PSYC10003 Lecture Notes - Lecture 10: Orbitofrontal Cortex, Biological Neural Network, Temporal Lobe

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MBB1 Lecture 10
The neural basis of emotion
The concept of emotion
Emotions consist of patterns physiological response and species-typical behaviours
In humans, these responses are accompanied by feelings, which are powerful
motivators
o Thus exert influence on how we are likely to behave in certain situations
o Emotional behaviours likely played a big part in the evolution of the CNS
Darwin suggested certain responses accompany similar emotional states in all
members of the same species facial expressions accompany the same feelings for
all humans
o Thought expressions of emotion evolved through natural selection evolve
from behaviours indicating what an animal will do next
E.g. behaviours originally serving the function of fighting would evolve to become a
display of the intention to fight
o So a threat display may remove the need for a real fight, causing fewer
deaths
So these displays must be easily distinguishable from other displays
Emotions as responsive patterns
Three components of emotional responses:
Behavioural muscular changes that are appropriate to the situation that elicits
them
o E.g. dog defending territory against robber may adopt aggressive posture
hopes of robber adopting submissive posture
Darwin called these clearly distinguishable opposite movements the
principle of antithesis
Autonomic physiological changes induced by the ANS facilitate behavioural
responses
o dog example, sympathetic branch of ANS increases so dogs heart rate
increases and blood is diverted from digestive system to muscles
hormonal reinforce autonomic changes
o dog eaple, dogs adeal edulla seetes epiephie ad
norepinephrine to further increase blood flow to muscles
Neural control of emotional response patterns
Bad oseed a sha age i ats hose cerebral hemispheres had been surgically
removed
o Sham rage excessively aggressive manner in response to slight stimulation
(e.g. simple touch made them hiss, bare teeth and arch back)
o Sham rage absent after removal of hypothalamus
Conclusion: hypothalamus is responsible for expression of aggressive
behaviour
And cortex normally inhibits and controls such behaviour
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The limbic system of emotion
A distinct circuit of brain structures sub-serves emotional expression
o Includes hypothalamus, anterior thalamus, cingulate gyrus, fornix and
hippocampus, amygdala, orbitofrontal cortex and some nuclei of the basal
ganglia
o This neural circuit is the limbic system
Hippoapus foed the etal eleet i Mleas lii sste (eeied iputs
from various senses and internal organs), but it is now clear that the hippocampus
has a more important role in learning and memory than emotion
o Despite shortcomings, the concept of the limbic system is still used
Klüver-Bucy syndrome and the amygdala
Bilateral ablation of temporal lobes in rhesus monkeys resulted in impaired visual
recognition
The monkeys ate anything that was edible, showed increased sexual activity,
exploration of all items with mouth and the absence of fear
Thought that this arises from damage to amygdala (in anterior temporal lobe)
Syndrome is occasionally described in humans a patient became indifferent to
people and events after brain damage caused by an infection
o Would gaze for hours at the TV even when it was off, would imitate actions
of others and engaged in oral exploration of anything within reach
o Despite being heterosexual before damage, he often made sexual advances
towards other male patients
Structure of the amygdala
It plays a key role in the physiological and behavioural reactions to objects and situations
that have certain biological significance E.g. painful, signifying presence of food or a mate
Medial nucleus receives sensory input (including from olfactory system) and relays
info to basal forebrain and hypothalamus
Lateral/basolateral nuclei receive sensory info from MSC, association cortex,
thalamus and hippocampus. They send axons to basal ganglia, thalamus and central
nucleus of amygdala
Central nucleus sends axons to regions of hypothalamus, midbrain, pons and
medulla that are responsible for the expression of various emotional responses
o Most important part of brain for expression of emotional response to
threatening stimuli damage abolishes fear responses to stimuli associated
with aversive events
o Electrical stimulation induces a reaction of fear or agitation
Basal nucleus receives axons from lateral and basolateral nuclei, and sends axons
to amygdaloid nuclei and midbrain
Orbitofrontal cortex and decision making
Located on ventral surface of frontal lobes, immediately above orbits with the eyes
More medial region is known as the ventromedial prefrontal cortex, and lateral
region is called the lateral-orbital prefrontal cortex
Precise role is unclear, partly because behaviours it is responsible for are difficult to
categorise
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