2022-03-24 09:30:10

Announcements

  • Exam 3 next Thursday, March 31

Today’s Topics

  • Fear & stress

Fear and stress

Inducing “fear-like” behavior in animals

Rat vs. Human

Amygdala circuits

Amygdala’s inputs

  • Convergent inputs
    • Thalamus (“direct” or “fast”“)
    • Cerebral cortex (“indirect” or “slow”)

Amygdala’s outputs

  • Project to
    • CG (central gray matter) of tegmentum: behavior
    • LH (lateral hyp): ANS
    • PVN (paraventricular n. of hyp): hormones
  • Fast-acting, involuntary responses
  • Lesions of amygdala impair ‘fear conditioning’

Cerebral cortex role

  • Response discrimination?
    • Cortex lesions cause generalized not cue-specific fear response
  • Fast, crude responses vs. slower, detailed ones
    • That’s a stick, not a snake!
    • Prefrontal cortex and response inhibition

But, are we really studying learned ‘fear’?

  • Amygdala connected to other ‘affective’ nodes in neural network
  • Emotion not just about subjective feelings

Amygdala as processing hub

Amygdala as key hub in circuit for survival

Emotion as global physiological/behavioral “state”

Stress

Stressors linked with biological imperatives

  • Sustenance
    • Hunger, thirst
  • Well-being/defense
    • Threat

Stressors linked with biological imperatives

  • Reproduction
    • Rejection
  • Affiliation
    • Loneliness

Stress and the brain

Regulating internal states

  • Homeostasis
    • Regulation of physiological variables (e.g., blood \(O_2\)) via negative feedback (Cannon, 1929)
  • Allostasis (Sterling, 1988)
    • Regulation is active process
    • Regulation is anticipatory, varies by circumstance
    • Target levels vary (Ramsay & Woods, 2014)

Brain under stress

  • Acute stress
    • Short duration
    • Fast action required
    • HPA (Cortisol), SAM (NE/Epi) axes
  • Brain detects threat
  • Mobilizes physiological, behavioral responses

Brain under stress

  • vs. Chronic stress
    • Long duration, persistent

Glucocorticoids

  • Adrenal cortex releases cortisol (hydrocortisone)
    • Increases blood glucose levels
    • Suppresses immune system
    • Reduces inflammation
    • Aids in metabolism
  • Receptors in brain and body

Cortisol and the brain

Glucocorticoid cascade hypothesis

  • Cort receptors in hippocampus, amygdala, hypothalamus
    • Hippocampus (hipp) regulates HPA axis via hypothalamus
  • Prolonged cortisol exposure reduces hippocampus response
    • Reduces volume, connectivity in hippocampus
  • Hipp critical for long-term memory formation
    • Chronic stress impairs long-term memory

But, cortisol -> stress link not straightforward

Stress and coping across the animal kingdom

  • Pain thresholds lower (sensitivity greater) when a mouse’s cage mate is also in pain
  • Rats will cooperate to release distressed cage mate, foregoing food rewards
  • (Sapolsky, 2016)

Why Zebras Don’t Get Ulcers

Your (zebra) stress ain’t like mine

  • Phasic (short-term) vs. chronic (long-term)
  • Physical stress (hunger, thirst, injury, disease) vs. social stress

Where in the brain is emotion processed?

Where in the brain is emotion processed?

‘Emotion’ responses in ‘cognitive’ areas

Main points

  • Biological approach to emotion
    • Behavior
    • Physiological states
    • Subjective feelings
    • Adaptive function
  • Networks of brain systems, multiple NT systems
  • Emotional and cognitive processing have strong similarities

References

Cannon, W. B. (1929). Organization for physiological homeostasis. Physiological Reviews, 9(3), 399–431. https://doi.org/10.1152/physrev.1929.9.3.399

Davis, M. (1992). The role of the amygdala in fear-potentiated startle: Implications for animal models of anxiety. Trends in Pharmacological Sciences, 13, 35–41. https://doi.org/10.1016/0165-6147(92)90014-W

Faresjö, Å., Theodorsson, E., Chatziarzenis, M., Sapouna, V., Claesson, H.-P., Koppner, J., & Faresjö, T. (2013). Higher Perceived Stress but Lower Cortisol Levels Found among Young Greek Adults Living in a Stressful Social Environment in Comparison with Swedish Young Adults. PLoS ONE, 8(9), e73828. https://doi.org/10.1371/journal.pone.0073828

LeDoux, J. (2012). Rethinking the Emotional Brain. Neuron, 73(4), 653–676. https://doi.org/10.1016/j.neuron.2012.02.004

Lindquist, K. A., Wager, T. D., Kober, H., Bliss-Moreau, E., & Barrett, L. F. (2012). The brain basis of emotion: A meta-analytic review. The Behavioral and Brain Sciences, 35(3), 121–143. https://doi.org/10.1017/S0140525X11000446

McEwen, B. S. (2007). Physiology and Neurobiology of Stress and Adaptation: Central Role of the Brain. Physiological Reviews, 87(3), 873–904. https://doi.org/10.1152/physrev.00041.2006

Medina, J. F., Repa, J. C., Mauk, M. D., & LeDoux, J. E. (2002). Parallels between cerebellum-and amygdala-dependent conditioning. Nature Reviews Neuroscience, 3(2), 122–131. https://doi.org/10.1038/nrn728

Pessoa, L. (2008). On the relationship between emotion and cognition. Nature Reviews Neuroscience, 9(2), 148–158. https://doi.org/10.1038/nrn2317

Ramsay, D. S., & Woods, S. C. (2014). Clarifying the roles of homeostasis and allostasis in physiological regulation. Psychological Review, 121(2), 225–247. https://doi.org/10.1037/a0035942

Sapolsky, R. M. (2016). Psychiatric distress in animals versus animal models of psychiatric distress. Nature Neuroscience, 19(11), 1387–1389. https://doi.org/10.1038/nn.4397

Sterling, P. (1988). Allostasis : A new paradigm to explain arousal pathology. Handbook of Life Stress, Cognition and Health. Retrieved from https://ci.nii.ac.jp/naid/10019518960/