Physiological Basis of Behavior

Neurotransmitters in Behavior - Chemical Mind Messengers

• Synaptic chemical messengers modulating mood, cognition, sleep, appetite, and behavior.
• Key Neurotransmitters & Functions:
  • Dopamine (DA): Reward, motivation, motor. Implicated in addiction, Parkinson''s (↓DA), Schizophrenia (↑DA).
  • Serotonin (5-HT): Mood, sleep, appetite, anxiety. ↓ linked to depression. SSRIs target.
  • Norepinephrine (NE): Alertness, arousal, stress response.
  • Acetylcholine (ACh): Learning, memory, muscle. ↓ in Alzheimer''s.
  • GABA (γ-aminobutyric acid): Main inhibitory NT. Reduces anxiety, excitability. Benzodiazepines act here.
  • Glutamate: Main excitatory NT. Learning, memory (LTP).
  • Endorphins: Pain relief, pleasure.
• NT imbalances are central to many psychiatric/neurological disorders.

  ⭐ The mesolimbic dopamine pathway is critical for reward processing and addiction.

Motivation & Reward Systems - Drive, Desire, Dopamine

• Motivation: Process initiating, guiding, and maintaining goal-oriented behaviors.
  • Drives: Internal tension states (e.g., hunger, thirst) pushing an organism to satisfy a physiological need and restore homeostasis.
• Reward System: Neural network reinforcing behaviors essential for survival and pleasure.
  • Key Structures: Ventral Tegmental Area (VTA), Nucleus Accumbens (NAc), Prefrontal Cortex (PFC).
  • Primary Neurotransmitter: Dopamine (DA); crucial for reward prediction, motivation ("wanting"), not just pleasure ("liking").
• Mesolimbic Pathway: VTA → NAc. Central to reward, motivation, and addiction.
  • DA release in NAc reinforces behaviors leading to reward.

⭐ The mesolimbic pathway (VTA to NAc) is critical for reward processing; dopamine here drives 'wanting' (motivation) more than 'liking' (pleasure).

• Desire: The subjective experience of "wanting," strongly mediated by DA release in anticipation of reward.
• Clinical Links: Dysregulation implicated in addiction (compulsive drug seeking), anhedonia in depression. 📌 Dopamine = Desire & Drive.

Sleep & Circadian Rhythms - Rest, Reset, Repeat

• Sleep Architecture: Cyclical pattern of NREM & REM sleep; ~90-120 min cycles.

  • NREM (Non-Rapid Eye Movement) Sleep:
    • N1: Light sleep; theta waves.
    • N2: Deeper; sleep spindles, K-complexes.
    • N3: Slow-wave sleep (SWS); delta waves; restorative.
  • REM (Rapid Eye Movement) Sleep: Paradoxical sleep; beta/alpha waves, muscle atonia, dreaming, memory consolidation. 📌 EEG Waves: Beta (awake/REM), Alpha (relaxed), Theta (N1), Spindles/K-complexes (N2), Delta (N3).

• Circadian Rhythm Regulation:

  • Suprachiasmatic Nucleus (SCN) of hypothalamus: Master biological clock.
  • Light (via retinohypothalamic tract) → SCN → ↓Pineal Melatonin.
  • Melatonin: ↑ in darkness, promotes sleep.
  • Orexin (Hypocretin): From lateral hypothalamus; promotes wakefulness. Deficiency → Narcolepsy.

⭐ Narcolepsy is characterized by excessive daytime sleepiness, cataplexy, hypnagogic/hypnopompic hallucinations, and sleep paralysis; often due to ↓orexin.

Learning, Memory & Emotions - Brain's Adaptive Toolkit

• Learning: Acquiring new info/behaviors.
  • Types: Associative (Classical, Operant Cond.), Non-associative (Habituation, Sensitization).
  • Key sites: Hippocampus, Amygdala, Cerebellum.
• Memory:
  • Process: Encoding → Storage → Retrieval.
  • Types: Sensory (brief), STM/Working Memory (capacity: 📌 Miller's Law 7±2 items), Long-Term (LTM).
  • LTM: Explicit (declarative: facts/events; Hippocampus), Implicit (non-declarative: skills/habits; Cerebellum, Basal Ganglia).
  • Consolidation: STM to LTM (Hippocampus crucial).
  • LTP (Long-Term Potentiation): Synaptic strengthening (Hebb's rule).

    ⭐ LTP in the hippocampus, involving NMDA & AMPA receptors, is a key mechanism for learning and memory.

• Emotions: Limbic System (key).
  • Amygdala: Fear, aggression, emotional memory.
  • Prefrontal Cortex (PFC): Emotional regulation.
• Stress Response: HPA axis (Cortisol), SNS (Adrenaline).

High‑Yield Points - ⚡ Biggest Takeaways

• Limbic system (amygdala, hippocampus, hypothalamus) is crucial for emotion, memory, and motivation.
• Key neurotransmitters: Dopamine (reward), Serotonin (mood, sleep), Norepinephrine (arousal), GABA (inhibition).
• Hypothalamus regulates homeostasis (hunger, thirst, temperature) and circadian rhythms (via SCN).
• Sleep: REM features dreaming, muscle atonia, paradoxical EEG; NREM is for restoration.
• Stress response involves the HPA axis (cortisol) and sympathetic nervous system (adrenaline/noradrenaline).
• Addiction is driven by dopaminergic reward pathways, notably the mesolimbic system.