The effects of cannabis abstinence on cognition and resting state network activity in people with multiple sclerosis: A preliminary study.

We previously reported that people with multiple sclerosis (pwMS) who have been using cannabis frequently over many years can have significant cognitive improvements accompanied by concomitant task-specific changes in brain activation following 28 days of cannabis abstinence. We now hypothesize that the default Mode Network (DMN), known to modulate cognition, would also show an improved pattern of activation align with cognitive improvement following 28 days of drug abstinence. Thirty three cognitively impaired pwMS who were frequent cannabis users underwent a neuropsychological assessment and fMRI at baseline. Individuals were then assigned to a cannabis continuation (CC, n = 15) or withdrawal (CW, n = 18) group and the cognitive and imaging assessments were repeated after 28 days. Compliance with cannabis withdrawal was checked with regular urine monitoring. Following acquisition of resting state fMRI (rs-fMRI), data were processed using independent component analysis (ICA) to identify the DMN spatial map. Between and within group analyses were carried out using dual regression for voxel-wise comparisons of the DMN. Clusters of voxels were considered statistically significant if they survived threshold-free cluster enhancement (TFCE) correction at p < 0.05. The two groups were well matched demographically and neurologically at baseline. The dual regression analysis revealed no between group differences at baseline in the DMN. By day 28, the CW group in comparison to the CC group had increased activation in the left posterior cingulate, and right, angular gyrus (p < 0.05 for both, TFCE). A within group analysis for the CC group revealed no changes in resting state (RS) networks. Within group analysis of the CW group revealed increased activation at day 28 versus baseline in the left posterior cingulate, right angular gyrus, left hippocampus (BA 36), and the right medial prefrontal cortex (p < 0.05). The CW group showed significant improvements in multiple cognitive domains. In summary, our study revealed that abstaining from cannabis for 28 days reverses activation of DMN activity in pwMS in association with improved cognition across several domains.

Investigating Cerebellar Modulation of Premovement Beta-Band Activity during Motor Adaptation.

Enhancing cerebellar activity influences motor cortical activity and contributes to motor adaptation, though it is unclear which neurophysiological mechanisms contributing to adaptation are influenced by the cerebellum. Pre-movement beta event-related desynchronization (ß-ERD), which reflects a release of inhibitory control in the premotor cortex during movement planning, is one mechanism that may be modulated by the cerebellum through cerebellar-premotor connections. We hypothesized that enhancing cerebellar activity with intermittent theta burst stimulation (iTBS) would improve adaptation rates and increase ß-ERD during motor adaptation. Thirty-four participants were randomly assigned to an active (A-iTBS) or sham cerebellar iTBS (S-iTBS) group. Participants performed a visuomotor task, using a joystick to move a cursor to targets, prior to receiving A-iTBS or S-iTBS, following which they completed training with a 45° rotation to the cursor movement. Behavioural adaptation was assessed using the angular error of the cursor path relative to the ideal trajectory. The results showed a greater adaptation rate following A-iTBS and an increase in ß-ERD, specific to the high ß range (20-30 Hz) during motor planning, compared to S-iTBS, indicative of cerebellar modulation of the motor cortical inhibitory control network. The enhanced release of inhibitory activity persisted throughout training, which suggests that the cerebellar influence over the premotor cortex extends beyond adaptation to other stages of motor learning. The results from this study further understanding of cerebellum-motor connections as they relate to acquiring motor skills and may inform future skill training and rehabilitation protocols.

Can we use peripheral vision to create a visuospatial map for compensatory reach-to-grasp reactions?

