The neurobiology of emotion and stress

Question 1

Quickly summarize the five main theories of emtion

Answer 1

James-Lange theory: Stimulus - activity/physiology - emotional experience

Cannon-Bard theory: Emotion-triggering stimulus and body’s arousal take place simultaneously (sham rage experiments)

Schachter-Singer theory: when an emotion is felt, a physiological arousal occurs and the person uses the immediate environment to search for emotional cues to label the physiological arousal

Opponent process theory: According to opponent-process theory, drug addiction is the result of an emotional pairing of pleasure and the emotional symptoms associated with withdrawal. At the beginning of drug or any substance use, there are high levels of pleasure and low levels of withdrawal. Over time, however, as the levels of pleasure from using the drug decrease, the levels of withdrawal symptoms increase, thus providing motivation to keep using the drug despite a lack of pleasure from it.

Cognitive appraisal theory: A theory of emotion which implicates people’s personal interpetations of an event in determining their emotional reaction. The most important part of this theory is the way we interpret the event (aka, was the event a positive or a negative occurence?) as well as what we think caused the situation.

Question 2

What was the impact of Darwin’s theory of emotion?

Answer 2

• Autonomic responses are an intrinsic part of the emotional experience
• The autonomic aspects of emotion are important for communication and in prep for behavioral responses

Question 3

What is William Jame’s theory of emotion?

Answer 3

• Autonomic responses are reflex reactions that occur quickly, commencing and sometimes finishing before conscious perception of emotion occurs
• emotional experience is the perception that arises from the autonomic changes, in other words, emotional experience follows and reflects autonomic reactivity.

Question 4

Why did Walter Cannon disagree with William James’ theory of emotion?

Answer 4

• Emotional situations produced the same kind of bodily emotional response
• You feel emotion before the stress response (eg. scare before you run away)
• Emotion does not depend on the cerebral cortex because you can elicit sham rage

Question 5

How can you elicit sham rage?

Answer 5

Damage or cut off the cortex and slightly stimulate animal

Shame rage is highly similar to the normal expression of rage, except that it was not directed toward the provoking stimulus. and subsides immediately when the inocuous stimulus is removed

Question 6

Describe the Cannon-Bard lesion experiments

Answer 6

• Serial transections to disconnect the cerebral cortex from outflow pathways

Forebrain transection: sham rage to innocuous stimuli

Forebrain + posterior hypothalamus: No coordinate shame rage response

Question 7

What did James W Papez and Charles Judson Herrick argue about the medial surface of the brain?

Answer 7

The limbic system (CG, Hippocampus, mammillary bodies and hypothalamus etc.) involved in emotion because it’s conserved across animals, and all vertebrates share same emotional responses (roughly).

Question 8

What is Kluver-Bucy syndrome and what did it reveal about emotion?

Answer 8

Temporal lobes removed, including amygdala and hippocampus, bilaterally in monkeys.

Made monkeys:

• Hypersexual
• Hyper oral tendencies
• Dietary changes
• Psychic blindness (fearless to threat)

Further lesion studies honed in on the amygdala’s role in this.

Question 9

What did Paul MacLean (the great synthesizer) add to the Papez circuit (limbic)?

Answer 9

Epileptic foci begin in hippocampus and the aura patients experience before a seizure is rage, while patients with tumours in the cingulate gyrus have abnormal emotional responses - implicating both the hippocampus and CG in emotional circuit

• Kept adding on brain structures, model got unwieldy.

Question 10

How did Downer show evidence for the amygdala’s involvement in processing emotional stimuli?

Answer 10

Lesioned the optic chiasm, so only ipsilateral information from retina

Lesioned one amygdala, and blinded side with amygdala still intact or side with lesioned amygdala.

Lesioned amygdala: blunted emotions to threat

Intact amygdala: Normal fear behaviour

This is a reproduction of the Kluver-Bucy syndrome (but more selective of anterior temporal lobe)

Question 11

What is the modern approach of studying emotion?

Answer 11

• study one emotion at a time (eg. fear)

- Fear is most popular as it is raw, primal, universal and easily producable.

Question 12

Why is fear the preferred emotion to study?

Answer 12

• Primal (evolutionary conserved)
• Universal
• Producible
• Present oriented (anxiety is future)
• Adaptive
• Root of many emotions and emotional disorders

Question 13

List 7 emotional disorders associated with fear

Answer 13

• Phobias
• PTSD
• Panic disorder
• Generalized anxiety disorder
• Obsessive compulsive disorder
• Paranoid states
• Emotional components of diseases

Question 14

What is anxiety disorder?

