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Background . Concussions affect nearly 3 million people a year and are the leading cause of traumatic brain injury-related emergency department visits among youth. Evidence shows neuromotor regions are sensitive to concussive events and that motor symptoms may be the earliest clinical manifestations of neurodegenerative traumatic brain injuries. However, little is known about the effects repeated concussions play on motor learning. Namely, how does concussion acuity (time since injury) affect different behavioral and neurophysiological components of motor learning? Methods . Using a 3-pronged approach, we assessed (1) behavioral measures of motor learning, (2) neurophysiological measures underlying retention of motor learning known as occlusion, and (3) quantitative survey data capturing affective symptoms of each participant. Collegiate student athletes were stratified across 3 groups depending on their concussion history: (1) NonCon, no history of concussion; (2) Chronic, chronic-state of concussion (>1 year postinjury), or (3) Acute, acute state of concussion (<2 weeks postinjury). Results . We found that athletes in both the acute and chronic state of injury following a concussion had impaired retention and aberrant occlusion in motor skill learning as compared with athletes with no history of concussion. Moreover, higher numbers of previous concussions (regardless of the time since injury) correlated with more severe behavioral and neurophysiological motor impairments by specifically hindering neurophysiological mechanisms of learning to affect behavior. Conclusions . These results indicate the presence of motor learning impairment that is evident within 2 weeks postinjury. Our findings have significant implications for the prognosis of concussion and emphasize the need for prevention, but can also direct more relevant rehabilitation treatment targets.

Persistent cognitive, affective, and motor symptoms have been associated with sports-related concussions including several neurophysiological changes in the primary motor cortex. In particular, previous research has provided some evidence of altered latencies of the corticomotor pathway and altered motor neuroplasticity. However, to date, no studies have assessed these neurophysiological metrics in a common group of athletes across different phases of injury and recovery. In this study corticomotor latencies and neuroplasticity were assessed in collegiate athletes with or without a history of prior concussion across two different phases of injury: either in an acute state of concussion (within 2 wk of injury) or in a chronic state of concussion (more than 1 yr after injury). Corticomotor latencies were determined by measuring the motor evoked potential (MEP) onset time, and motor neuroplasticity was assessed by measuring MEP amplitudes following application of anodal transcranial direct current stimulation (tDCS) over the primary motor cortex (M1). We found that concussed athletes had slower corticomotor latencies than nonconcussed athletes, and corticomotor latency was also positively correlated with the number of prior concussions. In contrast, there was no evidence of altered motor neuroplasticity in athletes regardless of concussion history. These findings suggest concussions may lead to permanent changes in the corticospinal tract that are exacerbated by repeated injury. NEW & NOTEWORTHY We are the first to assess corticomotor latencies and motor neuroplasticity in a common group of collegiate athletes across different phases of injury and recovery. We found that the number of concussions an individual sustains negatively impacts corticomotor latencies with a higher number of prior concussions correlating positively with longer latencies. Our findings indicate that concussions may lead to permanent changes in the corticospinal tract that are exacerbated by repeated injury.

We assessed corticomotor excitability in the primary motor cortex (M1) of participants with moderate-to-severe restless legs syndrome (RLS) symptoms using transcranial magnetic stimulation (TMS) in relation to the clinical and sleep aspects of the disease. Thirty-five participants (20 F; mean age: 59.23 ± 1.66 years; range: 42-78 years) affected by primary RLS (off medications) and 31 age-matched controls (19 F; mean age: 57.90 ± 1.50 years; range: 43-79 years) underwent TMS following two nights of polysomnography (PSG). Paired-pulse TMS measures [short-interval intracortical inhibition (SICI), long-interval intracortical inhibition (LICI), and intracortical facilitation (ICF)] of the dominant M1 hand and M1 leg muscles were collected and analyzed in relation to clinical features of RLS and PSG. We found decreased corticomotor excitability in M1 hand , whereas it was increased in M1 leg , which was greater in patients with more severe RLS. Participants with RLS with a history of dopamine-agonist-induced symptom augmentation showed decreased LICI (reduced inhibition) compared to nonaugmented participants with RLS for M1 leg . None of the TMS measures (M1 hand or M1 leg ) correlated with the PSG parameters. This study shows hyperexcitability in M1 leg , and this appears related to RLS disease severity and decreased excitability in M1 hand . The results provide new insight into the complex neurobiology of RLS, particularly in more advanced stages of the disease., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Action observation (AO), observing another individual perform an action, has been implicated in several higher cognitive processes including forming basic motor memories. Previous work has shown that physical practice (PP) results in cortical motor representational changes, referred to as use-dependent plasticity (UDP), and that AO combined with PP potentiates UDP in both healthy adults and stroke patients. In humans, AO results in activation of the ventral premotor cortex (PMv), however, whether this PMv activation has a functional contribution to UDP is not known. Here, we studied the effects disruption of PMv has on UDP when subjects performed PP combined with AO (PP + AO). Subjects participated in two randomized crossover sessions measuring the amount of UDP resulting from PP + AO while receiving disruptive (1 Hz) TMS over the fMRI-activated PMv or over frontal cortex (Sham). We found that, unlike the sham session, disruptive TMS over PMv reduced the beneficial contribution of AO to UDP. To ensure that disruption of PMv was specifically interfering with the contribution of AO and not PP, subjects completed two more control sessions where they performed only PP while receiving disruptive TMS over PMv or frontal cortex. We found that the magnitude of UDP for both control sessions was similar to PP + AO with TMS over PMv. These findings suggest that the fMRI activation found in PMv during AO studies is functionally relevant to task performance, at least for the beneficial effects that AO exerts over motor training.