Perturbation-induced reach-to-grasp reactions are dependent on vision to capture environmental features of potential support surfaces. Previous research proposed the use of an intrinsic visuospatial map of the environment to reduce delays in motor responses (e.g., stepping, grasping a handrail). Forming such a map from foveal vision would be challenging during movement as it would require constant foveal scanning. The objective of this study was to determine if compensatory reach-to-grasp reactions could be successfully executed while relying on a visuospatial map acquired using peripheral vision. Subjects were instructed to respond to a perturbation by grasping a handle randomly located at 0°, 20° or 40° in their field of view under three visual conditions: full vision throughout the entire trial (FV), vision available prior to perturbation only (MAP), and vision available post-perturbation only (ONLINE). Electromyography was used to determine reaction time and kinematic data were collected to determine initial reach angle. Overall, participants were successful in arresting whole-body motion across all visual conditions and handle locations. Initial reach angles were target specific when vision was available prior to perturbation onset (FV and MAP). However, the 40° handle location produced a greater initial reach angle in MAP, suggesting some limitations for mapping in the further visual periphery. These findings suggest that peripheral vision contributes to the ability to spatially locate targets by building an a priori visuospatial map, which benefits the control of rapid compensatory reach-to-grasp reactions evoked in the response to unpredictable events of instability.

EEG reveals deficits in sensory gating and cognitive processing in asymptomatic adults with a history of concussion.

OBJECTIVE: Individuals with a concussion history tend to perform worse on dual-tasks compared controls but the underlying neural mechanisms contributing to these deficits are not understood. This study used event-related potentials (ERPs) to investigate sensory gating and cognitive processing in athletes with and without a history of concussion while they performed a challenging dual-task. METHODS: We recorded sensory (P50, N100) and cognitive (P300) ERPs in 30 athletes (18 no previous concussion; 12 history of concussion) while they simultaneously performed an auditory oddball task and a working memory task that progressively increased in difficulty. RESULTS: The concussion group had reduced auditory performance as workload increased compared to the no-concussion group. Sensory gating and cognitive processing were reduced in the concussion group indicating problems with filtering relevant from irrelevant information and appropriately allocating resources. Sensory gating (N100) was positively correlated with cognitive processing (P300) at the hardest workload in the no-concussion group but negatively correlated in the concussion group. CONCLUSION: Concussions result in long-term problems in behavioral performance, which may be due to poorer sensory gating that impacts cognitive processing. SIGNIFICANCE: Problems effectively gating sensory information may influence the availability or allocation of attention at the cognitive stage in those with a concussion.

Chronic Exercise as a Modulator of Cognitive Control: Investigating the Electrophysiological Indices of Performance Monitoring.

Exercise may influence components of executive functioning, specifically cognitive control and action monitoring. We aimed to determine whether high level exercise improves the efficacy of cognitive control in response to differing levels of conflict. Fitter individuals were expected to demonstrate enhanced action monitoring and optimal levels of cognitive control in response to changing task demands. Participants were divided into the highly active (HA) or low-active group based on self-reported activity using the International Physical Activity Questionnaire. A modified flanker task was then performed, in which the level of conflict was modulated by distance of distractors from the target (close, far) and congruency of arrows (incongruent, congruent). Electroencephalography (EEG) was collected during 800 trials; trials were 80% congruent, 20% incongruent, 50% close, and 50% far. The error-related negativity (ERN) and error positivity (Pe) were extracted from the difference wave of correct and incorrect response locked epochs, the N2 from the difference wave of congruent and incongruent stimulus locked epochs and the P3 from stimulus locked epochs. The HA group showed a larger Pe amplitude compared to the low-active group. Close trials elicited a larger N2 amplitude than far trials in the HA group, but not the low-active group, the HA group also made fewer errors on far trials than on close trials. Finally, the P3 was smaller in the lowest conflict condition in the HA, but not the low-active group. These findings suggest that habitual, high levels of exercise may influence the endogenous processing involved in pre-response conflict detection and the post-error response.

Long-term effects of concussion on relevancy-based modulation of somatosensory-evoked potentials.

