Behavioral Neuroscience at a Glance

Domain 1 -- Brain Structure and Function

Organizational principles

The brain is organized both hierarchically (brainstem handles basic survival, cortex handles higher cognition) and laterally (left hemisphere is typically dominant for language, right for spatial processing and emotional prosody). Damage at any level produces specific, predictable deficits.

Major structures

Cerebral cortex. The wrinkled outer layer, ~2-4 mm thick, containing roughly 16 billion neurons. Divided into four lobes:

Prefrontal cortex (PFC). The most anterior part of the frontal lobe. Critical for executive functions: planning, inhibition, working memory, cognitive flexibility, and social behavior. The case of Phineas Gage (1848) -- an iron rod through his left frontal lobe transformed a responsible foreman into an impulsive, socially inappropriate man -- provided early evidence for PFC's role in personality and self-regulation.

Limbic system. A circuit of interconnected structures deep within the brain:

• Amygdala -- fear conditioning, threat detection, emotional memory. Lesions produce Kluver-Bucy syndrome (absence of fear, oral exploration of objects). LeDoux (1996) identified two pathways: a fast "low road" (thalamus to amygdala, rapid threat response) and a slow "high road" (thalamus to cortex to amygdala, deliberate evaluation).
• Hippocampus -- memory consolidation (transfer from short-term to long-term memory), spatial navigation. Patient H.M.'s bilateral hippocampal removal produced severe anterograde amnesia. London taxi drivers show enlarged posterior hippocampi (Maguire et al., 2000).
• Hypothalamus -- homeostatic regulation: hunger, thirst, temperature, circadian rhythms, hormonal control via the pituitary gland. The four F's: feeding, fighting, fleeing, and mating.

Basal ganglia. Subcortical nuclei (caudate, putamen, globus pallidus) involved in motor control, procedural learning, and reward processing. Degeneration of dopaminergic neurons in the substantia nigra causes Parkinson's disease (tremor, rigidity, bradykinesia).

Cerebellum. "Little brain" at the posterior base. Coordinates voluntary movement, balance, motor learning, and (increasingly recognized) cognitive functions including timing, prediction, and language processing. Contains more neurons than the rest of the brain combined.

Brainstem. Midbrain, pons, and medulla. Controls vital functions: breathing, heart rate, sleep-wake cycles, arousal. The reticular activating system (RAS) in the brainstem regulates overall cortical arousal.

Lateralization

• Left hemisphere -- language production (Broca's area) and comprehension (Wernicke's area) in ~95% of right-handers, sequential processing, analytical reasoning
• Right hemisphere -- spatial processing, face recognition, emotional prosody, holistic processing, musical perception

Split-brain studies (Sperry, 1968; Gazzaniga, 1967) in patients with severed corpus callosum revealed that the two hemispheres can operate independently, each with its own perceptions, memories, and even personality traits.

Domain 2 -- Neurotransmitter Systems

Neurotransmitters are chemical messengers released at synapses. They bind to receptors on the postsynaptic neuron, producing excitatory or inhibitory effects. The same neurotransmitter can have different effects at different receptor subtypes.

Major neurotransmitter systems

Synaptic transmission

The sequence: (1) action potential reaches axon terminal, (2) calcium influx triggers vesicle fusion, (3) neurotransmitter released into synaptic cleft, (4) binds postsynaptic receptors, (5) produces excitatory or inhibitory postsynaptic potential, (6) terminated by reuptake, enzymatic degradation, or diffusion.

Drugs alter behavior by modifying this process: agonists enhance transmission (by mimicking, increasing release, or blocking reuptake), antagonists reduce it (by blocking receptors or inhibiting release).

Domain 3 -- Neural Plasticity

The brain is not hard-wired. It changes structurally and functionally in response to experience, injury, and development. Plasticity is the biological basis of learning, memory, and recovery from brain damage.

Synaptic plasticity

Long-term potentiation (LTP). Bliss and Lomo (1973) discovered that brief high-frequency stimulation of a neural pathway produces a long-lasting increase in synaptic strength. LTP at hippocampal synapses requires NMDA receptor activation and is widely regarded as a cellular mechanism of learning and memory. The key properties -- input specificity, associativity, and cooperativity -- map onto the properties of associative learning.

