Limbic System: a group of connected structures. (Chudler, 87) Most lie hidden within the “medial” and “ventral” regions of the “cerebral hemispheres.” Extends from the “forebrain” to the “brainstem.” (Blumenfeld, 821) A cortical perimeter around the “corpus callosum.” (Patestas, 345) A ‘C-shape’ delineated by the "cingulate sulcus" and the "collateral sulcus." (Fisch, 280) Located deep inside the brain. (Bainbridge, 277)
The brain’s emotional center. (Ramachandran, 13) Involved in “memory” and “emotions.” (NCIt) It is implicated in the higher integration of “visceral,” “olfactory,” and “somatic” information. (MeSH) Electrical activity between the “temporal lobe” and the limbic system may spark religious feelings. (SAM, Oct/Nov 2007, 40) The "hippocampus" and the "amygdala" were the two key parts of the primate “nose brain” that, in evolution, gave rise to the cortex. To this day these limbic structures do much or most of the brain’s learning and remembering (and) the amygdala is the specialist for emotional matters. (Goleman2, 15) Also referred to as the ‘reptilian brain,’ ‘mammalian brain,’ ‘visceral brain,’ and 'limbic lobe structures.'
Limbic Functions: can be divided into four basic operations (“attention,” emotion, memory, “olfaction”). One limbic structure can be thought of as central to each of these four functions. (Blumenfeld, 820) (Important for controlling the emotional response to a given situation and also for memory. (Chudler, 87) Serve to balance emotional and cognitive mechanisms. Processes information about a certain situation and then, produces “visceral” responses. (Patestas, 345) The functions of the limbic system are ancient, and they play an important role for survival in the animal kingdom. (Blumenfeld, 820) The limbic system is unique to “mammals.” Functions in ‘species preservation,’ (which includes reproduction and associated instinctive behavior), ‘self-preservation’ (which includes feeding behavior and aggression), expression of emotion, (which include fear and motivation), memory and learning. (Patestas, 345)
Intracranial Self-Stimulation: administering a brief burst of electrical stimulation to specific sites in (an animal's) brain. Rats will press a lever hundreds or even thousands of times per hour to obtain this brain stimulation. (Kolb, 433) Also referred to as 'self-stimulation' and 'brain-stimulation reward.’
Limbic Nuclei: includes the “septal nuclei” and some “thalamic” and “hypothalamic” nuclei. (Patestas, 345)
Septal Nuclei: located in close proximity to the “corpus callosum.” Connected with the “hippocampal formation” via the “fornix,” and the hypothalamus via the medial ‘forebrain bundle.’ Continues as the "cingulate gyrus" which then continues as the "parahippocampal gyrus." (Patestas, 350) They have “afferent” and “efferent” connections with a variety of forebrain and "brain stem" areas including the “hippocampus,” the “lateral” “hypothalamus,” the “tegmentum,” and the amygdala. Included are the “dorsal,” “lateral,” “medial,” and triangular septal nuclei, (and others not defined here including the) ‘septofimbrial nucleus,’ ‘nucleus of diagonal band,’ ‘nucleus of anterior commissure,’ and the ‘nucleus of stria terminalis.’ (MeSH) Also referred to as "septal area” and “septal region."
Limbic Pathways: a number of pathways connect the various components of, and areas associated with, the limbic system. (Patestas, 356)
Papez Circuit: involves many different areas of the central nervous system. Involves the hippocampus, cingulate (cortex), (nuclei in the diencephalon), and anterior nucleus of the “thalamus.” Originates in the hippocampus. (Fisch, 378) Proposed by James Papez in the 1930’s. Although it is known today that the connections of the limbic system are much more complex, this circuit served as a basis for more modern research. (Patestas, 353)
Reward System: areas of the brain in or near the hypothalamus which, when stimulated, produce sensations of pleasure. (Oxford) Originates in the upper brainstem and connects to parts of the brain that are involved in emotion and cognition, including parts of the “frontal lobes” and the “nucleus accumbens.” (CampbellVA, 225) Mediates "addictive" behaviors. Drugs commandeer this circuit stimulating its activity. (Nestler, 145) The reason these sites (are) effective (in producing pleasure) is because “axons” emanating from the "tegmentum" project diffusely through the brain. (Kolb, 433) Registers rewarding events. By tying positive outcomes to the behaviors that led to them, this widespread neural circuit learns how to optimize behavior in the world. It aids us in getting food, drink, and mates and helps navigate life’s daily decisions. (Eagleman, 203) Also referred to as 'reward circuits.'
Mesolimbic Dopamine System: a set of nerve cells that originate in the "ventral tegmental area" and send (signals) to the front of the brain - most notably to the "nucleus accumbens." (Nestler, 145) Dopamine release in the mesolimbic pathways has a role in feelings of reward and pleasure. (Kolb, 433) Dopamine has long been believed to be a critical factor in reward processes. Although there are rewarding conditions that do not depend on domain, much of what we know about rewards centers around the role of dopamine. (LeDoux, 245) Dopamine release shows a marked increase when animals engage in intracranial self-stimulation. Drugs that enhance dopamine release (also) increase (intracranial) self-stimulation. It seems that the amount of dopamine released somehow determines how rewarding an event is. (Kolb, 433) Also referred to as 'dopamine reward system.'
Medial Forebrain Bundle: a major nerve pathway that passes through the hypothalamus. When dopamine cells are activated by inputs from the medial forebrain bundle, they release dopamine widely in the forebrain. (LeDoux, 244-245)
Nucleus Accumbens: the hub of the reward circuits. (Lambert, 40) When animals engage in behaviors such as feeding or sexual activity, the release of dopamine rapidly increases in the nucleus accumbens. Highly addictive drugs such as "nicotine" and "cocaine" increase the level of dopamine in the nucleus accumbens. (Kolb, 433) Connected to the “caudate nucleus” and the “putamen.” Receives input, and processes the emotional aspects of movement. (Patestas, 195)
Ventral Tegmental Area: VTA neurons communicate by dispatching dopamine to “receptors” on nucleus accumbens neurons. (Nestler, 145)
Limbic Structures: Older parts of the brain, including the cingulate gyrus, amygdala, hippocampus, hypothalamus, and “basal forebrain” structures. (CampbellVA, 101) Limbic structures have evolved, from a system devoted mainly to olfaction in simpler animals, to perform diverse functions, including the regulation of emotions, memory, and “autonomic” and ‘neuroendocrine’ control. (Blumenfeld, 41) Editor’s note - includes the hippocampal formation.
Cingulate Cortex: surrounds the corpus callosum. (Blumenfeld, 25) At its posterior (end) continues as the parahippocampal gyrus. (Patestas, 346) Consists of “mesocortex.” (Patestas, 346) An important part of the limbic system. Helps regulate emotions and “pain.” Thought to directly drive the body’s conscious response to unpleasant experiences. Involved in "fear," and "prediction" and avoidance of negative consequences. Can help orient the body away from negative stimuli. (3D Brain) Also referred to as ‘cingulate,’ and ‘cingulate gyrus.’
Subcallosal Gyrus: consists of gray matter, which underlies the surface of the "rostral" extent of the corpus callosum. Extends (to the “posterior”) as the cingulate gyrus. (Patestas, 346)