Fear and emotions

3 reasons we have emotions

1. Action → for survival reasons the allow us to react to situations sometimes with minimal conscious awareness e.g. how quickly do you observe people responding when scared

2. Social connection → we share our emotional experiences and empathise with others. Expressions of emotion make others respond to us e.g. how do you feel if you see someone crying, do you want to ask if they are ok?

3. Memory → emotions make us remember more vividly, and learn faster e.g. think of your most vivid memories - we create episodic memories of events that have emotion tied to them

James and Lange theory of emotion

1884-1885 developed the same theory independent of eachother

• ‘the experience of emotion is nothing more than the awareness of physiological responses to emotion arousing stimuli’

• E.g. see a bear, start shaking and sweating, HR increases, that is what makes me scared

stimulus → physiological response → experience of response → experience of emotion

4 critical points of James and Lange theory

1. Emotions are automatic responses triggered by stimuli perception at a cortical level

2. Both visceral (intuitive, in your gut) and behavioural responses vary depending on the specific emotions

3. The subjective experience of emotion is a result of perceiving changes within the body

4. The physiological changes directly follow the perception of the stimulus, and the awareness of these bodily changes constitutes the emotion itself

Cannon and bard theory of emotion

1972

• physical sensation and emotions aren’t always connected

• Animals and humans who had cortical lesions to the sensory cortex still experience emotions

• Other situations produce the same physiological changes e.g. fever, low blood sugar, excersise

• The viscera is insensitive - we are mostly unaware of what goes on in our body, we don’t feel the contractions of the stomach etc

• Visceral/physiological changes are too slow to give rise to emotions, emotional feelings are instantaneous

How does the thalamus act as a relay centre? Cannon and bard

1. Send signals to the amygdala and cerebral cortex to provoke feelings

2. Other signals send from the thalamus to the ANS and skeletal muscles create physiological reactions e.g. sweating

What is the Papez circuit

• proposed circuit of emotion

• Flow of thoughts and flow of feelings

• Thalamus is first relay station

Contains the:

• sensory cortex

• Anterior thalamus

• Hypothalmus - physiological response

• Cingulate cortex - conscious feelings

• Hippocampus

Papez-MacLean circuit

• Maclean proposed limbic circuit

• Added more brain structures: amygdala, frontal/orbital cortices, striatum, septum

• Thought to be involved in not only emotions but episodic memory too

Definition amygdala

→ organises the behavioural, vegetative and oral responses of anger, fear, anxiety and is involved in sexual and maternal behaviours

3 nuclei of the amygdala

1. Basolateral nuclei → consists of lateral, basal and accessory-basal nuclei, receives sensory inputs from cortex and thalamus

2. Medial nucleus → receive olfactory inputs from the bulb

3. Central nucleus (CE) → send outputs to motor cortex (for action) and hypothalamus (for vegetative functions etc.)

Le Doux animal testing

• uses classic fear conditioning in mammals

Physiological responses to fear:

• freezing

• Increase BP and HR

• Analgesia caused by stress

• Released ACTH

Translates to humans = some structures responsible for fear conditioning in mammals are also the same in humans

Connection between the amygdala and thalamus

• the amygdala receives sensory info via two routes (a rapid one from the thalamus, and a slower one from the sensory cortex)

• If the lesion was at the level of striatum or cortex, conditioning was still possible

• If the lesion was at the level of the thalamus or midbrain, no conditioning occurred

Conclusion = to learn emotional meaning to a stimulus requires a pathway between the thalamus and amygdala (but doesn’t always require cortical connections)

Sensory/attentional unawarness top-down vs bottom-up

Bottom-up → the salience(stands out from surroundings) of the stimulus capture the focus of attention (true also for emotionally salient stimuli)

Top-down → there is a conscious and ‘central’ decision on where to direct the focus of attention, via the fronto-parietal networks

• Sensory unawareness (bottom-up) → the stimulus energy is insufficient to generate conscious perception despite the allocation of attentional resources

3 reasons for sensory.attentional unawarness

• subliminal → exposition time is too brief

• Subthreshold → the stimuli is too weak

• Stimulus onset asynchrony → a second stimuli masks the first, when the inter stimulus interval is less than 30 ms

Conscious/unconscious emotional learning in amygdala

• subject shown angry face for <30ms then 45ms of expressionless face

• Only saw expressionless = masking

Tested 2 angry faces, one previously conditioned with white noise:

• masked presentation of the conditioned angry face activated the right amygdala

• The unmasked conditioned angry face activated left but not right amygdala

Conclusions:

1. Unconscious = right amygdala

2. Conscious = left amygdala

Attention an emotions for face vs object processing - study

• people instructed to either attend to faces or houses, brain activity measure using fMRI

• Higher activity in the fusiform face area FFA for faces than houses

• Greater FFA activation for fearful faces

• Amygdala activate for fearful but not neutral faces

• Left amygdala fires regardless of face vs house

This suggest the amygdala is not modulated by attention, contradicts other studies

Effect of attentional load on amygdala response

4 conditions:

FH fearful high distractor

NH normal high distractor

FL fearful low distractor

NL normal low distractor

• while early amygdala responding to emotional stimuli (40-140ms) was unaffected by attentional load = bottom up

• Later amygdala response (280-410ms), after frontoparietal cortex activity was modulated by attentional load = top down