Long-term depression (LTD). The complementary process: low-frequency stimulation produces a long-lasting decrease in synaptic strength. LTD enables forgetting and the weakening of unused connections, preventing saturation.

Neurogenesis

New neurons are generated in the adult brain, primarily in the hippocampal dentate gyrus and the subventricular zone (Eriksson et al., 1998). Adult hippocampal neurogenesis is enhanced by exercise, enriched environments, and learning, and suppressed by stress and depression. Its functional significance is debated but likely involves pattern separation in memory.

Critical periods

Hubel and Wiesel (1962) showed that monocular deprivation during a critical period in kitten development permanently altered visual cortex organization. The deprived eye lost cortical territory to the open eye (ocular dominance plasticity). Critical periods exist for language acquisition, binocular vision, and emotional attachment. After the critical period closes, the same experience produces much weaker plastic change.

Experience-dependent plasticity

The brain's structure reflects its owner's experience:

• Musicians show enlarged auditory cortex and motor cortex areas corresponding to their instrument (Schlaug et al., 1995)
• London taxi drivers show enlarged posterior hippocampi proportional to years of navigating (Maguire et al., 2000)
• Braille readers show expansion of somatosensory cortex for the reading finger (Pascual-Leone & Torres, 1993)
• Phantom limb pain reflects cortical reorganization after amputation (Ramachandran & Rogers-Ramachandran, 1996)

Domain 4 -- Psychopharmacology

Drug action mechanisms

Tolerance and dependence

• Tolerance -- decreasing effect with repeated administration. Mechanisms: receptor downregulation, metabolic changes.
• Physical dependence -- withdrawal symptoms upon cessation. The withdrawal syndrome is often the opposite of the drug's acute effects (e.g., alcohol withdrawal produces hyperexcitability).
• Psychological dependence -- compulsive drug-seeking behavior driven by reward circuitry (mesolimbic dopamine pathway). Robinson and Berridge's (1993) incentive-sensitization theory: addiction involves sensitized "wanting" (dopamine) dissociated from "liking" (opioid/endocannabinoid).

Major drug classes and psychological effects

Cross-References

• james agent: The mind-body problem, pragmatic integration of biological and psychological explanations, and the historical roots of behavioral neuroscience in James's Principles of Psychology.
• kahneman agent: Neural correlates of System 1 and System 2 processing, dopamine's role in reward prediction error, and the neuroscience of decision-making.
• cognitive-psychology skill: The cognitive processes (attention, memory, perception, language) whose neural substrates this skill describes.
• clinical-foundations skill: Neurobiological basis of psychopathology and pharmacological treatment mechanisms.
• developmental-psychology skill: Brain development across the lifespan, critical periods, and the interaction of maturation and experience.
• research-methods-psych skill: Neuroimaging methodology (fMRI, EEG, PET, lesion studies) as research tools.

References

• Bliss, T. V. P., & Lomo, T. (1973). Long-lasting potentiation of synaptic transmission in the dentate area of the anaesthetized rabbit following stimulation of the perforant path. Journal of Physiology, 232(2), 331-356.
• Eriksson, P. S., et al. (1998). Neurogenesis in the adult human hippocampus. Nature Medicine, 4(11), 1313-1317.
• Hubel, D. H., & Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. Journal of Physiology, 160(1), 106-154.
• LeDoux, J. E. (1996). The Emotional Brain. Simon & Schuster.
• Maguire, E. A., et al. (2000). Navigation-related structural change in the hippocampi of taxi drivers. Proceedings of the National Academy of Sciences, 97(8), 4398-4403.
• Robinson, T. E., & Berridge, K. C. (1993). The neural basis of drug craving: An incentive-sensitization theory of addiction. Brain Research Reviews, 18(3), 247-291.
• Sperry, R. W. (1968). Hemisphere deconnection and unity in conscious awareness. American Psychologist, 23(10), 723-733.