CiteULike: as3171's lfp

Temporal structure in neuronal activity during working memory in macaque parietal cortex.

B Pesaran — 2005-02-08T16:23:57-00:00

Nat Neurosci, Vol. 5, No. 8. (August 2002), pp. 805-811.

Many cortical structures have elevated firing rates during working memory, but it is not known how the activity is maintained. To investigate whether reverberating activity is important, we studied the temporal structure of local field potential (LFP) activity and spiking from area LIP in two awake macaques during a memory-saccade task. Using spectral analysis, we found spatially tuned elevated power in the gamma band (25-90 Hz) in LFP and spiking activity during the memory period. Spiking and LFP activity were also coherent in the gamma band but not at lower frequencies. Finally, we decoded LFP activity on a single-trial basis and found that LFP activity in parietal cortex discriminated between preferred and anti-preferred direction with approximately the same accuracy as the spike rate and predicted the time of a planned movement with better accuracy than the spike rate. This finding could accelerate the development of a cortical neural prosthesis.

Analysis of dynamic brain imaging data.

PP Mitra — 2005-11-23T18:04:55-00:00

Biophys J, Vol. 76, No. 2. (February 1999), pp. 691-708.

Modern imaging techniques for probing brain function, including functional magnetic resonance imaging, intrinsic and extrinsic contrast optical imaging, and magnetoencephalography, generate large data sets with complex content. In this paper we develop appropriate techniques for analysis and visualization of such imaging data to separate the signal from the noise and characterize the signal. The techniques developed fall into the general category of multivariate time series analysis, and in particular we extensively use the multitaper framework of spectral analysis. We develop specific protocols for the analysis of fMRI, optical imaging, and MEG data, and illustrate the techniques by applications to real data sets generated by these imaging modalities. In general, the analysis protocols involve two distinct stages: "noise" characterization and suppression, and "signal" characterization and visualization. An important general conclusion of our study is the utility of a frequency-based representation, with short, moving analysis windows to account for nonstationarity in the data. Of particular note are 1) the development of a decomposition technique (space-frequency singular value decomposition) that is shown to be a useful means of characterizing the image data, and 2) the development of an algorithm, based on multitaper methods, for the removal of approximately periodic physiological artifacts arising from cardiac and respiratory sources.

Local field potential reflects perceptual suppression in monkey visual cortex.

M Wilke — 2008-06-09T15:00:22-00:00

Proceedings of the National Academy of Sciences of the United States of America, Vol. 103, No. 46. (14 November 2006), pp. 17507-17512.

Neurophysiological and functional imaging experiments remain in apparent disagreement on the role played by the earliest stages of the visual cortex in supporting a visual percept. Here, we report electrophysiological findings that shed light on this issue. We monitored neural activity in the visual cortex of monkeys as they reported their perception of a high-contrast visual stimulus that was induced to vanish completely from perception on a subset of trials. We found that the spiking of neurons in cortical areas V1 and V2 was uncorrelated with the perceptual visibility of the target, whereas that in area V4 showed significant perception-related changes. In contrast, power changes in the lower frequency bands (particularly 9-30 Hz) of the local field potential (LFP), collected on the same trials, showed consistent and sustained perceptual modulation in all three areas. In addition, for the gamma frequency range (30-50 Hz), the responses during perceptual suppression of the target were correlated significantly with the responses to its physical removal in all areas, although the modulation magnitude was considerably higher in area V4 than in V1 and V2. These results, taken together, suggest that low-frequency LFP power in early cortical processing is more closely related to the representation of stimulus visibility than is spiking or higher frequency LFP activity.

Neurophysiology of the BOLD fMRI Signal in Awake Monkeys.

