Neural population dynamics in motor cortex are different for reach and grasp

Low-dimensional linear dynamics are observed in neuronal population
activity in primary motor cortex (M1) when monkeys make reaching
movements. This population-level behavior is consistent with a role for M1
as an autonomous pattern generator that drives muscles to give rise to
movement. In the present study, we examine whether similar dynamics are
also observed during grasping movements, which involve fundamentally
different patterns of kinematics and muscle activations. Using a variety
of analytical approaches, we show that M1 does not exhibit such dynamics
during grasping movements. Rather, the grasp-related neuronal dynamics in
M1 are similar to their counterparts in somatosensory cortex, whose
activity is driven primarily by afferent inputs rather than by intrinsic
dynamics. The basic structure of the neuronal activity underlying hand
control is thus fundamentally different from that underlying arm
control.Low-dimensional linear dynamics are observed in neuronal
population activity in primary motor cortex (M1) when monkeys make
reaching movements. This population-level behavior is consistent with a
role for M1 as an autonomous pattern generator that drives muscles to give
rise to movement. In the present study, we examine whether similar
dynamics are also observed during grasping movements, which involve
fundamentally different patterns of kinematics and muscle activations.
Using a variety of analytical approaches, we show that M1 does not exhibit
such dynamics during grasping movements. Rather, the grasp-related
neuronal dynamics in M1 are similar to their counterparts in somatosensory
cortex, whose activity is driven primarily by afferent inputs rather than
by intrinsic dynamics. The basic structure of the neuronal activity
underlying hand control is thus fundamentally different from that
underlying arm control.