Role of the primary somatosensory cortex in motor learning: An rTMS study

Somatosensation is thought to play an important role in skilled motor learning. The present study investigated how healthy adults learn a continuous implicit motor task when somatosensation is altered by 1 Hz repetitive transcranial magnetic stimulation (rTMS) delivered over the primary somatosensory cortex (S1). Twenty-seven right-handed participants enrolled in a two-part experiment. In Experiment 1, we verified that 20 min of 1 Hz rTMS over S1 disrupted cutaneous somatosensation (indexed by two-point discrimination) in the wrist/hand; the impact of 1 Hz rTMS on wrist proprioception (tested by limb-position matching) was variable. Sham rTMS had no effect on either measure. We exploited these effects in Experiment 2 by pairing either 1 Hz or sham rTMS with practice of a continuous tracking task over two separate sessions on different days. Implicit motor learning was indexed on a third, separate retention test day when no rTMS was delivered. Across practice in Experiment 2, both the 1 Hz and sham rTMS groups showed improved tracking performance; however, 1 Hz rTMS was associated with less accurate tracking and smaller improvements in performance. Importantly, at the no rTMS retention test the effects of altering sensation with stimulation over S1 were still evident in the persistently less accurate tracking behavior of the 1 Hz rTMS group. The current study shows that disruption of somatosensation during task practice impairs the magnitude of change associated with motor learning, perhaps through the development of an inaccurate internal model.     

Transfer of motor learning engages specific neural substrates during motor memory consolidation dependent on the practice structure

The authors investigated how brain activity during motor-memory consolidation contributes to transfer of learning to novel versions of a motor skill following distinct practice structures. They used 1 Hz repetitive Transcranial Magnetic Stimulation (rTMS) immediately after constant or variable practice of an arm movement skill to interfere with primary motor cortex (M1) or dorsolateral prefrontal cortex (DLPFC). The effect of interference was assessed through skill performance on two transfer targets: one within and one outside the range of practiced movement parameters for the variable practice group. For the control (no rTMS) group, variable practice benefited delayed transfer performance more than constant practice. The rTMS effect on delayed transfer performance differed for the two transfer targets. For the within-range target, rTMS interference had no significant affect on the delayed transfer after either practice structure. However, for the outside-range target, rTMS interference to DLPFC but not M1 attenuated delayed transfer benefit following variable practice. Additionally, for the outside-range target, rTMS interference to M1 but not DLPFC attenuated delayed transfer following constant practice. This suggests that variable practice may promote reliance on DLPFC for memory consolidation associated with outside-range transfer of learning, whereas constant practice may promote reliance on M1 for consolidation and long-term transfer.     

Transfer of Motor Learning Engages Specific Neural Substrates During Motor Memory Consolidation Dependent on the Practice Structure

The authors investigated how brain activity during motor-memory consolidation contributes to transfer of learning to novel versions of a motor skill following distinct practice structures. They used 1 Hz repetitive Transcranial Magnetic Stimulation (rTMS) immediately after constant or variable practice of an arm movement skill to interfere with primary motor cortex (M1) or dorsolateral prefrontal cortex (DLPFC). The effect of interference was assessed through skill performance on two transfer targets: one within and one outside the range of practiced movement parameters for the variable practice group. For the control (no rTMS) group, variable practice benefited delayed transfer performance more than constant practice. The rTMS effect on delayed transfer performance differed for the two transfer targets. For the within-range target, rTMS interference had no significant affect on the delayed transfer after either practice structure. However, for the outside-range target, rTMS interference to DLPFC but not M1 attenuated delayed transfer benefit following variable practice. Additionally, for the outside-range target, rTMS interference to M1 but not DLPFC attenuated delayed transfer following constant practice. This suggests that variable practice may promote reliance on DLPFC for memory consolidation associated with outside-range transfer of learning, whereas constant practice may promote reliance on M1 for consolidation and long-term transfer.     