OBJECTIVE: The purpose of this investigation was to better understand the effects of concussions on the ability to selectively up or down-regulate incoming somatosensory information based on relevance. METHODS: Median nerve somatosensory-evoked potentials (SEPs) were elicited from electrical stimulation and recorded from scalp electrodes while participants completed tasks that altered the relevance of specific somatosensory information being conveyed along the stimulated nerve. RESULTS: Within the control group, SEP amplitudes for task-relevant somatosensory information were significantly greater than for non-relevant somatosensory information at the earliest cortical processing potentials (N20-P27). Alternatively, the concussion history group showed similar SEP amplitudes for all conditions at early processing potentials, however a pattern similar to controls emerged later in the processing stream (P100) where both movement-related gating and facilitation of task-relevant information were present. CONCLUSIONS: Previously concussed participants demonstrated impairments in the ability to up-regulate relevant somatosensory information at early processing stages. These effects appear to be chronic, as this pattern was observed on average several years after participants' most recent concussion. SIGNIFICANCE: Given the role of the prefrontal cortex in relevancy-based facilitation during movement-related gating, these findings lend support to the notion that this brain area may be particularly vulnerable to concussive forces.

The effect of acute aerobic exercise on the consolidation of motor memories.

Acute aerobic exercise performed prior to training may assist with motor skill acquisition through enhancement of motor cortical plasticity. In addition, high-intensity exercise performed after training improves retention, although the mechanisms of this are unclear. We hypothesized that acute continuous moderate-intensity exercise performed post-motor training would also assist with motor skill retention and that this behavioral change would be positively correlated with neural markers of training-related cortical adaptation. Participants [n = 33; assigned to an exercise (EXE) or control (CON) group] completed a single visuomotor training session using bilateral wrist movements while movement-related cortical potentials (MRCPs) were collected. After motor training, the EXE group exercised for 20 min [70% of heart rate reserve (HRR)] and the CON group read for the same amount of time. Both groups completed two post-training tests after exercise/rest: 10 min and ~ 30 min once heart rate returned to resting level in EXE. Retention and transfer tests were both completed 1 and 7 days later. MRCPs measured training-related neural adaptations during the first visit and motor performance was assessed as time and trajectory to the target. The EXE group had better performance than CON at retention (significant 7 days post-training). MRCP amplitudes increased from early to late motor training and this amplitude change was correlated with motor performance at retention. Results suggest that moderate-intensity exercise post-motor training helps motor skill retention and that there may be a relationship with motor training-related cortical adaptations that is enhanced with post-motor training exercise.

Investigating Parietal and Premotor Influence on Motor Cortical Excitability Associated with Visuomotor Associative Plasticity.

The brain changes in response to sensory signals it is exposed to. It has been shown that long term potentiation-like neuroplasticity can be experimentally induced via visual paired-associative stimulation (V-PAS). V-PAS combines afferent visual stimuli with a transcranial magnetic stimulation pulse to induce plasticity. Preparation of a reaching movement to generate activity in superior parietal occipital cortex (SPOC) was used in this study as an additional afferent contributor to modulate the resultant plasticity. We hypothesized that V-PAS with a reaching movement would induce greater cortical excitability than V-PAS alone and would exhibit facilitated SPOC to M1 projections. All four experiments enrolled groups of 10 participants to complete variations of V-PAS in a repeated measures design. SPOC to M1 projections facilitated motor cortex excitability following V-PAS regardless of intervention received. We did not observe evidence indicating extra afferent information provided an additive effect to participants. Investigation of PMd to M1 projections confirmed disinhibition and suggested interneuronal populations within M1 may be mechanistically involved. Future research should look to rule out the existence of an upper limit for effective afference during V-PAS and investigate the average influence of V-PAS on cortical excitability in the larger population.

Discontinuing cannabis improves depression in people with multiple sclerosis: A short report.

To assess whether symptoms of depression change when people with multiple sclerosis (pwMS) discontinue cannabis use, 40 cognitively impaired pwMS who smoked cannabis almost daily were randomly assigned to either a cannabis continuation (CC) or cannabis withdrawal (CW) group. Both groups were followed for 28 days. All participants completed the Hospital Anxiety and Depression Scale. At day 28 the 11-nor-9-carboxy-Δ9-tetrahydro-cannabinol (THCCOOH)/creatinine ratio in the CW group declined to zero (p = 0.0001), but remained unchanged in the CC group (p = 0.709). Depression scores in those pwMS who were using cannabis to manage their depression remained statistically unchanged in the CC group, but declined in the CW group (p = 0.006). Despite pwMS using cannabis to help their mood, depression improved significantly off the drug. Our finding provides a cautionary note in relation to cannabis use in pwMS, at least with respect to depression.

Transient inhibition of the cerebellum impairs change-detection processes: Cerebellar contributions to sensorimotor integration.

Patients with cerebellar lesions have shown altered responses to unpredictable stimuli. This finding has led to the belief that the cerebellum is involved in comparing incoming stimuli with previously experienced stimuli in order to predict and coordinate responses. The role of the cerebellum is thought to extend beyond motor control to higher-order executive functions, which allow for the evaluation of stimuli that influence our personal reactions, emotions, and thoughts. This current study tested the role of the cerebellum on cognitive function by examining incoming sensory stimuli being unattended by the participant. Median and ulnar nerve somatosensory evoked potentials (SEPs) were elicited by electrical stimulation via surface electrodes. Nerve stimulation was presented in an oddball fashion where median and ulnar stimulation were presented as frequent and deviant stimuli, respectively. Electroencephalography (EEG) was used to measure participants' cortical responses both before and after either continuous theta burst stimulation (cTBS) used to transiently inhibit cerebellar activity, or a sham condition. The N140 was shown to be modulated in response to deviant stimuli, resulting in a large negativity pre-cTBS, referred to as the mismatch-negativity (MMN). Following cTBS, the MMN was reduced, resulting in similar waveform patterns in response to both the frequent and deviant stimuli. The mechanisms that are thought to modulate this change within the N140 in response to deviant stimuli are believed to be different from those that govern its response to frequent stimuli. The cerebellum may be involved in attentive change-detection processes that are critical for a wide-range of everyday processes.

The contribution of the prefrontal cortex to relevancy-based gating of visual and tactile stimuli.

Patients with lesions of the prefrontal cortex (PFC) show increased distractibility and impairments in inhibiting cortical responses to irrelevant stimuli. This study was designed to test the role of the PFC in the early modality-specific modulation of event-related potentials (ERPs) generated during a sensory selection task. The task required participants to make a scaled motor response to the amplitudes of visual and tactile stimuli presented individually or concurrently. Task relevance was manipulated and continuous theta burst stimulation (cTBS) was used to transiently inhibit PFC activity to test the contribution of the PFC to modulation of sensory gating. Electroencephalography (EEG) was collected from participants both before and after cTBS was applied. The somatosensory-evoked N70 ERP was shown to be modulated by task relevance before but not after cTBS was applied to the PFC, and downregulating PFC activity through the use of cTBS abolished any relevancy differences in N70 amplitude. In conclusion, this study demonstrated that early modality-specific changes in cortical somatosensory processing are modulated by attention, and that this effect is subserved by prefrontal cortical activity.

A Single Session of Aerobic Exercise Mediates Plasticity-Related Phosphorylation in both the Rat Motor Cortex and Hippocampus.

A single session of aerobic exercise may offer one means to "prime" motor regions to be more receptive to the acquisition of a motor skill; however, the mechanisms whereby this priming may occur are not clear. One possible explanation may be related to the post-translational modification of plasticity-related receptors and their associated intracellular signaling molecules, given that these proteins are integral to the development of synaptic plasticity. In particular, phosphorylation governs the biophysical properties (e.g., Ca2+ conductance) and the migratory patterns (i.e., trafficking) of plasticity-related receptors by altering the relative density of specific receptor subunits at synapses. We hypothesized that a single session of exercise would alter the subunit phosphorylation of plasticity-related receptors (AMPA receptors, NMDA receptors) and signaling molecules (PKA, CaMKII) in a manner that would serve to prime motor cortex. Young, male Sprague-Dawley rats (n = 24) were assigned to either exercise (Moderate, Exhaustion), or non-exercising (Sedentary) groups. Immediately following a single session of treadmill exercise, whole tissue homogenates were prepared from both the motor cortex and hippocampus. We observed a robust (1.2-2.0× greater than sedentary) increase in tyrosine phosphorylation of AMPA (GluA1,2) and NMDA (GluN2A,B) receptor subunits, and a clear indication that exercise preferentially affects pPKA over pCaMKII. The changes were found, specifically, following moderate, but not maximal, acute aerobic exercise in both motor cortex and hippocampus. Given the requirement for these proteins during the early phases of plasticity induction, the possibility exists that exercise-induced priming may occur by altering the phosphorylation of plasticity-related proteins.

