Publications by authors named "Ethan R Buch"

26 Publications

  • Page 1 of 1

Consolidation of human skill linked to waking hippocampo-neocortical replay.

Cell Rep 2021 Jun;35(10):109193

Human Cortical Physiology and Neurorehabilitation Section, NINDS, NIH, Bethesda, MD, USA. Electronic address:

The introduction of rest intervals interspersed with practice strengthens wakeful consolidation of skill. The mechanisms by which the brain binds discrete action representations into consolidated, highly temporally resolved skill sequences during waking rest are not known. To address this question, we recorded magnetoencephalography (MEG) during acquisition and rapid consolidation of a sequential motor skill. We report the presence of prominent, fast waking neural replay during the same rest periods in which rapid consolidation occurs. The observed replay is temporally compressed by approximately 20-fold relative to the acquired skill, is selective for the trained sequence, and predicts the magnitude of skill consolidation. Replay representations extend beyond the hippocampus and entorhinal cortex to the contralateral sensorimotor cortex. These results document the presence of robust hippocampo-neocortical replay supporting rapid wakeful consolidation of skill.
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http://dx.doi.org/10.1016/j.celrep.2021.109193DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8259719PMC
June 2021

Phase-dependent offline enhancement of human motor memory.

Brain Stimul 2021 Jul-Aug;14(4):873-883. Epub 2021 May 25.

Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.

Background: Skill learning engages offline activity in the primary motor cortex (M1). Sensorimotor cortical activity oscillates between excitatory trough and inhibitory peak phases of the mu (8-12 Hz) rhythm. We recently showed that these mu phases influence the magnitude and direction of neuroplasticity induction within M1. However, the contribution of M1 activity during mu peak and trough phases to human skill learning has not been investigated.

Objective: To evaluate the effects of phase-dependent TMS during mu peak and trough phases on offline learning of a newly-acquired motor skill.

Methods: On Day 1, three groups of healthy adults practiced an explicit motor sequence learning task with their non-dominant left hand. After practice, phase-dependent TMS was applied to the right M1 during either mu peak or mu trough phases. The third group received sham TMS during random mu phases. On Day 2, all subjects were re-tested on the same task to evaluate offline learning.

Results: Subjects who received phase-dependent TMS during mu trough phases showed increased offline skill learning compared to those who received phase-dependent TMS during mu peak phases or sham TMS during random mu phases. Additionally, phase-dependent TMS during mu trough phases elicited stronger whole-brain broadband oscillatory power responses than phase-dependent TMS during mu peak phases.

Conclusions: We conclude that sensorimotor mu trough phases reflect brief windows of opportunity during which TMS can strengthen newly-acquired skill memories.
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http://dx.doi.org/10.1016/j.brs.2021.05.009DOI Listing
May 2021

Phase-dependent transcranial magnetic stimulation of the lesioned hemisphere is accurate after stroke.

Brain Stimul 2020 Sep - Oct;13(5):1354-1357. Epub 2020 Jul 17.

Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.

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http://dx.doi.org/10.1016/j.brs.2020.07.005DOI Listing
July 2020

Differential Brain Mechanisms of Selection and Maintenance of Information during Working Memory.

J Neurosci 2019 05 4;39(19):3728-3740. Epub 2019 Mar 4.

Human Cortical Physiology and Neurorehabilitation Section, NINDS, NIH, Bethesda, Maryland 20892.

Working memory is our ability to select and temporarily hold information as needed for complex cognitive operations. The temporal dynamics of sustained and transient neural activity supporting the selection and holding of memory content is not known. To address this problem, we recorded magnetoencephalography in healthy participants performing a retro-cue working memory task in which the selection rule and the memory content varied independently. Multivariate decoding and source analyses showed that selecting the memory content relies on prefrontal and parieto-occipital persistent oscillatory neural activity. By contrast, the memory content was reactivated in a distributed occipitotemporal posterior network, preceding the working memory decision and in a different format than during the visual encoding. These results identify a neural signature of content selection and characterize differentiated spatiotemporal constraints for subprocesses of working memory. Our brain selects and maintains information during short time windows in a way that is essential to reasoning and learning. Recent advances in multivariate analysis of brain activity allowed the characterization of brain regions that stores the memory. We applied multivariate analysis to time-resolved brain signals to characterize the spatiotemporal signature underlying these subprocesses. The selection of information relies on sustained oscillatory activity in a network that includes the ventrolateral prefrontal cortex while memory content is transiently replayed in an occipitotemporal network that differs from encoding. Our results characterized differentiated spatiotemporal activity underlying encoding, selection, and maintenance of information during working memory.
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http://dx.doi.org/10.1523/JNEUROSCI.2764-18.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6510345PMC
May 2019

Longitudinal Structural and Functional Differences Between Proportional and Poor Motor Recovery After Stroke.

