Difficulty: Introductory to Intermediate | Prerequisites: Basic understanding of neurons and the nervous system (Ch. 2–3 recommended).
This chapter covers the physical structure of the brain, from the spinal cord up through the brain stem, cerebellum, and forebrain to the cerebral cortex. It is the foundation for nearly everything else in the course: once you understand which brain regions handle which functions, topics like memory, learning, emotion, and psychopathology slot into place. You should already have a basic sense of what neurons do and how they communicate. The chapter also introduces neuroplasticity, the idea that the brain rewires itself in response to experience, injury, and the environment.
The brain is a collection of specialised regions, not one uniform organ. Lower structures (brain stem, cerebellum) handle survival basics and motor coordination; mid-level structures (hypothalamus, thalamus, hippocampus, amygdala, basal ganglia) manage drives, sensory gating, memory, and emotion; the cerebral cortex handles higher thought, planning, and conscious experience. The brain remains plastic throughout life, rewiring itself through experience, and new neurons can even be generated in the hippocampus.
Phrenology
The early 19th-century practice of assessing personality traits and mental abilities by measuring bumps on the skull. In simple terms, people once believed head shape revealed character. It was wrong, but it pushed the field toward localising brain function.
Equipotentiality
The (now discredited) idea that the cortex contributes equally to all mental abilities. Think of it as the old belief that every part of the brain does the same job.
Broca's area
A region on the front left side of the brain involved with speech production. It was the first strong evidence that the brain contains specialised functional areas.
Brain stem
The thickened top of the spinal cord that controls breathing, swallowing, vomiting, urination, and orgasm. In simple terms, it keeps the body's automatic survival functions running. Electrically stimulating it can cause an anaesthetised animal to walk.
Reticular formation
A network of neurons in the brain stem that projects into the cerebral cortex and controls arousal and sleep. Think of it as the brain's on/off switch for wakefulness.
Cerebellum
Latin for "little brain." Uniform in cellular organisation but its different parts serve different functions because of differences in origin. Involved in motor learning, balance, empathy, language planning, and remembering events. Works unconsciously.
Ataxia
Clumsiness and loss of motor coordination resulting from damage to the cerebellum.
Forebrain
Consists of the cerebral cortex and the sub-cortical regions (the limbic system). Important for controlling basic drives such as eating, emotions, and higher thought.
Limbic system
Sub-cortical structures that form a "border" (the literal meaning of "limbic") between the older cerebellum/brain stem and the cerebral cortex. Controls basic drives and emotions.
Hypothalamus
Regulates vital functions including body temperature, bodily rhythms, blood pressure, and glucose levels. Also drives thirst, hunger, aggression, and lust. Controls the pituitary gland. In simple terms, it is the master regulator of the body's internal environment and basic motivational drives.
Thalamus
The gateway to the cortex. All incoming sensory information (except smell) must pass through it before reaching the cortex. During sleep, the thalamus shuts the gate on incoming sensations.
Hippocampus
Essential for memory, particularly spatial memory and the arrangement of things. Grey matter in the hippocampus appears to grow with use (London taxi drivers have enlarged hippocampi). Think of it as the brain's filing clerk for new memories.
Amygdala
Connects the cerebral cortex and hypothalamus by linking primitive emotional pathways with new associations, connecting memories with emotions to potentially override instinctive responses. Plays a significant role in eliciting fear and interpreting emotional facial expressions. Also involved in sexual arousal.
Basal ganglia
Important for planning and producing movement. Receives input from the cerebral cortex and projects to motor centres via the thalamus. Damage can range from tremors to Parkinson's and Huntington's disease. Also involved in habit learning.
Nucleus accumbens
A structure important in experiencing rewards. These reward responses can be influenced by nurture (e.g. viewing an expensive sports car).
Cerebral cortex
The outer layer of the brain, roughly the size of a newspaper when unfolded. The site of most higher functions, from thought to consciousness. Divided into two hemispheres connected by a massive bridge of millions of axons (the corpus callosum), with four lobes in each hemisphere.
