimental subjects showed generalization of learning across the three visuomotor rotations. Experimental subjects also exhibited transfer of learning ability to the gain change and the movement sequence, resulting in faster learning than that seen in the control subjects. However, transient perturbations affected the movements of the experimental subjects to a greater extent than those of the control subjects. These data demonstrate that humans can acquire a general enhancement in motor skill learning capacity through experience, but it comes with a cost. Although movement becomes more adaptable following multiple learning experiences, it also becomes less stable to external perturbation.

Dynamics of learning and transfer of muscular and spatial relative phase in bimanual coordination: evidence for abstract directional codes.

JJ Temprado — 2005-11-15T13:46:16-00:00

Exp Brain Res, Vol. 160, No. 2. (January 2005), pp. 180-188.

The present study addressed whether the timing of muscle activation and the relative direction of limb movements are dissociable constraints that may affect learning and transfer of bimanual coordination patterns, either independently or in combination. Subjects were assigned to two experimental groups in which the to-be-learned muscular phasing (135 degrees ) was either practiced with 45 degrees (i.e., predominantly isodirectional) or 135 degrees (i.e., predominantly nonisodirectional) of spatial relative phase (RP) across 2 days of practice. Prior to, during, and following practice, probe tests were held in which various relative phasing patterns were administered to assess transfer of learning. Converging evidence was obtained that the relative direction of moving limbs prominently constrained transfer of learning rather than muscular relationships. Acquisition of a specific pattern resulted in spontaneous positive transfer of learning to a new coordination pattern having the same spatial RP but not to a pattern with a different spatial RP, irrespective of muscular phasing relationships. In summary, the present results suggest that learning and transfer of coordination patterns is mediated by abstract directional codes that become part of the memory representation for bimanual coordination.

The role of working memory in motor learning and performance.

JP Maxwell — 2005-11-15T12:33:34-00:00

Conscious Cogn, Vol. 12, No. 3. (September 2003), pp. 376-402.

Three experiments explore the role of working memory in motor skill acquisition and performance. Traditional theories postulate that skill acquisition proceeds through stages of knowing, which are initially declarative but later procedural. The reported experiments challenge that view and support an independent, parallel processing model, which predicts that procedural and declarative knowledge can be acquired separately and that the former does not depend on the availability of working memory, whereas, the latter does. The behaviour of these two processes was manipulated by providing or withholding visual (and auditory) appraisal of outcome feedback. Withholding feedback was predicted to inhibit the use of working memory to appraise success and, thus, prevent the formation of declarative knowledge without affecting the accumulation of procedural knowledge. While the first experiment failed to support these predictions, the second and third experiments demonstrated that procedural and declarative knowledge can be acquired independently. It is suggested that the availability of working memory is crucial to motor performance only when the learner has come to rely on its use.

Power electronics

Cyril Lander — 2006-03-03T14:04:40-00:00

Learning-induced LTP in neocortex.

MS Rioult-Pedotti — 2006-12-01T14:46:18-00:00

Science, Vol. 290, No. 5491. (20 October 2000), pp. 533-536.

The hypothesis that learning occurs through long-term potentiation (LTP)- and long-term depression (LTD)-like mechanisms is widely held but unproven. This hypothesis makes three assumptions: Synapses are modifiable, they modify with learning, and they strengthen through an LTP-like mechanism. We previously established the ability for synaptic modification and a synaptic strengthening with motor skill learning in horizontal connections of the rat motor cortex (MI). Here we investigated whether learning strengthened these connections through LTP. We demonstrated that synapses in the trained MI were near the ceiling of their modification range, compared with the untrained MI, but the range of synaptic modification was not affected by learning. In the trained MI, LTP was markedly reduced and LTD was enhanced. These results are consistent with the use of LTP to strengthen synapses during learning.

