The Limbic System

“It is very difficult to imagine a lonelier and more emotionally empty being than a crocodile” — Paul MacLean

Review of the design of the human brain

archipallium

medulla oblongata, pons, cerebellum, mesencephalon, thalamus, some basal nuclei

Paul MacLean: the “R-complex”

deals with self-preservation

development of the olfactory complex

paleopallium

Paul Broca: the “limbic lobe”

deals with distinction of agreeable and disagreeable

development of specific affective behaviors, emotions and feelings

neopallium

neocortex

the “rational” brain

deals with skilled intellectual tasks

development of language, symbolic mathematics, morality

Paul MacLean, again: “it is the mother of invention and the father of abstractive thought”

Brain structures and the formation of emotions

James–Lange theory

1. frightening stimulus

2. feeling of fear

3. somatovisceral response

Cannon–Bard theory

William James: physical sensations are the emotion

1. frightening stimulus

2. message divides in thalamus

3. projection to cortex for subjective experience

4. projection to hypothalamus for somatovisceral response

errors of the Cannon–Bard theory

James Papez

emotion is not a function a specific brain center

it is a circuit involving:

hypothalamus & mammillary bodies

anterior thalamic nucleus

cingulate gyrus

hippocampus

Paul MacLean

refined Papez’s idea as the limbic system

added new components:

prefrontal area

parahippocampal gyrus

amygdala

medial thalamic nucleus

septal area

prosencephalic basal nuclei

Areas involved with emotions

amygdala

when triggered gives rise to fear and aggression

hippocampus

involved with memory

fornix & parahippocampal gyrus

connecting pathways of the limbic system

PHG plays an important role in the formation and retrieval of topographical memory

thalamus

medial dorsal and anterior nuclei associated with emotional reactivity

medial dorsal nucleus connects with prefrontal area and hypothalamus

anterior nuclei connect with mammillary bodies:

mammillary_bodies_schematic

via the fornix then connect with hippocampus and cingulate gyrus

hypothalamus

numerous connections with prosencephalon and mesencephalon

controls vegetative functions and some motivated behaviors

lateral portions involved with pleasure and rage

medial portion involved with aversion and displeasure

cingulate gyrus

cerebrum_sagittal_view

frontal portion coordinates smells & sights with pleaseant memories

participates in emotional reaction to pain, regulation of aggressive behavior

cingulectomy

cingulotomy

brainstem

responsible for “emotional reactions” of lower tetrapods

reticular formation

locus cœruleus

concentrated mass of NE-secreting neurons

responsible for physiological responses to stress and panic

ventral tegmental area

dopamine-secreting neurons

nucleus accumbens

located where the head of the caudate and the anterior portion of the putamen meet just lateral to the septum pellucidum

thought to play an important role in reward, pleasure, and addiction

besides cocaine and amphetamine, almost every drug abused by humans has been shown to increase dopamine levels in the nucleus accumbens

septal area

lies rostral to the thalamus

role in pleasurable sensations

multiple spikes resembling focal seizures have been recorded by EEG from the septal region of normal men during orgasm or during orgasmic sensations induced by electrical or cholinergic stimulation of the region

prefrontal area

comprises the non-motor rostral portions of the frontal lobe

has extensive connections with thalamus, amygdala, and other subcortical areas

implicated in planning complex cognitive behaviors, personality expression, and moderating correct social behavior

in 2005, University of Toronto researchers traced the origin of fear memories to the prefrontal cortex

the prefrontal lobotomy

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