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🧠Intro to Brain and Behavior

Major Brain Structures

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Why This Matters

When you're tested on brain structures, you're not just being asked to label a diagram—you're being asked to demonstrate that you understand how the brain organizes its work. The brain operates through specialization and integration: different structures handle different jobs, but they constantly communicate to produce unified behavior. Understanding this principle helps you predict what happens when specific areas are damaged and explains why certain functions cluster together.

Think of the brain as having distinct "levels" of operation: some structures keep you alive without any conscious effort, others process and route information, and still others enable the complex thinking that makes you you. As you study these structures, don't just memorize locations—know what functional category each belongs to and how it connects to behavior you can observe. That's what exam questions will really test.


Survival and Automatic Functions

These structures handle the processes you never have to think about—breathing, heart rate, body temperature, and basic drives. They operate largely outside conscious awareness and are evolutionarily ancient.

Brainstem

  • Controls life-sustaining functions—breathing, heart rate, blood pressure, and sleep-wake cycles happen here automatically
  • Three divisions (midbrain, pons, medulla oblongata) each handle specific relay and regulatory tasks
  • Damage is often fatal because these functions cannot be consciously overridden or compensated by other brain regions

Hypothalamus

  • Master regulator of homeostasis—controls hunger, thirst, body temperature, and circadian rhythms through feedback loops
  • Commands the endocrine system by directing the pituitary gland to release hormones, linking brain activity to body-wide changes
  • Drives motivated behaviors like eating, drinking, and sexual behavior—key for understanding biological bases of motivation

Compare: Brainstem vs. Hypothalamus—both maintain survival functions automatically, but the brainstem handles immediate life support (breathing, heartbeat) while the hypothalamus regulates longer-term needs (hunger, temperature, hormones). If asked about autonomic regulation, brainstem is your answer; for drives and hormones, go with hypothalamus.


Information Relay and Integration

These structures act as the brain's switchboard operators—they don't generate complex thoughts themselves but ensure information gets to the right place at the right time. Without them, sensory data would never reach conscious awareness.

Thalamus

  • The brain's relay station—almost all sensory information (except smell) passes through here before reaching the cortex
  • Filters and prioritizes incoming signals, playing a role in attention and what reaches conscious awareness
  • Regulates arousal states including sleep, alertness, and consciousness—damage can cause coma-like states

Corpus Callosum

  • Largest white matter structure—a thick band of 200+ million nerve fibers connecting left and right hemispheres
  • Enables hemispheric coordination so that information processed on one side can influence the other
  • Split-brain studies (when severed) reveal how the hemispheres specialize, a classic exam topic for lateralization

Compare: Thalamus vs. Corpus Callosum—both are relay structures, but the thalamus routes information vertically (from body/senses up to cortex), while the corpus callosum routes information horizontally (between hemispheres). Know which direction of communication each handles.


Emotion and Memory Systems

The limbic system structures work together to process emotional experiences and form lasting memories. These areas explain why emotional events are remembered better than neutral ones.

Amygdala

  • Emotional processing center—especially critical for detecting threats and generating fear responses
  • Tags memories with emotional significance, which is why frightening or exciting events stick with you
  • Influences decision-making by connecting emotional weight to choices—damage impairs social judgment and threat detection

Hippocampus

  • Essential for forming new explicit memories—without it, you cannot convert short-term experiences into long-term storage
  • Spatial navigation hub—contains "place cells" that create mental maps of your environment
  • Highly vulnerable to stress and neurodegenerative disease; often the first structure affected in Alzheimer's

Compare: Amygdala vs. Hippocampus—both are limbic structures involved in memory, but the amygdala handles emotional memory (remembering that something was scary) while the hippocampus handles declarative memory (remembering facts and events). Patient H.M., who had his hippocampus removed, could still form emotional memories but not new factual ones—a classic case study.


Movement and Motor Control

These structures ensure your movements are smooth, coordinated, and appropriately learned. Motor control involves multiple brain areas working in concert, not a single "movement center."

Cerebellum

  • Coordination and balance center—fine-tunes motor movements so they're smooth rather than jerky
  • Motor learning specialist—essential for acquiring skills like riding a bike or playing an instrument
  • Emerging cognitive role—research shows involvement in attention, language, and timing functions beyond movement

Basal Ganglia

  • Voluntary movement regulation—initiates and inhibits movements; dysfunction causes either too much movement (Huntington's) or too little (Parkinson's)
  • Habit formation hub—procedural memories and automatic routines are stored here
  • Reward processing connects to dopamine pathways, linking movement disorders to motivation and addiction research

Compare: Cerebellum vs. Basal Ganglia—both regulate movement but in different ways. The cerebellum coordinates and fine-tunes ongoing movements (damage causes ataxia—clumsy, uncoordinated motion). The basal ganglia initiate and select movements (damage causes tremors, rigidity, or involuntary movements). FRQs often ask you to distinguish these motor roles.


Higher Cognition and Executive Function

The cerebral cortex—especially the prefrontal region—handles what makes human thought distinctive: planning, reasoning, language, and self-control. These areas mature last developmentally and are most expanded in humans compared to other species.

Cerebral Cortex

  • The "thinking cap"—outermost layer responsible for perception, language, reasoning, and conscious experience
  • Four lobes with specialized functions: frontal (planning, movement), parietal (touch, spatial awareness), temporal (hearing, memory), occipital (vision)
  • Highly plastic—can reorganize after injury, especially in younger brains, demonstrating neuroplasticity principles

Prefrontal Cortex

  • Executive function headquarters—planning, decision-making, impulse control, and working memory all depend on this region
  • Last to fully develop—not mature until mid-20s, explaining adolescent risk-taking and impulsivity
  • Personality and social behavior are shaped here; famous case of Phineas Gage showed damage dramatically alters personality

Compare: Cerebral Cortex vs. Prefrontal Cortex—the prefrontal cortex is part of the cerebral cortex (specifically the front of the frontal lobe), but exam questions treat them differently. "Cerebral cortex" questions usually focus on the four lobes and sensory/motor processing. "Prefrontal cortex" questions focus on executive functions, personality, and development.


Quick Reference Table

ConceptBest Examples
Survival/Autonomic FunctionsBrainstem, Hypothalamus
Sensory RelayThalamus
Hemispheric CommunicationCorpus Callosum
Emotional ProcessingAmygdala
Memory FormationHippocampus
Motor CoordinationCerebellum, Basal Ganglia
Executive FunctionPrefrontal Cortex
Higher Cognition (General)Cerebral Cortex

Self-Check Questions

  1. Which two structures are both involved in memory but handle different types of memory? Explain what each contributes.

  2. A patient has damage that causes uncoordinated, jerky movements but can still initiate actions normally. Which structure is most likely affected—cerebellum or basal ganglia? Why?

  3. If sensory information from your hand never reaches conscious awareness, which relay structure has likely been damaged?

  4. Compare and contrast the hypothalamus and brainstem: What survival functions does each regulate, and how do their "time scales" of operation differ?

  5. An FRQ asks you to explain why teenagers often make impulsive decisions despite knowing the risks. Which brain structure and what developmental fact should anchor your response?