Rapid modulation of distributed brain activity by Transcranial Magnetic Stimulation of human motor cortex

This paper reviews the effects of single and repetitive transcranial magnetic stimuli (rTMS) delivered to one cortical area and measured across distributed brain regions using electrophysiological measures (e.g. motor thresholds, motor evoked potentials, paired-pulse stimulation), functional neuroimaging (including EEG, PET and fMRI) and behavioural measures. Discussion is restricted to changes in excitability in the primary motor cortex and behaviour during motor tasks following transcranial magnetic stimulation delivered to primary motor and premotor areas. Trains of rTMS have lasting effects on the excitability of intrinsic and corticofugal neurones, altering the responsiveness of local and remote sites. These effects lead to distributed changes in synaptic activity at rest, and during a range of motor tasks. It is possible to impair or improve performance following rTMS, but for most simple motor tasks performance is unaltered. Changes in distributed activity observed with functional imaging during motor behaviour may represent compensatory activity, enabling maintenance of performance; stimulation of additional cortical areas appears to impair performance. A detailed understanding of the distributed changes in excitability following rTMS may facilitate future attempts to modulate motor behaviour in the healthy brain and for therapeutic purposes.     

Influence of Motor Cortex Stimulation During Motor Training on Neuroplasticity as a Potential Therapeutic Intervention

Rehabilitation options to promote neuroplasticity may be enhanced when patients are engaged in motor practice during repetitive transcranial magnetic stimulation (rTMS). Twelve participants completed 3 separate sessions: motor practice, motor practice with rTMS, and rTMS only: motor practice consisted of 30 isometric contractions and subthreshold rTMS was 30, 3-s trains at 10 Hz. Assessments included the Box and Block Test (BBT), force steadiness (10% of the maximum voluntary contraction), and TMS (cortical excitability, intracortical inhibition, and intracortical facilitation). Participants significantly increased BBT scores following the combined condition. Force steadiness improved after all 3 conditions (p < .05). TMS outcomes depended on intervention condition with significant increases in facilitation following the motor practice plus rTMS condition. All interventions influenced motor control, yet are likely modulated differently when combining motor practice plus rTMS. These results help guide the clinical utility of rTMS as an intervention to influence motor control.     

Does Transcranial Direct Current Stimulation Affect the Learning of a Fine Sequential Hand Motor Skill with Motor Imagery?

Learning a fine sequential hand motor skill, like playing the piano or learning to type, improves not only due to physical practice, but also due to motor imagery. Previous studies revealed that transcranial direct current stimulation (tDCS) and motor imagery independently affect motor learning. In the present study, we investigated whether tDCS combined with motor imagery above the primary motor cortex influences sequence-specific learning. Four groups of participants were involved: an anodal, cathodal, sham stimulation, and a control group (without stimulation). A modified discrete sequence production (DSP) task was employed: the Go/NoGo DSP task. After a sequence of spatial cues, a response sequence had to be either executed, imagined, or withheld. This task allows to estimate both non-specific learning and sequence-specific learning effects by comparing the execution of unfamiliar sequences, familiar imagined, familiar withheld, and familiar executed sequences in a test phase. Results showed that the effects of anodal tDCS were already developing during the practice phase, while no effects of tDCS on sequence-specific learning were visible during the test phase. Results clearly showed that motor imagery itself influences sequence learning, but we also revealed that tDCS does not increase the influence of motor imagery on sequence learning.     

Effects of dynamic and isometric motor practice on position control,force control and corticomuscular coherence in preadolescent children

In this study, we investigated the effects of motor practice with an emphasis on either position or force control on motor performance, motor accuracy and variability in preadolescent children. Furthermore, we investigated corticomuscular coherence and potential changes following motor practice.We designed a setup allowing discrete wrist flexions of the non-dominant hand and tested motor accuracy and variability when the task was to generate specific movement endpoints (15–75 deg) or force levels (5–25% MVC). All participants were tested in both tasks at baseline and post motor practice without augmented feedback on performance. Following baseline assessment, participants (44 children aged 9–11 years) were randomly assigned to either position (PC) or force control (FC) motor practice or a resting control group (CON). The PC and FC groups performed four blocks of 40 trials motor practice with augmented feedback on performance.Following practice, improvements in movement accuracy were significantly greater in the PC group compared to the FC and CON groups (p < 0.001). None of the groups displayed changes in force task performance indicating no benefits of force control motor practice and low transfer between tasks (p-values:0.08–0.45). Corticomuscular coherence (C4-FCR) was demonstrated during the hold phase in both tasks with no difference between tasks. Corticomuscular coherence did not change from baseline to post practice in any group. Our findings demonstrate that preadolescent children improve position control following dynamic accuracy motor practice. Contrary to previous findings in adults, preadolescent children displayed smaller or no improvements in force control following isometric motor practice, low transfer between tasks and no changes in corticomuscular coherence.     