Single session, high-intensity aerobic exercise fails to affect plasticity-related protein expression in the rat sensorimotor cortex.

Typical responses in muscle following acute aerobic exercise have been well documented, but the responses in brain have remained relatively unexplored. Recent reports suggest that a single bout of aerobic exercise can prime motor regions of the human brain to experience use-dependent plasticity, however, the mechanisms underlying this priming phenomenon are unclear. As a result, we asked whether a graded test to exhaustion (GXT), the most widely employed test to examine relationships between exercise and integrated responses within the musculoskeletal, cardiopulmonary, and neuropsychological systems, would be able to upregulate the expression of plasticity-related proteins in sensorimotor cortex in rats. We examined immediate responses in animals following either a GXT, or two resting conditions: non-exercising treadmill controls (TC), and acclimatization controls (AC). Young, male Sprague-Dawley rats (n = 20) on a reverse light cycle (12 h/12 h) were exposed to a treadmill acclimatization procedure consisting of 8 days of increasing exercise intensity (10 m/min up to 25 m/min) for 10 min at the same time each day. The acclimatization was followed by 2 days of rest to reduce any carryover effects. On testing day, rats performed either a GXT, or rested (TC and AC), were then sacrificed and sensorimotor cortex dissected. Homogenates were probed for a physiological marker of stress (HSP 70), and plasticity-related proteins (CaMKII, GluN2A, GluN1, GluA1, GluA2) by Western blotting analysis. Both our acclimatization protocol and single event GXT yielded no observable differences in protein expression, suggesting that single session exercise does not prime brain via altered plasticity-related protein expression.

Cortical processing of irrelevant somatosensory information from the leg is altered by attention during early movement preparation.

The ability to actively suppress, or gate, irrelevant sensory information is needed for safe and efficient walking in sensory-rich environments. Both attention and the late phase of motor preparation alter somatosensory evoked potentials (SEPs) in healthy adults. The aim of this study was to examine the effect of attention on the processing of irrelevant somatosensory information during the early phase of preparation of plantarflexion movements. Young healthy individuals received tibial nerve stimulation while electroencephalography (EEG) recorded SEPs over the Cz electrode. Three conditions were tested in both legs: 1) Rest, 2) Attend To the stimulated limb, and 3) Attend Away from the stimulated limb. In conditions 2 and 3, vibration (80 Hz) was applied over the medial soleus muscle to cue voluntary plantarflexion movements of the stimulated (Attend To) or non-stimulated leg (Attend Away). Only SEPs delivered during early preparation were averaged for statistical analysis. Results demonstrated a main effect of condition for the N40 and N70 indicating that SEP amplitudes in the Attend To condition were smaller than rest (p ≤ 0.02). For the P50, no interaction effects or main effects were found (p ≥ 0.08). There was no main effect of leg for any component measured. The results indicate that gating of irrelevant sensory information during early preparation occurs in the leg when attention is directed within the same limb. If attention alters the somatosensory stimuli from a leg movement, then directing attention may affect safe community walking.

Sensorimotor integration in healthy aging: Baseline differences and response to sensory training.

Sensorimotor integration is the process through which somatosensory information is incorporated to inform motor output. Given its important behavioural implications, understanding the influence of healthy aging on the underlying neurophysiology of sensorimotor integration and whether it is modifiable through intervention is important. The aims of the current work were to: 1) profile aging-related differences in sensorimotor integration, and 2) to determine if sensorimotor integration in older adults can be modulated in response to sensory training. A group of older healthy individuals and younger healthy individuals participated in two experimental sessions. First, baseline neurophysiology of sensorimotor integration was assessed. Short-latency afferent inhibition, afferent facilitation, and long-latency afferent inhibition provided nerve-based assessment of sensorimotor integration. Vibration-based measures of sensorimotor integration combined vibration of abductor pollicis brevis with single and paired-pulse transcranial magnetic stimulation techniques. In the second experimental session, a 15-min block of sensory training designed to modulate sensorimotor integration preceded the same neurophysiological assessment. Results indicate that there are aging-related differences in nerve-based measures of sensorimotor integration, specifically short- and long-latency afferent inhibition. In contrast, there are not aging-related differences when peripheral muscle belly vibration is used to probe sensorimotor integration. Following sensory training there is a reduction in the cortical response to vibration. These results suggest that there is differential aging-related modulation of sensorimotor integration, based on the type of afferent information. Additionally, sensorimotor integration is modifiable with a single session of sensory training, and this ability for neuroplastic change is retained with healthy aging.

