OPTICAL STUDIES OF NEURON ACTIVITY & ORGANIZATION

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There are two long-term objectives of the proposal. First, to understand in neuronal detail how simpler nervous systems are able to generate behaviors and how these nervous systems are able to accomplish simple forms of learning. The second is to understand what happens in cortex during epileptic seizures. In order to better accomplish these scientific goals, we also have the methodological goal of improving optical techniques for monitoring neuron activity. We have been using optical methods to monitor neuron activity in the Aplysia abdominal ganglion during the gill-withdrawal reflex. Our preliminary results suggest that between 250 and 420 neurons in the ganglion are activated by a mechanical stimulus to the siphon. However this estimate comes from a recording that is perhaps 35% complete. We propose experiments to improve the completeness of the recording, experiments to allow preliminary identification of many of these neurons, and analyses to allow us to follow the activity of individual neurons during a series of trials involving habituation and sensitization. We also plan experiments to try to see if the same behavioral plasticity can be achieved with fewer neurons. If this is successful we propose to make a model of the neuron interactions that generate the behavior. We have been able to monitor activity in bicuculline induced inter-ictal epileptiform discharges in rat somatosensory cortex. Our results were surprising in two regards. First, they indicated that the optical measurements and the ball electrode measurements could give very disparate results. Second, they indicated that there were qualitative differences between discharges induced by sensory stimulation and spontaneous discharges. Our first aim is to confirm these result. Then we plan a local application of bicuculline to study the spread (or absence of spread) of the epileptic activity away from the treated region. Finally we plan a simultaneous measurement from both the bicuculline treated and the untreated contralateral somatosensory cortex. These experiments are meant to lead toward measurements in more sophisticated models (primates) of the human disease. These experiment may also lead to the use of optical monitoring techniques for determining the location of epileptic foci in surgical patients.