Long-term motor cortex plasticity induced by an electronic neural implant

Andrew Jackson — 2006-10-25T21:40:07-00:00

Nature (22 October 2006)

Molecular shuttles based on motor proteins: active transport in synthetic environments.

H Hess — 2005-11-03T04:03:26-00:00

J Biotechnol, Vol. 82, No. 1. (November 2001), pp. 67-85.

Active transport in cells, utilizing molecular motors like kinesin and myosin, provides the inspiration for the integration of active transport into synthetic devices. Hybrid devices, employing motor proteins in a synthetic environment, are the first prototypes of molecular shuttles. Here the basic characteristics of motor proteins are discussed from an engineering point of view, and the experiments aimed at incorporating motor proteins, such as myosins and kinesins, into devices are reviewed. The key problems for the construction of a molecular shuttle are: guiding the direction of motion, controlling the speed, and loading and unloading of cargo. Various techniques, relying on surface topography and chemistry as well as flow fields and electric fields, have been developed to guide the movement of molecular shuttles on surfaces. The control of ATP concentration, acting as a fuel supply, can serve as a means to control the speed of movement. The loading process requires the coupling of cargo to the shuttle, ideally by a strong and specific link. Applications of molecular shuttles can be envisioned, e.g. in the field of nano-electro-mechanical systems (NEMS), where scaling laws favor active transport over fluid flow, and in the bottom-up assembly of novel materials.

Self-assembled microdevices driven by muscle.

J Xi — 2005-11-03T03:57:00-00:00

Nat Mater, Vol. 4, No. 2. (February 2005), pp. 180-184.

Current procedures for manual extraction of mature muscle tissue in micromechanical structures are time consuming and can damage the living components. To overcome these limitations, we have devised a new system for assembling muscle-powered microdevices based on judicious manipulations of materials phases and interfaces. In this system, individual cells grow and self-assemble into muscle bundles that are integrated with micromechanical structures and can be controllably released to enable free movement. Having realized such an assembly with cardiomyocytes we demonstrate two potential applications: a force transducer able to characterize in situ the mechanical properties of muscle and a self-assembled hybrid (biotic/abiotic) microdevice that moves as a consequence of collective cooperative contraction of muscle bundles. Because the fabrication of silicon microdevices is independent of the subsequent assembly of muscle cells, this system is highly versatile and may lead to the integration of cells and tissues with a variety of other microstructures.

Powering an inorganic nanodevice with a biomolecular motor.

RK Soong — 2005-11-03T03:56:33-00:00

Science, Vol. 290, No. 5496. (24 November 2000), pp. 1555-1558.

Biomolecular motors such as F1-adenosine triphosphate synthase (F1-ATPase) and myosin are similar in size, and they generate forces compatible with currently producible nanoengineered structures. We have engineered individual biomolecular motors and nanoscale inorganic systems, and we describe their integration in a hybrid nanomechanical device powered by a biomolecular motor. The device consisted of three components: an engineered substrate, an F1-ATPase biomolecular motor, and fabricated nanopropellers. Rotation of the nanopropeller was initiated with 2 mM adenosine triphosphate and inhibited by sodium azide.

Control of a biomolecular motor-powered nanodevice with an engineered chemical switch.

H Liu — 2005-11-03T03:56:08-00:00

Nat Mater, Vol. 1, No. 3. (November 2002), pp. 173-177.

The biophysical and biochemical properties of motor proteins have been well-studied, but these motors also show promise as mechanical components in hybrid nano-engineered systems. The cytoplasmic F(1) fragment of the adenosine triphosphate synthase (F1-ATPase) can function as an ATP-fuelled rotary motor and has been integrated into self-assembled nanomechanical systems as a mechanical actuator. Here we present the rational design, construction and analysis of a mutant F1-ATPase motor containing a metal-binding site that functions as a zinc-dependent, reversible on/off switch. Repeated cycles of zinc addition and removal by chelation result in inhibition and restoration, respectively, of both ATP hydrolysis and motor rotation of the mutant, but not of the wild-type F1 fragment. These results demonstrate the ability to engineer chemical regulation into a biomolecular motor and represent a critical step towards controlling integrated nanomechanical devices at the single-molecule level.

