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Biological Basis of Behavior #1 – Comprehensive Study Notes

Introduction

  • Course context: Biological Basis of Behavior #1 (PSYCH 1001, Dr. Nicola Grissom).
  • Slide 1 contained MRI-like metadata (e.g., FOV 2965; TR 6300.0 ms; slice refs 23/180; voxel size 5\,\text{cm})—signals that hard neuroscientific data will be integrated with psychological concepts.
  • Mention of “Study 1” hints the lecture series will interleave real research examples.

Story 1 – Phineas Gage & the Ventromedial Prefrontal Cortex (vmPFC)

  • Historical case (1848) demonstrating the link between frontal cortex and personality / “self.”
    • Gage: 25-year-old railroad foreman, previously quiet, conscientious, organized.
    • Accident: explosive blast drove a 3\,\text{ft} (\approx0.91\,\text{m}), 13\,\text{lb} (\approx5.9\,\text{kg}) iron tamping rod through left lower jaw → out of skull vertex.
    • Destroyed tissue: lower & medial frontal lobe → ventromedial prefrontal cortex (vmPFC).
  • Consequences
    • Survival: Lived 12 additional years → cerebral resilience.
    • Abilities intact: motor skills, memories, language, general intelligence.
    • Personality shift: became irritable, profane, irresponsible; incapable of crew management.
  • Significance
    • Early empirical evidence that discrete cortical regions govern social restraint, planning, moral judgment.
    • Prefigures modern neuropsychological findings on frontal-lobe injury, psychopathy, & decision science.

Story 2 – Hemispatial Neglect & the Parietal Cortex

  • Definition: “Hemispatial (unilateral) neglect” = failure to attend to stimuli on the side opposite a cortical lesion.
  • Typical cause: Stroke damaging the parietal lobe near the temporal border (gray region A; black focus spot).
  • Core symptomatology
    • Patient behaves as though left half of space does not exist.
    • Metacognitive deficit: often unaware of their own unawareness (anosognosia).
  • Illustrates that perception is an active, brain-constructed model—damage deletes half the model.

Story 3 – Patient H.M. & the Medial Temporal Lobes

  • Clinical background
    • Severe, life-threatening epilepsy; abnormal EEG discharges in both medial temporal lobes.
    • Surgical intervention at age 27: bilateral removal of hippocampus, amygdala, surrounding cortex (Scoville & Milner, 1957).
  • Post-operative profile
    • Preserved: general intelligence, language, personality, short-term/working memory (e.g., can rehearse a phone number).
    • Impaired: long-term declarative memory formation (anterograde amnesia). Material lost once attention shifts.
    • Retrograde span: intact childhood memories up to ~2 years before surgery; hence “stuck in 1953.”
    • Modern surgery: only one medial temporal lobe resected to avoid global amnesia.
  • Importance
    • Demonstrated the hippocampus is critical for consolidation of new episodic memories, not for storage of old ones.
    • Laid foundation for the multiple-memory-systems model (declarative vs procedural, explicit vs implicit).

Integrative Principle – Collaboration of Brain Areas

  • Perception, memory, and personality are distributed properties emerging from interaction among cortical & subcortical systems.
  • The three stories show that focal lesions → highly specific behavioral syndromes.
  • Debunks the popular myth that humans use only 10\% of their brain—we use 100\%, constantly.

Brain Plasticity & Everyday Experience

  • While extreme damage is rare, everyone experiences micro-level neural change:
    • Forming new memories, mood fluctuations, shifts in executive functions (focus, self-control).
  • Principle: “Brains are plastic.” Synaptic strength & circuit connectivity adapt to experience, environment, and endocrine state.
  • Goal of biological psychology: understand how neural structure & communication underlie behavior.

Nervous System Architecture – High-Level Overview

  • Four framing questions for the week:
    1. Major units of the nervous system.
    2. Anatomical brain organization (cortex vs subcortex).
    3. Cellular composition (neurons & glia).
    4. Intraneuronal machinery (ion channels, organelles).

Central (CNS) vs Peripheral (PNS) Nervous System

  • CNS = brain + spinal cord.
    • Protection: bony casing (skull, vertebrae) + meninges (dura, arachnoid, pia).
  • PNS = all neural elements outside bony casing.
    • Somatic PNS: voluntary skeletal muscle control.
    • Autonomic PNS: involuntary regulation of organs, glands, smooth muscle.

