Dynamic coding of tactile-to-motor transformation in human and macaque posterior parietal cortex – DYN-T2M

Posterior parietal cortex (PPC) is a central structure for sensorimotor transformation. Yet, its contribution to planning movements towards the own body is still unclear. This project investigates the implementation of goal-directed tactile-motor processing in human and non-human primate (macaque) PPC. It aims at (i) identifying the involved parietal regions, (ii) elucidating the spatial codes used by them, and (iii) characterizing the dynamics within and between regions involved in transforming tactile information from skin to space in dependence on the involved effector executing the motor response. The three key approaches are (a) to devise homologous, directly linkable experiments across the two species and across different methods (fMRI, behavior, neurophysiology); (b) to investigate tactile behavior across two effector systems (saccades, hand reaching) to identify common and specialized processing mechanisms, and (c) to complement these common experiments by human-specific research where directly comparable paradigms are not feasible.

Experiments exploit a common set of critical features. Delayed movement tasks involving pro and anti-movements will disentangle sensory and motor aspects of the inspected tasks. Experiments will directly compare sensorimotor transformation of visual and tactile stimuli for saccade and reach planning, and scrutinize the role monkey lateral, medial, and ventral intraparietal visuo-motor regions play in the context of touch. A central manipulation will be the dissociation of skin-centered, body part-centered, and eye-centered spatial coding through postural manipulations such as limb crossing, during which, say, a right body part is located in left space.

The project’s overarching hypotheses are that (1) common principles underlie human and macaque tactually guided motor planning across all effector systems, (2) posterior regions currently associated with eye-centered motor planning, such as macaque LIP/MIP, more generally code all sensory information in an eye-centered code, (3) anterior regions, associated with self-motion and body representation, such as macaque VIP and SPL, more generally code all sensory information in a skin or body-centered code, and (4) all regions dynamically recode spatial information from a sensory to a motor goal-related code.

The project’s major scientific contribution is the extension of current visuo-motor control concepts into the tactile domain, as a first step of incorporating information on body and self in sensorimotor control. More generally, the project will contribute an integrated cross-species characterization of sensorimotor processing spanning modalities and effectors. Overall, it will, thus, offer new perspectives for understanding the organizing principles underlying the functional and regional organization of PPC.