Goodman, J. M.
Tabot, G.A.
Suresh, A.K.
Hatsopoulos, N.G.
Bensmaia, S.J.
We effortlessly grasp and manipulate objects with our hands even
though each hand has 30 degrees of freedom. An appealing hypothesis of
how the brain achieves such dexterity is by reducing the space of
possible hand movements. Indeed, examination of kinematics of the hand
using principle components analysis reveals correlated combinations of
joints – synergies –, which may reflect this simplified control
strategy. According to this hypothesis, synergies should reflect
neuronal representations of the hand in primary motor and somatosensory
cortices, which themselves should also occupy a reduced dimensionality.
To test this idea, we have monkeys grasp a wide variety of objects to
evoke highly varied hand kinematics. While monkeys perform this task, we
track the time-varying joint angles of the hand during the course of
these movements and simultaneously record from populations of single
neural units in primary somatosensory and motor cortices. We then assess
whether canonical kinematic synergies are preferentially encoded by
single cortical neurons or by cortical populations. While we do find
that single units in both S1 and M1 tend to preferentially encode
multiple joints, the combinations of joints that are tracked or
controlled are not what would be predicted based on a naïve
interpretation of the synergy hypothesis.