Changes in cortical grasp-related activity before and after object contact

Grasping, a seemingly simple manual behavior, requires the coordinated control of dozens of joints, guided by sensory signals from muscles, tendons, and skin. As the motor cortex controls finger movement and exerted forces, the somatosensory cortex must process the barrage of proprioceptive and tactile signals that convey details about the object’s shape, its local features (e.g., edges and curvature), and forces applied to it. In the present study, we aimed to understand the transformation in these sensorimotor signals at the time of contact with an object. We analyzed object-specific signals in the primary motor cortex (M1) and Brodmann’s areas 3a, 1, and 2 of the somatosensory cortex of macaque monkeys. We found object information distributed throughout sensorimotor cortex, some of which was independent of contact, while most was dramatically altered by it. While all areas conveyed object information after contact, those carrying postural representations (M1, area 3a) were also informative before contact, during the hand pre-shaping epoch. Although their mappings retained some similarity between epochs, decoders built on the pre-contact epoch did not perform well on the post-contact epoch, suggesting intermixing between postural and force-related signals. After contact, individual neurons in M1 retained some information about the object, but the populational encoding of object identity weakened, reflecting perhaps, the delegation of control to subcortical structures. Unexpectedly, although it was active, area 2 was uninformative about the object before contact, despite its proprioceptive inputs. However, after contact, area 2 emerged as the most informative region of any epoch, likely reflecting its convergent proprioceptive and cutaneous input, and supporting its proposed role in haptic object perception. These results underscore the diverse activity within the sensorimotor cortex during grasping, highlighting the intricate neural processes involved in this fundamental behavior.