Occipital lobe
Devoted to vision. Contains the primary visual cortex (PVC). Visual information is represented in a way that preserves spatial relationships. The right side processes information from the left visual field and vice versa.
Parietal lobe
Devoted to touch. Contains the primary somatosensory cortex. Also very important for spatial relationships between the self and objects. Damage to the right parietal lobe can cause hemineglect.
Somatosensory homunculus
Literally "little man." A map of the body's sensory representation in the parietal lobe, where neurons for nearby body parts (e.g. finger and palm) are physically close together in the cortex. The more an area is used, the more cortical surface it occupies.
Hemineglect
A condition (usually from stroke damage to the right parietal region) where patients neglect the left side of their body and even the left side of their mental imagery.
Temporal lobes
Contain the primary auditory cortex and specialised visual areas for recognising faces and detailed objects. Also important for memory (hippocampal formation and amygdala are housed here). The fusiform face area is involved in face recognition.
Fusiform face area
A region in the temporal lobe involved in recognition of faces. Some argue it is really about recognition in any area of expertise, not faces exclusively.
Frontal lobes
Essential for planning and movement. Contain the primary motor cortex, which projects directly to the spinal cord to move the body's muscles. Works contralaterally (right hemisphere controls left side and vice versa).
Prefrontal cortex (PFC)
Occupies about 30% of the human brain. Indispensable for rational and directed activity. Where we contemplate our own existence, follow cultural norms, and consider what others are thinking. Its complexity (not size alone) is what differentiates human sophistication.
Orbitofrontal cortex
Located behind the eyes, within the prefrontal cortex. Especially important for personality, emotion, and impulse control. Damage leads to loss of social awareness. The case of Phineas Gage demonstrated this: after a pole destroyed much of his orbitofrontal cortex, he became profane, immature, and inefficient.
Plasticity (neuroplasticity)
The brain's ability to be malleable and constantly changing. It can determine which parts are underused or overused and adjust accordingly. Our brains continue to adapt throughout life based on experience. In simple terms, the brain rewires itself.
Hebbian learning
"Neurons that fire together wire together." A pattern of firing is made more likely to recur, leading us to recall an event. Repetition of an action also helps encode memory.
Neurogenesis
The process of generating new neurons in the brain, occurring primarily in the hippocampus. Contrary to the older belief that we never replace neurons. Memories initially held in the hippocampus are transferred to the cerebral cortex. Social status in animals appears to affect neurogenesis rates.
Stem cells
Master cells able to regenerate themselves and develop into any type of tissue. Could potentially be used to treat Parkinson's or Huntington's. The purest forms are embryonic, which raises ethical considerations.
Knowledge that the brain controls thought dates back to Roman gladiators receiving head injuries
Phrenology (19th century) attempted to map the mind through skull bumps
Rat lesion studies tested whether the brain acts as a whole or in parts
Equipotentiality was disproved; we now know the brain consists of many highly specialised areas
Broca's area provided the first strong evidence of functional specialisation
Modern brain imaging has revolutionised our ability to study consciousness and mental processes
A rope of neural tissue running from the pelvis to the brain
Made up of grey matter (neurons) and white matter (axons and fatty sheaths)
Capable of both relaying information and acting on its own
All muscles have stretch receptors (dendritic tips of neurons with cell bodies in the spinal cord) that detect changes in length, triggering a contraction reflex
The spinal cord thickens and becomes the brain stem
Controls breathing, swallowing, vomiting, urination, orgasm, and reflexes of the head (gagging, eye and ear sensations)
Electrically stimulating the brain stem can cause an anaesthetised animal to walk
Contains the reticular formation, a network of neurons that projects into the cerebral cortex and controls arousal and sleep
Uniform in cellular organisation, but different parts have different effects due to differences in origin
Involved in motor learning, balance, empathy, language planning, and remembering events
Works unconsciously
Damage causes ataxia (clumsiness, loss of motor coordination), possible personality changes, lack of normal emotional responses, and greater likelihood of mental disorders
