amygdala (from Latin ''amygdale,'' almond or tonsil) A

complex of nuclei embedded (like the meat of an almond) in the anteromedial temporal lobe.

cingulate gyrus (from Latin ''cingulum or cingo,'' girdle, to surround) A long curved gyrus that surrounds the corpus callosum on the medial side of the cerebral hemisphere.

hippocampus (from Greek''hippocampos,''seahorse) Avery specialized region of the cerebral cortex, which is deeply folded into the lateral ventricle. In marsupials and rodents the hippocampus is largely situated in the dorsomedial cortex, dorsal to the thalamus, but in humans and other primates it has shifted into the medial temporal lobe.

limbic system (from Latin, ''limbus,'' edge, border, or fringe) A system of interconnected brain structures situated around the medial edge of the cerebral hemisphere.

nucleus accumbens septi (from Latin ''accumbens,'' leaning) The rostral, ventromedial portion of the corpus striatum, comparable to the caudate nucleus and putamen, that is immediately lateral to the septum and appears to "lean" against it.

nucleus basalis of Meynert Prominent nuclei of large cells in the basal forebrain, most of which use either acetylcholine or GABA as neurotransmitter.

orbital cortex (from Latin ''orbita or orbis,'' wheel-track, circle) The cortex situated dorsal to the bony "orbit" that encases the eye.

prefrontal cortex Traditionally, the cortex in front of the "excitable" frontal cortex (i.e., the motor cortex, which was found in the 19th century to evoke body movements when excited with electrical stimulation).

The internal state of the body is largely controlled by the autonomic nuclei in the spinal cord and brain stem, which provide for reflex control of visceral functions, and by the hypothalamus, which provides for higher level coordination of autonomic and endocrine functions. As anyone who has checked his or her heart rate during an exciting action movie knows, however, visceral function is also modulated in relation to forebrain analysis of visual, olfactory, and other sensory stimuli. Furthermore, such visceral reactions are also modified in relation to previous experience, as you can tell if you watch the same action movie so many times that the surprises become expected. The modulations related to present and past sensory experience are both dependent on several forebrain structures that are linked together as the ''limbic system.'' On the one hand, these structures have substantial connections to the hypothalamus and brain stem and provide an interface between forebrain sensory systems and visceral control areas. On the other hand, the limbic structures interact with the cerebral cortex, thalamus, and basal ganglia to relate visceral function to the ongoing sensory environment and to cognitive functions. In particular, these provide for the modulation of visceral and other functions across time, such that responses are altered in relation to previous experience. In humans and other primates, at least, this process is directly involved in conscious emotion and memory.

As defined by Broca (1878) and later by Papez (1937), the limbic system generally consists of a group of structures around the medial edge of the cerebral hemisphere. ("Limbus" means border or edge; e.g., to be "in limbo'' is to be suspended between two states.) These structures include the amygdala, the hippocampus, the parahippocampal gyrus, and related structures, such as the orbital/medial prefrontal cortex, cingulate cortex, anterior and mediodorsal thalamic nuclei, the ventromedial corpus striatum (i.e., the accumbens nucleus and medial caudate nucleus), and the nucleus basalis of Meynert.

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