基于fNIRS的运动执行与运动想象脑激活模式比较

使用《运动想象问卷−修订版》筛选出的30名被试(男女各半), 采用功能性近红外光谱成像技术(fNIRS)监测被试在执行实际举哑铃(男生, 4磅和8磅; 女生, 2磅和4磅)任务和想象举同等重量哑铃任务时, 其大脑皮层氧合血红蛋白浓度的变化。结果发现：男女被试在运动执行与运动想象任务下都激活了主运动皮层; 且运动执行的大脑激活水平高于运动想象。在执行实际运动任务时, 运动强度显著影响大脑皮层血氧浓度的变化, 表现出左半球偏侧化优势; 在执行想象运动任务时, 运动强度没有影响大脑皮层血氧浓度的变化, 且无偏侧化现象。     

Network-level dynamics underlying a combined rTMS and psychotherapy treatment for major depressive disorder: An exploratory network analysis

BackgroundDespite the growing use of repetitive transcranial magnetic stimulation (rTMS) as a treatment for depression, there is a limited understanding of the mechanisms of action and how potential treatment-related brain changes help to characterize treatment response. To address this gap in understanding we investigated the effects of an approach combining rTMS with simultaneous psychotherapy on global functional connectivity.MethodWe compared task-related functional connectomes based on an idiographic goal priming task tied to emotional regulation acquired before and after simultaneous rTMS/psychotherapy treatment for patients with major depressive disorders and compared these changes to normative connectivity patterns from a set of healthy volunteers (HV) performing the same task.ResultsAt baseline, compared to HVs, patients demonstrated hyperconnectivity of the DMN, cerebellum and limbic system, and hypoconnectivity of the fronto-parietal dorsal-attention network and visual cortex. Simultaneous rTMS/psychotherapy helped to normalize these differences, which were reduced after treatment. This finding suggests that the rTMS/therapy treatment regularizes connectivity patterns in both hyperactive and hypoactive brain networks.ConclusionsThese results help to link treatment to a comprehensive model of the neurocircuitry underlying depression and pave the way for future studies using network-guided principles to significantly improve rTMS efficacy for depression.     

Neurophysiologic markers of primary motor cortex for laryngeal muscles and premotor cortex in caudal opercular part of inferior frontal gyrus investigated in motor speech disorder: a navigated transcranial magnetic stimulation (TMS) study

Transcranial magnetic stimulation studies have so far reported the results of mapping the primary motor cortex (M1) for hand and tongue muscles in stuttering disorder. This study was designed to evaluate the feasibility of repetitive navigated transcranial magnetic stimulation (rTMS) for locating the M1 for laryngeal muscle and premotor cortical area in the caudal opercular part of inferior frontal gyrus, corresponding to Broca’s area in stuttering subjects by applying new methodology for mapping these motor speech areas. Sixteen stuttering and eleven control subjects underwent rTMS motor speech mapping using modified patterned rTMS. The subjects performed visual object naming task during rTMS applied to the (a) left M1 for laryngeal muscles for recording corticobulbar motor-evoked potentials (CoMEP) from cricothyroid muscle and (b) left premotor cortical area in the caudal opercular part of inferior frontal gyrus while recording long latency responses (LLR) from cricothyroid muscle. The latency of CoMEP in control subjects was 11.75 ± 2.07 ms and CoMEP amplitude was 294.47 ± 208.87 µV, and in stuttering subjects CoMEP latency was 12.13 ± 0.75 ms and 504.64 ± 487.93 µV CoMEP amplitude. The latency of LLR in control subjects was 52.8 ± 8.6 ms and 54.95 ± 4.86 in stuttering subjects. No significant differences were found in CoMEP latency, CoMEP amplitude, and LLR latency between stuttering and control-fluent speakers. These results indicate there are probably no differences in stuttering compared to controls in functional anatomy of the pathway used for transmission of information from premotor cortex to the M1 cortices for laryngeal muscle representation and from there via corticobulbar tract to laryngeal muscles.     

