Perhaps the oldest, most widely recognized, and least understood electrical phenomena of the human brain is sickness and in health are its characteristic large amplitude electrical oscillations. Recently, there has been a major advance towards understanding the relationship between brain oscillations and brain function. Electrocortical oscillations in the high frequency gamma band (approx.40 Hz) appear to play a role in the temporal synchronization of information processing in sensory cortex. Yet, their functional significance and mechanism of neurogenesis is still a matter of much speculation and controversy. In this experimental series, both of these issues will be addressed by performing high resolution mapping of the two dimensional distribution of evoked and spontaneous gamma oscillation on the surface of vibrissa/barrel cortex in the rat using 64 channel electrode arrays, and by comparing these spatiotemporal maps to concurrent recordings performed in specific and nonspecific nuclei of somatosensory thalamus. Results previously obtained in the auditory system, concerning thalamic modulation of cortical gamma oscillations, will first be extrapolated to the somatosensory system, to establish structural and functional analogies that should strongly support or refute hypothesis about the participation of distinct thalamic systems in the generation or modulation of cortical gamma oscillations. Second, possible synchronization within reciprocally connected thalamocortical circuits during gamma oscillation will be studied. The vibrissa thalamocortical interactions at the level of individual cortical columns. The spatial and temporal properties of gamma oscillation in the vibrissa/barrel field, and possible thalamocortical synchronization, will be studied in the unanesthetized and unrestrained rat perfuming an active tactile discrimination task. These experiments would provide a basis for understanding the neurogenesis of gamma oscillations in the rodent, and their relationship to underlying anatomy and synaptic innervation, bridging a major gap in our understanding between single cell properties and the response properties of larger multi-synaptic neural systems. These experiments will also provide a starting point for conduction similar more limited studies in humans, the long range goal of our research program.
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