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.
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