The Limbic System

Dr. Kenira J. Thompson

Ponce School of Medicine

Dept. of Physiology

840-2575 Ext. 2166

Email: kthompson@psm.edu

Lecture Goals• Review functional anatomy of the limbic system• Describe behavior and cognitive disturbances associated

with limbic system pathology.

“Is emotion a magic product, or is it a physiological process which depends on an anatomic process?”

(Papez, 1937).

Broca’s Limbic Lobe, 1878(“Le Grand Lobe Limbique”)

C’est magnifique!

Limbic Functions (HOME)

• Homeostatic functions (autonomic and endocrine control)

• Olfaction• Memory• Emotions and Drives

What is the limbic system?

• Set of interconnected cortical and subcortical structures that form a border (or limbus) around the brain stem.

Limbicsystem

Sensory-motorsystems

Hypothal

Main Components• Limbic cortex

– Parahippocampal gyrus, cingulate gyrus, Medial Orbitofrontal cortex• Hippocampal formation

– Dentate gyrus, hippocampus, subiculum• Amygdala• Olfactory cortex• Diencephalon

– Hypothalamus, thalamus (anterior nucleus, mediodorsal nucleus)• Basal Ganglia

– Ventral striatum (Nucleus Accumbens, Caudate, Putamen)• Basal forebrain• Septal nuclei• Brainstem• Also includes the tracts that link these structures: fornix, mammillothalamic,

stria terminalis, etc.

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limbic structures occupy a medial position in the brainset of medial tructures that separate the hypothalamus from sensory-motor cortices. main vessels that serve the limbic system are theanterior and posterior cerebral arteries,the anteiror choroidal artery, and the circle of willis.

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cortical structures of the limbic lobe from a ventral view.

Papez Circuit

• James Papez (1937)– Was the first to identify that emotion is not a function of any

specific brain center but a circuit involving 4 basic structures.

Revised Papez Circuit

• Paul McLean (1970)-– Revised Papez’s theory and called the circuit the limbic system.– Added more structures to the system:

• Prefrontal cortex• Parahippocampal gyrus• Important subcortical structures (amygdala, thalamic nuclei, septal

area, etc.).

Cingulate cortex

Neocortex

HippocampusAnterior nuclei of Thalamus

Hypothalamus

Emotional experience

fornix

Emotional expression

Three limbic circuits

• Amygdala-Hippocampus– Affects behaviors related to self-preservation

• Cingulate gyrus- septum– Relates to pleasure, especially sexual enjoyment (stimulation of

this region in rats results in penile erection, self-grooming)

• Hypothalamus-anterior thalamus– Important for cooperative social behavior

Cingulate Gyrus

CC

1

CAUDATE

CINGULATE

Anterior nucleus thalamus

Mamillary bodies

T

Parahippocampal gyrus

Fornix

Cingulate Gyrus and Depression

Depressed Patient After Fluoxetine

Hypothalamus

Damage to hypothalamicnuclei results in:Abnormalities in motivatedbehaviors such as feeding, drinking, sexual behavior,fighting, temp. regulation.

Also regulates secretion of hormones via the pituitary gland (secretions control other endocrine organs, such as the thyroid, adrenal glands, ovaries, testes).

Brain transections and sham rage

Rage reaction in cats with hypothalamic stimulation

Korsakoff’s Syndrome

• Severe anterograde amnesia• Results from thyamine deficiency (Vit. B1)• Usually caused by alcoholism• Severe degeneration of mammillary bodies.• Patients tend to confabulate to cover up memory deficit

Amygdala• Buried within the anterior-inferiortemporal lobe.

• Essential in the control of:love, friendliness, affection,fear, rage, aggression.

3

Amygdala

P

H

TemporalLobe

Fx

TEMPORALLOBE

STRIA TERMINALIS

Amygdala Nuclei

Amygdala Projections

Amygdala Lesions

• Result in:– Reduced ability to identify motivational and emotional

significance of events– Electrical stimulation of amygdala can lead to emotional attacks

(rage)– Rabies virus (especially attacks the temporal lobe) leads to violent

behavior

Kluver-Bucy Syndrome• Results from bilateral removal of the amygdala and

inferior temporal cortex. Includes:– Tameness, loss of fear– Indiscriminate dietary behavior– Greatly increased autoerotic sexual activity– Tendency to attend to every visual stimulus– Tendency to examine all objects by mouth– Visual agnosia (cannot recognize objects visually)– Inability to recognize facial expression

Human brain activity in response to emotional stimuli

Amygdala activity associated with enhanced emotional memory

Neural circuit for learned fear

Tone Auditory cortex

BLA

Central nucleus

Hypothalamus

PAG

Cerebral cortex

(Autonomic Response)

(BehavioralReaction)

(Emotional Experience)

A neural circuit for aggression

Emotion and Memory

Hippocampal formation…why is it important?

• Making new memories• Involved in severe mental illness

– Reduced volume in schizophrenia, PTSD, depression

• Directly affected by estrogen (Wooley, NWU)

• Neurogenesis

Hippocampus

Mamm

A

TemporalLobe

4

PHG

Mammilothalamic tract

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comprised of subiculum, hippocampus, and dentate gyrus.subiculum-continuous to the cortex of the parahippo gyrus.transition area from the 3 layered hippocampus (archicortex) to the 5 layer entorhinal ctx.

Hippocampus (cortical connections)

Neurogenesis

Hippocampus and Alzheimer’s Disease

Ischemia

Hippocampus and Depression

Hippocampus and Estrogen

Reward System Projections

This will makeme famous!

DOPAMINE

Self-stimulationReward pathways

Nucleus Accumbens

CP

2

Dopamine receptors (D3) in Nuc. Accumbens

Cocaine Addict