Emotional control: Limbic system .Emotional control: Limbic system 1. The limbic system 2. The amygdala

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  • 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