Jozien B M Goense — 2008-05-07T01:47:32-00:00

Current biology : CB (23 April 2008)

BACKGROUND: Simultaneous intracortical recordings of neural activity and blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in primary visual cortex of anesthetized monkeys demonstrated varying degrees of correlation between fMRI signals and the different types of neural activity, such as local field potentials (LFPs), multiple-unit activity (MUA), and single-unit activity (SUA). One important question raised by the aforementioned investigation is whether the reported correlations also apply to alert subjects. RESULTS: Monkeys were trained to perform a fixation task while stimuli within the receptive field of each recording site were used to elicit neural responses followed by a BOLD response. We show - also in alert behaving monkeys - that although both LFP and MUA make significant contributions to the BOLD response, LFPs are better and more reliable predictors of the BOLD signal. Moreover, when MUA responses adapt but LFP remains unaffected, the BOLD signal remains unaltered. CONCLUSIONS: The persistent coupling of the BOLD signal to the field potential when LFP and MUA have different time evolutions suggests that BOLD is primarily determined by the local processing of inputs in a given cortical area. In the alert animal the largest portion of the BOLD signal's variance is explained by an LFP range (20-60 Hz) that is most likely related to neuromodulation. Finally, the similarity of the results in alert and anesthetized subjects indicates that at least in V1 anesthesia is not a confounding factor. This enables the comparison of human fMRI results with a plethora of electrophysiological results obtained in alert or anesthetized animals.

Low-Frequency Local Field Potentials and Spikes in Primary Visual Cortex Convey Independent Visual Information

Andrei Belitski — 2008-06-02T10:17:41-00:00

J. Neurosci., Vol. 28, No. 22. (28 May 2008), pp. 5696-5709.

Local field potentials (LFPs) reflect subthreshold integrative processes that complement spike train measures. However, little is yet known about the differences between how LFPs and spikes encode rich naturalistic sensory stimuli. We addressed this question by recording LFPs and spikes from the primary visual cortex of anesthetized macaques while presenting a color movie. We then determined how the power of LFPs and spikes at different frequencies represents the visual features in the movie. We found that the most informative LFP frequency ranges were 1-8 and 60-100 Hz. LFPs in the range of 12-40 Hz carried little information about the stimulus, and may primarily reflect neuromodulatory inputs. Spike power was informative only at frequencies <12 Hz. We further quantified "signal correlations" (correlations in the trial-averaged power response to different stimuli) and "noise correlations" (trial-by-trial correlations in the fluctuations around the average) of LFPs and spikes recorded from the same electrode. We found positive signal correlation between high-gamma LFPs (60-100 Hz) and spikes, as well as strong positive signal correlation within high-gamma LFPs, suggesting that high-gamma LFPs and spikes are generated within the same network. LFPs <24 Hz shared strong positive noise correlations, indicating that they are influenced by a common source, such as a diffuse neuromodulatory input. LFPs <40 Hz showed very little signal and noise correlations with LFPs >40 Hz and with spikes, suggesting that low-frequency LFPs reflect neural processes that in natural conditions are fully decoupled from those giving rise to spikes and to high-gamma LFPs. 10.1523/JNEUROSCI.0009-08.2008

Free choice activates a decision circuit between frontal and parietal cortex

Bijan Pesaran — 2008-04-17T05:20:02-00:00

Nature (16 April 2008)

Measurements of Simultaneously Recorded Spiking Activity and Local Field Potentials Suggest that Spatial Selection Emerges in the Frontal Eye Field.

IE Monosov — 2008-03-03T15:48:38-00:00

Neuron, Vol. 57, No. 4. (28 February 2008), pp. 614-625.

The frontal eye field (FEF) participates in selecting the location of behaviorally relevant stimuli for guiding attention and eye movements. We simultaneously recorded local field potentials (LFPs) and spiking activity in the FEF of monkeys performing memory-guided saccade and covert visual search tasks. We compared visual latencies and the time course of spatially selective responses in LFPs and spiking activity. Consistent with the view that LFPs represent synaptic input, visual responses appeared first in the LFPs followed by visual responses in the spiking activity. However, spatially selective activity identifying the location of the target in the visual search array appeared in the spikes about 30 ms before it appeared in the LFPs. Because LFPs reflect dendritic input and spikes measure neuronal output in a local brain region, this temporal relationship suggests that spatial selection necessary for attention and eye movements is computed locally in FEF from spatially nonselective inputs.

Parallel and serial neural mechanisms for visual search in macaque area V4.

NP Bichot — 2005-05-11T13:54:34-00:00

Science, Vol. 308, No. 5721. (22 April 2005), pp. 529-534.

