Gait-combined closed-loop brain stimulation can improve walking dynamics in Parkinsonian gait disturbances: a randomised-control trial.

OBJECTIVE: Gait disturbance lowers activities of daily living in patients with Parkinson's disease (PD) and related disorders. However, the effectiveness of pharmacological, surgical and rehabilitative treatments is limited. We recently developed a novel neuromodulation approach using gait-combined closed-loop transcranial electrical stimulation (tES) for healthy volunteers and patients who are post-stroke, and achieved significant entrainment of gait rhythm and an increase in gait speed. Here, we tested the efficacy of this intervention in patients with Parkinsonian gait disturbances. METHODS: Twenty-three patients were randomly assigned to a real intervention group using gait-combined closed-loop oscillatory tES over the cerebellum at the frequency of individualised comfortable gait rhythm, and to a sham control group. RESULTS: Ten intervention sessions were completed for all patients and showed that the gait speed (F (1, 21)=13.0, p=0.002) and stride length (F (1, 21)=8.9, p=0.007) were significantly increased after tES, but not after sham stimulation. Moreover, gait symmetry measured by swing phase time (F (1, 21)=11.9, p=0.002) and subjective feelings about freezing (F (1, 21)=14.9, p=0.001) were significantly improved during gait. CONCLUSIONS: These findings showed that gait-combined closed-loop tES over the cerebellum improved Parkinsonian gait disturbances, possibly through the modulation of brain networks generating gait rhythms. This new non-pharmacological and non-invasive intervention could be a breakthrough in restoring gait function in patients with PD and related disorders.

Association between postoperative delirium and heart rate variability in the intensive care unit and readmissions and mortality in elderly patients with cardiovascular surgery.

This study aimed to investigate the relationship between heart rate variability (HRV), a parameter of the autonomic nervous system activity (ANSA), and postoperative delirium and postoperative events. This retrospective cohort study included elderly patients aged 65 years or older who were admitted to the intensive care unit (ICU) after cardiovascular surgery. ANSA was measured using HRV parameters for 1 h at daytime and 1 h at night-time before ICU discharge. The primary endpoint was the effect of HRV parameters and delirium on mortality and readmission rates within 1 year after discharge, and the secondary endpoint was the association between HRV parameters and delirium. Cox proportional hazards models were used to examine the association between HRV parameters and postoperative events by adjusting for delirium and pre and postoperative information. A total of 71 patients, 39 without delirium and 32 with delirium, met the inclusion criteria. The incidence of death and readmission within 1 year was significantly higher in the delirium group and in the group with higher daytime HF (high frequency power) and r-MSSD (square root of the squared mean of the difference of successive NN intervals), parameters of the parasympathetic nervous system activity (PNSA), than that in other groups. Furthermore, the delirium group had significantly higher HF and r-MSSD than the nondelirium group. Even after adjusting for confounding factors in the multivariate analysis, a trend of higher daytime HF and r-MSSD was observed, indicating a significant effect on the occurrence of combined events within 1 year of discharge. ICU delirium has been associated with higher daytime HF and r-MSSD, parameters of PNSA. ICU delirium was a prognostic factor, and increased daytime PNSA may worsen the prognosis of elderly patients after cardiovascular surgery.

Magnification of visual feedback modulates corticomuscular and intermuscular coherences differently in young and elderly adults.

Beta-band (15-30 â€‹Hz) corticomuscular and intermuscular coherences are important markers of the corticospinal interaction. The purpose of this study was to investigate whether amount of visual feedback during an isometric pinch grip contraction would influence these coherences in young and elderly adults. Thirty-three healthy young and elderly subjects performed pinch grip force-matching task with right thumb and index finger, while scalp electroencephalogram (EEG) and electromyogram (EMG) from the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles were recorded. The amount of visual feedback was altered by manipulation of visual gain (low and high). Beta-band corticomuscular coherence was computed between EEG over the sensorimotor cortex and EMG from the FDI muscle and between EEG and EMG from the APB muscle (EEG-FDI and EEG-APB coherences). Also, beta-band intermuscular coherence was computed between EMG signals from the FDI and APB muscles (EMG-EMG coherence). Task performance was quantified as standard deviation (SD) of force and mean force error (MFE). EEG-FDI coherence was larger at high than low visual gain in the elderly but not in the young subjects, whereas there was no effect of age or visual gain on EEG-APB coherence. EMG-EMG coherence was smaller at high than low visual gain in the young and elderly subjects. The MFE was smaller at high than low visual gain in the young and elderly subjects, but the SD of force was smaller at high than low visual gain only in the young subjects. These results suggest that the effect of aging on beta-band coherence depends on the amount of visual feedback and further that visual feedback modulates beta-band corticomuscular and intermuscular coherences differently.

