Forebrain pathways of reward in Rattus norvegicus

Investigated self-stimulation effects in 121 adult male albino rats using bipolar electrodes and sine-wave current. Self-stimulation loci could be separated into 2 categories: olfactory and extraolfactory. The former included the anterior olfactory nucleus, the lateral septal area, the medial forebrain bundle, and the anterior commissure, but not the diagonal band of Broca. The extraolfactory placements were in pregenual or frontal cortex, the cingulum, corpus callosum, and caudate nucleus. Silver-impregnation experiments employing the Fink-Heimer procedure revealed that this extraolfactory system originates in frontal cortex, ascends via cingulum and through corpus callosum, to descend as part of the internal capsule in the caudate nucleus. At hypothalamic levels it is part of the most medial tip of the internal capsule, interdigitating, thereby, with lateral portions of the medial forebrain bundle. It is suggested that (a) medial forebrain bundle self-stimulation may often be derivative of this extraolfactory fronto-mesencephalic pathway, and (b) inferring the site of stimulation by the electrode-tip placement only may lead to incorrect identification. (26 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved).