Neuroscience of Emotion: The Amygdala, Stress, and Cognitive Regulation

Administrative and Course Announcements

• Assessment Submission:

  • There was a noted "Nuku disaster" regarding recent submissions.
  • Students who submitted via Qualtrics are encouraged to also submit on the Nuku page to facilitate grade management and feedback.
  • No late penalties will be applied for those who submitted on time via the alternative portal.

• Class Incentives:

  • Sweets from a Korean supermarket, nuts, and protein bars were provided as rewards for Mentimeter participation.

Mentimeter Revision: Mating Strategies and Evolutionary Biology

• Vasopressin Receptors and Mating:

  • The level of vasopressin receptors, particularly in male animals, significantly influences mating strategies.
  • Certain species (described as sounding "gracie" in the transcript) are often confused; higher expression of these receptors is linked to specific mating behaviors.

• Investment in Offspring:

  • High levels of investment (e.g., extracurricular activities for human children) often require higher income and dual-parental cooperation.
  • In animals, resources that are scarce or environments that are harsh and rapidly changing favor biparental arrangements to increase offspring survival chances.

• Monogamy in Birds vs. Mammals:

  • Mammals: Females can theoretically raise offspring alone because they can lactate.
  • Birds: Monogamy is much more common due to high thermal requirements for egg incubation. A partner is necessary to provide food or take over incubation duties.
  • Environmental Factor: The ambient temperature often determines whether a bird species engages in a monogamous or polygamous mating strategy.

The Philosophy and Evolutionary Purpose of Emotions

• Historical Context:

  • Philosophers traditionally viewed rationality and reason as superior faculties, while emotions and reactivity were seen as elements to be suppressed.
  • Cultural Reference: The character Spock from Star Trek (though the lecturer identifies more with Stargate) epitomizes the ideal of rational thinking devoid of emotion.

• Why Do Emotions Exist?

  • Social Communication: As social animals, humans use emotions to interact and bond.
  • Survival and Speed: Emotions allow for quick information processing and rapid responses to environmental stimuli.
  • The Negative Bias (BBB Bias): Humans are evolutionarily "built" to detect threats rather than to be happy. The cost of a "false alarm" (a racing heart) is low compared to the high cost of ignoring a real threat.
  • Evolutionary Problems: Emotions developed to react to threats, manage resources, ensure status, and promote bonding. Examples include jealousy, anxiety, and anger when resources are shared unfairly.

The Neuroanatomy of Emotion: The Tripartite Network

• The Amygdala:

  • Often called the "fear center" or "emotional center."
  • It is almond-shaped (the name is derived from this shape).
  • It is part of the limbic system, which also involves the olfactory bulb (explaining why smells trigger immediate strong emotions) and the thalamus (the sensory signal relay).

• The Prefrontal Cortex (PFC):

  • Plays a regulatory and inhibitory role.
  • Regions of the PFC generally inhibit overactivity in the amygdala.
  • Damage to certain regions leads to heightened emotional reactivity.

• The Hippocampus:

  • The memory center of the brain.
  • Provides context for raw emotions. It helps the brain learn which environments are dangerous and facilitates "fear extinction" (unlearning a fear association when an environment is no longer a threat).

Information Processing Pathways: Low Road vs. High Road

• The Low Road:

  • Path: Thalamus $\rightarrow$ Amygdala.
  • Function: Extremely fast but unrefined processing. It allows for immediate reactions to potential threats (e.g., jumping away from a rope that looks like a snake).
  • Evolutionary Trade-off: Favors "safety first" by allowing false positives.

• The High Road:

  • Path: Thalamus $\rightarrow$ Sensory Cortex $\rightarrow$ Amygdala.
  • Function: More careful, slow examination of the stimulus. It allows for error correction (e.g., realizing the "snake" is actually just a rope).
  • Social Use: Necessary for processing subtle social cues and complex threats.

The Four Components of Emotion

• Cognitive: Information evaluation. Professor Gina Grimshaw is noted for viewing emotion as a form of cognition rather than an opposing force.

• Feeling: The subjective experience.

• Physiological Response: Bodily changes (e.g., beating heart).

• Action: Behaviors such as running or posture.

• The James-Lange Theory (Introduction):

  • Suggests a bottom-up process where bodily action and physiological responses occur first.
  • Emotion is the mind's interpretation of those physical actions (e.g., "I am running, therefore I must be afraid").

