SpectralIntegrationinPrimaryAuditoryCortexAttributable toTemporallyPreciseConvergenceofThalamocorticaland IntracorticalInput

Primary sensory cortex integrates sensory information from afferent feedforward thalamocortical projection systems and convergent intracortical microcircuits. Both input systems have been demonstrated to provide different aspects of sensory information. Here we haveusedhigh-densityrecordingsoflaminarcurrentsourcedensity(CSD)distributionsinprimaryauditorycortexofMongoliangerbils in combination with pharmacological silencing of cortical activity and analysis of the residual CSD, to dissociate the feedforward thalamocorticalcontributionandtheintracorticalcontributiontospectralintegration.Wefoundatemporallyhighlypreciseintegration ofbothtypesofinputswhenthestimulationfrequencywasinclosespectralneighborhoodofthebestfrequencyofthemeasurementsite, in which the overlap between both inputs is maximal. Local intracortical connections provide both directly feedforward excitatory and modulatory input from adjacent cortical sites, which determine how concurrent afferent inputs are integrated. Through separate excitatory horizontal projections, terminating in cortical layers II/III, information about stimulus energy in greater spectral distance is providedevenoverlongcorticaldistances.Theseprojectionseffectivelybroadenspectraltuningwidth.Basedonthesedata,wesuggest amechanismofspectralintegrationinprimaryauditorycortexthatisbasedontemporallypreciseinteractionsofafferentthalamocorticalinputsanddifferentshort-andlong-rangeintracorticalnetworks.Theproposedconceptualframeworkallowsintegrationofdifferentandpartlycontroversialanatomicalandphysiologicalmodelsofspectralintegrationintheliterature.