Neural associations of the frontal cortex.

Recent anatomical findings in the monkey indicate that the frontal cortex receives associative afferents from the visual, auditory, and somatosemsory areas of the cortex. The inferior parietal lobule and the inferior temporal cortex are important way-stations in these cortico-cortical afferent pathways. The olfactory system represents a fourth sensorium having access to the frontal cortex, namely, by way of substantial projections from the pirifom cortex and olfactory tubercle to the medial subdivision of the thalamic mediodorsal nucleus. Additional afferents to this nucleus originate from various fore- and midbrain structures implicated in the circuitry of the limbic system; such afferents could well be ediators of information related to the organism's internal milieu. On the efferent side, the frontal cortex is associated with the inferior parietal, temporal, cinguloparahippocampal cortex, and entorhinal area; it is the only cortical region known to project directly to the hypothalamus and hypothalamus-related structures in the paramedian midbrain tegmentum. The mosaic of origin and termination of the various connections indicates that the convexity of the frontal lobe (especially its caudal half) is reciprocally associated with the parietal and temporal cortex, while the major associations with the hippocampal mechanism originate from two separate areas, viz. the caudal orbitofrontal cortex and a region dorsal to the sulcus principalis, frontal fields from which also the major fronto-hypothalamic connections arise.