Force modulation relies on accurate proprioception, and force-matching tasks alter cortico-cerebellar connectivity. Cortico-cerebellar (N24) and cortico-motor pathways are impacted following acquisition of a motor tracing task (MTT), measured using both somatosensory evoked potentials (SEPs) and transcranial magnetic stimulation. This study compared changes in early SEP peak amplitudes and motor performance following a force matching tracking task (FMTT) to an MTT. 30 (18 females) right-handed, participants aged 21.4 ± 2.76, were electrically stimulated over the right-median nerve at 2.47 Hz and 4.98Hz (Averaged 1000 sweeps/rate) to elicit SEPs, recorded via a 64-channel electroencephalography cap, pre and post task acquisition using the right abductor pollicis brevis muscle. Retention was measured 24 hours later. Significant time by group interactions occurred for the N20 SEP: 6.3% decrease post FMTT vs 5.5% increase post MTT (p = 0.013). P25 SEP: 4.0 % decrease post FMTT vs 10.3% increase post MTT (p = 0.006). N18 SEP 113.4 % increase post FMTT vs 4.4 % decrease post MTT (p = 0.006). N18 and N30 showed significant effect of time (both p < 0.001). Motor Performance: Significant time by group interactions - post-acquisition: FMTT improved 15.3% vs 24.3% for MTT (p = 0.025), retention: FMTT improved 17.4 % and MTT by 30.1% (p= 0.004). Task-dependent differences occurred in SEP peaks associated with cortical somatosensory processing (N20 and P25), and cerebellar input (N18), with similar changes in sensorimotor integration (N30), with differential improvements in motor performance, indicating neurophysiological differences in cerebellar and sensory processing for tasks reliant on proprioception.

The cerebellum undergoes neuroplastic changes in response to motor learning. Healthy human individuals demonstrate reduced cerebellar inhibition (CBI) following motor learning. Alterations in neck sensory input due to muscular fatigue are known to impact upper limb sensorimotor processing, suggesting that neck fatigue may also impact cerebellum to motor cortex (M1) pathways in response to motor learning. Therefore, this study aimed to determine whether cervical extensor muscle (CEM) fatigue alters CBI in response to motor learning. We examined sixteen participants (8 CEM fatigue and 8 CEM control). A double cone TMS coil stimulated the ipsilateral cerebellar cortex 5 ms prior to application of contralateral test stimuli of the M1 to the right first dorsal interosseous muscle. Cerebellar-MI activity curves were established pre- and post- motor skill acquisition (consisting of tracing sinusoidal-pattern waves with the index finger), and following either the CEM fatigue or control intervention. The control group showed greater cerebellar disinhibition than the fatigue group following motor skill acquisition (p<0.006), while the fatigue group showed similar levels of CBI pre- and post-motor skill acquisition. Both groups improved in accuracy following acquisition (p= 0.012), and retention (p= 0.007), but the control group improved significantly more (17% at acquisition and 22% at retention) vs lower (6% and 9%) improvements for the fatigue group. Lessened cerebellar disinhibition in the CEM fatigue vs. control group, coupled with diminished motor learning, suggests that CEM fatigue affects the cerebellar-MI interaction, influencing the cerebellum's ability to adjust motor output to acquire and learn a novel motor task.

Upper limb control depends on accurate internal models of limb position relative to the head and neck, accurate sensory inputs, and accurate cortical processing. Transient alterations in neck afferent feedback induced by muscle vibration may impact upper limb proprioception. This research aimed to determine the effects of neck muscle vibration on upper limb proprioception using a novel elbow repositioning task (ERT). 26 right-handed participants aged 22.21 ± 2.64 performed the ERT consisting of three target angles between 80–90° (T1), 90–100° (T2) and 100–110° (T3). Controls (CONT) (n = 13, 6F) received 10 min of rest and the vibration group (VIB) (n = 13, 6F) received 10 min of 60 Hz vibration over the right sternocleidomastoid and left cervical extensor muscles. Task performance was reassessed following experimental manipulation. Significant time by group interactions occurred for T1: (F1,24 = 25.330, p < 0.001, ηp2 = 0.513) where CONT improved by 26.08% and VIB worsened by 134.27%, T2: (F1,24 = 16.157, p < 0.001, ηp2 = 0.402) where CONT improved by 20.39% and VIB worsened by 109.54%, and T3: (F1,24 = 21.923, p < 0.001, ηp2 = 0.447) where CONT improved by 37.11% and VIB worsened by 54.39%. Improvements in repositioning accuracy indicates improved proprioceptive ability with practice in controls. Decreased accuracy following vibration suggests that vibration altered proprioceptive inputs used to construct body schema, leading to inaccurate joint position sense and the observed changes in elbow repositioning accuracy.

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder that has noted alterations to motor performance and coordination, potentially affecting learning processes and the acquisition of motor skills. This work will provide insight into the role of altered neural processing and sensorimotor integration (SMI) while learning a novel visuomotor task in young adults with ADHD. This work compared adults with ADHD (n = 12) to neurotypical controls (n = 16), utilizing a novel visuomotor tracing task, where participants used their right-thumb to trace a sinusoidal waveform that varied in both frequency and amplitude. This learning paradigm was completed in pre, acquisition, and post blocks, where participants additionally returned and completed a retention and transfer test 24 hours later. Right median nerve short latency somatosensory evoked potentials (SEPs) were collected pre and post motor acquisition. Performance accuracy and variability improved at post and retention measures for both groups for both normalized (p < 0.001) and absolute (p < 0.001) performance scores. N18 SEP: increased in the ADHD group post motor learning and decreased in controls (p < 0.05). N20 SEP: increased in both groups post motor learning (p < 0.01). P25: increased in both groups post motor learning (p < 0.001). N24: increased for both groups at post measures (p < 0.05). N30: decreased in the ADHD group and increased in controls (p < 0.05). These findings suggest that there may be differences in cortico-cerebellar and prefrontal processing in response novel visuomotor tasks in those with ADHD.

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder, where differences are often present relating to the performance of motor skills. Our previous work elucidated unique event-related potential patterns of neural activity in those with ADHD when performing visuomotor and force-matching motor paradigms. The purpose of the current study was to identify whether there were unique neural sources related to somatosensory function and motor performance in those with ADHD. Source localization (sLORETA) software identified areas where neural activity differed between those with ADHD and neurotypical controls when performing a visuomotor tracing task and force-matching task. Median nerve somatosensory evoked potentials (SEPs) were elicited, while whole-head electroencephalography (EEG) was performed. sLORETA localized greater neural activity post-FMT in those with ADHD, when compared with their baseline activity (p < 0.05). Specifically, greater activity was exhibited in BA 31, precuneus, parietal lobe (MNI coordinates: X = −5, Y = −75, and Z = 20) at 156 ms post stimulation. No significant differences were found for any other comparisons. Increased activity within BA 31 in those with ADHD at post-FMT measures may reflect increased activation within the default mode network (DMN) or attentional changes, suggesting a unique neural response to the sensory processing of force and proprioceptive afferent input in those with ADHD when performing motor skills. This may have important functional implications for motor tasks dependent on similar proprioceptive afferent input.