Our previous research on monkeys and prosimian galagos used half-second trains of electrical pulses delivered via microelectrodes to define eight small regions (domains) in posterior parietal cortex (PPC) where stimulation produced different complex movements. Functionally matched sets of domains were also found in motor (M1) and premotor (PMC) cortex that were additional parts of parallel parietal-frontal networks. In our study to date, we have described some of the connections of domains with each other in the same region, and across regions, with feedforward projections from PPC being focused on functionally matched PMC and M1 domains. Using optical imaging, we found that stimulating PPC domains activated matching PMC and M1 domains. Furthermore, lesioning or cooling M1 domains blocked the effects of stimulation matched, but not mismatched PPC domains. We propose to further determine the organization and functions of these domains and networks by determining their connections with other regions of cortex and subcortical structures. In addition, we will determine whether connections between domains are mainly excitatory or suppressive by selectively labeling neurons that terminate on inhibitory neurons, and by optically imaging cortical activation patterns during electrical stimulation. Also we will electrically stimulate sets of two domains at once to see if the movements produced reflect competition or cooperation. We predict that the motor effects of stimulating pairs of matching domains in PPC and M1 at the same time will be additive, resulting in faster and more extensive movements, and that stimulating mismatched pairs of domains will result in mutual or alternating suppression, the dominance of one domain action on the other, a blending of two movements, or two separate movements depending on the movements of each member of the pair. Finally, we will stimulate multiple sites within the reaching domain to see if an internal map of reach locations exist, and in a similar manner see if the looking domains have a map of visual targets. Our methods of investigation include electrical microstimulation of domains, optical imaging of intrinsic signals of evoked activity during electrical stimulation of domains or sensory input to domains, and the tracing brain connections with a number of tracers, including modified rabies virus and adeno-associated virus. The results are expected to produce a new and greatly expanded understanding of the functional organization of parietal-frontal networks in primates, how functional domains interact with each other, how they are guided by sensory information, and how they mediate different classes of behaviors. The connection patterns of domains with other areas of cortex and subcortical structures will reveal the more extended networks, and differences in connections of functionally matched domains will suggest their specialized roles. These studies will help us to evaluate our proposal that the primary function of each set of domains is to interact to mediate a given action, with the decision process based on sensory information in PPC, on largely prefrontal cortex inputs in PMC, and on all sources of information in M1.
The goal of our project is to determine how subregions of posterior parietal cortex mediate classes of useful behaviors, such as reaching and grasping food. These studies will reveal neural networks for such behaviors and provide an understanding of their functions and interactions. The data will have clinical relevance for treatments and recoveries after stroke or other damage to posterior parietal cortex.
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