Integration of Ascending, Callosal, and Feedback Signals in the Formation of Sensory Maps
We are evaluating and comparing the contributions ascending, lateral and feedback pathways make to the neuronal representation of sound in primary auditory cortex. We are measuring the responses of individual neurons before, during, and after reversible deactivation of ascending signals from thalamus, transcallosal projections arising from area A1 in the opposite hemisphere, and feedback signals from presumptive higher-order areas like AAF and PAF. The strength and specificity of the individual neuronal representation is quantified by using electrophysiological recording. Cooling deactivation is applied to reversibly deactivate lateral and feedback cortical pathways and GABA microinjection is used to reversibly deactivate ascending pathways from the medial geniculate nucleus (MGN). Finally, the capacity of neurons to integrate signals from categorically different sources is being assessed by comparing the effects of separate and combined deactivations on the same neurons. These comparisons are revealing additive, synergistic, and subliminal influences.