Biology

• Triune model


  Proposed by Paul MacLean in the 1960s, it showed three metaphorical layers of the brain
• Ancient part of the brain

  • Mediates automatic, regulatory functions
  • Senses changes in body temperature, blood glucose levels, and injuries, and initiates appropriate responses
• More evolved region


  • Expanded in mammals
  • Mediates emotions - a mammalian invention
  • Sends commands to the ancient layer to generate emotional responses
• Recently evolved neocortex


  • Handles cognition, memory storage, sensory processing, abstractions, philosophy, and self-reflection
  • Sends signals to the emotional layer to generate appropriate responses
• There is overlap between the three layers, and the flow of information and commands is not strictly top-down
• Automatic aspects of behavior

  • Simplicity - layer 1
  • Emotion - layer 2
  • Thought - layer 3
• Limbic system


  • Layer 2, the "centrum" for emotions
  • Regulates the olfactory system and autonomic functions
• Hypothalamus


  The interface between layers 1 and 2, regulating automatic reactions throughout the body
• Autonomic nervous system


  Midbrain and brainstem regions that project down the spine and out to the body
• Parts of the autonomic nervous system

  • Sympathetic nervous system - mediates the "fight or flight" stress response
  • Parasympathetic nervous system - mediates calm, vegetative states
• Cortex


  • The brain's upper surface, the newest part of the brain
  • Handles sensory information, movement, language, memory, and decision-making
• Lobes of the cortex

  • Frontal lobe
  • Temporal lobe
  • Parietal lobe
  • Occipital lobe
• Hemispheres of the brain

  • Left hemisphere - analytical
  • Right hemisphere - intuitive and creative
• Amygdala


  An archetypal limbic structure involved in aggression, fear, anxiety, and social/emotional decision-making
• Stimulating the amygdala can induce rage, and damage to it can impair the detection of angry facial expressions
• In PTSD, the amygdala is overactive and slow to calm down after being activated, and it expands in size with long-term PTSD
• Basolateral amygdala (BLA)


  Learns fear and sends the information to the central amygdala
• Amygdala


  Injects implicit distrust and vigilance into social decision-making, and plays a role in male sexual motivation
• The amygdala can respond to stimuli that are too fleeting or faint for the cortex to detect
• Amygdala


  Receives information about triggers of fear, aggression, and pain from ancient, core brain structures
• Insular cortex


  Projects to the amygdala, mediating disgust responses
• Amygdala


  Talks to other limbic structures like the hippocampus to facilitate fear learning
• Amygdala outputs


  Mostly about setting off alarms throughout the brain and body
• BNST (bed nucleus of the stria terminalis)


  Projects to parts of the hypothalamus that initiate the hormonal stress response
• Locus coeruleus


  Sends norepinephrine-releasing projections throughout the brain, particularly the cortex, influencing arousal
• Frontal cortex


  Handles working memory, executive function, gratification postponement, long-term planning, emotion regulation, and impulse control
• Frontal cortex


  • Most recently evolved brain region
  • More complexly wired and bigger than in other apes
  • Last brain region to fully mature
  • Contains unique "economy" neurons
• Insula


  Part of the frontal cortex that mediates gustatory and moral disgust
• Anterior cingulate


  Part of the frontal cortex that is central to empathy
• Prefrontal cortex


  • Newest part of the frontal cortex, central to executive function and decision-making
  • Resolves conflicts between options, balancing cognition and emotions
  • Initiates behavior by sending orders to other frontal regions
• Cognitive processes orchestrated by the frontal cortex

  • Strategic memory retrieval
  • Task focus and attention
  • Task switching and adaptation
  • Executive function and strategic thinking
• Frontal cortex


  • Neurons are expensive and vulnerable
  • Expends significant energy on rule-tracking and self-control
  • High metabolic rates make it vulnerable to damage
  • Cognitive load can decrease performance and prosocial behavior
• Automaticity and effortful control

  With practice, demanding tasks become automatic, shifting to reflexive brain regions and reducing frontal cortex workload
• Moral decision-making


  Automaticity often facilitates morally challenging acts, bypassing frontal cortex deliberation
• Frontal cortex


  • Larger in species with bigger average social group sizes
  • Particular subregions are larger in individuals with larger social networks
• Damage to the frontal cortex

  Can cause behavioral disinhibition, socially inappropriate behavior, apathy, and lack of initiative
• Dorsolateral prefrontal cortex (dlPFC)


  The most rational, cognitive, and utilitarian part of the prefrontal cortex
• Ventromedial prefrontal cortex (vmPFC)

  Involved in emotional aspects of decision-making, activating when forgoing immediate rewards for larger later ones
• Frontal cortex-limbic system relationship

  Can be top-down, with the frontal cortex calming the amygdala, or bottom-up, with gut feelings influencing decisions
• Mesolimbic/mesocortical dopamine system


  Involved in reward, motivation, and the pleasure of anticipation rather than the reward itself