Neurorehabil Neural Repair 2017 Dec 12;31(12):1029-1041. Epub 2017 Nov 12.

3 National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.

Background: Evolution of motor function during the first months after stroke is stereotypically bifurcated, consisting of either recovery to about 70% of maximum possible improvement ("proportional recovery, PROP") or in little to no improvement ("poor recovery, POOR"). There is currently no evidence that any rehabilitation treatment will prevent POOR and favor PROP.

Objective: To perform a longitudinal and multimodal assessment of functional and structural changes in brain organization associated with PROP.

Methods: Fugl-Meyer Assessments of the upper extremity and high-density electroencephalography (EEG) were obtained from 63 patients, diffusion tensor imaging from 46 patients, at 2 and 4 weeks (T0) and at 3 months (T1) after stroke onset.

Results: We confirmed the presence of 2 distinct recovery patterns (PROP and POOR) in our sample. At T0, PROP patients had greater integrity of the corticospinal tract (CST) and greater EEG functional connectivity (FC) between the affected hemisphere and rest of the brain, in particular between the ventral premotor and the primary motor cortex. POOR patients suffered from degradation of corticocortical and corticofugal fiber tracts in the affected hemisphere between T0 and T1, which was not observed in PROP patients. Better initial CST integrity correlated with greater initial global FC, which was in turn associated with less white matter degradation between T0 and T1.

Conclusions: These findings suggest links between initial CST integrity, systems-level cortical network plasticity, reduction of white matter atrophy, and clinical motor recovery after stroke. This identifies candidate treatment targets.
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http://dx.doi.org/10.1177/1545968317740634DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6368856PMC
December 2017

Effects of tDCS on motor learning and memory formation: A consensus and critical position paper.

Clin Neurophysiol 2017 Apr 29;128(4):589-603. Epub 2017 Jan 29.

Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA. Electronic address:

Motor skills are required for activities of daily living. Transcranial direct current stimulation (tDCS) applied in association with motor skill learning has been investigated as a tool for enhancing training effects in health and disease. Here, we review the published literature investigating whether tDCS can facilitate the acquisition, retention or adaptation of motor skills. Work in multiple laboratories is underway to develop a mechanistic understanding of tDCS effects on different forms of learning and to optimize stimulation protocols. Efforts are required to improve reproducibility and standardization. Overall, reproducibility remains to be fully tested, effect sizes with present techniques vary over a wide range, and the basis of observed inter-individual variability in tDCS effects is incompletely understood. It is recommended that future studies explicitly state in the Methods the exploratory (hypothesis-generating) or hypothesis-driven (confirmatory) nature of the experimental designs. General research practices could be improved with prospective pre-registration of hypothesis-based investigations, more emphasis on the detailed description of methods (including all pertinent details to enable future modeling of induced current and experimental replication), and use of post-publication open data repositories. A checklist is proposed for reporting tDCS investigations in a way that can improve efforts to assess reproducibility.
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http://dx.doi.org/10.1016/j.clinph.2017.01.004DOI Listing
April 2017

3D-printed head models for navigated non-invasive brain stimulation.

Clin Neurophysiol 2016 10 25;127(10):3341-2. Epub 2016 Aug 25.

Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, United States. Electronic address:

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http://dx.doi.org/10.1016/j.clinph.2016.08.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5108057PMC
October 2016

Predicting motor improvement after stroke with clinical assessment and diffusion tensor imaging.

Neurology 2016 05 29;86(20):1924-5. Epub 2016 Apr 29.

From the Human Cortical Physiology and Neurorehabilitation Section (E.R.B., L.G.C.), NINDS, NIH, Bethesda, MD; and University Hospital and University of Geneva (S.R., P.N., A.S., A.G.G.), Switzerland.

