The limbic system includes structures from widely separated parts of the brain. Some of these structures are the amygdala, the cingulate gyrus, the dentate gyrus, the hippocampus, the hypothalamus and the anterior thalamic nuclei. These structures are able to function as a system because they are connected by fiber tracts such as the fornix and the mammilothalamic tract. This system is better thought of as a functional system that serves the role of an emotional or affective brain--as contrasted with the brain cerebrum , the thinking brain. The functional importance of the limbic system is that it is responsible for emotional responses and memory formation.
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The limbic system comprises a group of widely scattered structures in the cerebral hemispheres and the brain stem. The most well-known of these are the amygdala, the cingulate gyrus, the septal nuclei, the hippocampus, the dentate gyrus, the parahippocampal gyrus, the hypothalamus, and the anterior thalamic nuclei. These structures are connected by fiber tracts such as the fornix, the stria terminalis, the mammilothalamic tract, and the median forebrain bundles. Specific limbic structures have well-known roles. For example, the amygdala mediates the flight or fight response to threats. Also, the cingulate gyrus is concerned with the expression of grief and the resolution of mental perplexity. The limbic system is important in helping us remember whether a certain behavior was rewarded or punished. If that lesson is learned and remembered, the motivation will develop to order future behavior to avoid punishment or to receive rewards. The connections between the cerebral cortex and other parts of the limbic system allow emotions to influence logical thinking and permit reason to control the expressions of emotion. Finally, through the hypothalamus, the limbic system can affect autonomic visceral functions. These are some of the so-called psychosomatic responses in which emotional stress causes increases in blood pressure, heart rate, and/or respiratory rate.