Role of beta-band resting-state functional connectivity as a predictor of motor learning ability.

It has been suggested that resting-state functional connectivity (rs-FC) between the primary motor area (M1) region of the brain and other brain regions may be a predictor of motor learning, although this suggestion is still controversial. In the work reported here, we investigated the relationship between M1 seed-based rs-FC and motor learning. Fifty-three healthy volunteers undertook random button-press and sequential motor learning tasks. Five-minute resting-state data acquisition was performed between the two tasks. Oscillatory neural activities during the random task and the rest period were measured using magnetoencephalography. M1 seed-based rs-FC was calculated for the alpha and beta bands using amplitude envelope correlation, in which the seed location was defined as an M1 position with peak event-related desynchronization value. The relationship between rs-FC and the performance of motor learning was examined using whole brain correlation analysis. The results showed that beta-band resting-state cross-network connectivity between the sensorimotor network and the core network, particularly the theory of mind network, affected the performance of subsequent motor learning tasks. Good learners could be distinguished from poor learners by the strength of rs-FC between the M1 and the left superior temporal gyrus, a part of the theory of mind network. These results suggest that cross-network connectivity between the sensorimotor network and the theory of mind network can be used as a predictor of motor learning performance.

Coordination of plantar flexor muscles during bipedal and unipedal stances in young and elderly adults.

To investigate the effects of aging on coordination of plantar flexor muscles during bipedal and unipedal stances, we examined a relationship between the center of pressure sway and electromyographic activity of these muscles, and also the common neural input, using a coherence analysis. Healthy young and elderly adults were asked to perform bipedal and unipedal standing. The electromyograms were recorded unilaterally from the medial and lateral gastrocnemius (MG and LG) and soleus (SL) muscles, and the common input was analyzed for MG-LG, MG-SL, and LG-SL pairs in two frequency bands: a delta band, that is associated with force variability, and a beta band, that could reflect the corticospinal drive. Main results indicated that the MG and SL muscles worked for lateral sway, while the LG muscle worked for medial sway during the unipedal stance. The delta-band coherence for the MG-SL pair and the beta-band coherences for all the pairs were larger during the unipedal than bipedal stance for both groups. The delta-band coherence for the MG-SL pair was larger for the elderly than young adults during the unipedal stance. In addition, the beta-band coherence for the MG-SL pair was larger than the other pairs during the unipedal stance for the elderly. These findings suggest that the oscillatory activity between the MG and SL muscles is strongly involved in the control of unipedal stance, and aging would increase the cortical drive to these muscles to deal with the postural sway that could be affected by forces generated cooperatively by them.

Auditory stimulus has a larger effect on anticipatory postural adjustments in older than young adults during choice step reaction.

PURPOSE: The study aim was to compare the influence of an auditory stimulus (AS) on anticipatory postural adjustments (APAs) between young and older adults during a choice step reaction. METHODS: Sixteen young and 19 older adults stepped forward in response to a visual imperative stimulus of an arrow. We used a choice reaction time (CRT) task and a Simon task which consisted of congruent and incongruent conditions. The direction of the presented arrow and its spatial location matched in the congruent condition while they did not in the incongruent condition. The AS was presented randomly and simultaneously with the visual stimulus. Incorrect weight shifts before lifting off the foot, termed APA errors, stepping errors, temporal parameters, and APA amplitudes were analyzed. RESULTS: The APA error rate was higher in trials with than without AS in all task conditions for the older group, while this increase occurred only in the incongruent condition for the young group. The stepping error rate was also increased in the presence of AS in the incongruent condition for the older group. Reaction times were faster with AS in both groups. The APA amplitude of erroneous APA trials became larger with AS in the incongruent condition for both groups, and this effect appeared greater for the older group. CONCLUSIONS: The effect of AS on APAs is larger in the elderly during a choice step reaction. In the presence of incongruent visual information, this effect becomes even greater, potentially inducing not only APA errors but also stepping errors.

