Beyond the primary olfactory cortex: olfactory-related areas in the neocortex, thalamus and hypothalamus

The extrinsic projections from the primary olfactory cortexto other areas of the forebrain in the rat are described, onthe basis of experiments using anterograde and retrograde axonaltracers, as well as electrophysiological recording of unit activity.The areas shown to receive olfactory inputs are (i) in the neocortex:the lateral and ventrolateral orbital areas, and the ventralagranular insular area, all of which are in the dorsal bankof the rhinal sulcus; (ii) in the thalamus: the central segmentof the mediodorsal nucleus and the ventral part of the submedicalnucleus; (iii) in the hypothalamus: the lateral hypothalamicarea, especially its caudal half, and probably the nucleus gemiru,with some input also to more medial hypothalamic structures;(iv) the hippocampus and dentate gyrus; and (v) the deep nucleiof the amygdala. Anterograde and retrograde axonal tracing experimentshave shown that all of these areas receive fibers from cellsin or closely related to the primary olfactory cortex, and cellsin all of them except the nucleus gemini and the deep nucleiof the amygdala have been shown to be driven by electrical stimulationof the olfactory bulb.