Abstract
Little is known about how temporal interactions of sensory inputs of different modalities affect thalamic information processing. We examined effects of temporal interactions between auditory and somatosensory inputs on thalamic cell activity, based on c-Fos expression induced by pure tone bursts (frequency, 8 kHz; duration, 200 ms) and/or foot shock stimuli (intensity, 1.0 mA; duration, 500 ms). Five sets of auditory and somatosensory stimuli (inter-set interval, 5 min) were given to awake rats with the following sequences in a set: 1) ten pure tone bursts (interval, 800 ms) and a foot shock stimulus immediately after the tone bursts (A-S, n = 6), 2) a foot shock stimulus and ten tone bursts immediately after the shock stimulus (n = 6), 3) tone bursts either before or after a shock stimulus (pseudo-random, n = 6). Additionally, only pure tone bursts (n = 5) or foot shock stimuli (n = 6) were given. Animals were euthanized with Nembutal (i.p.) at 90 min after the sensory stimuli, and brains were processed to reveal c-Fos expression. c-Fos positive cells were counted in the dorsal (MGD), ventral (MGV) and medial (MGM) divisions of the medial geniculate body and the suprageniculate nucleus (SG). In the MGD and MGV, the number of c-Fos positive cells was significantly large in A-S group as compared with those in the other groups. In the MGM and SG, there was no significant difference in the degree of c-Fos expression among the groups. The results suggest that a specific temporal interaction is crucial for cross-modal sensory integration in the thalamus. [J Physiol Sci. 2007;57 Suppl:S113]
