Sensory Motor Transformations in Human Cortex

Abstract: The long-term objective of this application is to understand cortical processing of sensory to
motor transformations within the human cerebral cortex. A vast number of computations must be
performed to achieve sensory-guided motor control. Standing out among these computations, visual
information of the goals of action must be transformed from the coordinates of the retina to the
coordinates of effectors used for movement, for instance limb coordinates for reaching under visual
guidance and to world coordinates for interactions in the environment. Once an object is grasped,
somatosensory signals from the hand are required for dexterous manipulation of grasped objects. Internal
models within the sensory motor pathway are essential for estimating the current state of the body and the
external environment, accounting for lags in sensory feedback, and calibrating the body to the
environment.
We will use the rare opportunity of being able to record from populations of single neurons in a clinical
study designed to develop neural prosthetics for tetraplegic participants paralyzed by spinal cord injuries.
Cortical implants of microelectrode arrays will be made within three key locations in the sensorimotor
system: primary motor cortex, primary somatosensory cortex, and posterior parietal cortex. These
microelectrode arrays enable both recording and intracortical microstimulation.
We will test the hypothesis that somatosensory and motor cortex represent imagined reaches in hand
coordinates, but posterior parietal cortex is task dependent, and its population neural activity can flexibly
change coordinate frames to enable encoding of the spatial relations within the body (arm and eyes),
between the body and world (arm and reach targets; objects relative to self), and within the world (relative
position of objects in the world) as required by task demands. Percepts evoked by intracortical
microstimulation and imagined sensations will be used to understand the representation of cutaneous and
proprioceptive information within primary somatosensory cortex and posterior parietal cortex. The
hypothesis to be tested is that imagined sensation and electrically evoked sensations are highly
overlapping—not just in primary somatosensory cortex but also in posterior parietal cortex. Lastly, we
hypothesize that the posterior parietal cortex contains in humans an internal model of state estimation that
shows plasticity for both natural and brain-control behaviors and transfers this learning to motor cortex.
These studies will not only greatly advance our understanding of the human sensorimotor cortical circuit,
but also will provide basic knowledge for the design of future neural prosthetics.

Grant Number: 5U01NS123127-05
NIH Institute/Center: NIH
Principal Investigator: RICHARD ANDERSEN