Thalamocortical Mechanisms in Odor-Guided Behavior

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Abstract
The core subnucleus of the mediodorsal thalamic nucleus (MD) receives direct input from the olfactory cortex in the rat. This part of the MD projects to the frontal neocortex of the rhinal sulcus (RS), while other parts of the MD project to the anterior medial wall of the neocortex (MW). Rats were tested on odor threshold, detection of specific odors and 3 odor discriminations both before and after lesions of MD, MW, RS or sham lesions. Olfactory threshold and detection ability remained unaffected by any lesion; subjects with MD and RS lesions were markedly impaired on odor discriminations. Subjects were more profoundly impaired when the stimuli to be discriminated were novel or difficult to associate. The MD and its olfactory projection target, RS, may mediate cognitive, rather than sensory aspects of odor-guided behavior in the rat.