Emotional control: Limbic system

1. The limbic system

2. The amygdala

2.1 Anatomy of the amygdala

2.2 Principles of function of

the amygdala

Antonio R. Damasio „Descartes‘ Error: Emotion, Reason and the Human

Brain“ Vintage, 2006.

Joseph LeDoux „The emotional brain“ Phoenix, 1999.

Elliot („A modern Phineas Gage“):

- no difference in the IQ

- no difference in memory skills

- no difference in making decisions at laboratory conditions

- Strong difficulties to plan the future and to come to decisions in real

life situations

deficit in emotions that support to come to decisions and to focus

attention also for longer time

Limbic system

phylogenetically old

system (

„emotional

brain“)

Cingulate gyrus (G.

cinguli, auch G.

limbicus)

derived from limbus

(lat.): border

ring or gyri in the

medial

hemispheres

Concept of limbic system rests upon functional connections

(anatomically not precisely described)

Ring of Papez (James Papez, 1937): „circuit for emotions“

reciprocal connections

higher centers are connected via the cingulate gyrus (form of „primitive

cortex“ with 3-layer structure)

Central role of cingulate gyrus: stimulation causes different responses

inhibition of respiration, „arrest reaction“, aggressive behavior,

sometimes pleasurable emotions

Cingulate gyrus

appears also to be

involved in

mediating

consciousness (Fischer et al., „A human

brain network determined

from coma-causing

brainstem lesions“,

Neurology 2016)

According to A. Damasio:

- circuits involving the amygdala and the cingulate gyrus: involved in

primary emotions (inborn, preorganized emotions)

- Additional circuits involving the somatosensory cortex and prefrontal

cortex: involved in secondary emotions (more complex and learned

emotions)

Amygdala („Mandelkern“)

Complex structure, consisting of about 10 distinct nuclei

Contains cortical regions (nucleus corticalis) and non-cortical regions

transitory structure between cortex and nuclei

Rich in peptidergic neurons

Optical tract

Hypothalamus

Topical organization of the amygdala

Distinct reactions are associated with distinct

regions

rage

escape

Distinct vegetative reactions, e.g. chewing,

activation of the salivary gland

Involved in mediating both:

- unconscious emotional state („primary emotions“) and

- conscious feeling („secondary emotions“)

role in „negative emotions“ (fear) and in linking „negative emotions“

with other aspects of cognition, i.e. learning and memory

(from: Dudel, Menzel, Schmidt (Hrsg.) Neurowissenschaften, Springer)

Coordinating role between the regions

concerned with the somatic

expression of emotion

(hypthalamus, brain stem nuclei),

sensory input and neocortical

areas concerned with conscious

feeling (prefrontal cortices)

Connections of the amygdala

thalamus

Somatosensory cortex

and association

cortices

Input: Thalamus and cortex regions via

(baso)lateral nuclei

Output: Cortex regions via central

nucleus and nucleus basalis (part

of the telencephalon) and

autonomic and endocrine systems

Connection of the amygdala to the

hypothalamus

amygdala

hypothalamus

Parahippocampal gyrus

Stria terminalis

Amygdalofugal

tract

Output connections of the amygdala to the hypothalamus

pituitary gland

The amygdala in stress response

GABA-ergic projections from the

amygdala to the

hypothalamus

release of CRH

(corticotropin-releasing

hormone)

release of ACTH

release of cortisol from

the adrenal cortex

HPA-axis (Hypothalamus-Pituitary gland-Adrenal gland)

Kim et al. (2015) Stress effects on the hippocampus:

a critical review. Learning & Memory 22:411–416

cortisol receptors in the

hippocampus

negative influence on LTP

Functions of the amygdala

Emotional states can also be learned: e.g., classical conditioning of fear

(„Pavlovian fear conditioning“): pairing of a neutral stimulus with a

fearful shock

Critical neural changes occur in the lateral nucleus of the amygdala if a

sound (neutral conditioned stimulus, CS) is paired with an electrical

shock (aversive unconditioned stimulus, US)

Lateral nucleus

Central nucleus

Long term potentiation (LTP) in pyramidal neurons from

the lateral nucleus of the amygdala

CS (neutral conditioned stimulus) produces low EPSP in pyramidal neuron

When paired with aversive unconditioned stimulus (US), postsynaptic

changes occur, which lead to an increase in the concentration of AMPA-

Receptors

Subsequent CS produces high EPSP

From: Blair et al., „Synaptic plasticity in the lateral amygdala: a cellular hypothesis of

fear conditioning“ Learning & Memory 8: 229-242(2001)

Donald O. Hebb (1949): „what fires together, wires together“

Where is fear memory stored?

Evidence that the lateral nucleus of the amygdala is not only involved in

acquisition of fear memory but is also an essential locus of fear

memory storage

(Schafe, Doyere and LeDoux (2005) Tracking the fear engram: The lateral amygdala is an essential locus of

fear memory storage. J. Neurosci. 25:10010-10015.)

Lateral nucleus

Central nucleus

Reconsolidation theory of fear memory

Could have consequences for treatment of patients with post traumatic

stress disorder

Experiment in the laboratory of Joseph LeDoux:

- Fear conditioning of a rat

- Remembering (tone) together with application of an inhibitor of protein

synthesis (anisomycin)

- Memory was erased

(Nader et al. (2000) Fear memories require protein synthesis in the amygdala for

reconsolidation after retrieval. Nature 406:722-726)

Überblicksartikel: LeDoux (2009) Manipulating memory. The Scientist 23:40-45

The act of remembering might render memories fragile, subject to change

or perhaps erasure

GABAergic system in central nucleus appears to be critical for function of

the amygdala:

Injection of GABA agonists and benzodiazepines (e.g., valium)

decrease anxiety

Neurochemistry of emotions

Infusion of GABA also decreases anxiety

Activation of GABA-ergic mechanisms

GABA-ergic chloride-channel:

benzodiazepines increase affinity

to GABA

Increased influx of Cl

Increased hyperpolarisation