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http://dx.doi.org/10.1212/WNL.0000000000002675DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4873682PMC
May 2016

Plasticity of Sensorimotor Networks: Multiple Overlapping Mechanisms.

Neuroscientist 2017 04 8;23(2):185-196. Epub 2016 Jul 8.

1 National Institute of Neurological Disorders and Stroke (NINDS), Bethesda, MD, USA.

Redundancy is an important feature of the motor system, as abundant degrees of freedom are prominent at every level of organization across the central and peripheral nervous systems, and musculoskeletal system. This basic feature results in a system that is both flexible and robust, and which can be sustainably adapted through plasticity mechanisms in response to intrinsic organismal changes and dynamic environments. While much early work of motor system organization has focused on synaptic-based plasticity processes that are driven via experience, recent investigations of neuron-glia interactions, epigenetic mechanisms and large-scale network dynamics have revealed a plethora of plasticity mechanisms that support motor system organization across multiple, overlapping spatial and temporal scales. Furthermore, an important role of these mechanisms is the regulation of intrinsic variability. Here, we review several of these mechanisms and discuss their potential role in neurorehabilitation.
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http://dx.doi.org/10.1177/1073858416638641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5108685PMC
April 2017

Altered Human Memory Modification in the Presence of Normal Consolidation.

Cereb Cortex 2016 09 12;26(9):3828-3837. Epub 2015 Aug 12.

Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.

Following initial learning, the memory is stabilized by consolidation mechanisms, and subsequent modification of memory strength occurs via reconsolidation. Yet, it is not clear whether consolidation and memory modification are the same or different systems-level processes. Here, we report disrupted memory modification in the presence of normal consolidation of human motor memories, which relate to differences in lesioned brain structure after stroke. Furthermore, this behavioral dissociation was associated with macrostructural network architecture revealed by a graph-theoretical approach, and with white-matter microstructural integrity measured by diffusion-weighted MRI. Altered macrostructural network architecture and microstructural integrity of white-matter underlying critical nodes of the related network predicted disrupted memory modification. To the best of our knowledge, this provides the first evidence of mechanistic differences between consolidation, and subsequent memory modification through reconsolidation, in human procedural learning. These findings enable better understanding of these memory processes, which may guide interventional strategies to enhance brain function and resulting behavior.
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http://dx.doi.org/10.1093/cercor/bhv180DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5004751PMC
September 2016

Causal manipulation of functional connectivity in a specific neural pathway during behaviour and at rest.

Elife 2015 Feb 9;4. Epub 2015 Feb 9.

Department of Experimental Psychology, Oxford University, Oxford, United Kingdom.

Correlations in brain activity between two areas (functional connectivity) have been shown to relate to their underlying structural connections. We examine the possibility that functional connectivity also reflects short-term changes in synaptic efficacy. We demonstrate that paired transcranial magnetic stimulation (TMS) near ventral premotor cortex (PMv) and primary motor cortex (M1) with a short 8-ms inter-pulse interval evoking synchronous pre- and post-synaptic activity and which strengthens interregional connectivity between the two areas in a pattern consistent with Hebbian plasticity, leads to increased functional connectivity between PMv and M1 as measured with functional magnetic resonance imaging (fMRI). Moreover, we show that strengthening connectivity between these nodes has effects on a wider network of areas, such as decreasing coupling in a parallel motor programming stream. A control experiment revealed that identical TMS pulses at identical frequencies caused no change in fMRI-measured functional connectivity when the inter-pulse-interval was too long for Hebbian-like plasticity.
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http://dx.doi.org/10.7554/eLife.04585DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4353194PMC
February 2015

Non-invasive brain stimulation in neurorehabilitation: local and distant effects for motor recovery.

Front Hum Neurosci 2014 27;8:378. Epub 2014 Jun 27.

Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, NIH Bethesda, MD, USA ; Center for Neuroscience and Regenerative Medicine, Uniformed Services University of Health Sciences Bethesda, MD, USA.