Performance monitoring and response conflict resolution associated with choice stepping reaction tasks.

Choice reaction requires response conflict resolution, and the resolution processes that occur during a choice stepping reaction task undertaken in a standing position, which requires maintenance of balance, may be different to those processes occurring during a choice reaction task performed in a seated position. The study purpose was to investigate the resolution processes during a choice stepping reaction task at the cortical level using electroencephalography and compare the results with a control task involving ankle dorsiflexion responses. Twelve young adults either stepped forward or dorsiflexed the ankle in response to a visual imperative stimulus presented on a computer screen. We used the Simon task and examined the error-related negativity (ERN) that follows an incorrect response and the correct-response negativity (CRN) that follows a correct response. Error was defined as an incorrect initial weight transfer for the stepping task and as an incorrect initial tibialis anterior activation for the control task. Results revealed that ERN and CRN amplitudes were similar in size for the stepping task, whereas the amplitude of ERN was larger than that of CRN for the control task. The ERN amplitude was also larger in the stepping task than the control task. These observations suggest that a choice stepping reaction task involves a strategy emphasizing post-response conflict and general performance monitoring of actual and required responses and also requires greater cognitive load than a choice dorsiflexion reaction. The response conflict resolution processes appear to be different for stepping tasks and reaction tasks performed in a seated position.

Accessory stimulus modulates executive function during stepping task.

When multiple sensory modalities are simultaneously presented, reaction time can be reduced while interference enlarges. The purpose of this research was to examine the effects of task-irrelevant acoustic accessory stimuli simultaneously presented with visual imperative stimuli on executive function during stepping. Executive functions were assessed by analyzing temporal events and errors in the initial weight transfer of the postural responses prior to a step (anticipatory postural adjustment errors). Eleven healthy young adults stepped forward in response to a visual stimulus. We applied a choice reaction time task and the Simon task, which consisted of congruent and incongruent conditions. Accessory stimuli were randomly presented with the visual stimuli. Compared with trials without accessory stimuli, the anticipatory postural adjustment error rates were higher in trials with accessory stimuli in the incongruent condition and the reaction times were shorter in trials with accessory stimuli in all the task conditions. Analyses after division of trials according to whether anticipatory postural adjustment error occurred or not revealed that the reaction times of trials with anticipatory postural adjustment errors were reduced more than those of trials without anticipatory postural adjustment errors in the incongruent condition. These results suggest that accessory stimuli modulate the initial motor programming of stepping by lowering decision threshold and exclusively under spatial incompatibility facilitate automatic response activation. The present findings advance the knowledge of intersensory judgment processes during stepping and may aid in the development of intervention and evaluation tools for individuals at risk of falls.

Action observation with kinesthetic illusion can produce human motor plasticity.

After watching sports, people often feel as if their sports skills might have been improved, even without any actual training. On some occasions, this motor skill learning through observation actually occurs. This phenomenon may be due to the fact that both action and action observation (AO) can activate shared cortical areas. However, the neural basis of performance gain through AO has not yet been fully clarified. In the present study, we used transcranial magnetic stimulation to investigate whether primary motor cortex (M1) plasticity is a physiological substrate of AO-induced performance gain and whether AO itself is sufficient to change motor performance. The excitability of M1, especially that of its intracortical excitatory circuit, was enhanced after and during AO with kinesthetic illusion but not in interventions without this illusion. Moreover, behavioral improvement occurred only after AO with kinesthetic illusion, and a significant correlation existed between the performance gain and the degree of illusion. Our findings indicated that kinesthetic illusion is an essential component of the motor learning and M1 plasticity induced by AO, and this insight may be useful for the strategic rehabilitation of stroke patients.

Human motor plasticity induced by mirror visual feedback.

The clinical use of mirror visual feedback (MVF) was initially introduced to alleviate phantom pain, and has since been applied to the improvement of hemiparesis following stroke. However, it is not known whether MVF can restore motor function by producing plastic changes in the human primary motor cortex (M1). Here, we used transcranial magnetic stimulation to test whether M1 plasticity is a physiological substrate of MVF-induced motor behavioral improvement. MVF intervention in normal volunteers using a mirror box improved motor behavior and enhanced excitatory functions of the M1. Moreover, behavioral and physiological measures of MVF-induced changes were positively correlated with each other. Improved motor performance occurred after observation of a simple action, but not after repetitive motor training of the nontarget hand without MVF, suggesting the crucial importance of visual feedback. The beneficial effects of MVF were disrupted by continuous theta burst stimulation (cTBS) over the M1, but not the control site in the occipital cortex. However, MVF following cTBS could further improve the motor functions. Our findings indicate that M1 plasticity, especially in its excitatory connections, is an essential component of MVF-based therapies.

