The middle and inferior temporal gyri (areas 21 and 37) receive a massive contingent of fibers from the striate cortex (area 17) and the parastriate visual association areas (areas 18 and 19). These temporal visual areas make abundant connections with the medial limbic, rhinencephalic (olfactory), orbitofrontal, parietal, and occipital cortices, allowing for an intimate interconnection between the cortices subserving vision and hearing.
The superior part of the dominant temporal lobe is concerned with the acoustic or receptive aspects of language, as discussed in Chap. 22, which is devoted to this subject. The middle and inferior convolutions are sites of visual discriminations; they receive fiber systems from the striate and parastriate visual cortices and, in turn, project to the contralateral visual association cortex, the prefrontal heteromodal cortex, the superior temporal cortex, and the limbic and paralimbic cortex. Presumably, these systems subserve such functions as spatial orientation, estimation of depth and distance, stereoscopic vision, and hue perception. Similarly, the unimodal auditory cortex is closely connected with a series of auditory association areas in the superior temporal convolution, and the latter are connected with prefrontal and temporoparietal heteromodal areas and the limbic areas (see Mesulam, 1998). Most of these auditory connections have been worked out in the macaque but the limited number of well-studied lesions in patients suggests that they are also involved in complex verbal and nonverbal auditory discriminations in humans.
The most important functions of the hippocampus and other structures of the hippocampal formation (dentate gyrus, subiculum, entorhinal cortex, and parahippocampal gyrus) are learning and memory, already discussed in Chap. 20. There is an abundance of connections between the medial temporal lobe and the entire limbic system. For this reason, MacLean referred to these parts as the “visceral brain,” and Williams, as the “emotional brain.” Also included in this anatomic concept are the hippocampus, the amygdaloid nuclei, the fornices and limbic portions of the inferior and medial frontal regions, the cingulate cortices, and the septal and associated subcortical nuclei referred to as the limbic system (see Chap. 24).
Most of the temporal lobe cortex, including Heschl gyri, has nearly equally developed pyramidal and granular layers. In this respect, it resembles more the granular cortex of the frontal and prefrontal regions and inferior parts of the parietal lobes. Unlike the six-layered neocortex, the hippocampus and dentate gyrus are typical of the phylogenetically older three-layered allocortex.
A massive fiber system projects from the striate and parastriate zones of the occipital lobes to the inferior and medial parts of the temporal lobes. The temporal lobes are connected to one another through the anterior commissure and middle part of the corpus callosum; the inferior or uncinate fasciculus connects the anterior temporal and orbital frontal regions. The arcuate fasciculus connects the posterosuperior temporal lobe to the motor cortex and Broca area.