Recent electrophysiological, anatomical, and lesion-behavioral studies have implicated parts of the thalamic mediodorsal nucleus (MD) and orbitofrontal cortex in some aspects of olfactory modulated behavior. Various data suggest that this thalamocortical subsystem may be less involved in the detection of stimulus differences than it is in mediation of the consequences of the discriminative process. One function of the subsystem may be to modulate those autonomic and skeletal-motor responses, which are appropriate for particular olfactory stimuli. We propose to analyze autonomic (heart rate) and skeletal-motor (sniffing) responses of rabbits to attractive and aversive odorants and then determine if discharges of any neurons in MD are correlated with these responses rather than the sensory aspects of the stimuli. In addition, the input and output connections of the system will be traced by autoradiographic and horseradish peroxidase methods. Partiular emphasis will be placed on localizing the precise destinations of inputs which originate in different basal olfactory and olfactory-related structures. This will provide a basis for assessing the functional significance of different inputs which may influence different parts of the thalamocortical system.