Non-invasive brain stimulation (NIBS) may enhance motor recovery after neurological injury through the causal induction of plasticity processes. Neurological injury, such as stroke, often results in serious long-term physical disabilities, and despite intensive therapy, a large majority of brain injury survivors fail to regain full motor function. Emerging research suggests that NIBS techniques, such as transcranial magnetic (TMS) and direct current (tDCS) stimulation, in association with customarily used neurorehabilitative treatments, may enhance motor recovery. This paper provides a general review on TMS and tDCS paradigms, the mechanisms by which they operate and the stimulation techniques used in neurorehabilitation, specifically stroke. TMS and tDCS influence regional neural activity underlying the stimulation location and also distant interconnected network activity throughout the brain. We discuss recent studies that document NIBS effects on global brain activity measured with various neuroimaging techniques, which help to characterize better strategies for more accurate NIBS stimulation. These rapidly growing areas of inquiry may hold potential for improving the effectiveness of NIBS-based interventions for clinical rehabilitation.
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http://dx.doi.org/10.3389/fnhum.2014.00378DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4072967PMC
July 2014

Can cortical stimulation of inferior frontal cortex enhance proactive control?

J Neurosci 2014 Apr;34(18):6125-7

Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, United Kingdom, Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom, Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20814, and Center for Neuroscience and Regenerative Medicine, Uniformed Services University of Health Sciences, Bethesda, Maryland 20814.

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http://dx.doi.org/10.1523/JNEUROSCI.0590-14.2014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4004802PMC
April 2014

Noninvasive brain stimulation: from physiology to network dynamics and back.

Nat Neurosci 2013 Jul 25;16(7):838-44. Epub 2013 Jun 25.

Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, US National Institutes of Health, Bethesda, Maryland, USA.

Noninvasive brain stimulation techniques have been widely used for studying the physiology of the CNS, identifying the functional role of specific brain structures and, more recently, exploring large-scale network dynamics. Here we review key findings that contribute to our understanding of the mechanisms underlying the physiological and behavioral effects of these techniques. We highlight recent innovations using noninvasive stimulation to investigate global brain network dynamics and organization. New combinations of these techniques, in conjunction with neuroimaging, will further advance the utility of their application.
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http://dx.doi.org/10.1038/nn.3422DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4876726PMC
July 2013

Parietofrontal integrity determines neural modulation associated with grasping imagery after stroke.

Brain 2012 Feb 9;135(Pt 2):596-614. Epub 2012 Jan 9.

Human Cortical Physiology and Stroke Neurorehabilitation Section, NINDS, NIH, Bethesda, MD 20892, USA.

Chronic stroke patients with heterogeneous lesions, but no direct damage to the primary sensorimotor cortex, are capable of longitudinally acquiring the ability to modulate sensorimotor rhythms using grasping imagery of the affected hand. Volitional modulation of neural activity can be used to drive grasping functions of the paralyzed hand through a brain-computer interface. The neural substrates underlying this skill are not known. Here, we investigated the impact of individual patient's lesion pathology on functional and structural network integrity related to this volitional skill. Magnetoencephalography data acquired throughout training was used to derive functional networks. Structural network models and local estimates of extralesional white matter microstructure were constructed using T(1)-weighted and diffusion-weighted magnetic resonance imaging data. We employed a graph theoretical approach to characterize emergent properties of distributed interactions between nodal brain regions of these networks. We report that interindividual variability in patients' lesions led to differential impairment of functional and structural network characteristics related to successful post-training sensorimotor rhythm modulation skill. Patients displaying greater magnetoencephalography global cost-efficiency, a measure of information integration within the distributed functional network, achieved greater levels of skill. Analysis of lesion damage to structural network connectivity revealed that the impact on nodal betweenness centrality of the ipsilesional primary motor cortex, a measure that characterizes the importance of a brain region for integrating visuomotor information between frontal and parietal cortical regions and related thalamic nuclei, correlated with skill. Edge betweenness centrality, an analogous measure, which assesses the role of specific white matter fibre pathways in network integration, showed a similar relationship between skill and a portion of the ipsilesional superior longitudinal fascicle connecting premotor and posterior parietal visuomotor regions known to be crucially involved in normal grasping behaviour. Finally, estimated white matter microstructure integrity in regions of the contralesional superior longitudinal fascicle adjacent to primary sensorimotor and posterior parietal cortex, as well as grey matter volume co-localized to these specific regions, positively correlated with sensorimotor rhythm modulation leading to successful brain-computer interface control. Thus, volitional modulation of ipsilesional neural activity leading to control of paralyzed hand grasping function through a brain-computer interface after longitudinal training relies on structural and functional connectivity in both ipsilesional and contralesional parietofrontal pathways involved in visuomotor information processing. Extant integrity of this structural network may serve as a future predictor of response to longitudinal therapeutic interventions geared towards training sensorimotor rhythms in the lesioned brain, secondarily improving grasping function through brain-computer interface applications.
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http://dx.doi.org/10.1093/brain/awr331DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3286199PMC
February 2012

Noninvasive associative plasticity induction in a corticocortical pathway of the human brain.