The effect of rest following massed practice of continuous and discrete motor tasks

Theories of the rest-related phenomena of reminiscence and warm-up decrement regard them as independent, being due to different factors. In this study it was found that rest following massed practice of a continuous task increased performance (reminiscence) and rest following massed practice of a discrete task lowered performance (warm-up decrement). The near-zero correlation found between the phenomena indicates that they are indeed independent and task-specific. Implications of the findings for the prediction of the effect of rest, and the fact that much motor learning and performance is task-specific, is discussed.     

The Effect of Rest Following Massed Practice of Continuous and Discrete Motor Tasks

Theories of the rest-related phenomena of reminiscence and warm-up decrement regard them as independent, being due to different factors. In this study it was found that rest following massed practice of a continuous task increased performance (reminiscence) and rest following massed practice of a discrete task lowered performance (warm-up decrement). The near-zero correlation found between the phenomena indicates that they are indeed independent and task-specific. Implications of the findings for the prediction of the effect of rest, and the fact that much motor learning and performance is task-specific, is discussed.     

Enhancing picture naming with transcranial magnetic stimulation

The enhancement of cognitive function in healthy subjects by medication, training or intervention yields increasing political, social and ethical attention. In this paper facilitatory effects of single-pulse TMS and repetitive TMS on a simple picture naming task are presented. A significant shortening of picture naming latencies was observed after single-pulse TMS over Wernicke's area. The accuracy of the response was not affected by this speed effect. After TMS over the dominant motor cortex or over the non-dominant temporal lobe, however, no facilitation of picture naming was observed. In the rTMS experiments only rTMS of Wernicke's area had an impact on picture naming latencies resulting in a shortening of naming latencies without affecting the accuracy of the response. rTMS over the visual cortex, Broca's area or over the corresponding sites in the non-dominant hemisphere had no effect. Single-pulse TMS is able to facilitate lexical processes due to a general preactivation of language-related neuronal networks when delivered over Wernicke's area. Repetitive transcranial magnetic stimulation over Wernicke's area also leads to a brief facilitation of picture naming possibly by shortening linguistic processing time. Whether TMS or rTMS can be used to aid linguistic therapy in the rehabilitation phase of aphasic patients should be subject of further investigations.     

Rapid plastic changes of human primary motor cortex with repetitive motor practice and transcranial magnetic stimulation

Excitability changes of human primary motor cortex are assumed to be associated with motor learning processes. To examine motor behavioral and neural mechanisms in these processes, the adaptive motor learning processes of the index finger abduction were investigated using motor evoked potential (MEP) elicited from the first dorsal interosseous and extensor carpi radialis muscles. Practice effects were examined on changes of MEP amplitudes elicited from these muscles during motor imagery. Given general consensus that the MEP amplitude change during motor imagery is a useful parameter reflecting changes in excitability of the human primary motor cortex, the present results, that MEP amplitudes of both muscles increased with repeated practice by the index finger abduction and that magnitudes of MEP amplitudes of both muscles (motor learning curves) were clearly different, suggested that participation of the muscles performing the index finger abduction gradually changed with practice. Short-term plastic changes of human primary motor cortex occur with repetitive practice and such adaptive change in human primary motor cortex is expressed in human voluntary movement that becomes more automatic.     

Modulations of use-dependent excitability changes of human motor cortex (M1) by practice condition

Effects of repetitive index finger abductions on excitability changes in the human primary motor cortex (Ml) are assumed to be dependent on practice conditions of the task. To address how different effects occur dependent on various practice conditions, motor evoked potentials (MEPs) elicited from the first dorsal interosseous (FDI) muscle were investigated. Practice effects on the index finger abduction were examined for changes in excitability of first dorsal interosseous muscle under three forearm position changes (neutral vs prone) and two muscle contraction modes (isometric vs isotonic). Analysis showed that after practice MEP amplitude increased in the prone position but not in the neutral position and MEP increases in the isotonic contraction were larger than those in the isometric mode. These results suggest that use-dependent excitability changes are largely dependent on practice conditions because the amount of afferent input depends on the practice conditions.     