The Neural Control of Vocalization in Mammals: A Review

U Jürgens — 2008-07-31T19:22:31-00:00

Journal of Voice, Vol. In Press, Corrected Proof

Summary The review describes a model of vocal control, based mainly on research in the squirrel monkey, which consists of two hierarchically organized pathways. One runs from the anterior cingulate cortex via the periaqueductal gray (PAG) into the reticular formation of pons and medulla oblongata, and from there to the phonatory motoneurons. This pathway controls the readiness to vocalize. Although the anterior cingulate cortex in this pathway plays a role in voluntary initiation of vocal behavior, the PAG is involved in vocal gating at a more elementary level. The second pathway runs from the motor cortex via the reticular formation to the phonatory motoneurons and includes two feedback loops providing the motor cortex with preprocessed information needed by the latter to generate the final motor commands. One of these feedback loops involves the basal ganglia and the other the cerebellum. The motor cortex together with its feedback loops is involved in the production of learned vocal patterns. These structures seem to be dispensable, however, for the production of innate vocal patterns, such as the nonverbal emotional vocal utterances of humans and most nonhuman mammalian vocalizations. These innate vocal patterns seem to be generated in the pontine and medullary reticular formation.

Spatial and temporal characteristics of rapid cursor-positioning movements with electromechanical mice in human-computer interaction.

N Walker — 2006-06-07T11:08:02-00:00

Human Factors, Vol. 35, No. 3. (September 1993), pp. 431-458.

This research examines how people make movements with pointing devices during human-computer interaction. It specifically concerns the perceptual-motor processes that mediate the speed and accuracy of cursor positioning with electromechanical mice. In three experiments we investigated the spatial and temporal characteristics of positioning movements made with a mouse, analyzing subjects' speed and accuracy as a function of the types of targets that the movements had to reach. Experiment 1 required rapid and accurate horizontal movements to targets that were vertical ribbons located at various distances from the mouse's starting location. The targets for Experiments 2 and 3, respectively, were vertical lines having various heights and rectangular boxes having various heights and widths. Constraints on movement distance along the primary (that is, horizontal) line of motion had the greatest effects on total positioning times. However, constraints on movement distance along a secondary (vertical) line of motion also affected total positioning times significantly. These effects may be localized in different phases of movements (e.g., movement execution and verification). The duration of movement execution (i.e., physical motion) depends primarily on the target distance, whereas the duration of movement verification (i.e., check for endpoint accuracy) depends primarily on target height and width. A useful account of movement execution is provided by stochastic optimized-submovement models, which have significant implications for designing mice and menu-driven displays.

The effect of target size and inertial load on the control of rapid aiming movements

Michael Khan — 2006-06-07T10:59:10-00:00

Experimental Brain Research, Vol. 124, No. 2. (January 1999), pp. 151-158.

Motor-output variability: a theory for the accuracy of rapid motor acts.

RA Schmidt — 2006-06-07T10:41:45-00:00

Psychol Rev, Vol. 47, No. 5. (September 1979), pp. 415-451.

Learning a pointing task with a kinematically redundant limb: Emerging synergies and patterns of final position variability

Slobodan Jaric — 2006-06-07T10:28:35-00:00

Human Movement Science, Vol. 18, No. 6. (December 1999), pp. 819-838.