J Neurosci 2011 Nov;31(48):17669-79

Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, United Kingdom.

Coincident pairing of presynaptic and postsynaptic activity selectively strengthens synaptic connections, a key mechanism underlying cortical plasticity. Using paired associative transcranial magnetic stimulation (TMS), we demonstrate selective potentiation of physiological connectivity between two human brain regions, ventral premotor cortex (PMv) and primary motor cortex (M1) after repeated paired-pulse TMS of PMv and M1. The effect was anatomically specific: paired stimulation of the presupplementary motor area and M1 did not induce changes in PMv-M1 pathway connectivity. The effect was dependent on stimulation order: repeated stimulation of PMv before M1 led to strengthening of the PMv-M1 pathway, while repeated stimulation of M1 before PMv diminished the strength of the PMv-M1 pathway. The expression of the change in the pathway depended on the cognitive state of the subject at the time of testing: when the subject was tested at rest, paired PMv-M1 stimulation led to an increased inhibitory influence of PMv over M1, but when the subject was tested while engaged in a visuomotor task, PMv-M1 stimulation led to an increased facilitatory influence of PMv over M1. Plasticity evolved rapidly, lasted for at least 1 h, and began to reverse 3 h after intervention.
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http://dx.doi.org/10.1523/JNEUROSCI.1513-11.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6623800PMC
November 2011

Rewiring the brain: potential role of the premotor cortex in motor control, learning, and recovery of function following brain injury.

Neurorehabil Neural Repair 2012 Mar-Apr;26(3):282-92. Epub 2011 Sep 16.

Rehabilitation Institute of Chicago, Chicago, IL 60611, USA.

The brain is a plastic organ with a capability to reorganize in response to behavior and/or injury. Following injury to the motor cortex or emergent corticospinal pathways, recovery of function depends on the capacity of surviving anatomical resources to recover and repair in response to task-specific training. One such area implicated in poststroke reorganization to promote recovery of upper extremity recovery is the premotor cortex (PMC). This study reviews the role of distinct subdivisions of PMC: dorsal (PMd) and ventral (PMv) premotor cortices as critical anatomical and physiological nodes within the neural networks for the control and learning of goal-oriented reach and grasp actions in healthy individuals and individuals with stroke. Based on evidence emerging from studies of intrinsic and extrinsic connectivity, transcranial magnetic stimulation, functional neuroimaging, and experimental studies in animals and humans, the authors propose 2 distinct patterns of reorganization that differentially engage ipsilesional and contralesional PMC. Research directions that may offer further insights into the role of PMC in motor control, learning, and poststroke recovery are also proposed. This research may facilitate neuroplasticity for maximal recovery of function following brain injury.
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http://dx.doi.org/10.1177/1545968311420845DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4886541PMC
June 2012

White matter microstructural correlates of superior long-term skill gained implicitly under randomized practice.

Cereb Cortex 2012 Jul 12;22(7):1671-7. Epub 2011 Sep 12.

Human Cortical Physiology and Stroke Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20814, USA.

We value skills we have learned intentionally, but equally important are skills acquired incidentally without ability to describe how or what is learned, referred to as implicit. Randomized practice schedules are superior to grouped schedules for long-term skill gained intentionally, but its relevance for implicit learning is not known. In a parallel design, we studied healthy subjects who learned a motor sequence implicitly under randomized or grouped practice schedule and obtained diffusion-weighted images to identify white matter microstructural correlates of long-term skill. Randomized practice led to superior long-term skill compared with grouped practice. Whole-brain analyses relating interindividual variability in fractional anisotropy (FA) to long-term skill demonstrated that 1) skill in randomized learners correlated with FA within the corticostriatal tract connecting left sensorimotor cortex to posterior putamen, while 2) skill in grouped learners correlated with FA within the right forceps minor connecting homologous regions of the prefrontal cortex (PFC) and the corticostriatal tract connecting lateral PFC to anterior putamen. These results demonstrate first that randomized practice schedules improve long-term implicit skill more than grouped practice schedules and, second, that the superior skill acquired through randomized practice can be related to white matter microstructure in the sensorimotor corticostriatal network.
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http://dx.doi.org/10.1093/cercor/bhr247DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3377966PMC
July 2012

Distributed and causal influence of frontal operculum in task control.