Mirror visual feedback can induce motor learning in patients with callosal disconnection.

Mirror therapy using mirror visual feedback (MVF) has been applied to the stroke rehabilitation of hemiparesis. One possible mechanism of mirror therapy is the functional interhemispheric connectivity between sensorimotor areas via corpus callosum. To test this hypothesis, we investigated the MVF-induced motor learning in 2 patients with callosal disconnection. Callosal connection in patients was evaluated by clinical measures and the interhemispheric inhibition (IHI) using transcranial magnetic stimulation. Both patients suffered from somatosensory cognitive disconnection, and one showed the loss of IHI. Motor training with MVF significantly improved the motor behavior of both patients. Extending our previous study, the results of callosal patients suggested that the visual feedback through a mirror might play the crucial important role for the improvement of motor performance, rather than interhemispheric interaction via corpus callosum.

EMG-EMG coherence during voluntary control of human standing tasks: a systematic scoping review.

Background: Intra- or inter-muscular (EMG-EMG) coherence is a simple and non-invasive method for estimating central nervous system control during human standing tasks. Although this research area has developed, no systematic literature review has been conducted. Objectives: We aimed to map the current literature on EMG-EMG coherence during various standing tasks to identify the research gaps and summarize previous studies comparing EMG-EMG coherence between healthy young and elderly adults. Methods: Electronic databases (PubMed, Cochrane Library, and CINAHL) were searched for articles published from inception to December 2021. We incorporated studies that analyzed EMG-EMG coherence of the postural muscles in various standing tasks. Results: Finally, 25 articles fulfilled the inclusion criteria and involved 509 participants. Most participants were healthy young adults, while only one study included participants with medical conditions. There was some evidence that EMG-EMG coherence could identify differences in standing control between healthy young and elderly adults, although the methodology was highly heterogeneous. Conclusion: The present review indicates that EMG-EMG coherence may help elucidate changes in standing control with age. In future studies, this method should be used in participants with central nervous system disorders to understand better the characteristics of standing balance disabilities.

Intermuscular Coherence during Quiet Standing in Sub-Acute Patients after Stroke: An Exploratory Study.

Asymmetrically impaired standing control is a prevalent disability among stroke patients; however, most of the neuromuscular characteristics are unclear. Therefore, the main purpose of this study was to investigate between-limb differences in intermuscular coherence during quiet standing. Consequently, 15 patients who had sub-acute stroke performed a quiet standing task without assistive devices, and electromyography was measured on the bilateral tibialis anterior (TA), soleus (SL), and medial gastrocnemius (MG). The intermuscular coherence of the unilateral synergistic (SL-MG) pair and unilateral antagonist (TA-SL and TA-MG) pairs in the delta (0-5 Hz) and beta (15-35 Hz) bands were calculated and compared between the paretic and non-paretic limbs. The unilateral synergistic SL-MG coherence in the beta band was significantly greater in the non-paretic limb than in the paretic limb (p = 0.017), while unilateral antagonist TA-MG coherence in the delta band was significantly greater in the paretic limb than in the non-paretic limb (p < 0.01). During quiet standing, stroke patients showed asymmetry in the cortical control of the plantar flexor muscles, and synchronous control between the antagonistic muscles was characteristic of the paretic limb. This study identified abnormal muscle activity patterns and asymmetrical cortical control underlying impaired standing balance in patients with sub-acute stroke using an intermuscular coherence analysis.

Writing's shadow: corticospinal activation during letter observation.

