The Limbic System
The limbic system is a series of forebrain structures that control somatic and visceral behavior associated with strong emotions, such as rage and fear. Anatomically, the limbic system has a complex organization and is composed of the limbic cortex and many subcortical nuclei.
The cortical part of the limbic system forms a ring at the medial surface of the cerebral hemisphere, including, among other structures, the cingulate and supracallosal gyri, the piriform lobe, and the hippocampus. The subcortical part is composed of the hypothalamus, septal area, amygdala, habenular nuclei, and dorsal part of the mesencephalic tegmentum. There are numerous associations between these structures and other regions of the brain. The limbic system is often considered to be primarily a "visceral brain" because many of its major functions are expressed through visceral motor activity. The types of behaviors most influenced by the limbic system are those essential for the preservation of the individual or the species.Olfactory inputs that relay through the piriform lobes may influence many structures of the system. Of all the sensory inputs, olfaction exhibits the most profound effects on visceral motor activities that are associated with emotional behavior such as eating, rage, sexual activity, fear, and drinking. The limbic system also receives optic, auditory, exteroceptive, and enteroceptive stimuli.
The efferent pathways from the cortical limbic regions involve nearly all the subcortical nuclei of the system. A major portion of the influences of the limbic cortex is mediated through the efferent systems of the amygdaloid nuclei. Electrical stimulation of the amygdala produces a wide variety of visceral and somatic reactions and many behavioral reactions, such as aggression and anxiety.
The hippocampus is concerned with memory functions, such as the processing of recently acquired memory and its more permanent consolidation. The hypothalamus also plays an essential part in the limbic system's control of emotional expression and behavior through its integration of autonomic, endocrine, and somatic functions.