Proc Natl Acad Sci U S A 2011 Mar 22;108(10):4230-5. Epub 2011 Feb 22.

Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, United Kingdom.

It has been suggested that the frontal operculum (fO) is a key node in a network for exerting control over cognitive processes. How it exerts this influence, however, has been unclear. Here, using the complementary approaches of functional MRI and transcranial magnetic stimulation, we have shown that the fO regulates increases and decreases of activity in multiple occipitotemporal cortical areas when task performance depended on directing attention to different classes of stimuli held in memory. Only one region, the fO, was significantly more active when subjects selectively attended to a single stimulus so that it determined task performance. The stimuli that guided task performance could belong to three categories--houses, body parts, and faces--associated with three occipitotemporal regions. On each trial, the pattern of functional correlation between the fO and the three occipitotemporal regions became either positive or negative, depending on which stimulus was to be attended and which ignored. Activation of the fO preceded both activity increases and decreases in the occipitotemporal cortex. The causal dependency of the distributed occipitotemporal pattern of activity increases and decreases on the fO was demonstrated by showing that transcranial magnetic stimulation-mediated interference of the fO diminished top-down selective attentional modulation in the occipitotemporal cortex, but it did not alter bottom-up activation of the same areas to the same stimuli when they were presented in isolation. The fO's prominence in cognitive control may stem from a role in regulating the level of activity of representations in posterior brain areas that are relevant or irrelevant, respectively, for response selection.
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http://dx.doi.org/10.1073/pnas.1013361108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3054014PMC
March 2011

Cortical and subcortical interactions during action reprogramming and their related white matter pathways.

Proc Natl Acad Sci U S A 2010 Jul 9;107(30):13240-5. Epub 2010 Jul 9.

Department of Experimental Psychology, University of Oxford, John Radcliffe Hospital, Oxford OX1 3UD, United Kingdom.

The right inferior frontal gyrus (rIFG) and the presupplementary motor area (pre-SMA) have been identified with cognitive control-the top-down influence on other brain areas when nonroutine behavior is required. It has been argued that they "inhibit" habitual motor responses when environmental changes mean a different response should be made. However, whether such "inhibition" can be equated with inhibitory physiological interactions has been unclear, as has the areas' relationship with each other and the anatomical routes by which they influence movement execution. Paired-pulse transcranial magnetic stimulation (ppTMS) was applied over rIFG and primary motor cortex (M1) or over pre-SMA and M1 to measure their interactions, at a subsecond scale, during either inhibition and reprogramming of actions or during routine action selection. Distinct patterns of functional interaction between pre-SMA and M1 and between rIFG and M1 were found that were specific to action reprogramming trials; at a physiological level, direct influences of pre-SMA and rIFG on M1 were predominantly facilitatory and inhibitory, respectively. In a subsequent experiment, it was shown that the rIFG's inhibitory influence was dependent on pre-SMA. A third experiment showed that pre-SMA and rIFG influenced M1 at two time scales. By regressing white matter fractional anisotropy from diffusion-weighted magnetic resonance images against TMS-measured functional connectivity, it was shown that short-latency (6 ms) and longer latency (12 ms) influences were mediated by cortico-cortical and subcortical pathways, respectively, with the latter passing close to the subthalamic nucleus.
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http://dx.doi.org/10.1073/pnas.1000674107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2922153PMC
July 2010

A network centered on ventral premotor cortex exerts both facilitatory and inhibitory control over primary motor cortex during action reprogramming.

J Neurosci 2010 Jan;30(4):1395-401

Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, United Kingdom.