Hypothalamus: regulates body temperature, rhythms, blood pressure, glucose; drives thirst, hunger, aggression, lust; influences motivation via brain projections; controls the pituitary gland and therefore the endocrine system; sex differences in the anterior hypothalamus (half the size in homosexual men compared to heterosexual men, roughly the same size as in women); fetal masculinisation experiments in rats produced male-like hypothalami in females
Thalamus: gateway to the cortex for all senses except smell; during sleep, shuts the gate on incoming sensations
Hippocampus: essential for memory and spatial arrangements; grey matter grows with use (London taxi drivers have enlarged hippocampi); neurogenesis occurs here
Amygdala: connects cerebral cortex and hypothalamus via emotional pathways; links memories with emotions to override instinctive responses; major role in fear, interpreting fearful facial expressions, and sexual arousal; over-excitation in the amygdala and hippocampus can lead to epileptic seizures (1–3% of the population)
Basal ganglia: planning and producing movement; receives input from the cerebral cortex, projects to motor centres via thalamus; damage causes tremors, rigidity, Parkinson's, Huntington's; involved in habit learning (e.g. looking both ways before crossing a street)
Nucleus accumbens: experiencing rewards; reward responses can be shaped by nurture
Occipital lobe: devoted to vision; primary visual cortex (PVC) preserves spatial relationships; right side processes left visual field; surrounding areas process colour, motion, and form
Parietal lobe: devoted to touch; primary somatosensory cortex maps the body (somatosensory homunculus); important for spatial relationships; right parietal damage causes hemineglect (patients neglect the left side of their body and even their mental imagery)
Temporal lobes: primary auditory cortex (left hemisphere decodes words and sentences); specialised visual areas for recognising faces and objects; contains hippocampal formation and amygdala; fusiform face area involved in face recognition (possibly recognition expertise more broadly)
Frontal lobes: primary motor cortex projects to the spinal cord; works contralaterally; supplemented by nearby regions
Prefrontal cortex (PFC): about 30% of the human brain; indispensable for rational, directed activity; complexity (not size) is what matters; where we contemplate our existence, behave according to cultural norms, think about others' thoughts
Orbitofrontal cortex: personality, emotion, impulse control; damage leads to loss of social awareness; lobotomy targeted this area; Phineas Gage case demonstrated the effects of orbitofrontal damage
The brain is extremely malleable and constantly changing
The environment affects not only the products of DNA activity but also DNA activity itself
Early in development, cells moved from one brain area to another will develop as if they naturally belong there
Chemical gradients guide axon connections and tell neurons what to become
Critical periods exist: kittens with eyes stitched closed at birth never develop visual connections (does not occur in adults)
Enriched environments produce larger brains (rats with toys vs. shoe boxes)
Learning occurs throughout life through rewiring, but decreases in old age
All memories consist of physical changes in the brain
Hebbian learning: "fire together, wire together" – co-activation of neurons strengthens their connection; patterns of firing become more likely to recur; repetition of an action aids memory encoding
Neurogenesis: new neurons are generated in the hippocampus, contrary to the old belief that the brain cannot replace neurons; memories initially held in the hippocampus are transferred to the cerebral cortex; social hierarchy affects neurogenesis (dominant animals produce more neurons); neurogenesis may slow age-related decline and explain plasticity
The homunculus model: the more an area is used, the more cortical surface it occupies (but distraction during stimulation blocks this growth)
Phantom limbs: patients sometimes feel stimulus from a missing limb, suggesting the brain has not fully reorganised; stimulating the cheek may produce phantom limb sensations because the somatosensory homunculus places the cheek near the hand
Prosthetic limb control via neural signals has been demonstrated in monkeys (tracking neurological firings to control a robotic arm)
After cortical injury, surrounding grey matter can assume the function of the damaged area
This reorganisation is much more prevalent in children (hemispherectomy for epilepsy: children can regain most function)
Stem cells could potentially regenerate damaged brain or spinal cord tissue
The purest stem cells are embryonic, requiring fetal cells, which raises ethical objections
England set the rule at 14 days (before twins can split or a nervous system forms)
The concept of neuroplasticity underlies modern rehabilitation after strokes and brain injuries: therapists design exercises that encourage the brain to reroute functions through undamaged tissue. Prosthetic limb research relies directly on brain-computer interfaces that read motor cortex signals, allowing patients to control robotic arms with their thoughts.