The study tested a hypothesis that practice of arm pointing movement can lead to a reorganization of the joint coordination reflected in the emergence of several synergies based on the same set of joints. In particular, involvement of the wrist may represent a choice by the central nervous system and not be driven by the typical “freezing-to-freeing” sequence. The effects of practice on the kinematic patterns and variability of a “fast and accurate” pointing movement using a pointer were studied. An obstacle was placed between the initial position and the target to encourage a curvilinear trajectory and larger wrist involvement. Practice led to a decrease in variability indices accompanied by an increase in movement speed of the endpoint and of the elbow and the shoulder, but not of the wrist joint. Five out of six subjects decreased the peak-to-peak amplitude of wrist motion. Before practice, the variability along the line connecting the endpoint to the shoulder (extent) was similar to that in the direction orthogonal to this line. After practice, variability was reduced along the extent, but not along the orthogonal direction perpendicular to this line. Prior to practice, indices of variability of the endpoint were lower than those of the marker placed over the wrist; after practice, the endpoint showed higher variability indices than the wrist. We interpret the data as consequences of the emergence of two synergies: (a) Pointing with a non-redundant set of the elbow and shoulder joints; and (b) keeping wrist position constant. The former synergy is based on a structural unit involving the elbow and the shoulder, while the latter is based on a structural unit that includes all the major arm joints.

The control of goal-directed limb movements: Correcting errors in the trajectory

Digby Elliott — 2006-06-07T10:16:26-00:00

Human Movement Science, Vol. 18, No. 2-3. (June 1999), pp. 121-136.

A number of recent models of limb control have attempted to explain speed-accuracy trade-off in goal-directed movements on the basis of the characteristics of the muscular impulses that are specified prior to movement initiation. In contrast, studies from our laboratory have demonstrated that, even for very rapid aiming movements, the characteristics of the movement trajectory change with the availability of visual information about the position of the limb and the target during the movement. Moreover, when the movement of the limb is perturbed at movement initiation by an electromagnetic force, performers can rapidly adjust their aiming movements in order to hit the target if visual feedback is available. The performer can also rapidly adjust to unexpected changes in target size and amplitude. Visually based adjustments to the movement trajectory can be either discrete or continuous.PsycINFO classification: 2330; 2343

BRAIN PLASTICITY AND HAND SURGERY: AN OVERVIEW

G Lundborg — 2008-06-17T18:46:19-00:00

The Journal of Hand Surgery: Journal of the British Society for Surgery of the Hand, Vol. 25, No. 3. (June 2000), pp. 242-252.

The hand is an extension of the brain, and the hand is projected and represented in large areas of the motor and sensory cortex. The brain is a complicated neural network which continuously remodels itself as a result of changes in sensory input. Such synaptic reorganizational changes may be activity-dependent, based on alterations in hand activity and tactile experience, or a result of deafferentiation such as nerve injury or amputation. Inferior recovery of functional sensibility following nerve repair, as well as phantom experiences in virtual, amputated limbs are phenomena reflecting profound cortical reorganizational changes. Surgical procedures on the hand are always accompanied by synaptic reorganizational changes in the brain cortex, and the outcome from many hand surgical procedures is to a large extent dependent on brain plasticity.

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.

A research survey of induction motor operation with non-sinusoidal supply wave forms

GK Singh — 2005-12-06T22:03:00-00:00

Electric Power Systems Research, Vol. 75, No. 2-3. (August 2005), pp. 200-213.

The developments in the power electronics field have lead to an ever-increasing use of static switching devices to control the torque and speed of ac motors. Invariably, the output voltage and current waveforms of these devices contain numerous harmonics and these harmonics have detrimental effects on the motor performance in form of derating and torque pulsation, especially at low speed. The order and magnitude of these harmonics depend on the design as well as nature of load being supplied. The extensive research has been underway for a long time in order to assess the effects these harmonics have on induction motor performance, and to investigate the various issues related to the use of induction motor to improve the drive performance and reduce the losses. This paper, therefore, presents a comprehensive review of research and developments in the induction motor operation with non-sinusoidal supply waveforms since its inception. Attempts are made to highlight the current and future issues involved in the development of induction motor drive technology to impart good dynamic stability with improved performance. A list of 167 research publications on the subject is also appended for a quick reference.

