Which of the following is NOT listed as part of the limbic circuit described (amygdala, hippocampus, fornix, cingulate cortex, septum, olfactory bulb, mammillary bodies)?

• A. Corpus callosum
• B. Amygdala
• C. Hippocampus
• D. Fornix

Answer: (A)

The limbic circuit is a network of structures that underpin emotion, memory, and motivation. In the described list, the amygdala handles emotion processing, the hippocampus is central to forming and retrieving memories, the fornix carries signals from the hippocampus to the mammillary bodies, the cingulate cortex participates in emotional regulation and autonomic control, the septum is involved in reward and reinforcement, the olfactory bulb links smells to emotional memory, and the mammillary bodies act as a relay within the limbic loop (as in the classic Papez circuit). The corpus callosum, by contrast, is the major white matter tract that connects the two cerebral hemispheres to enable interhemispheric communication. It is not a limbic nucleus or a relay within the limbic circuit, so it isn’t listed as part of the limbic system in this context.