Limbic System, the Temporal Lobe, and Prefrontal Cortex

The neurologist Paul Broca in the later half of the 19th century initially designated all of the structures on the medial surface of the cerebral hemisphere “the great limbic lobe.” This region, due to its strong olfactory input, was also designated the rhinencephalon. The olfactory portion of the brain (rhinencephalon, or archipallium) comprises much of the telencephalon in fish, amphibians, and most mammals. In mammals the presence of a large olfactory lobe adjacent to the hippocampus was once considered to be evidence of the important olfactory functions of these regions. However, when comparative anatomists examined the brains of sea mammals that had rudimentary olfactory apparatus (e.g., dolphins and whales), the presence of a large hippocampus suggested other than olfactory functions for this region.