The Limbic System Broca s Limbic Lobe MacLean s Limbic System Papez circuit Today s Limbic System Today s Emotional Brain Amygdala. A/Prof. Pascal CARRIVE SOMS UNSW Australia
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.
1. Broca s Limbic Lobe Cingulate gyrus 1870 s. Paul Broca describes a limbic lobe (limbic = border) Cingulate gyrus hippocampus Olfactory bulb Broca thought that the limbic lobe was involved in the processing of olfaction Hippocampus
2. MacLean s Limbic System 1950 s. Paul MacLean Cingulate g f Ant Hyp Hippocampus MacLean limbic system is Broca s limbic lobe plus: fornix hypothalamus anterior nucleus of the thalamus septal area parahippocampal g. Septal area Parahippocampal g The core of the system is the circuit of Papez for the processing of emotion
3. Papez circuit Sensory experience Emotional experience (affect) Neocortex 1930s. James Papez Thalamus (anterior n.) Hypothalamus Cingulate gyrus Emotional expression fornix Thalamus Hippocampus Sensory stimulus Papez circuit was based on neurological, histopathological 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)
4. Today s Limbic System Further additions to MacLean s limbic system in the last 60 years : orbitofrontal cortex Accumbens n Dorsomedial n. of thalamus dorsomedial nucleus of the thalamus accumbens nucleus Orbitofrontal Cortex Cingulate g f DM Ant Hyp Hippocampus However, Papez circuit has not been confirmed experimentally and MacLean s concept of limbic system has gradually been abandoned Septal area Parahippocampal g The term limbic remains to refer to emotional function in a loose sense, but it is a source of confusion.
5. Today s Emotional Brain Accumbens n Dorsomedial n. of thalamus Cingulate g Papez circuit has not been confirmed Hippocampus involved in declarative memory, not directly in emotion processing Orbitofrontal Cortex DM Hyp Only the anterior part of the cingulate gyrus is involved in emotion Amygdala is the master controller of the emotion system Septal area
6. Amygdala. location
6. Amygdala. Internal organization Corticomedial nuclei olfactory input Central nucleus Basolateral nuclei Nearly 27 subnuclei! 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 Outputs to hypothalamus, brainstem All other inputs All other outputs
6. Amygdala. Inputs Ant cingulate g Insular cortex Sensory experience Somatosensory and visceral sensory input Orbitofrontal Cortex DM Hyp Thalamus S1,2 Raw and processed sensory information reaches the from: Thalamus Primary somatosensory cortex Insula Anterior Cingulate g Orbitofrontal cortex Somatosensory Visceral sensory Hypothalamus
6. Amygdala. Inputs Orbitofrontal Cortex Ant cingulate g Visual stimulus Insular cortex DM Hyp Thalamus V2,3 V1 Visual and auditory Raw and processed visual information reaches the from: Thalamus visual cortex Ant Cingulate Orbitofrontal cortex Same for auditory information (temporal lobe instead of occipital) Sensory experience
6. Amygdala. Inputs Orbitofrontal Cortex Olfactory stimulus Ant cingulate g Insular cortex DM Hyp Thalamus Hippocampus Olfactory stimulus Raw and processed visual information reaches the from: Olfactory bulb Primary olfactory cortex Orbitofrontal cortex Others Hippocampus and parahippocampal g. Primary olfactory cortex Sensory experience
6. Amygdala. Outputs Ant cingulate g Insular cortex Emotional experience? Descending output to: Hypothalamus Brainstem responsible for: Emotional expression Feedback output to: Orbitofrontal Cortex DM Thalamus Hyp Hippocampus V2,3 Orbitofrontal cortex Ant Cingulate cortex Insular cortex Visual cortex Auditory cortex Primary olfactory cortex Thalamus Emotional expression feedback with affective valence for: Emotional experience? Hippocampus
6. Amygdala. Outputs Basal ganglia loop Accumbens n Orbitofrontal Cortex ventral pallidum DM 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 Ventral Tegmental area (dopamine)
6. Amygdala. Place in the emotional brain Ant cingulate g Insular cortex Emotional experience? The : drives the expression of emotions via descending projections Orbitofrontal Cortex Emotional Learning DM Hyp Thalamus Hippocampus V2,3 Emotional expression 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)
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 -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