Fast Electrical Oscillations in Somatosensory Cortex

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Perhaps the oldest, most widely recognized, and least understood electrical phenomena of the human brain in sickness and in health are its characteristic large amplitude electrical oscillations. Recently, there has been a major advance towards understanding the relationship between oscillations and brain function. Electrocortical oscillations in the gamma bind (approximately 4o Hz), and much higher frequency fast and very fast oscillations (FO and VFO; approximately 300 and 500 Hz, respectively), appear to play a role in temporal coding in sensory cortex. Yet, their functional significance and underlying cellular mechanisms are still a matter of speculation and controversy. In the present experimental series, we address both of these issues by combining in vivo three dimensional extracellular recording with intracellular recording and labeling to study the neural circuitry responsible for generating and propagating fast oscillations in the posteromedial barrel subfield (PMBSF) of rat somatosensory cortex. First, we will extrapolate our results in the auditory system concerning thalamic modulation of cortical gamma oscillations, to the somatosensory system. In so doing, we will establish structural and functional analogies that should strongly support or refute hypotheses about the participation of distinct thalamic systems in the generation or modulation of cortical gamma oscillations, to the somatosensory system. In so doing, we will establish structural and functional analogies that should strongly support or refute hypotheses about the participation of distinct thalamic systems in the generation or modulation of cortical gamma oscillations. Second, we will determine the neural generators of thalamically evoked gamma oscillations in the PMBSF and compare these to our results from intracellular recordings in auditory cortex to evaluate our hypotheses that the generation of cortical gamma oscillations may be based on common cell types in both sensory modalities and not rely on specialized neural pacemakers. Third, we will measure the spatiotemporal response field of single vibrissa stimulation to establish the somatotopic organization and two dimensional shape of stimulus evoked gamma, FO and VFO in the PMBSF and to better anticipate how each oscillatory class could contribute to temporal interactions between adjacent cortical columns. Fourth, we will evaluate possible spatiotemporal interaction patterns of fast oscillations measured at the surface of the PMBSF, evoked by multi-vibrissal stimulation. By looking at how each class of fast oscillations may propagate from multiple start points in the PMBSF and interact in phase sensitive ways within sub-regions of the field, we expect to better understand how these oscillations may encoded the precise timing of sequential transient vibrissal contact with objects and/or how they may synchronize activity in multiple cortical columns when activated by a common and more prolonged stimulus. Finally, we will explore both sub- and suprathreshold events at the intracortical and intracellular level that support temporal integration of each oscillatory class within the PMBSF and histologically label and identify neurons and their processes responsible for this spatio integration.