Limbic System

•A functional anatomic system of interconnectedcortical and subcortical structures•Area of intimate processing between the hypothalamus and cortical information processing•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 behaviour. •The limbic system is also involved in feelings of pleasure that are related to our survival, such as those experienced from eating and sex.

• The limbic system is also involved in feelings of pleasure that are related to our survival, such as those experienced from eating and sex.

• Named by Paul Broca: limbic means border and it names structures forming a border between hypothalamus and cerebral cortex

• Olfactory and limbic system are called the rhinocephalon (smell brain)

• 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.

Thalamus• The thalamus is part of the limbic system so it is

located in the internal portion of the brain or the center of the brain.

• The thalamus controls your sensory integration and motor integration.

• The thalamus recieves sensory information and relays it to the cerebral cortex.

• The cerebral cortex also sends information to the thalamus which then transmits this information to other parts of the brain and the brain stem

• Functions:• The thalamus has multiple functions• Many different functions are linked to various

regions of the thalamus. This is the case for many of the sensory systems (except for the olfactory system), such as the auditory, somatic, visceral, gustatory and visual systems where localized lesions provoke specific sensory deficits. A major role of the thalamus is devoted to "motor" systems

•For the visual system, for example, inputs from the retina are sent to the lateral geniculate nucleus of the thalamus, which in turn projects to the primary visual cortex (area V1) in the occipital lobe.

•Similarly the medial geniculate nucleus acts as a key auditory relay between the inferior colliculus of the midbrain and the primary auditory cortex, and the ventral posterior nucleus is a key somatosensory relay, which sends touch and proprioceptive information to the primary somatosensory cortex

•The thalamus also plays an important role in regulating states of sleep and wakefulness. Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming thalamo-cortico-thalamic circuits that are believed to be involved with consciousness.

• The thalamus plays a major role in regulating arousal, the level of awareness, and activity. Damage to the thalamus can lead to permanent coma.

Hypothalamus

• Location:• Directionally, the hypothalamus is inferior to the

thalamus. It is posterior to the optic chiasm and bordered on the sides by the temporal lobes and optic tracts.

• The hypothalamus is composed of several different areas and is located at the base of the brain. It is only the size of a pea (about 1/300 of the total brain weight), but is responsible for some very important behaviors.

• hypothalamus Is part of the limbic system• Function:• The hypothalamus is involved in several

functions of the body including: • Autonomic Function Control• Endocrine Function Control• Homeostasis• Motor Function Control• Food and Water Intake Regulation• Sleep-Wake Cycle Regulation

Hippocampus • The hippocampus consists of two “horns” that

curve back from the amygdala.  It appears to be very important in converting things that are “in your mind” at the moment (in short-term memory) into things that you will remember for the long run (long-term memory). 

• If the hippocampus is damaged, a person cannot build new memories, and lives instead in a strange world where everything they experience just fades away, even while older memories from the time before the damage are untouched! 

Amygdala • The amygdalas are two almond-shaped masses of

neurons on either side of the thalamus at the lower end of the hippocampus. 

• When it is stimulated electrically, animals respond with aggression.  And if the amygdala is removed, animals get very tame and no longer respond to things that would have caused rage before.  But there is more to it than just anger: 

• When removed, animals also become indifferent to stimuli that would have otherwise have caused fear and even sexual responses.

Related areas • Besides the hypothalamus, hippocampus, and amygdala,

there are other areas in the structures near to the limbic system that are intimately connected to it:

• The cingulate gyrus is the part of the cerebrum that lies closest to the limbic system, just above the corpus callosum.  It provides a pathway from the thalamus to the hippocampus, seems to be responsible for focusing attention on emotionally significant events, and for associating memories to smells and to pain.

• The ventral tegmental area of the brain stem (just below the thalamus) consists of dopamine pathways that seem to be responsible for pleasure.  People with damage here tend to have difficulty getting pleasure in life, and often turn to alcohol, drugs, sweets, and gambling.

• The basal ganglia (including the caudate nucleus, the putamen(round structure located at da base of forebrain), the globus pallidus, and the substantia nigra) lie over and to the sides of the limbic system, and are tightly connected with the cortex above them.  They are responsible for repetitive behaviors, reward experiences, and focusing attention.  If you are interested in learning more about the basal ganglia.

• The prefrontal cortex, which is the part of the frontal lobe which lies in front of the motor area, is also closely linked to the limbic system.  Besides apparently being involved in thinking about the future, making plans, and taking action, it also appears to be involved in the same dopamine pathways as the ventral tegmental area, and plays a part in pleasure and addiction.