Chapter 10 - brain substrates
how emotions activate the brain
There is no specialized emotional circuit
each emotion activates many different brain regions.
no single brain region is activated by all different emotions
No single brain region is activated by all the different emotions
Amygdala (LOOK AT DIAGRAM)
small almond shaped structure that lies at the anterior tip of the hippocampus
collection of MANY different subregions/nuclei
lateral nucleus
Primary entry point for sensory information into the amygdala
info comes from the thalamus
Central nucleus
receives input from other amygdala nuclei. Projects out of amygdala to two places
motor centres - behavioural responses such as freezing and startle
ANS - controls arousal and stress hormones
Basolateral nucleus
receives input from lateral nucleus and projects to cortex, basil ganglia and hippocampus.
provides a pathway by which amygdala can modulate memory storage and retrieval in those structures.
organizes the expression of emotional responses
Stimulation can cause species - typical defensive responses (in rabbits = freezing and lowered heart rate).
Damage = impairments of emotional learning in humans and other animals.
required for fear conditioning
Ex: CS (coloured shape) paired with blast of noise (US). in normal and hippocampal patients CS comes to evoke a skin conductance response due to emotional arousal
in patients with bilateral amygdala damage the US is effective but the association with the CS is never learned (left).
There are two pathways from the thalamus to the amygdala
indirect
Direct
"fast and rough"
Gets to amy quickly but minimal processing does not allow for fine distinctions between stimuli
Reacts quickly (activates flight or fight)
12 ms
19 ms
slow but accurate
involvement of cortex allows much finer discrimination of stimulus details
provides extra information allowing subject to terminate response if stimulus not dangerous.
emotional learning refines neural responses in the lateral amygdala.
odors paired with a shock have more neural activity than others not paired with shock.
suggests encoding of emotional relevance of the stimuli
emotional events activate the amygdala
degree of amygdala activation predicts memory boost for emotional material
amy activation correlates with stronger feelings of remembering emotional material both at encoding and recall
emotional arousal and amygdala activation may promote encoding of contextual details, creating a sense of remembering and causing information to be stored as episodic rather than semantic memory
modulate memories to increase storage of emotional memories
inputs from hormonal system via the brain stem
outputs to the hippocampus
outputs from the CN activate ANS which signal adrenal glands to release epinephrine
Helps mediate fight or flight
eppy activates brainstem nuclei to release nor-eppy
these nuclei project to Basil lateral
BLA projects to hippocampus and cortex. strong activation of this pathway predicts better encoding
enhancing eppy boosts emotional memory
rats given a foot shock upon entering a dark chamber hesitate about 60 seconds before re-entering the same chamber
boosting epinephrine just after training increases hesitation
Hippocampus
lesions abolish contextual learning
animals remember the context in which they learned something
lesions do not abolish CS-US relationship
abolishes episodic memory
frontal lobes
Important for planning & decision making
important for social behaviour
Involved in expressing emotions and reading emotions from others
Damage causes impairment in emotional responses
Can be too much or too little
emotional balance is controlled by the frontal lobe
pre-frontal cortex
plays a role in reading expression in others
mPFC
important for processing emotional stimuli in a manner that is appropriate to context in which stimuli occur
fear learning
frontal lobe damage can impair extinction of fear responses, leading to preservation (repetition) of the response
rats with lesions to mPFC continue to respond to CS after extinction (when control rats have learned to ignore it).
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