Answer 14

an umbrella term that covers several
different forms of a type of common psychiatric disorder,
characterized by excessive rumination, worrying,
uneasiness, apprehension and fear about future
uncertainties either based on real or imagined events,
which may affect both physical and psychological health.

Question 15

List the ares that the amygdala coordinates components of emotion with

Answer 15

• Lateral hypothalamus
• Dorsal motor nucleus of Vagus
• Parabrachial nucleus
• VTA, LC, PPN
• Nucleus reticularis
• Periaqueductal gray
• Trigeminal and facial nuclei
• PVN hypothalamus

Question 16

True or false? Almost all animals experience fear conditioning as a universal survival mechanism

Answer 16

True! From fruit flys to humans

Question 17

The amygdala receives projections from where in order to receive information from emotional stimuli

Answer 17

The sensory thalamus

Question 18

Describe the low and high roads to fear

Answer 18

A fear inducing stimulus reaches the thalamus and is relayed either directly to the lateral nucleus of the amygdala (the low road for unconsicous reactions to a threat) or the via the cortex and hippocampus (the high road, involving more detailed and conscious processing of stimuli).

High road: Slow but accurate
Low road: Quick and dirty

Question 19

Describe the neural circuit of fear conditioning

Answer 19

• Conditioned and unconditioned stimuli converge in the lateral amygdala from both the thalamic and cortical areas
• The lateral amygdala then communicates directly with the central amygdala
• The central amygdala connects with the brainstem and hypothalamic areas that control the expresssion of fear responses, including freezing behaviour (mediated by the central gray and cingulate gyrus), autonomic nervous system (mediated by the lateral hypothalamus, LH), and hormonal responses (mediated by the PVN hypothalamus)

Question 20

Where does the central amygdala connect to for the expression of conditioned fear responses?

How is this convergent input?

Answer 20

The central amygdala connects with the brainstem and hypothalamic areas that control the expresssion of fear responses, including

• Freezing behaviour (mediated by the central gray and cingulate gyrus),
• Autonomic nervous system (mediated by the lateral hypothalamus, LH),
• Hormonal responses (mediated by the PVN hypothalamus)

Convergent input: Dissociation between conditioned stimulus and unconditioned response takes place in individual neurons.

Question 21

Describe a model of associative learning in the amygdala relevant to emotional function

Answer 21

• During fear conditioning, strong stimulatory inputs detecting pain are relayed to LA neurons in the amygdala and depolarize them, simultaneously neutral sensory stimuli that represent auditory information are relayed to the same LA neurons and reinforce their depolarization.
• These LA neurons become more sensitive to future tones
• Following fear conditioning the tone along is able to depolarize the neurons that support the neural circuitry of emotional expression of fear
• Associative learning occurs by strenghthening synaptic linkages between the previously neutral inputs (tone) and the neurons of the amygdala (Hebbian synaptic mech?)

Question 22

Describe LTP in the amygdala

Answer 22

Adversive unconditioned stimuli (eg. a foot shock) strongly depolarizes LA neurons

Conditioned stimulus (eg. a tone) evokes excitatory postsynaptic potentials (EPSPs_ at sensory input synapses onto LA pyramidal neurons

• Ca influx through NMDA receptors causes LA neurons to fire action potentials.
• Glutamate opens a calcium channel only when the postsynaptic membrane is depolarized, in this case, by foot shock pain
• Any weak inputs (eg. tone) that are synchrously active with the foot shock pain input allow local calcium entry into the dendrite
• Ca entry causes new postsynaptic Glu receptors to insert into postsynaptic site, potentiating the formerly weak synapse.

After, the CS alone is sufficient to cause excitatory postsynaptic potentials EPSPs at sensory input synapses onto LA pyramidal neurons in amygdala

Question 23

Describe patient SM

Answer 23

The woman who was never afraid

• Autosomal recessive condition called Urbach-Wiethe disease
• Bilateral calsification and atrophy of the anterior-medial temporal lobes
• Amygdala in each hemisphere extensively damaged, with little injury to hippocampal formation or nearby temporal neocortex.

SM could not recognize the emotion of fear, especially with eye region of faces. If asked to look at eyes, she recovered accuracy.

SM couldn’t draw fearful faces.