Suppression of somatosensory stimuli during motor planning may explain levels of balance and mobility after stroke.

The ability to actively suppress, or gate, irrelevant sensory information is required for safe and efficient walking in sensory-rich environments. Both motor attention and motor planning alter somatosensory evoked potentials (SEPs) in healthy adults. This study's aim was to examine the effect of motor attention on processing of irrelevant somatosensory information during plantar flexion motor planning after stroke. Thirteen healthy older adults and 11 individuals with stroke participated. Irrelevant tibial nerve stimulation was delivered while SEPs were recorded over Cz, overlaying the leg portion of the sensorimotor cortex at the vertex of the head. Three conditions were tested in both legs: (1) Rest, (2) Attend To, and (3) Attend Away from the stimulated limb. In conditions 2 and 3, relevant vibration cued voluntary plantar flexion movements of the stimulated (Attend To) or non-stimulated (Attend Away) leg. SEP amplitudes were averaged during motor planning per condition. Individuals with stroke did not show attention-mediated gating of the N40 component associated with irrelevant somatosensory information during motor planning. It may be that dysfunction in pathways connecting to area 3b explains the lack of attention-mediated gating of the N40. Also, attention-mediated gating during motor planning explained significant and unique variance in a measure of community balance and mobility combined with response time. Thus, the ability to gate irrelevant somatosensory information appears important for stepping in both older adults and after stroke. Our data suggest that therapies that direct motor attention could positively impact walking after stroke.

Sensorimotor integration in chronic stroke: Baseline differences and response to sensory training.

BACKGROUND: The integration of somatosensory information from the environment into the motor cortex to inform movement is essential for motor function. As motor deficits commonly persist into the chronic phase of stroke recovery, it is important to understand potential contributing factors to these deficits, as well as their relationship with motor function. To date the impact of chronic stroke on sensorimotor integration has not been thoroughly investigated. OBJECTIVES: The current study aimed to comprehensively examine the influence of chronic stroke on sensorimotor integration, and determine whether sensorimotor integration can be modified with an intervention. Further, it determined the relationship between neurophysiological measures of sensorimotor integration and motor deficits post-stroke. METHODS: Fourteen individuals with chronic stroke and twelve older healthy controls participated. Motor impairment and function were quantified in individuals with chronic stroke. Baseline neurophysiology was assessed using nerve-based measures (short- and long-latency afferent inhibition, afferent facilitation) and vibration-based measures of sensorimotor integration, which paired vibration with single and paired-pulse TMS techniques. Neurophysiological assessment was performed before and after a vibration-based sensory training paradigm to assess changes within these circuits. RESULTS: Vibration-based, but not nerve-based measures of sensorimotor integration were different in individuals with chronic stroke, as compared to older healthy controls, suggesting that stroke differentially impacts integration of specific types of somatosensory information. Sensorimotor integration was behaviourally relevant in that it related to both motor function and impairment post-stroke. Finally, sensory training modulated sensorimotor integration in individuals with chronic stroke and controls. CONCLUSION: Sensorimotor integration is differentially impacted by chronic stroke based on the type of afferent feedback. However, both nerve-based and vibration-based measures relate to motor impairment and function in individuals with chronic stroke.

Symmetry of cortical planning for initiating stepping in sub-acute stroke.