Neuronal variability: noise or part of the signal?

Richard Stein — 2005-04-29T23:08:02-00:00

Nature Reviews Neuroscience, Vol. 6, No. 5. (01 May 2005), pp. 389-397.

Use-induced motor plasticity affects the processing of abstract and concrete language

Arthur Glenberg — 2008-04-16T14:18:49-00:00

Current Biology, Vol. 18, No. 7. (8 April 2008), pp. R290-R291.

Summary Traditional analyses of language [1] emphasize an arbitrary correspondence between linguistic symbols and their extensions in the world, but recent behavioral and neurophysiological [2] and [3] studies have demonstrated a processing link between a symbol and its extension: that is, comprehension of language about concrete events relies in part on a simulation process that calls on neural systems used in perceiving and acting on those extensions. It is an open question, however, whether this simulation process is necessary for abstract language understanding [4] and [5]. Here we report how, using a new technique based on use-induced neural plasticity [6], we have obtained evidence for a causal link between the motor system and the comprehension of both concrete and abstract language.

Reconfigurable, braced, three-dimensional DNA nanostructures

Russell Goodman — 2008-02-07T20:41:18-00:00

Nat Nano, Vol. 3, No. 2. (February 2008), pp. 93-96.

Impact of expected reward on neuronal activity in prefrontal cortex, frontal and supplementary eye fields and premotor cortex.

MR Roesch — 2005-06-16T21:25:21-00:00

J Neurophysiol, Vol. 90, No. 3. (September 2003), pp. 1766-1789.

In several regions of the macaque brain, neurons fire during delayed response tasks at a rate determined by the value of the reward expected at the end of the trial. The activity of these neurons might be related either to the internal representation of the appetitive value of the expected reward or to motivation-dependent variations in the monkey's level of motor preparation or motor output. According to the first interpretation, reward-related activity should be most prominent in areas affiliated with the limbic system. According to the second interpretation, it should be most prominent in areas affiliated with the motor system. To distinguish between these alternatives, we carried out single-neuron recording while monkeys performed a memory-guided saccade task in which a visual cue presented early in each trial indicated whether the reward would be large or small. Neuronal activity accompanying task performance was monitored in the dorsolateral prefrontal cortex (PFC), the frontal eye field (FEF), a transitional zone caudal to the frontal eye field (FEF/PM), premotor cortex (PM), the supplementary eye field (SEF), and the rostral part of the supplementary motor area (SMAr). The tendency for neuronal activity to increase after cues that predicted a large reward became progressively stronger in progressively more posterior areas both in the lateral sector of the frontal lobe (PFC < FEF < FEF/PM < PM) and in the medial sector (SEF < SMAr). The very strong reward-related activity of premotor neurons was presumably attributable to the monkey's motivation-dependent level of motor preparation or motor output. This finding points to the need to determine whether reward-related activity in other nonlimbic brain areas, including dorsolateral prefrontal cortex and the dorsal striatum, genuinely represents the value of the expected reward or, alternatively, is related to motivational modulation of motor signals.

Motor, somatosensory and auditory cortex localization by fMRI and MEG.

C Stippich — 2005-10-14T16:22:52-00:00

Neuroreport, Vol. 9, No. 9. (22 June 1998), pp. 1953-1957.

Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were performed in six subjects during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using identical stimulation paradigms. Both functional imaging modalities localized brain activity in adjacent areas of anatomically correct cortex. The mean distances measured between fMRI activity and the corresponding MEG dipoles were 10.1 mm (motor), 10.7 mm (somatosensory), 13.5 mm (auditory right hemisphere) and 14.3 mm (auditory left hemisphere). The distances found may reflect the correlation between electrophysiological and hemodynamic responses due to the different underlying substrates of neurophysiology measured by fMRI and MEG: BOLD contrast vs neuronal biomagnetic activity.

