A central issue in systems neuroscience is how sensory signals are transformed into motor plans. Many studies of sensory to motor transformations focus on the conversion of spatial information from a sensory to a motor frame of reference (reference frame transformation). Normal behavior, however, also involves selecting the mode of the response. For example, we must decide whether to look at something or to reach for it, or both. We propose that the sensory to motor transformation includes a stage distinct from the reference frame transformation, in which the mode of the response is selected (response selection). We hypothesize that response selection occurs in the parietal cortex, and that it precedes the reference frame transformation. We will test our hypotheses using single unit recording in parietal fields PRR (parietal reach region) and LIP (lateral intraparietal area) of monkey.
We are trying to understand the role of the posterior parietal cortex (PPC) during the sensorimotor transformations. Especially, we focus on how spatial information (target) gets combined with effector information (right arm, left arm, or eye) in PPC. PPC is an ideal place for combining the two information since it is located adjacent to both visual and somatosensory areas. We have been recording in PRR and LIP in behaving monkeys. Lately, we have been investigating how PRR cells represent limb-specific reach plans (Chang et al. 2005), and how PRR cells predict reach behavior on a trial-by-trial basis (Dickinson and Snyder, 2004).
In addition to correlating cells to behavior through recording in behaving monkeys, we also approach the same question by direclty manipulating PPC areas. In doing so, we can either stimulate, or inactivate those sites of interest and test behaviors between pre-manipulation and post-manipulation. In muscimol inactivation study, we inject muscimol into PRR and nearby regions and observe changes in firing rate and reaching behavior in detail.
Click here for the movie of the Standard Memory task
Click here for the movie of the Cue-delay-target task
Click here for the movie of the cell with Eye-centered frame of reference
Click here for the movie of the cell with Arm-centered frame of reference
Click here for the movie of the cell with Eye-centered frame of reference with Eye position gain field