Somatic PNS Information Loop

  1. Sensory fibers carry environmental data → CNS.
  2. CNS integrates & decides.
  3. Motor fibers carry commands → muscles (voluntary & reflexive).
  4. Actions create new sensory input → cycle continues (perception–action loop).

Autonomic PNS – Two Functional “Presets”

  • Analogy: Instagram-like image filters that globally alter the “look” of physiological state.
Sympathetic Nervous System (SNS)
  • “Fight or Flight.”
    • Accelerates systems needed now (heart rate, respiration, glucose mobilization).
    • Inhibits expendable functions (digestion, growth, reproduction).
Parasympathetic Nervous System (PNS-para)
  • “Rest & Digest.”
    • Promotes relaxation, energy storage, routine maintenance.
    • Cultural meme: “not a phone in sight — just vibes.”

Endocrine Interface – Autonomic Extension

  • Neural commands are fast (<1\,\text{s}) via motor neurons; hormones modulate physiology over \text{minutes}–\text{hours}.
  • Example: Hypothalamic–Pituitary–Adrenal (HPA) axis during stress
    1. Brain (especially hypothalamus) perceives a stressor.
    2. Hypothalamus signals pituitary → releases ACTH.
    3. Adrenal glands secrete cortisol.
    4. Cortisol alters multiple systems—including brain circuits for memory & attention.
    5. Rising cortisol provides negative feedback: brain says “enough.”
    • Chronic stress can dysregulate detection & feedback, illustrating endocrine power and vulnerability.

Comparative & Developmental Neuroanatomy

  • CNS follows a conserved bauplan across vertebrates.
  • Data from Figure 3.6 (approximate averages):
    • Human: 1500\,\text{g}, 86\times10^9 neurons.
    • Chimpanzee: 380\,\text{g}, 28\times10^9 neurons (diverged \sim5-7 MYA).
    • Macaque: 87\,\text{g}, 6\times10^9 neurons (diverged 25-30 MYA).
    • Marmoset: 8\,\text{g}, 630\times10^6 neurons (diverged \sim35 MYA).
    • Mouse: 0.4\,\text{g}, 70\times10^6 neurons (rodent line diverged 75 MYA).
  • Growth ratios (human vs mouse):
    • Forebrain: \sim4\times larger proportional expansion.
    • Midbrain: \sim17\times.
    • Whole brain: \sim3800\times mass increase.

Cortex: Size & Wrinkling (Gyrification)

  • Surface area increases faster than skull volume → folding = more cortical sheet per volume.
  • Humorous slide comparison
    • Mouse: “smooth, cute, can’t think = no sad.”
    • Human: “bumpy, weird, ugly, thinks = sad!”
  • Take-home: wrinkling = computational capacity, not aesthetic defect.

Mammalian Brain Homology

  • Rodents and primates share all major structures and topological connectivity patterns.
  • Differences lie in scale and cortical complexity (e.g., granular prefrontal expansion in primates).
  • Supports use of animal models for translational neuroscience.

Next Class Preview

  • Deep dive into divisions & structures of the brain:
    • Cortical regions
    • Subcortical regions: limbic system, midbrain, hindbrain.
  • Inter-regional communication pathways (white matter tracts, neurotransmission).

Ethical, Philosophical & Practical Implications

  • How much of who we are is neurally generated vs socially constructed?
  • Medical ethics: balancing life-saving neurosurgery against potential identity/memory loss (e.g., H.M.).
  • Rehabilitation & legal systems must consider neurological injury in behavior and responsibility.

Key Terms & Concepts (Quick Reference)

  • vmPFC: Ventromedial Prefrontal Cortex – morality, planning, social behavior.
  • Hemispatial neglect: Perceptual unawareness of contralesional space.
  • Hippocampus: Declarative memory consolidation.
  • Plasticity: Experience-dependent neural change.
  • Somatic vs Autonomic PNS: Voluntary vs involuntary control.
  • SNS vs PNS-para: Emergency mobilization vs restorative mode.
  • HPA axis: Hypothalamus → Pituitary → Adrenal → Cortisol.
  • Gyrification: Folding of cortex to maximize surface area.