Proximal Upper Limb Sensorimotor Integration in Response to Novel Motor Skill Acquisition.

Previous studies have shown significant changes in cortical and subcortical evoked potential activity levels in response to motor training with the distal upper-limb muscles. However, no studies to date have assessed the neurological processing changes in somatosensory evoked potentials (SEPs) associated with motor training whole-arm movements utilizing proximal upper-limb muscles. The proximal upper-limb muscles are a common source of work-related injuries, due to repetitive glenohumeral movements. Measuring neurophysiological changes following performance of a proximal motor task provide insight into potential neurophysiological changes associated with occupational postures and movements involving proximal upper limb muscles. This study sought to assess the impact of a novel motor skill acquisition task on neural processing of the proximal upper-limb muscle groups, through the measurement of short-latency median nerve SEPs. One group of 12 participants completed a novel motor training task, consisting of tracing a sinusoidal waveform varying in amplitude and frequency. Baseline SEP measurements were recorded from each participant, followed by a mental recitation control task. Pre-test SEP measurements were then recorded, followed by the motor training task, and post-test SEP recordings. The participants completed the tracing with their right thumb, using glenohumeral rotation only to move their hand. Significant improvements in task accuracy were demonstrated, indicating that motor acquisition had occurred. Significant changes were also seen in the N11, N13, N20, N24, P25, and the N30 SEP peaks were seen following the motor training task. Conclusion: Early SEPs appear to be a sensitive measure of changes in sensorimotor integration in response to novel motor skill acquisition within the proximal upper-limb muscles.

Differential Changes in Early Somatosensory Evoked Potentials between the Dominant and Non-Dominant Hand, Following a Novel Motor Tracing Task.

During training in a novel dynamic environment, the non-dominant upper limb favors feedback control, whereas the dominant limb favors feedforward mechanisms. Early somatosensory evoked potentials (SEPs) offer a means to explore differences in cortical regions involved in sensorimotor integration (SMI). This study sought to compare differences in SMI between the right (Dom) and left (Non-Dom) hand in healthy right-handed participants. SEPs were recorded in response to median nerve stimulation, at baseline and post, a motor skill acquisition-tracing task. One group (n = 12) trained with their Dom hand and the other group (n = 12), with their Non-Dom hand. The Non-Dom hand was significantly more accurate at baseline (p < 0.0001) and both groups improved with time (p < 0.0001), for task accuracy, with no significant interaction effect between groups for both post-acquisition and retention. There were significant group interactions for the N24 (p < 0.001) and the N30 (p < 0.0001) SEP peaks. Post motor acquisition, the Dom hand had a 28.9% decrease in the N24 and a 23.8% increase in the N30, with opposite directional changes for the Non-Dom hand; 22.04% increase in N24 and 24% decrease in the N30. These SEP changes reveal differences in early SMI between Dom and Non-Dom hands in response to motor acquisition, providing objective, temporally sensitive measures of differences in neural mechanisms between the limbs.

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.

The effects of subclinical neck pain on sensorimotor integration following a complex motor pursuit task.

Recurrent subclinical neck pain (SCNP) may be associated with neural plastic changes in sensory processing and sensorimotor integration (SMI); however, its impact on motor learning has not been investigated. The aim of this study was to investigate whether SCNP alters neural markers of SMI during a complex motor acquisition task as compared to a healthy control group. Peripheral N9, spinal N13, brainstem N18, and cortical N20, P25, N24 and N30 early somatosensory evoked potentials (SEPs) were recorded following median nerve stimulation for 24 participants (12 control and 12 SCNP) before and after a 10-min tracing motor task intervention. Retention was assessed 24-48 h later. Significant amplitude differences were observed for both N18 and N24 SEP waveforms between groups, indicating there may be a difference in SMI due to altered afferent input as a result of SCNP. Accuracy increased significantly for both groups post-motor training; however, at retention only the control group showed an additional increase in accuracy. Both N18 and N24 SEP peaks are linked with cerebellar pathways, suggesting that SCNP impacts these connections. Significant correlations between these peaks and performance data were also seen. The differential changes in neurophysiological markers of SMI seen in SCNP suggest that SEPs have the potential to be used as an early screening tool for those at risk of having maladaptive neural plastic changes in response to motor training as a result of SCNP.

Interactive effect of acute pain and motor learning acquisition on sensorimotor integration and motor learning outcomes.