Students often think the brain is "fixed" after childhood. It is not. Plasticity continues throughout life, though it is strongest in early development.
Students confuse the thalamus and the hypothalamus. The thalamus is a sensory relay station (gateway to the cortex). The hypothalamus is the master regulator of drives, body temperature, and the endocrine system.
Students assume that equipotentiality is correct, that all parts of the cortex do the same thing. The evidence since Broca's area has consistently shown functional specialisation.
Students think neurogenesis means the entire brain regenerates. Neurogenesis occurs primarily in the hippocampus, not everywhere.
⚠️ Know the four lobes and what each one does (occipital = vision, parietal = touch/spatial, temporal = auditory/faces/memory, frontal = planning/movement).
⚠️ Be able to distinguish between the hypothalamus (drives, homeostasis, pituitary control) and the thalamus (sensory relay, sleep gating). Smell bypasses the thalamus.
⚠️ Understand the Phineas Gage case and what it demonstrates about the orbitofrontal cortex (personality, impulse control, social awareness).
⚠️ Hebbian learning ("fire together, wire together") is a common exam concept. Know the phrase and what it means for memory.
⚠️ Understand what neurogenesis is, where it occurs (hippocampus), and why it was a surprising discovery (it contradicted the old belief that neurons are never replaced).
⚠️ Know the somatosensory homunculus and the concept of hemineglect.
True or False: The thalamus relays all sensory information to the cortex, including smell. (False. Smell bypasses the thalamus.)
Fill in the blank: The principle that "neurons that fire together wire together" is called __________ learning. (Hebbian)
True or False: Equipotentiality is the accepted modern view of brain function. (False. The brain consists of many specialised areas.)
Fill in the blank: The condition in which patients neglect the left side of their body after right parietal damage is called __________. (Hemineglect)
True or False: Neurogenesis occurs throughout the entire brain. (False. It occurs primarily in the hippocampus.)
Q: What is Broca's area, and why is it historically significant?
A: Broca's area is a region on the front left side of the brain involved with speech. It is significant because it provided the first strong evidence that the brain contains functionally specialised areas, disproving equipotentiality.
Q: Describe the role of the hypothalamus. Why is it considered a "master regulator"?
A: The hypothalamus regulates body temperature, bodily rhythms, blood pressure, and glucose levels. It also drives thirst, hunger, aggression, and lust. It controls the pituitary gland, which releases hormones into the bloodstream, influencing nearly every system in the body.
Q: Explain the difference between classical conditioning of fear and the role of the amygdala in innate fear responses.
A: The amygdala plays a role in both. It elicits innate fear responses (evolved to protect from danger) and is implicated in fear conditioning (learning to fear a previously neutral stimulus). It connects memories with emotions, allowing learned associations to override instinctive responses.
Q: What does the Phineas Gage case tell us about the orbitofrontal cortex?
A: Gage survived a pole driven through his head that damaged his orbitofrontal cortex. Afterwards, he became profane, immature, and inefficient, demonstrating that the orbitofrontal cortex is critical for personality, emotion regulation, impulse control, and social awareness.
Q: Explain Hebbian learning and neurogenesis as two mechanisms by which the brain encodes memory.
A: Hebbian learning operates on the principle that neurons that fire together wire together, strengthening connections through repeated co-activation. Neurogenesis is the generation of new neurons in the hippocampus, where memories are initially retained before being transferred to the cerebral cortex. Both contribute to the brain's plasticity and its ability to form and maintain memories.
This material connects directly to Chapter 6 (Learning and Reward), where the amygdala's role in fear conditioning and the limbic system's involvement in motivation and reward become central. It also connects to Chapter 7 (Memory), where the hippocampus, frontal lobes, and the concept of consolidation are explored in depth. Understanding brain structure here makes Chapter 13 (Mental Disorders) more concrete, as many disorders are linked to dysfunction in specific brain regions (e.g. prefrontal cortex in depression, basal ganglia in OCD, dopamine pathways in schizophrenia).
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