Spatio-temporal modulation of cortical activity during motor deadaptation depends on the feedback of task-related error

Motor adaptations are responsible for recalibrating actions and facilitating the achievement of goals in a constantly changing environment. Once consolidated, the decay of motor adaptation is a process affected by available sensory information during deadaptation. However, the cortical response to task error feedback during the deadaptation phase has received little attention. Here, we explored changes in brain cortical responses due to feedback of task-related error during deadaptation. Twelve healthy volunteers were recruited for the study. Right hand movement and EEG were recorded during repetitive trials of a hand reaching movement. A visuomotor rotation of 30° was introduced to induce motor adaptation. Volunteers participated in two experimental sessions organized in baseline, adaptation, and deadaptation blocks. In the deadaptation block, the visuomotor rotation was removed, and visual feedback was only provided in one session. Performance was quantified using angle end-point error, averaged speed, and movement onset time. A non-parametric spatiotemporal cluster-level permutation test was used to analyze the EEG recordings. During deadaptation, participants experienced a greater error reduction when feedback of the cursor was provided. The EEG responses showed larger activity in the left centro-frontal parietal areas during the deadaptation block when participants received feedback, as opposed to when they did not receive feedback. Centrally distributed clusters were found for the adaptation and deadaptation blocks in the absence of visual feedback. The results suggest that visual feedback of the task-related error activates cortical areas related to performance monitoring, depending on the accessible sensory information.

Effects of Prolonged and Acute Muscle Pain on the Force Control Strategy During Isometric Contractions

Musculoskeletal pain is associated with multiple adaptions in movement control. This study aimed to determine whether changes in movement control acquired during acute pain are maintained over days of pain exposure. On day 0, the extensor carpi radialis brevis muscle of healthy participants was injected with nerve growth factor (NGF) to induce persistent movement-evoked pain (n = 13) or isotonic saline as a control (n = 13). On day 2, short-lasting pain was induced by injection of hypertonic saline into extensor carpi radialis brevis muscles of all participants. Three-dimensional force components were recorded during submaximal isometric wrist extensions on day 0, day 4, and before, during, and after saline-induced pain on day 2. Standard deviation (variation of task-related force) and total excursion of center of pressure (variation of force direction) were assessed. Maximal movement-evoked pain was 3.3 ± .4 (0-10 numeric scale) in the NGF-group on day 2 whereas maximum saline-induced pain was 6.8 ± .3 cm (10-cm visual analog scale). The difference in centroid position of force direction relative to day 0 was greater in the NGF group than in the control group (P < .05) on day 2 (before saline-induced pain) and day 4, reflecting changes in tangential force direction used to achieve the task. During saline-induced pain in both groups, tangential and task-related force variation was greater than before and after saline-induced pain (P < .05).

PERSPECTIVE

Persistent movement-evoked pain changes force direction from the pain-free direction. Acute pain leads to increased variation in force direction irrespective of persistent movement-evoked pain preceding the acutely painful event. These differences provide novel insight into the search for and consolidation of new motor strategies in the presence of pain.

Spatial reorganisation of muscle activity correlates with change in tangential force variability during isometric contractions

The aim of this study was to quantify the effects of spatial reorganisation of muscle activity on task-related and tangential components of force variability during sustained contractions. Three-dimensional forces were measured from isometric elbow flexion during submaximal contractions (50s, 5-50% of maximal voluntary contraction (MVC)) and total excursion of the centre of pressure was extracted. Spatial electromyographic (EMG) activity was recorded from the biceps brachii muscle. The centroids of the root mean square (RMS) EMG and normalised mutual information (NMI) maps were computed to assess spatial muscle activity and spatial relationship between EMG and task-related force variability, respectively. Result showed that difference between the position of the centroids at the beginning and at the end of the contraction of the RMS EMG and the NMI maps were different in the medial-lateral direction (P<0.05), reflecting that muscle regions modulate their activity without necessarily modulating the contribution to the task-related force variability over time. Moreover, this difference between shifts of the centroids was positively correlated with the total excursion of the centre of pressure at the higher levels of contractions (>30% MVC, R(2)>0.30, P<0.05), suggesting that changes in spatial muscle activity could impact on the modulation of tangential forces. Therefore, within-muscle adaptations do not necessarily increase force variability, and this interaction can be quantified by analysing the RMS EMG and the NMI map centroids.