We can recognize handwritten letters despite the variability among writers. One possible strategy is exploiting the motor memory of orthography. By using TMS, we clarified the excitatory and inhibitory neural circuits of the motor corticospinal pathway that might be activated during the observation of handwritten letters. During experiments, participants looked at the handwritten or printed single letter that appeared in a random order. The excitability of the left and right primary motor cortex (M1) was evaluated by motor-evoked potentials elicited by single-pulse TMS. Short interval intracortical inhibition (SICI) of the left M1 was evaluated using paired-pulse TMS. F waves were measured for the right ulnar nerve. We found significant reduction of corticospinal excitability only for the right hand at 300-400 msec after each letter presentation without significant changes in SICI. This suppression is likely to be of supraspinal origin, because of no significant alteration in F-wave amplitudes. These findings suggest that the recognition of handwritten letters may include the implicit knowledge of "writing" in M1. The M1 activation associated with that process, which has been shown in previous neuroimaging studies, is likely to reflect the active suppression of the corticospinal excitability.

Brain-Computer Interface Training Based on Brain Activity Can Induce Motor Recovery in Patients With Stroke: A Meta-Analysis.

BACKGROUND: Brain-computer interface (BCI) is a procedure involving brain activity in which neural status is provided to the participants for self-regulation. The current review aims to evaluate the effect sizes of clinical studies investigating the use of BCI-based rehabilitation interventions in restoring upper extremity function and effective methods to detect brain activity for motor recovery. METHODS: A computerized search of MEDLINE, CENTRAL, Web of Science, and PEDro was performed to identify relevant articles. We selected clinical trials that used BCI-based training for post-stroke patients and provided motor assessment scores before and after the intervention. The pooled standardized mean differences of BCI-based training were calculated using the random-effects model. RESULTS: We initially identified 655 potentially relevant articles; finally, 16 articles fulfilled the inclusion criteria, involving 382 participants. A significant effect of neurofeedback intervention for the paretic upper limb was observed (standardized mean difference = .48, [.16-.80], P = .006). However, the effect estimates were moderately heterogeneous among the studies (I2 = 45%, P = .03). Subgroup analysis of the method of measurement of brain activity indicated the effectiveness of the algorithm focusing on sensorimotor rhythm. CONCLUSION: This meta-analysis suggested that BCI-based training was superior to conventional interventions for motor recovery of the upper limbs in patients with stroke. However, the results are not conclusive because of a high risk of bias and a large degree of heterogeneity due to the differences in the BCI interventions and the participants; therefore, further studies involving larger cohorts are required to confirm these results.

Repetitive training of contralateral limb through reconsolidation strengthens motor skills.

Consolidated memories become transiently labile after memory reactivation, allowing update through reconsolidation. Although previous reports have indicated that the effects of post-reactivation training depend on the type of practice, it is unclear whether post-reactivation motor skill training of one limb can enhance the performance of the opposite limb. The present study aimed to investigate whether post-reactivation training (performing an isometric pinch force task) under two different training conditions using the left limb would enhance motor skills of the right limb through reconsolidation. Motor skills were measured in 38 healthy right-handed young adults during three sessions (S): S1 (right-hand training), S2 (memory reactivation and left-hand training 6 h after S1), and S3 (right-hand motor skill test 24 h after S1). Participants were assigned to one of three groups according to the task performed during S2: untrained controls (no training), left-hand training (constant force conditions), or left-hand training (variable force conditions). Left-hand training after memory reactivation during S2 significantly enhanced the motor skills of the right hand. Notably, constant training conditions significantly increased performance compared to the control group. These findings suggest that post-reactivation training in one limb effectively enhances motor skills in the opposite limb, and the effects depend on the training strategy, which has important implications for motor rehabilitation.

Relationships between stress urinary incontinence and trunk muscle mass or spinal alignment in older women.

OBJECTIVES: Relationships between stress urinary incontinence (SUI) and physical function and spinal alignment have not been fully elucidated; therefore, we examined these relationships in older women. METHODS: The participants of this cross-sectional study comprised 21 women with SUI (SUI group) and 41 continent women (continent group) aged >65 years who participated in a community-based health-check survey from 2018 to 2019. We examined age, body mass index, number of deliveries, age at first childbirth, and medical histories as participants' characteristics. SUI was evaluated using the International Consultation on Incontinence Questionnaire-Short Form (ICIQ-SF). We also assessed spinal alignment and physical activity, grip strength, trunk and lower limb muscle mass, gait speed, and one-leg standing time as measures of participants' physical function. RESULTS: Body mass index was significantly higher in the SUI group compared with continents (P = 0.04), and trunk muscle mass in the SUI group was significantly lower (P < 0.01). Additionally, the thoracic kyphosis angle in the SUI group was significantly larger (P = 0.02). In the logistic regression analysis, trunk muscle mass (odds ratio = 0.546, P = 0.03) and increased thoracic kyphosis angle (odds ratio = 1.066, P = 0.045) were independent factors affecting SUI. Furthermore, there was a negative weak correlation between total ICIQ-SF score and trunk muscle mass (r = -0.36, P < 0.01), and a positive weak correlation between total ICIQ-SF score and thoracic kyphosis angle (r = 0.27, P < 0.05). CONCLUSION: Trunk muscle mass and thoracic kyphosis angle relate to SUI status and severity among Japanese community-dwelling older women.

