Primary motor cortical activity during unimanual movements with increasing demand on precision

Abstract

In functional magnetic resonance imaging (fMRI) studies, performance of unilateral hand movements is associated with primary motor cortex activity ipsilateral to the moving hand (M1ipsi), in addition to contralateral activity (M1contra). The magnitude of M1ipsi activity increases with the demand on precision of the task. However, it is unclear how demand-dependent increases in M1ipsi recruitment relate to the control of hand movements. To address this question, we used fMRI to measure blood oxygenation level-dependent (BOLD) activity during performance of a task that varied in demand on precision. Participants (N = 23) manipulated an MRI-compatible joystick with their right or left hand to move a cursor into targets of different sizes (small, medium, large, extra-large). Performance accuracy, movement time, and number of velocity peaks scaled with target size, whereas reaction time, maximum velocity, and initial direction error did not. In the univariate analysis, BOLD activation in M1contra and M1ipsi was higher for movements to smaller targets. Representational similarity analysis, corrected for mean activity differences, revealed multivoxel BOLD activity patterns during movements to small targets were most similar to those for medium targets and least similar to those for extra-large targets. Only models that varied with demand (target size, performance accuracy, and number of velocity peaks) correlated with the BOLD dissimilarity patterns, though differently for right and left hands. Across individuals, M1contra and M1ipsi similarity patterns correlated with each other. Together, these results suggest that increasing demand on precision in a unimanual motor task increases M1 activity and modulates M1 activity patterns.

Neural Correlates of Motor Skill Learning Are Dependent on Both Age and Task Difficulty

“…A similar finding was found in a previous study using a visuomotor tracking task, where smaller pre-training beta activity over the ipsilateral cortex was related to better performance after practice (Espenhahn et al, 2019). Although the functional role of the ipsilateral cortex in motor control and learning is still under debate (Uehara and Funase, 2014;Barany et al, 2020;Cabibel et al, 2020), these results are consistent with the view that a more lateralized activity pattern is beneficial for motor performance (Takeuchi et al, 2012).…”

Bimanual digit training improves right-hand dexterity in older adults by reactivating declined ipsilateral motor-cortical inhibition

“…3 b) likely represents a chronic decline in ipsilateral M1 inhibition. As described above, ipsilateral SM1-PMD activity is often reported when people perform complex finger movements 33 and precision-demanding tasks 48 , 49 . This could be caused by an “active” disinhibition, in which the brain utilizes the ipsilateral SM1-PMD by affirmatively releasing interhemispheric inhibition; this could be distinct from the chronic decline observed in older adults.…”

Bimanual digit training improves right-hand dexterity in older adults by reactivating declined ipsilateral motor-cortical inhibition

“…The reduction/loss of ipsilateral M1 deactivation detected during the illusion in the older adults (Figure 2b) likely represents a chronic decline in ipsilateral M1 inhibition. As described above, ipsilateral SM1-PMD activity is often reported when people perform complex finger movements [33] and precision-demanding tasks [46,47]. This could be caused by an "active" disinhibition, in which the brain utilizes the ipsilateral SM1-PMD by affirmatively releasing interhemispheric inhibition; this could be distinct from the chronic decline observed in older adults.…”