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

Sensorimotor integration and motor learning during a novel force-matching task in young adults with attention-deficit/hyperactivity disorder

Introduction

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder that exhibits unique neurological and behavioral characteristics. Those with ADHD often have noted impairments in motor performance and coordination, including during tasks that require force modulation. The present study provides insight into the role of altered neural processing and SMI in response to a motor learning paradigm requiring force modulation and proprioception, that previous literature has suggested to be altered in those with ADHD, which can also inform our understanding of the neurophysiology underlying sensorimotor integration (SMI) in the general population.

Methods

Adults with ADHD (n = 15) and neurotypical controls (n = 15) performed a novel force-matching task, where participants used their right-thumb to match a trace template that varied from 2-12% of their Abductor Pollicis Brevis maximum voluntary contraction. This motor task was completed in pre, acquisition, and post blocks. Participants also completed a retention test 24 h later. Median nerve somatosensory-evoked potentials (SEPs) were collected pre and post motor acquisition. SEPs were stimulated at two frequencies, 2.47 Hz and 4.98 Hz, and 1,000 sweeps were recorded using 64-electrode electroencephalography (EEG) at 2,048 Hz. SEP amplitude changes were normalized to each participant's baseline values for that peak.

Results

Both groups improved at post measures (ADHD: 0.85 ± 0.09; Controls: 0.85 ± 0.10), with improvements maintained at retention (ADHD: 0.82 ± 0.11; Controls: 0.82 ± 0.11). The ADHD group had a decreased N18 post-acquisition (0.87 ± 0.48), while the control N18 increased (1.91 ± 1.43). The N30 increased in both groups, with a small increase in the ADHD group (1.03 ± 0.21) and a more pronounced increase in controls (1.15 ± 0.27).

Discussion

Unique neural differences between groups were found after the acquisition of a novel force-matching motor paradigm, particularly relating to the N18 peak. The N18 differences suggest that those with ADHD have reduced olivary-cerebellar-M1 inhibition when learning a novel motor task dependent on force-modulation, potentially due to difficulties integrating the afferent feedback necessary to perform the task. The results of this work provide evidence that young adults with ADHD have altered proprioceptive processing when learning a novel motor task when compared to neurotypical controls.

When the non-dominant arm dominates: the effects of visual information and task experience on speed-accuracy advantages

Speed accuracy trade-off, the inverse relationship between movement speed and task accuracy, is a ubiquitous feature of skilled motor performance. Many previous studies have focused on the dominant arm, unimanual performance in both simple tasks, such as target reaching, and complex tasks, such as overarm throwing. However, while handedness is a prominent feature of human motor performance, the effect of limb dominance on speed-accuracy relationships is not well-understood. Based on previous research, we hypothesize that dominant arm skilled performance should depend on visual information and prior task experience, and that the non-dominant arm should show greater skill when no visual information nor prior task information is available. Forty right-handed young adults reached to 32 randomly presented targets across a virtual reality workspace with either the left or the right arm. Half of the participants received no visual feedback about hand position throughout each reach. Sensory information and task experience were lowest during the first cycle of exposure (32 reaches) in the no-vision condition, in which visual information about motion was not available. Under this condition, we found that the left arm group showed greater skill, measured in terms of position error normalized to speed, and by error variability. However, as task experience and sensory information increased, the right arm group showed substantial improvements in speed-accuracy relations, while the left arm group maintained, but did not improve, speed-accuracy relations throughout the task. These differences in performance between dominant and non-dominant arm groups during the separate stages of the task are consistent with complimentary models of lateralization, which propose different proficiencies of each hemisphere for different features of control. Our results are incompatible with global dominance models of handedness that propose dominant arm advantages under all performance conditions.