Influence of thalamic cooling on sensory responses in association cortex

Evoked responses to light flash, click, and paw stimuli were recorded in the four cortical association areas in the acutely prepared cat. Average evoked responses (AEP) for 100 trials were formed before, during, and after localized cooling in the midline thalamus. Cooling of the midline thalamus reduced the magnitude of responses to click and paw stimuli, and increased or did not change the responses to light flash. There was very little similarity in trial-to-trial fluctuations of EP magnitude across cortical areas, and cooling did not reduce the similarity that existed. Waveform similarity was reduced by cooling for responses across the cortex to a single stimulus modality, whereas similarity of responses in a single cortical area to all three stimuli was not changed. The temporal components of the AEP influenced by thalamic cooling were different for different stimuli and cortical locations. It was concluded that the midline thalamo-cortical projection through the centromedian area to association cortices is particularly well-differentiated for multisensory responses in a single cortical region, and that the system should not be thought of as nonspecific but as convergent or multisensory.