Postural Representations of the Hand in the Primate Sensorimotor Cortex

Abstract

Manual dexterity requires proprioceptive feedback about the state of the hand. To date, study of the neural basis of proprioception in the cortex has focused primarily on reaching movements to the exclusion of hand-specific behaviors such as grasping. To fill this gap, we record both timevarying hand kinematics and neural activity evoked in somatosensory and motor cortices as monkeys grasp a variety of objects. We find that neurons in the somatosensory cortex, as well as in the motor cortex, preferentially track time-varying postures of multi-joint combinations spanning the entire hand. This contrasts with neural responses during reaching movements, which preferentially track time-varying movement kinematics of the arm, such as velocity and speed of the limb, rather than its time-varying postural configuration. These results suggest different representations of arm and hand movements suited to the different functional roles of these two effectors.

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

“…Whatever the case may be, the low-dimensional linear dynamics observed in M1 during reaching are not present during grasping, consistent with an emerging view that the cortical circuits that track and control the hand differ from those that track and control the proximal limb ( Goodman et al, 2019 ; Rathelot and Strick, 2009 ).…”

“…The VICON system tracked the three-dimensional positions of the markers, and time-varying joint angles were computed using inverse kinematics based on a musculoskeletal model of the human arm ( https://simtk.org/projects/ulb_project ) ( Anderson and Pandy, 2001 ; Anderson and Pandy, 1999 ; de Leva, 1996 ; Delp et al, 1990 ; Dempster and Gaughran, 1967 ; Holzbaur et al, 2005 ; Yamaguchi and Zajac, 1989 ) implemented in Opensim ( https://simtk.org/frs/index.php?group_id=91 ) ( Delp et al, 2007 ) with segments scaled to the sizes of those in a monkey limb using Opensim’s built-in scaling function. Task and kinematic recording methods are reported in an earlier publication ( Goodman et al, 2019 ). We used a linear discriminant classifier as detailed in this previous publication to determine whether objects indeed evoked distinct kinematics ( Figure 1—figure supplement 1 ).…”

“…In other words, grasping and reaching movements are associated with overlapping distributions of joint angular speeds and ranges of motion. Panels A-E and G are reproduced from (Goodman et al, 2019). Figure 1.…”

Biomimetic sensory feedback through peripheral nerve stimulation improves dexterous use of a bionic hand

“…Position control (i.e., postural control) provided improved performance relative to velocity control ( fig. S6), which is consistent with the natural encoding schemes of the hand (56). The participant received cutaneous sensory feedback from the index contact sensor; proprioceptive sensory feedback was not provided, although endogenous proprioception of residual forearm muscles and efference copy may have been present.…”

Electrocorticography Evidence of Tactile Responses in Visual Cortices

“…The specificity of the responses we observed in low-level visual cortex may reside on specific retinotopic-like maps in visual cortex for tactile location as recently shown for spatial sound (Norman and Thaler 2019). It has been also shown that the response fields of sensorimotor neurons are distributed over the entire hand (Goodman et al 2019). Taken together with our observations, one could argue that this specific organization is reflected in visual cortex.…”