Visual/Spatial Properties of Posterior Parietal Neurons

California Institute Of Technology, Pasadena CA

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Abstract

DESCRIPTION (From the Applicant's Abstract): Although the posterior parietal cortex (PPC) has long been appreciated to be an area for association of different sensory modalities for spatial awareness and for spatial attention, recent studies have pointed to an additional, and very major, role of this area in movement planning. One important advance has been the fmding that there is an anatomical map of intentions within the PPC, with different areas specialized for different behaviors. In Aim 1 we will determine the inter-relationship between some of these areas in movement planning. In particular, we will examine whether area LIP has an executive role in decision making for both eye and limb movements, or if LIP is primarily involved in the former, and areas MIP and 5 in the latter. Another important advance has been the elucidation of the spatial representations in some PPC cortical areas. These results have led to a general proposal that the early stages of movement planning are performed in eye-centered coordinates in primates, regardless of the sensory input or eventual motor output. However, the activity of many PPC neurons is gain modulated by eye, head and limb position. Aim 2 will examine whether these PPC "gain fields" may effect the decisions to make eye and hand movements. Classically it has been believed that the coordinate transformation for reaching results from the transformation of the traget object from retinal to body coordinates, and then the subtraction of the object location in body-coordinates from the location of the hand in body coordinates to generate the motor error in limb coordinates. Our finding that early movement planning occurs in eye-coordinates in PPC suggests an alternative scheme, in which the hand is represented in eye coordinates and is subtracted from the location of the target in eye coordinates to produce the motor error signal. We will test this new idea in aim 3. Lastly, in aim 4 we will examine the spatial representation of sound location in an auditory area, Tpt, that provides input to the PPC. These experiments are designed to determine the stage in auditory processing pathway where head-centered auditory fields are converted into eye-centered auditory fields similar to those encountered in the PPC.