Maintained Representations of the Ipsilateral and Contralateral Limbs during Bimanual Control in Primary Motor Cortex

Abstract

Primary motor cortex (M1) almost exclusively controls the contralateral side of the body. However, M1 activity is also modulated during ipsilateral body movements. Previous work has shown that M1 activity related to the ipsilateral arm is independent of the M1 activity related to the contralateral arm. How do these patterns of activity interact when both arms move simultaneously? We explored this problem by training 2 monkeys (male, Macaca mulatta) in a postural perturbation task while recording from M1. Loads were applied to one arm at a time (unimanual) or both arms simultaneously (bimanual). We found 83% of neurons (n = 236) were responsive to both the unimanual and bimanual loads. We also observed a small reduction in activity magnitude during the bimanual loads for both limbs (25%). Across the unimanual and bimanual loads, neurons largely maintained their preferred load directions. However, there was a larger change in the preferred loads for the ipsilateral limb (;25%) than the contralateral limb (;9%). Lastly, we identified the contralateral and ipsilateral subspaces during the unimanual loads and found they captured a significant amount of the variance during the bimanual loads. However, the subspace captured more of the bimanual variance related to the contralateral limb (97%) than the ipsilateral limb (66%). Our results highlight that, even during bimanual motor actions, M1 largely retains its representations of the contralateral and ipsilateral limbs.

Rotational dynamics in motor cortex are consistent with a feedback controller

“…Instead, all necessary dynamics are generated by the inputs to the network and these activity patterns can be largely arbitrary or unstructured. Here, we examined the dynamics of a network performing a posture perturbation task, where the network had to respond to sensory feedback about the periphery to generate an appropriate motor correction ( Cross et al, 2020 ; Heming et al, 2019 ; Omrani et al, 2014 ; Omrani et al, 2016 ; Pruszynski et al, 2014 ). Sensory input plays an important role for correctly performing the task, and thus, the hypothesis is that rotational dynamics should be absent in the network.…”

Rotational dynamics in motor cortex are consistent with a feedback controller

“…In contrast, rotational dynamics appear to be absent in systems that are dominated by external inputs, such as muscle activity driven by neural inputs (Churchland et al, 2012), or MC activity during grasping driven by sensory inputs (Suresh et al, 2020). Here, we examined the dynamics of a network performing a posture perturbation task, where the network had to respond to sensory feedback about the periphery to generate an appropriate motor correction (Cross et al, 2020; Heming et al, 2019; Omrani et al, 2014, 2016; Pruszynski et al, 2014). Sensory input plays an important role for correctly performing the task and thus the hypothesis is that rotational dynamics should be absent in the network.…”

Visuomotor information drives interference between the hands more than dynamic motor information during bimanual reaching

“…Thus, it is possible that interference may also result from ipsilateral contributions of the left hemisphere. Future work could attempt to further understand ipsilateral M1 contributions to bimanual movements (Cross et al ., 2020), the contribution of ipsilateral vs. contralateral activity in the context of interference, and whether these processes interact with different types of sensorimotor information.…”