Strengthening the GABAergic System Through Neurofeedback Training Suppresses Implicit Motor Learning.

Gamma-aminobutyric acid (GABA) activity within the primary motor cortex (M1) is essential for motor learning in cortical plasticity, and a recent study has suggested that real-time neurofeedback training (NFT) can self-regulate GABA activity. Therefore, this study aimed to investigate the effect of GABA activity strengthening via NFT on subsequent motor learning. Thirty-six healthy participants were randomly assigned to either an NFT group or control group, which received sham feedback. GABA activity was assessed for short intracortical inhibition (SICI) within the right M1 using paired-pulse transcranial magnetic stimulation. During the NFT intervention period, the participants tried to modulate the size of a circle, which was altered according to the degree of SICI in the NFT group. However, the size was altered independently of the degree of SICI in the control group. We measured the reaction time before, after (online learning), and 24 h after (offline learning) the finger-tapping task. Results showed the strengthening of GABA activity induced by the NFT intervention, and the suppression of the online but not the offline learning. These findings suggest that prior GABA activity modulation may affect online motor learning.

Association between Social Frailty and Sleep Quality among Community-dwelling Older Adults: A Cross-sectional Study.

OBJECTIVE: We examined the association between social frailty and subjective sleep quality among community-dwelling adults. METHODS: This cross-sectional study recruited Japanese adults over the age of 60 years from health check-ups held in a public townhall in a suburban area between 2018 and 2019. Social frailty was evaluated using five criteria (living alone, not visiting friends sometimes, going out less frequently than the last year, not feeling helpful to friends or family, and not talking to someone every day) and categorized into three groups: non-frailty, pre-frailty, and frailty. Sleep quality was assessed according to the Pittsburgh Sleep Quality Index (PSQI) by giving participants a self-reported questionnaire. We performed multivariable linear regression analysis, denoting social frailty as an independent variable, and the global PSQI score as a dependent variable. RESULTS: Data from 300 older adults were analyzed, 51.0% of whom were female. The participants' mean age was 73.0 years (standard deviation = 5.8). Multivariable analysis revealed the notable association between social frailty and a high global PSQI score (compared with non-frailty, frailty: ß = 0.94, 95% CI = 0.08 to 1.80, p = 0.033). Of the five determiners of social frailty, not talking with someone every day was especially associated with a high global PSQI score (ß = 1.57, 95% CI = 0.49 to 2.66, p = 0.005). CONCLUSION: The present study suggests that social frailty is associated with poor sleep quality among community-dwelling older adults. Our findings indicate the importance of social frailty on sleep quality among older adults.

Transcranial static magnetic stimulation -From bench to bedside and beyond.

Non-invasive brain stimulation (NIBS) techniques are extensively applied for the treatment of neuropsychiatric disorders and offer a powerful tool for addressing fundamental questions in neuroscience research. Recently, the use of static magnetic fields (SMFs) as a tool of NIBS has led to the development of a safe and promising method of neuromodulation called transcranial static magnetic stimulation (tSMS). However, the neurophysiological mechanisms regarding the effect of tSMS on the cortical elements are not yet fully understood. Here, we focus on the modulation of cortical excitability and oscillatory brain activity induced by tSMS. We believe that understanding the physiological mechanisms of this novel method is an important step for developing these techniques into potentially useful tools for the treatment of specific patient groups. Reviewing the neurophysiological evidence provided by human and animal studies suggests that tSMS may affect brain oscillations and alter behavioral parameters through the modulation of cortical excitability. In this review, we outline possible accounts and future directions to better understand the link between neural modification and accompanied behavioral changes.