The overall goal of this research plan is to understand the role of the basal ganglia (BG) and superior colliculus (SC) in saccadic eye movement choice and decision-making. This application focuses on developing an in vitro brain slice model with which we will extend our recent in vivo results and investigate the biophysics of a circuit involved in choice and decision-making. This proposal aims to link the properties of neurons and their circuits to behavior in order to elucidate the role of the SC and the BG in eye-movement related cognitive processes. We have four specific aims;1) Map response patterns across the SC. Voltage imaging will be used to map the spatial patterns of signal spread following electrical stimulation in the superficial SC (sSC) and intermediate SC (iSC).
This aim will provide a basic assessment of the spatial extent of both intra- and inter-laminar circuitry within the SC;2) Evaluate inhibition and excitation in SC activity patterns. In this aim we will test for the existence of three specific interlaminar pathways: an excitatory pathway arising from the sSC extending to the iSC, an inhibitory pathway arising from the iSC and extending into the sSC and an excitatory pathway arising from the iSC and extending into the sSC. We will use voltage imaging in conjunction with patch clamping to study responses to sSC and iSC stimulation, and resolve these responses into contributions mediated by glutamatergic and GABAergic synapses. Experiments with synaptic receptor antagonists will assess the role of glutamatergic and GABAergic transmission in both intra- and interlaminar circuits;3) Determine the influence of BG output on the response pattern across the SC. The experiments of this aim will test the hypothesis that translation of visual information from sSC into motor information in iSC is modulated by inhibition from the substantia nigra pars reticulata of the BG. We will apply electrical stimulation in the nigra to determine how the nigra modulates SC responses to sSC and iSC stimulation;4) Map response patterns across the SC in monkey SC. We will develop an in vitro preparation of the SC using monkey tissue. Experiments as outlined in aims 1 and 2 will be performed. We will test the hypothesis that the underlying circuits in monkey and rodent SC are homologous. Because the BG and its target structures are implicated in many neurological and psychiatric disease states, the results of our experiments should lead to important insights into the functioning of these circuits and the biophysical mechanisms underlying complex behavioral and cognitive processing in both health and disease.
A sine qua non of higher mental function is our ability to make decisions. Extreme fluctuations in choice behavior may underlie certain neurological and psychiatric diseases such as schizophrenia, attention deficit disorder, Tourette Syndrome and obsessive compulsive disorder. Eye movement abnormalities are also associated with these cortico-basal ganglia diseases. Therefore, a deeper understanding of the basal ganglia - superior colliculus pathway and circuitry and ultimately their role in higher mental function, may lead to better diagnostics, better ways to assess therapies and should provide important insights into the mechanisms of symptomology in these disease states.
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