To find a target object in a crowded scene, a face in a crowd for example, the visual system might turn the neural representation of each object on and off in a serial fashion, testing each representation against a template of the target item. Alternatively, it might allow the processing of all objects in parallel but bias activity in favor of those neurons that represent critical features of the target, until the target emerges from the background. To test these possibilities, we recorded neurons in area V4 of monkeys freely scanning a complex array to find a target defined by color, shape, or both. Throughout the period of searching, neurons gave enhanced responses and synchronized their activity in the gamma range whenever a preferred stimulus in their receptive field matched a feature of the target, as predicted by parallel models. Neurons also gave enhanced responses to candidate targets that were selected for saccades, or foveation, reflecting a serial component of visual search. Thus, serial and parallel mechanisms of response enhancement and neural synchrony work together to identify objects in a scene. To find a target object in a crowded scene, a face in a crowd for example, the visual system might turn the neural representation of each object on and off in a serial fashion, testing each representation against a template of the target item. Alternatively, it might allow the processing of all objects in parallel but bias activity in favor of those neurons that represent critical features of the target, until the target emerges from the background. To test these possibilities, we recorded neurons in area V4 of monkeys freely scanning a complex array to find a target defined by color, shape, or both. Throughout the period of searching, neurons gave enhanced responses and synchronized their activity in the gamma range whenever a preferred stimulus in their receptive field matched a feature of the target, as predicted by parallel models. Neurons also gave enhanced responses to candidate targets that were selected for saccades, or foveation, reflecting a serial component of visual search. Thus, serial and parallel mechanisms of response enhancement and neural synchrony work together to identify objects in a scene.

Gamma-band synchronization in visual cortex predicts speed of change detection

Thilo Womelsdorf — 2005-12-22T22:43:36-00:00

Nature (21 December 2005)

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.

Behavioral Shifts and Action Valuation in the Anterior Cingulate Cortex

Rene Quilodran — 2008-01-24T15:58:11-00:00

Neuron, Vol. 57, No. 2. (24 January 2008), pp. 314-325.

Summary Rapid optimization of behavior requires decisions about when to explore and when to exploit discovered resources. The mechanisms that lead to fast adaptations and their interaction with action valuation are a central issue. We show here that the anterior cingulate cortex (ACC) encodes multiple feedbacks devoted to exploration and its immediate termination. In a task that alternates exploration and exploitation periods, the ACC monitored negative and positive outcomes relevant for different adaptations. In particular, it produced signals specific of the first reward, i.e., the end of exploration. Those signals disappeared in exploitation periods but immediately transferred to the initiation of trials--a transfer comparable to learning phenomena observed for dopaminergic neurons. Importantly, these were also observed for high gamma oscillations of local field potentials shown to correlate with brain imaging signal. Thus, mechanisms of action valuation and monitoring of events/actions are combined for rapid behavioral regulation.

Frequency decomposition of conditional Granger causality and application to multivariate neural field potential data

Yonghong Chen — 2006-01-27T16:32:00-00:00

Journal of Neuroscience Methods, Vol. 150, No. 2. (30 January 2006), pp. 228-237.

It is often useful in multivariate time series analysis to determine statistical causal relations between different time series. Granger causality is a fundamental measure for this purpose. Yet the traditional pairwise approach to Granger causality analysis may not clearly distinguish between direct causal influences from one time series to another and indirect ones acting through a third time series. In order to differentiate direct from indirect Granger causality, a conditional Granger causality measure in the frequency domain is derived based on a partition matrix technique. Simulations and an application to neural field potential time series are demonstrated to validate the method.

Beta oscillations in a large-scale sensorimotor cortical network: directional influences revealed by Granger causality.

A Brovelli — 2006-02-09T21:36:02-00:00

Proc Natl Acad Sci U S A, Vol. 101, No. 26. (29 June 2004), pp. 9849-9854.