Previous work has demonstrated differential changes in early somatosensory evoked potentials (SEPs) when motor learning acquisition occurred in the presence of acute pain; however, the learning task was insufficiently complex to determine how these underlying neurophysiological differences impacted learning acquisition and retention. To address this limitation, we have utilized a complex motor task in conjunction with SEPs. Two groups of 12 participants (n = 24) were randomly assigned to either a capsaicin (capsaicin cream) or a control (inert lotion) group. SEP amplitudes were collected at baseline, after application, and after motor learning acquisition. Participants performed a motor acquisition task followed by a pain-free retention task within 24-48 h. After motor learning acquisition, the amplitude of the N20 SEP peak significantly increased (P < 0.05) and the N24 SEP peak significantly decreased (P < 0.001) for the control group while the N18 SEP peak significantly decreased (P < 0.01) for the capsaicin group. The N30 SEP peak was significantly increased (P < 0.001) after motor learning acquisition for both groups. The P25 SEP peak decreased significantly (P < 0.05) after the application of capsaicin cream. Both groups improved in accuracy after motor learning acquisition (P < 0.001). The capsaicin group outperformed the control group before motor learning acquisition (P < 0.05) and after motor learning acquisition (P < 0.05) and approached significance at retention (P = 0.06). Improved motor learning in the presence of capsaicin provides support for the enhancement of motor learning while in acute pain. In addition, the changes in SEP peak amplitudes suggest that early SEP changes reflect neurophysiological alterations accompanying both motor learning and mild acute pain.

The effect of local vs remote experimental pain on motor learning and sensorimotor integration using a complex typing task.

Recent work demonstrated that capsaicin-induced acute pain improved motor learning performance; however, baseline accuracy was very high, making it impossible to discern the impact of acute pain on motor learning and retention. In addition, the effects of the spatial location of capsaicin application were not explored. Two experiments were conducted to determine the interactive effects of acute pain vs control (experiment 1) and local vs remote acute pain (experiment 2) on motor learning and sensorimotor processing. For both experiments, somatosensory evoked potential (SEP) amplitudes and motor learning acquisition and retention (accuracy and response time) data were collected at baseline, after application, and after motor learning. Experiment 1: N11 (P < 0.05), N13 (P < 0.05), and N30 (P < 0.05) SEP peak amplitudes increased after motor learning in both groups, whereas the N20 SEP peak increased in the control group (P < 0.05). At baseline, the intervention group outperformed the control group in accuracy (P < 0.001). Response time improved after motor learning (P < 0.001) and at retention (P < 0.001). Experiment 2: The P25 SEP peak decreased in the local group after application of capsaicin cream (P < 0.01), whereas the N30 SEP peaks increased after motor learning in both groups (P < 0.05). Accuracy improved in the local group at retention (P < 0.005), and response time improved after motor learning (P < 0.005) and at retention (P < 0.001). This study suggests that acute pain may increase focal attention to the body part used in motor learning, contributing to our understanding of how the location of pain impacts somatosensory processing and the associated motor learning.

Do pursuit movement tasks lead to differential changes in early somatosensory evoked potentials related to motor learning compared with typing tasks?

Central nervous system (CNS) plasticity is essential for development; however, recent research has demonstrated its role in pathology, particularly following overuse and repetition. Previous studies investigating changes in sensorimotor integration (SMI) have used relatively simple paradigms resulting in minimal changes in neural activity, as determined through the use of somatosensory evoked potentials (SEPs). This study sought to utilize complex tasks and compare separate motor paradigms to determine which one best facilitates long-term learning. Spinal, brainstem, and cortical SEPs were recorded following median nerve stimulation at the wrist pre- and postinterventions. Eighteen participants performed the same paradigms, a control condition of 10 min of mental recitation and two interventions, one consisting of 10 min of tracing and the other 10 min of repetitive typing. Significant increases in the N13, N20, P25, and N30 SEP peaks were seen for both interventions. A significant decrease in the N24 SEP peak was observed for both interventions. Significant improvements in accuracy were seen for both interventions postacquisition but only for tracing during retention. The changes seen following motor learning were congruent with those associated with long-term learning, which was also reflected by significant increases in accuracy during retention. Tracing or the pursuit movement paradigm was shown to be a more effective learning tool. The identification of a task that is sufficiently novel and complex, leading to robust changes in SEP peaks, indicates a task that can be utilized in future work to study clinical populations and the effect of experimental interventions on SMI.