The limbic system is a set of evolutionarily primitive brain structures located on top of the brainstem and buried under the cortex. Limbic system structures are involved in many of our emotions and motivations, particularly those that are related to survival. Such emotions include fear, anger, and emotions related to sexual behavior. The limbic system is also involved in feelings of pleasure that are related to our survival, such as those experienced from eating and sex.
Certain structures of the limbic system are involved in memory as well. Two large limbic system structures, the amygdala and hippocampus play important roles in memory. The amygdala is responsible for determining what memories are stored and where the memories are stored in the brain. It is thought that this determination is based on how huge an emotional response an event invokes. The hippocampus sends memories out to the appropriate part of the cerebral hemisphere for long-term storage and retrieves them when necessary. Damage to this area of the brain may result in an inability to form new memories.
Part of the forebrain known as the diencephalon is also included in the limbic system. The diencephalon is located beneath the cerebral hemispheres and contains the thalamus and hypothalamus. The thalamus is involved in sensory perception and regulation of motor functions (i.e., movement). It connects areas of the cerebral cortex that are involved in sensory perception and movement with other parts of the brain and spinal cord that also have a role in sensation and movement. The hypothalamus is a very small but important component of the diencephalon. It plays a major role in regulating hormones, the pituitary gland, body temperature, the adrenal glands, and many other vital activities.
Limbic System Structures
Amygdala – almond shaped mass of nuclei involved in emotional responses, hormonal secretions, and memory.
Cingulate Gyrus – a fold in the brain involved with sensory input concerning emotions and the regulation of aggressive behavior.
Fornix – an arching, fibrous band of nerve fibers that connect the hippocampus to the hypothalamus.
Hippocampus – a tiny nub that acts as a memory indexer — sending memories out to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary.
Hypothalamus – about the size of a pearl, this structure directs a multitude of important functions. It wakes you up in the morning, and gets the adrenaline flowing. The hypothalamus is also an important emotional center, controlling the molecules that make you feel exhilarated, angry, or unhappy.
Olfactory Cortex – receives sensory information from the olfactory bulb and is involved in the identification of odors.
Thalamus – a large, dual lobed mass of grey matter cells that relay sensory signals to and from the spinal cord and the cerebrum.
In summary, the limbic system is responsible for controlling various functions in the body. Some of these functions include interpreting emotional responses, storing memories, and regulating hormones. The limbic system is also involved with sensory perception, motor function, and olfaction.
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