Previous studies have shown that synchronized beta frequency (14-30 Hz) oscillations in the primary motor cortex are involved in maintaining steady contractions of contralateral arm and hand muscles. However, little is known about the role of postcentral cortical areas in motor maintenance and their patterns of interaction with motor cortex. We investigated the functional relations of beta-synchronized neuronal assemblies in pre- and postcentral areas of two monkeys as they pressed a hand lever during the wait period of a visual discrimination task. By using power and coherence spectral analysis, we identified a beta-synchronized large-scale network linking pre- and postcentral areas. We then used Granger causality spectra to measure directional influences among recording sites. In both monkeys, strong Granger causal influences were observed from primary somatosensory cortex to both motor cortex and inferior posterior parietal cortex, with the latter area also exerting Granger causal influences on motor cortex. Granger causal influences from motor cortex to postcentral sites, however, were weak in one monkey and not observed in the other. These results are the first, to our knowledge, to demonstrate in awake monkeys that synchronized beta oscillations bind multiple sensorimotor areas into a large-scale network during motor maintenance behavior and carry Granger causal influences from primary somatosensory and inferior posterior parietal cortices to motor cortex.

Learning-related coordination of striatal and hippocampal theta rhythms during acquisition of a procedural maze task

William Decoteau — 2007-07-03T15:11:01-00:00

PNAS, Vol. 104, No. 13. (27 March 2007), pp. 5644-5649.

The striatum and hippocampus are conventionally viewed as complementary learning and memory systems, with the hippocampus specialized for fact-based episodic memory and the striatum for procedural learning and memory. Here we directly tested whether these two systems exhibit independent or coordinated activity patterns during procedural learning. We trained rats on a conditional T-maze task requiring navigational and cue-based associative learning. We recorded local field potential (LFP) activity with tetrodes chronically implanted in the caudoputamen and the CA1 field of the dorsal hippocampus during 6-25 days of training. We show that simultaneously recorded striatal and hippocampal theta rhythms are modulated differently as the rats learned to perform the T-maze task but nevertheless become highly coherent during the choice period of the maze runs in rats that successfully learned the task. Moreover, in the rats that acquired the task, the phase of the striatal-hippocampal theta coherence was modified toward a consistent antiphase relationship, and these changes occurred in proportion to the levels of learning achieved. We suggest that rhythmic oscillations, including theta-band activity, could influence not only neural processing in cortico-basal ganglia circuits but also dynamic interactions between basal ganglia-based and hippocampus-based forebrain circuits during the acquisition and performance of learned behaviors. Experience-dependent changes in coordination of oscillatory activity across brain structures thus may parallel the well known plasticity of spike activity that occurs as a function of experience. 10.1073/pnas.0700818104

Neural Mechanisms of Visual Attention: How Top-Down Feedback Highlights Relevant Locations

Yuri Saalmann — 2007-06-15T08:59:06-00:00

Science, Vol. 316, No. 5831. (15 June 2007), pp. 1612-1615.

Attention helps us process potentially important objects by selectively increasing the activity of sensory neurons that represent the relevant locations and features of our environment. This selection process requires top-down feedback about what is important in our environment. We investigated how parietal cortical output influences neural activity in early sensory areas. Neural recordings were made simultaneously from the posterior parietal cortex and an earlier area in the visual pathway, the medial temporal area, of macaques performing a visual matching task. When the monkey selectively attended to a location, the timing of activities in the two regions became synchronized, with the parietal cortex leading the medial temporal area. Parietal neurons may thus selectively increase activity in earlier sensory areas to enable focused spatial attention. 10.1126/science.1139140

Top-Down Versus Bottom-Up Control of Attention in the Prefrontal and Posterior Parietal Cortices

Timothy Buschman — 2007-03-30T13:28:45-00:00

Science, Vol. 315, No. 5820. (30 March 2007), pp. 1860-1862.

Attention can be focused volitionally by "top-down" signals derived from task demands and automatically by "bottom-up" signals from salient stimuli. The frontal and parietal cortices are involved, but their neural activity has not been directly compared. Therefore, we recorded from them simultaneously in monkeys. Prefrontal neurons reflected the target location first during top-down attention, whereas parietal neurons signaled it earlier during bottom-up attention. Synchrony between frontal and parietal areas was stronger in lower frequencies during top-down attention and in higher frequencies during bottom-up attention. This result indicates that top-down and bottom-up signals arise from the frontal and sensory cortex, respectively, and different modes of attention may emphasize synchrony at different frequencies. 10.1126/science.1138071