Ventral premotor cortex (PMv) is widely accepted to exert an important influence over primary motor cortex (M1) when hand movements are made. Although study of these interactions has typically focused on their excitatory nature, given its strong connections with both ventral and opercular frontal regions, one feature of the influence of PMv over M1 may be inhibitory. Paired-pulse transcranial magnetic stimulation (ppTMS) was used to examine functional interactions between human PMv and M1 during the selection and reprogramming of a naturalistic goal-directed action. One of two cylinders was illuminated on each trial. It was then grasped and picked up. On some trials, however, subjects had to reprogram the action as the illuminated cylinder was switched off and the other illuminated simultaneously with reach initiation. At a neurophysiological level, the PMv paired-pulse effect (PPE) on M1 corticospinal activity was facilitatory after the initial target presentation and during movement initiation. When reprogramming was required, however, the PPE became strongly inhibitory. This context-dependent change from facilitation to inhibition occurred within 75 ms of the change of target. Behaviorally, PMv-M1 ppTMS disrupted reprogramming. Diffusion-weighted magnetic resonance image scans were taken of each subject. Intersubject differences in the facilitation-inhibition contrast of PMv-M1 interactions were correlated with fractional anisotropy of white-matter in ventral prefrontal, premotor, and intraparietal brain areas. These results suggest that a network of brain areas centered on PMv inhibits M1 corticospinal activity associated with undesired movements when action plans change.
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http://dx.doi.org/10.1523/JNEUROSCI.4882-09.2010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2880444PMC
January 2010

Short-latency influence of medial frontal cortex on primary motor cortex during action selection under conflict.

J Neurosci 2009 May;29(21):6926-31

Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, United Kingdom.

Medial frontal cortex (MFC) is crucial when actions have to be inhibited, reprogrammed, or selected under conflict, but the precise mechanism by which it operates is unclear. Importantly, how and when the MFC influences the primary motor cortex (M1) during action selection is unknown. Using paired-pulse transcranial magnetic stimulation, we investigated functional connectivity between the presupplementary motor area (pre-SMA) part of MFC and M1. We found that functional connectivity increased in a manner dependent on cognitive context: pre-SMA facilitated the motor evoked-potential elicited by M1 stimulation only during action reprogramming, but not when otherwise identical actions were made in the absence of conflict. The effect was anatomically specific to pre-SMA; it was not seen when adjacent brain regions were stimulated. We discuss implications for the anatomical pathways mediating the observed effects.
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http://dx.doi.org/10.1523/JNEUROSCI.1396-09.2009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6665588PMC
May 2009

Noninvasive cortical stimulation enhances motor skill acquisition over multiple days through an effect on consolidation.

Proc Natl Acad Sci U S A 2009 Feb 21;106(5):1590-5. Epub 2009 Jan 21.

Human Cortical Physiology Section and Stroke Neurorehabilitation Clinic, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.

Motor skills can take weeks to months to acquire and can diminish over time in the absence of continued practice. Thus, strategies that enhance skill acquisition or retention are of great scientific and practical interest. Here we investigated the effect of noninvasive cortical stimulation on the extended time course of learning a novel and challenging motor skill task. A skill measure was chosen to reflect shifts in the task's speed-accuracy tradeoff function (SAF), which prevented us from falsely interpreting variations in position along an unchanged SAF as a change in skill. Subjects practiced over 5 consecutive days while receiving transcranial direct current stimulation (tDCS) over the primary motor cortex (M1). Using the skill measure, we assessed the impact of anodal (relative to sham) tDCS on both within-day (online) and between-day (offline) effects and on the rate of forgetting during a 3-month follow-up (long-term retention). There was greater total (online plus offline) skill acquisition with anodal tDCS compared to sham, which was mediated through a selective enhancement of offline effects. Anodal tDCS did not change the rate of forgetting relative to sham across the 3-month follow-up period, and consequently the skill measure remained greater with anodal tDCS at 3 months. This prolonged enhancement may hold promise for the rehabilitation of brain injury. Furthermore, these findings support the existence of a consolidation mechanism, susceptible to anodal tDCS, which contributes to offline effects but not to online effects or long-term retention.
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http://dx.doi.org/10.1073/pnas.0805413106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2635787PMC
February 2009

Comparison of population activity in the dorsal premotor cortex and putamen during the learning of arbitrary visuomotor mappings.

Exp Brain Res 2006 Feb 12;169(1):69-84. Epub 2005 Nov 12.

