10. neuroscience + emotion PDF

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Summary

The ‘limbic system’ The limbic system is referred to in most textbooks of biological psychology It consists of cingulate cortex, hippocampus, Amygdala, mammillo-thalamic tract anterior thalamus the hypothalamus, .Origin of the term ‘limbic lobe’ came from Broca, 1878 who looked at more than 30 speci...

Description

The ‘limbic system’ -

The limbic system is referred to in most textbooks of biological psychology

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It consists of -

cingulate cortex,

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hippocampus,

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Amygdala,

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mammillo-thalamic tract

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anterior thalamus

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the hypothalamus,

.Origin of the term ‘limbic lobe’ came from Broca, 1878 who looked at more than 30 species of mammal’s brains

Papez circuit Originates in cortex …“built up in the hippocampal formation and . . .transferred to the mammillary body and thence through the anterior thalamic nuclei to the cortex of the gyrus cinguli” (Papez, 1937, p. 728)

Early evidence linking Papez circuit to emotion -

Decorticate animals may produce sham rage -

intense aggression usually poorly directed.

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Original studies from Cannon, Bard and others (1930’s). Implication was that some cortical areas inhibit sub-cortically generated rage respons

Klüver-Bucy syndrome. First described in 1938. -

Lesions in experimental animals that produce damage deep into the temporal lobes, including amygdala, lead to a syndrome including: -

marked taming

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inappropriate oral behaviour (eating indigestible objects)

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Hypersexuality, inappropriately directed

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These changes had been noted in human patients some years earlier.

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Electrical stimulation in hypothalamic sites could elicit attack, defense or flight depending on exact site (Hess and others 1950’s).

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All of these early studies were consistent with involvement of limbic structures and the Papez

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Stimulation of lateral Hypothalamus produced directed rage

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Delgado later became ‘well known’ for implanting a bull with electrodes and stopping it charging at him

Papez circuit: a functional model -

In Le Doux’s version of Papez’s circuit the cingulate cortex integrates signals from hypothalamus and sensory cortex.

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Although the Papez circuit is usually associated with emotion it is also heavily implicated in memory.

The ‘somatic marker hypothesis’ revisited -

Clinical evidence using the Iowa gambling task indicates the importance of frontal cortex and amygdala in emotion-related decision making.

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Participants with damage to either prefrontal cortex or amygdala are impaired in acquiring the task, and also show no anticipatory SCRs.

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However, on a simple aversive classical conditioning task VMF and amygdala damage produce differe effects on skin conductance – almost entirely absent in the amygdala group.

Fear conditioning in rodents -

In this task the rat, or mouse, learns about the relationship between a specific CS (tone) and US (shoc result of repeated pairings while in a particular context.

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Later the animal can be tested with both the cue in its home cage, and in the conditioning context wi the cue

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In both cases a freezing response provides a measure of recall of the association.

Differential effects of hippocampal and amygdala lesions on fear conditioning -

Amygdala lesions abolish both specific CS and contextual conditioning whereas the hippocampal les effects are confined to context

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The cortical lesion is a general control for the effects of surgery and has no effect.

The ‘anatomy’ of fear -

Note that this diagram makes some very specific predictions about the different roles of the ‘input’ and ‘output’ nuclei of the amygdala (lateral and central nuclei, LA and CE in the figure).

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The central nucleus projects to the central gray (CG) in the midbrain and to the lateral and paraventricular nuclei of the hypothalamus.

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Predictions following from the Le Doux model:

process such as long-term potentiation within this structure. -

Conditioning with a strong emotional component is modified by monoamine hormones- suc effects should be demonstrable in the lateral nucleus

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These have mostly been fulfilled.

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However, there is also more recent evidence to suggest that a pathway from the paraventricular nucleus of the thalamus, activated by stress and pain, projects directly to the central nucleus of the amygdala and that conditioning may also be supported by changes in the supposedly ‘output’ nucleus.

Panksepp’s emotional arousal systems -

This figure shows Panksepp’s conception of the relationship between four primary emotions. His full list includes seven. -

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Positive emotions in red, negative in blue.

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This listing provides an example of an approach – it is not here to memorise!!

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Panksepp’s seeking system is broadly similar to the ‘wanting’ or incentive motivation processes discu Robinson & Berridge. Anatomically based on the medial forebrain bundle where Jim Olds, working w Peter Milner, originally identified self-stimulation in the early 1950’s.

Basic emotional systems

Key brain areas

Key neuromodulators

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Emotion is distinguished from other psychological processes by the dimension of affect (pleasure and displeasure or aversion).

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Fear is especially well understood at the neural level, involving interactions between cortical sites, am hippocampus, hypothalamus and brainstem.

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Other emotions are likely to depend on neural systems partially independent from that for fear, and a subject matter of affective neuroscience.

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Consciously perceived human emotions involve a complex interaction of these basic mechanisms wit developmental and social influences....