• Negative Contrast Example:

  • A video of a dog expecting a large amount of food but receiving very little illustrates "negative contrast."
  • Biological Mechanism: Dopamine levels increase in anticipation; when the reward is less than expected, dopamine drops sharply, provoking anger.

Hormonal Factors and Chronic Stress

• The HPA Axis and Cortisol:

  • The Amygdala activates the Hypothalamus.
  • The Hypothalamus releases Corticotropin-Releasing Hormone (CRH) or Factor (CRF).
  • This leads to the release of Cortisol, which increases heart rate and blood glucose for "fight or flight."

• Neurotoxic Effects of Chronic Stress:

  • Short-term cortisol elevation is beneficial for focus.
  • Chronic exposure is neurotoxic, especially to the hippocampus.
  • The "Winter Tree" Metaphor: In stressed animals, neurons show thinned dendritic branching, resulting in fewer connections and hippocampal atrophy.
  • Immune System: Chronically elevated cortisol compromises the immune system and inflammatory markers because the body de-prioritizes long-term health in a perceived constant state of crisis.

• Startle Response Research:

  • Startle amplitude measures how much an animal (in a chamber) jumps in response to a loud sound.
  • Injecting CRF produces a dose-dependent increase in startle response ($\text{Startle Amplitude} \propto \text{CRF Dose}$).
  • Amygdala lesions abolish the ability of context to modulate this startle response.

Case Studies in Amygdala Dysfunction

• Patient SM:

  • A famous patient (like "Henley Morison") who has complete bilateral amygdala damage due to a rare genetic disorder.
  • Emotional Profile: Friendly, capable of happiness, sadness, and disgust, but entirely lacks fear.
  • Deficits: Cannot recognize fear in drawings or faces. She is not afraid of snakes, spiders, or "haunted" houses.
  • Highlighting Function: She lacks the "highlighter" function of the amygdala. She does not remember emotionally salient stories (sad or happy) better than neutral ones; the emotional importance is lost.

• Klüver-Bucy Syndrome (Monkey Studies):

  • Experimentally induced by removing the amygdala.
  • Monkeys became extremely docile and lost innate fears of snakes.
  • Social Consequences: They lost the ability to recognize social boundaries and personal space. Because they invaded other monkeys' territories, they were frequently attacked and bullied.

Social Cognition and Eyes

• Social Attention:

  • Patient SM does not focus on the eye region of faces (shown via eye-tracking data).
  • Cooperative Eye Hypothesis: Humans have a large white sclera (white part of the eye) that creates high contrast. This likely evolved to allow social animals to communicate emotions and intentions (like fear) immediately and silently.

• Ambiguity and Anxiety:

  • The amygdala is most reactive not just to fear, but to ambiguity. High alert occurs when a situation is uncertain or a signal is unclear.
  • Anxiety involves a chronic state of increased amygdala activity, leading to negative interpretations of neutral stimuli.

Genetic Influences

• Serotonin Transporter Polymorphism (5-HTTLPR):
  • Short Allele / Heterozygous Type: Linked to higher amygdala engagement and hyper-reactivity to negative signals.
  • Long Allele Type: Lower levels of amygdala engagement.
  • Hyper-reactivity is associated with susceptibility to PTSD, anxiety, and other affective disorders.
  • Hyper-reactivity may have been evolutionarily advantageous in collective cultures to detect subtle social signals, but it increases vulnerability in modern high-stress environments.

Emotional Regulation and Neuroplasticity

• PFC-Amygdala Circuitry:

  • Ventral Medial PFC (vmPFC): Directly interacts with and inhibits the amygdala. It is engaged during cognitive reappraisal and mindfulness.
  • Lateral PFC: Associated with behavioral suppression (simply trying to hide the emotion). In this state, amygdala activity remains high even if behavior is controlled.

• Mediation and Training:

  • Meditation can strengthen the connection between the PFC and amygdala in as little as two to three months.
  • This practice allows the vmPFC to automatically modulate emotional reactivity by focusing on context and understanding rather than suppression.

Questions & Discussion

• Audience Question: Does an enlarged amygdala mean the sympathetic nervous system is more engaged?
• Response: Yes, and it can also mean the parasympathetic system is not engaged enough; the two systems are no longer working in a healthy balance.