Section on Neurophysiology, Laboratory of Systems Neuroscience, National Institute of Mental Health, National Institute of Health, 49 Convent Drive, MSC 4401, Building 49/Room B1EE17, Bethesda, MD 20892-4401, USA.

A previous study found that as monkeys learned novel mappings between visual cues and responses, neuronal activity patterns evolved at approximately the same time in both the dorsal premotor cortex (PMd) and the putamen. Here we report that, in both regions, the population activity for novel mappings came to resemble that for familiar ones as learning progressed. Both regions showed activity differences on trials with correct responses versus those with incorrect ones. In addition to these common features, we observed two noteworthy differences between PMd and putamen activity during learning. After a response choice had been made, but prior to feedback about the correctness of that choice (reward or nonreward), the putamen showed a sustained activity increase in activity, whereas PMd did not. Also in the putamen, this prereward activity was highly selective for the specific visuomotor mapping that had just been performed, and this selectivity was maintained until the time of the reward. After performance reached an asymptote, the degree of this selectivity decreased markedly to the level typical for familiar visuomotor mappings. These findings support the hypothesis that neurons in the striatum play a pivotal role in associative learning.
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http://dx.doi.org/10.1007/s00221-005-0130-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1413509PMC
February 2006

Effects of Parkinson's disease on visuomotor adaptation.

Exp Brain Res 2003 May 13;150(1):25-32. Epub 2003 Mar 13.

Department of Kinesiology, University of Maryland, 2363 HHP Building, College Park, MD 20742, USA.

Visuomotor adaptation to a kinematic distortion was investigated in Parkinson's disease (PD) patients and age-matched controls. Participants performed pointing movements in which the visual feedback of hand movement, displayed as a screen cursor, was normal (pre-exposure condition) or rotated by 90 degrees counterclockwise (exposure condition). Aftereffects were assessed in a post-exposure condition in which the visual feedback of hand movement was set back to normal. In pre- and early-exposure trials, both groups showed similar initial directional error (IDE) and movement straightness (RMSE, root mean square error), but the PD group showed reduced movement smoothness (normalized jerk, NJ) and primary submovement to total movement distance ratios (PTR). During late-exposure the PD subjects, compared with controls, showed larger IDE, RMSE, NJ, and smaller PTR scores. Moreover, PD patients showed smaller aftereffects than the controls during the post-exposure condition. Overall, the PD group showed both slower and reduced adaptation compared with the control group. These results are discussed in terms of reduced signal-to-noise ratio in feedback signals related to increased movement variability and/or disordered kinesthesia, deficits in movement initiation, impaired selection of initial movement direction, and deficits in internal model formation in PD patients. We conclude that Parkinson's disease impairs visuomotor adaptation.
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http://dx.doi.org/10.1007/s00221-003-1403-yDOI Listing
May 2003

Visuomotor adaptation in normal aging.

Learn Mem 2003 Jan-Feb;10(1):55-63

Department of Kinesiology, University of Maryland, College Park, Maryland 20742, USA.

Visuomotor adaptation to a gradual or sudden screen cursor rotation was investigated in healthy young and elderly subjects. Both age groups were equally divided into two subgroups; one subgroup was exposed to 11.25 degrees step increments of visual feedback rotation, every 45 trials (up to a total of 90 degrees), whereas a second subgroup was subjected to 90 degrees rotation from the onset of exposure. Participants performed discrete, horizontal hand movements to virtual targets in four randomized directions. Targets appeared on a computer screen in front of them, and a board prevented vision of the hand at all times. Differential effects of aging on visuomotor adaptation were found, depending on the time course of the visual distortion. In both age groups, early exposure to the sudden visual feedback distortion resulted in typical spiral-like trajectories, which became straighter by late exposure. However, the final adaptation level was reduced in the aged group, although the aftereffects were similar. When subjects were exposed to the gradual distortion, no statistically significant differences in measures of adaptation with advancing age were found. In this case, both age groups appeared to adapt equally. However, after removal of the distortion, elderly subjects showed reduced aftereffects as compared with the young group. These findings suggest differential effects of aging on adaptation to gradual versus sudden visual feedback distortions, and may help to explain the conflicting results obtained in previous visuomotor adaptation studies.
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http://dx.doi.org/10.1101/lm.50303DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC196655PMC
May 2003
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