The temporal–hippocampal region and retention: The role of temporo-entorhinal connections in rats

Results from previous studies suggest that the entorhinal cortex may be involved in mnemonic processes. The present study was carried out to investigate whether disruption of fibre connections between the temporal cortex and lateral entorhinal area may impair retention of a pre-operatively acquired simultaneous brightness discrimination task. The lesion resulted in a severe impairment in retaining the discrimination task (Experiment 1). The retention deficit could not be traced into the hippocampal formation by making perforant path lesions or hippocampal lesions (Experiment 2). The results indicate that the lateral entorhinal cortex is more crucial for reference memory than the hippocampal formation.     

Poststimulation time interval-dependent effects of motor cortex anodal tDCS on reaction-time task performance

Anodal transcranial direct current stimulation (tDCS) induces long-term potentiation-like plasticity, which is associated with long-lasting effects on different cognitive, emotional, and motor performances. Specifically, tDCS applied over the motor cortex is considered to improve reaction time in simple and complex tasks. The timing of tDCS relative to task performance could determine the efficacy of tDCS to modulate performance. The aim of this study was to compare the effects of a single session of anodal tDCS (1.5 mA, for 15 min) applied over the left primary motor cortex (M1) versus sham stimulation on performance of a go/no-go simple reaction-time task carried out at three different time points after tDCS—namely, 0, 30, or 60 min after stimulation. Performance zero min after anodal tDCS was improved during the whole course of the task. Performance 30 min after anodal tDCS was improved only in the last block of the reaction-time task. Performance 60 min after anodal tDCS was not significantly different throughout the entire task. These findings suggest that the motor cortex excitability changes induced by tDCS can improve motor responses, and these effects critically depend on the time interval between stimulation and task performance.     

Effects of test anxiety on motor learning: The processing efficiency hypothesis

Abstract

The hypothesis that, under test (stress) conditions, high trait-anxious individuals invest extra processing resources to reach motor learning levels similar to those of low-anxious individuals was investigated. A transfer procedure (practice trial, rest interval, and transfer trial) was employed to analyse motor learning effects. In Experiment 1, a secondary task (click detection) was used to measure the extra processing resources expenditure on motor learning during the practice trial. Neither motor performance in the transfer trial nor secondary task performance differed as a function of test condition or anxiety trait. A critical analysis of the secondary task paradigm suggested that it was not sensitive enough to reflect the amount of processing capacity expended on the primary motor tasks. In Experiment 2, subjects performed a loading task (verbal shadowing of sentences) concurrently with the motor tasks during the practice trial to prevent extra resources from being allocated to motor learning. Results showed that anxiety trait was associated to performance time increments on the high-demanding motor tasks in the transfer trial. A plausible explanation is that anxiety impairs learning because it reduces the efficiency of processing. An alternative interpretation, concerning an ability deficit of high trait-anxious individuals, is discussed.     

Recognition memory and prefrontal cortex: dissociating recollection and familiarity processes using rTMS

Recognition memory can be supported by both the assessment of the familiarity of an item and by the recollection of the context in which an item was encountered. The neural substrates of these memory processes are controversial. To address these issues we applied repetitive transcranial magnetic stimulation (rTMS) over the right and left dorsolateral prefrontal cortex (DLPFC) of healthy subjects performing a remember/know task. rTMS disrupted familiarity judgments when applied before encoding of stimuli over both right and left DLPFC. rTMS disrupted recollection when applied before encoding of stimuli over the right DLPFC. These findings suggest that the DLPFC plays a critical role in recognition memory based on familiarity as well as recollection.     

Motor Cortex Plasticity in Children With Spastic Cerebral Palsy: A Systematic Review

A review of the literature was performed to answer the following questions: Does motor cortex excitability correlate with motor function? Do motor cortex excitability and cortex activation change after a rehabilitation program that results in improvements in motor outcomes? Can the 10–20 electroencephalography (EEG) system be used to locate the primary motor cortex when employing transcranial direct current stimulation? Is there a bihemispheric imbalance in individuals with cerebral palsy similar to what is observed in stroke survivors? the authors found there is an adaptation in the geometry of motor areas and the cortical representation of movement is variable following a brain lesion. The 10–20 EEG system may not be the best option for locating the primary motor cortex and positioning electrodes for noninvasive brain stimulation in children with cerebral palsy.