The Limbic System

A/Prof. Pascal CARRIVE SOMS UNSW Australia

•  Broca’s Limbic Lobe •  MacLean’s Limbic System •  Papez circuit •  Today’s Limbic System •  Today’s Emotional Brain •  Amygdala.

•  Today the word “limbic” is associated with emotion processing, eg, “limbic system” refers to the brain emotional system.

•  The concept of limbic system as an emotional system is the legacy of McLean (1950’s) who refined the circuit for emotion proposed by Papez (1930’s) and used the anatomical name “limbic” introduced by Broca (1870’s).

•  The limbic system has evolved to the point that it is not longer anatomically correct or relevant. It should be abandoned and replaced by “brain emotional system” or “emotional brain”.

1870’s. Paul Broca

•  describes a “limbic” lobe •  (limbic = border)

•  Cingulate gyrus •  hippocampus

1. Broca’s Limbic Lobe

Hippocampus

Cingulate gyrus

Olfactory bulb

•  Broca thought that the

limbic lobe was involved in the processing of olfaction

f

Parahippocampal g

amygdala

Septal area

2. MacLean’s Limbic System

1950’s. Paul MacLean

MacLean limbic system is Broca’s limbic lobe plus: •  fornix •  hypothalamus •  anterior nucleus of the

thalamus •  septal area •  parahippocampal g. •  amygdala

The core of the system is the circuit of Papez for the processing of emotion

Cingulate g

Hyp

Ant

Hippocampus

•  he adds: •  parahipocampal g. •  amygdala •  septal area

Sensory experience

3. Papez circuit

Hippocampus Hypothalamus

Thalamus (anterior n.)

Neocortex

1930s. James Papez

•  Papez circuit was based on neurological, histopatho-logical and neuroanatomical observations

•  Papez proposed a circuit that transforms a sensory experience into an emotional response made of an:

•  emotional expression (behavioral, autonomic)

•  emotional experience (affect)

Emotional expression Sensory stimulus

fornix

Emotional experience

(affect)

Thalamus

Cingulate gyrus

f

Parahippocampal g

amygdala

Septal area

Orbito- frontal Cortex

Accumbens n

Dorsomedial n. of thalamus

4. Today’s Limbic System

Further additions to MacLean’s limbic system in the last 60 years : •  orbitofrontal cortex •  dorsomedial nucleus

of the thalamus •  accumbens nucleus

Cingulate g

Hyp

Ant

Hippocampus

DM

However, Papez circuit has not been confirmed experimentally and MacLean’s concept of limbic system has gradually been abandoned The term limbic remains to refer to emotional function in a loose sense, but it is a source of confusion.

amygdala

Septal area

Orbito- frontal Cortex

Accumbens n

Dorsomedial n. of thalamus

5. Today’s Emotional Brain

•  Papez circuit has not been confirmed

•  Hippocampus involved in declarative memory, not directly in emotion processing

•  Only the anterior part of the cingulate gyrus is involved in emotion

•  Amygdala is the master controller of the emotion system

Cingulate g

Hyp

DM

Cen t ra l nucleus

Basolateral nuclei

Corticomedial nuclei

amygdala

6. Amygdala. location

Cen t ra l nucleus

Basolateral nuclei

Corticomedial nuclei

6. Amygdala. Internal organization

Corticomedial nuclei • receive olfactory input

Basolateral nuclei 1.  receive all other inputs 2.  process the information 3.  sends processed information to central nucleus or back to cortex

Central nucleus • Is the main output nucleus to hypothalamus and brainstem

olfactory input

All other inputs

All other outputs

Outputs to hypothalamus,

brainstem

Nearly 27 subnuclei!

amygdala

Orbito- frontal Cortex

6. Amygdala. Inputs

Somatosensory and visceral sensory input

Raw and processed sensory information reaches the amygdala from: •  Thalamus •  Primary

somatosensory cortex

•  Insula •  Anterior Cingulate g •  Orbitofrontal cortex

•  Hypothalamus

Ant cingulate g

Hyp

DM

Insular cortex

Sensory experience

Somatosensory Visceral sensory

Thalamus

S1,2

amygdala

Orbito- frontal Cortex

6. Amygdala. Inputs

Visual and auditory

Raw and processed visual information reaches the amygdala from: •  Thalamus •  visual cortex •  Ant Cingulate •  Orbitofrontal cortex

•  Same for auditory information (temporal lobe instead of occipital)

Ant cingulate g

Hyp

DM

Insular cortex

Sensory experience

Visual stimulus

Thalamus V1

V2,3

amygdala

Orbito- frontal Cortex

6. Amygdala. Inputs

Olfactory stimulus

Raw and processed visual information reaches the amygdala from: •  Olfactory bulb •  Primary olfactory

cortex •  Orbitofrontal cortex

Others •  Hippocampus and

parahippocampal g.

Ant cingulate g

Hyp

DM

Insular cortex

Sensory experience

Olfactory stimulus

Thalamus

Primary olfactory

cortex

Hippocampus

amygdala

Orbito- frontal Cortex

6. Amygdala. Outputs Descending output to: •  Hypothalamus •  Brainstem responsible for: Emotional expression

Feedback output to: •  Orbitofrontal cortex •  Ant Cingulate cortex •  Insular cortex •  Visual cortex •  Auditory cortex •  Primary olfactory cortex •  Thalamus feedback with affective valence for: Emotional experience?

•  Hippocampus

Ant cingulate g

Hyp

DM

Insular cortex

Emotional expression

V2,3

Thalamus

Emotional experience?

Hippocampus

amygdala

Orbito- frontal Cortex

Accumbens n

6. Amygdala. Outputs

Basal ganglia loop

•  With accumbens nucleus, dorsomedial thalamus and orbitofrontal cortex.

•  Accumbens nucleus receives dopamine input from VTA. Codes for rewards and contributes to affective dimension of emotions

DM

Ventral Tegmental area (dopamine)

ventral pallidum

amygdala

Orbito- frontal Cortex

6. Amygdala. Place in the emotional brain

The amygdala: •  drives the expression of

emotions via descending projections

•  contributes to the emotional experience via reciprocal connections with multimodal association areas and ventral striatum/pallidum loop

•  It is also responsible for emotional learning (association between salient stimuli and aversive /appetitive stimuli)

Ant cingulate g

Hyp

DM

Insular cortex

Emotional expression

V2,3

Thalamus

Emotional experience?

Hippocampus

DM

Emotional Learning

Suggested readings

Goossens, L., Sunaert, S., Peeters, R., Griez, E. J. L., & Schruers, K. R. J. (2007). Amygdala hyperfunction in phobic fear normalizes after exposure. Biological Psychiatry, 62(10), 1119–1125. doi:10.1016/j.biopsych.2007.04.024 Ressler, K. J., & Mayberg, H. S. (2007). Targeting abnormal neural circuits in mood and anxiety disorders: from the laboratory to the clinic. Nature Neuroscience, 10(9), 1116–1124. doi:10.1038/nn1944 Blond, B. N., Fredericks, C. A., & Blumberg, H. P. (2012). Functional neuroanatomy of bipolar disorder: structure, function, and connectivity in an amygdala-anterior paralimbic neural system. Bipolar Disorders, 14(4), 340–355. doi:10.1111/j.1399-5618.2012.01015. Roxo, M. R., Franceschini, P. R., Zubaran, C., Kleber, F. D., & Sander, J. W. (2011). The limbic system conception and its historical evolution. TheScientificWorldJournal, 11, 2428–2441. doi:10.1100/2011/157150