Clustered functional MRI of overt speech production.

Peter Sörös — 2006-05-05T02:46:58-00:00

Neuroimage, Vol. 32, No. 1. (20 April 2006), pp. 376-387.

To investigate the neural network of overt speech production, event-related fMRI was performed in 9 young healthy adult volunteers. A clustered image acquisition technique was chosen to minimize speech-related movement artifacts. Functional images were acquired during the production of oral movements and of speech of increasing complexity (isolated vowel as well as monosyllabic and trisyllabic utterances). This imaging technique and behavioral task enabled depiction of the articulo-phonologic network of speech production from the supplementary motor area at the cranial end to the red nucleus at the caudal end. Speaking a single vowel and performing simple oral movements involved very similar activation of the cortical and subcortical motor systems. More complex, polysyllabic utterances were associated with additional activation in the bilateral cerebellum, reflecting increased demand on speech motor control, and additional activation in the bilateral temporal cortex, reflecting the stronger involvement of phonologic processing.

Centractin (ARP1) associates with spectrin revealing a potential mechanism to link dynactin to intracellular organelles

EA Holleran — 2008-06-05T14:40:39-00:00

J. Cell Biol., Vol. 135, No. 6. (1 December 1996), pp. 1815-1829.

10.1083/jcb.135.6.1815

Dynactin, a conserved, ubiquitously expressed component of an activator of vesicle motility mediated by cytoplasmic dynein

SR Gill — 2008-06-05T13:32:38-00:00

J. Cell Biol., Vol. 115, No. 6. (1 December 1991), pp. 1639-1650.

10.1083/jcb.115.6.1639

A microtubule-binding domain in dynactin increases dynein processivity by skating along microtubules

Tara Culver–hanlon — 2006-03-01T19:56:09-00:00

Nature Cell Biology, Vol. 8, No. 3. (12 February 2006), pp. 264-270.

From the Cover: Detection of fractional steps in cargo movement by the collective operation of kinesin-1 motors

Cecile Leduc — 2008-02-28T11:09:30-00:00

Proceedings of the National Academy of Sciences, Vol. 104, No. 26. (26 June 2007), pp. 10847-10852.

The stepping behavior of single kinesin-1 motor proteins has been studied in great detail. However, in cells, these motors often do not work alone but rather function in small groups when they transport cellular cargo. Until now, the cooperative interactions between motors in such groups were poorly understood. A fundamental question is whether two or more motors that move the same cargo step in synchrony, producing the same step size as a single motor, or whether the step size of the cargo movement varies. To answer this question, we performed in vitro gliding motility assays, where microtubules coated with quantum dots were driven over a glass surface by a known number of kinesin-1 motors. The motion of individual microtubules was then tracked with nanometer precision. In the case of transport by two kinesin-1 motors, we found successive 4-nm steps, corresponding to half the step size of a single motor. Dwell-time analysis did not reveal any coordination, in the sense of alternate stepping, between the motors. When three motors interacted in collective transport, we identified distinct forward and backward jumps on the order of 10 nm. The existence of the fractional steps as well as the distinct jumps illustrate a lack of synchronization and has implications for the analysis of motor-driven organelle movement investigated in vivo. 10.1073/pnas.0701864104

Spindle positioning by cortical pulling forces.

SW Grill — 2008-06-24T11:50:07-00:00

Developmental cell, Vol. 8, No. 4. (April 2005), pp. 461-465.

Proper spatial control of the cell division plane is essential to any developing organism. In most cell types, the relative size of the two daughter cells is determined by the position of the mitotic spindle within the geometry of the mother cell. We review the underlying mechanisms responsible for positioning of the mitotic spindle, both in cases where the spindle is placed in the center of the cell and in cases where the spindle is placed away from the center of the cell. We discuss the idea that cortical pulling forces are sufficient to provide a general mechanism for spindle positioning within symmetrically and asymmetrically dividing cells.