Corticofugal modulation of functional connectivity within the auditory thalamus of rat, guinea pig and cat revealed by cooling deactivation

Microelectrode recordings were simultaneously performed at multiple sites i n the medial geniculate body (MCB) of anesthetized cats, rats and guinea pi gs. We studied the effect of cortical deactivation on the association of ne ural activity within the thalamus during spontaneous activity. The corticof ugal influence was suppressed by temporary cooling of the auditory cortex. Pairs of spike trains recorded from the same electrode were distinguished f rom cases where units were in MCB but recorded with different electrodes. T ime domain analyses included crosscorrelations and search for precise repet ition of complex spatiotemporal firing patterns of reverberating thalamic c ircuits. As a complementary approach we performed bispectral analyses of si multaneously recorded local field potentials in order to uncover the freque ncy components of their power spectra which are non linearly coupled. All r esults suggest that new functional neuronal circuits might appear at the th alamic level in the absence of input from the cortex. The newly active intr athalamic connections would provide the necessary input to sustain the reve rberating activity of thalamic cell assemblies and generate low frequency n on-linear interactions. The dynamic control exerted by the cortex over the functional segregation of information processing carried out in the thalamu s conforms with theoretical neural network studies and with the functional selectivity-adaptive filtering theory of thalamic neuronal assemblies. Alth ough this general conclusion remains valid across species, specific differe nces are discussed in the frame of known differences of the microcircuitry elements. (C) 1999 Elsevier Science B.V. All rights reserved.