Anatomy of the medial temporal lobe

The medial temporal lobe concept is an example of neurojargon rich in clinical and behavioral meaning, but sparse in neuroanatomical meaning except for topography. Like the concept of anterior speech area, many know roughly where it is located and what its functional correlates are, but not a lot else. At least three anatomical entities qualify as components of the medial temporal lobe. These include the amygdaloid body, the hippocampal formation, and the parahippocampal cortices that cover them superficially and are visible on the external surface of the hemisphere. For the greater part of this century, topographical observations, dissection, and descriptive data from passive staining methods have formed the principal source of information about the anatomy of the medial temporal lobe. However, in the past two decades much new information has emerged from experimental neuroanatomical studies in nonhuman primates and from neuropathological studies in humans. With magnetic resonance imaging (MRI), previous neuroanatomical detail, which earlier may have seemed like descriptive minutia, has now come alive and assumed substantial relevance in neurological and psychiatric diagnosis. Some of the emerging concepts as they relate to the neuroanatomy of the primate brain are highlighted and summarized here.