OBJECTIVE: This study examined motor planning for stepping when the paretic leg was either stepping or standing (to step with the non-paretic leg), to understand whether difficulty with balance and walking post-stroke could be attributed to poor motor planning. METHODS: Individuals with stroke performed self-initiated stepping. Amplitude and duration of the movement-related cortical potential (MRCP) was measured from Cz. Electromyography (EMG) of biceps femoris (BF) and rectus femoris (RF) were collected. RESULTS: There were no differences between legs in stepping speed, MRCP or EMG parameters. The MRCPs when stepping with the paretic leg and the non-paretic leg were correlated. When the paretic leg was stepping, the MRCP amplitude correlated with MRCP duration, indicating a longer planning time was accompanied by higher cognitive effort. Slow steppers had larger MRCP amplitudes stepping with the paretic leg and longer MRCP durations stepping with the non-paretic leg. CONCLUSIONS: MRCP measures suggest that motor planning for initiating stepping are similar regardless of which limb is stepping. Individuals who stepped slowly had greater MRCP amplitudes and durations for planning. SIGNIFICANCE: Individuals who step slowly may require more time and effort to plan a movement, which may compromise their safety in the community.

Human dorsomedial parieto-motor circuit specifies grasp during the planning of goal-directed hand actions.

According to one influential view, two specialized parieto-frontal circuits control prehension: a dorsomedial stream for hand transport during reaching and a dorsolateral stream for preshaping the fingers during grasping. However, recent evidence argues that an area within the dorsomedial stream-macaque area V6A and, its putative human homolog, superior parietal occipital cortex (SPOC) - encodes both hand transport and grip formation. We tested whether planning varied hand actions modulates functional connectivity between left SPOC and ipsilateral primary motor cortex (M1) using a dual-site, paired-pulse transcranial magnetic stimulation paradigm with two coils (dsTMS). Participants performed three different hand actions to a target object comprising a small cylinder atop a larger cylinder. These actions were: reaching-to-grasp the top (GT) using a precision grip, reaching-to-grasp the bottom (GB) using a whole-hand grip, or reaching-to-touch (Touch) the side of the target object without forming a grip. Motor-evoked potentials (MEPs) from TMS to M1, with or without preceding TMS to SPOC, were recorded from first dorsal interosseous (FDI) and abductor digiti minimi (ADM) hand muscles in two experiments that varied timing parameters (the stimulus onset asynchrony, SOA, between the 'GO' cue and stimulation and interpulse interval, IPI, between SPOC and M1 stimulation). We found that preparatory response amplitudes in the SPOC-M1 circuit of different hand muscles were selectively modulated early in the motor plan for different types of grasps. First, based on SPOC-M1 interactions, across two experiments, the role of the ADM was facilitated during a whole-hand grasp of a large object (GB) relative to other conditions under certain timing parameters (SOA = 150 msec; IPI = 6 msec). Second, the role of the FDI was facilitated during hand action planning compared to rest. These findings suggest that the human dorsomedial parieto-motor stream plays a causal role in planning grip formation for object-directed actions.

A single aerobic exercise session accelerates movement execution but not central processing.

Previous research has demonstrated that aerobic exercise has disparate effects on speed of processing and movement execution. In simple and choice reaction tasks, aerobic exercise appears to increase speed of movement execution while speed of processing is unaffected. In the flanker task, aerobic exercise has been shown to reduce response time on incongruent trials more than congruent trials, purportedly reflecting a selective influence on speed of processing related to cognitive control. However, it is unclear how changes in speed of processing and movement execution contribute to these exercise-induced changes in response time during the flanker task. This study examined how a single session of aerobic exercise influences speed of processing and movement execution during a flanker task using electromyography to partition response time into reaction time and movement time, respectively. Movement time decreased during aerobic exercise regardless of flanker congruence but returned to pre-exercise levels immediately after exercise. Reaction time during incongruent flanker trials decreased over time in both an aerobic exercise and non-exercise control condition indicating it was not specifically influenced by exercise. This disparate influence of aerobic exercise on movement time and reaction time indicates the importance of partitioning response time when examining the influence of aerobic exercise on speed of processing. The decrease in reaction time over time independent of aerobic exercise indicates that interpreting pre-to-post exercise changes in behavior requires caution.