Cognitive Connie

Understanding brain structure & organisation

The human brain is the most complex biological structure known. Weighing approximately 1.4 kg and containing around 86 billion neurons, it is organised into a hierarchy of regions that collaborate to produce sensation, movement, memory, language, and thought.

Key figures

Franz Josef Gall

1758–1828

Anatomist who made early contributions to understanding the cortical localisation of brain function, though his broader system (phrenology — inferring mental traits from skull shape) was pseudoscientific. His core insight that different brain regions serve different functions anticipated modern neuroscience.

Paul Broca

1824–1880

French surgeon who, in 1861, linked damage to the left inferior frontal gyrus (now "Broca's area") to loss of speech production in patients who retained language comprehension. Provided the first rigorous anatomical evidence for functional localisation in the human cortex.

Wilder Penfield

1891–1976

Canadian neurosurgeon who electrically stimulated the cortex of awake patients during epilepsy surgery, systematically mapping the sensory and motor homunculi — the cortical representations of body regions on the primary somatosensory and motor strips.

Key concepts

Cerebral hemispheres

The two symmetrical halves of the cerebrum (left and right), separated by the longitudinal fissure and connected by the corpus callosum. Each hemisphere controls the contralateral (opposite) side of the body. While largely mirror images anatomically, the hemispheres show functional lateralisation — particularly for language (predominantly left) and visuospatial processing (predominantly right).

Cerebral cortex

The thin (2–4 mm) outer layer of neural tissue that forms the surface of the cerebrum. The cortex is highly folded (gyrification) to pack a large surface area (~2,500 cm²) into the skull. It consists of six layers of neurons and is divided into four lobes. The cortex is responsible for conscious perception, voluntary movement, language, reasoning, and memory.

Frontal lobe

The largest cortical lobe, occupying the anterior third of the brain. Contains the primary motor cortex (voluntary movement), premotor and supplementary motor areas (movement planning), and the prefrontal cortex (executive functions, decision-making, working memory, personality). Broca's area — critical for speech production — is located in the left inferior frontal gyrus.

Parietal lobe

Located behind the frontal lobe, posterior to the central sulcus. Contains the primary somatosensory cortex (body sensation) and the parietal association cortex, which integrates sensory information to support spatial awareness, attention, and the sense of body position (proprioception). Damage to the right parietal lobe can produce hemispatial neglect — ignoring the left side of space.

Temporal lobe

Located on the lateral surface below the lateral fissure (Sylvian fissure). Processes auditory information (primary auditory cortex), and contains Wernicke's area (left temporal lobe, language comprehension), the fusiform face area (face recognition), and the parahippocampal cortex. The hippocampus and amygdala are located within the medial temporal lobe.

Occipital lobe

The most posterior lobe, dedicated primarily to visual processing. Contains the primary visual cortex (V1, striate cortex) and multiple visual association areas that process colour, motion, form, and object recognition. Lesions cause specific visual deficits such as cortical blindness (V1 damage) or prosopagnosia (inability to recognise faces, fusiform area damage).

Corpus callosum

The largest white matter commissure, a band of approximately 200 million axons connecting corresponding areas of the left and right hemispheres. Enables rapid interhemispheric communication. When severed (split-brain surgery, or callosotomy, once used for epilepsy), the two hemispheres operate independently, producing striking dissociations famously studied by Roger Sperry and Michael Gazzaniga.

Cerebellum

A large, cauliflower-shaped structure at the posterior base of the brain. Although it contains only ~10% of brain volume, it houses over 50% of all neurons. Critical for the coordination, timing, and fine-tuning of movement, as well as procedural learning and balance. Damage produces ataxia — uncoordinated, unsteady movements. Modern research also implicates the cerebellum in cognitive functions including language and timing.

Brainstem

The stalk-like structure connecting the cerebral hemispheres and cerebellum to the spinal cord. Consists of the midbrain, pons, and medulla oblongata. Controls life-critical autonomic functions (breathing, heart rate, blood pressure), sleep-wake cycles, and relays sensory and motor signals between brain and body. Most cranial nerves originate here. Damage to the brainstem is often fatal.

Sulci and gyri

The grooves (sulci, singular sulcus) and ridges (gyri, singular gyrus) of the cerebral cortex. Gyrification expands the cortical surface area by approximately threefold, allowing more neurons to be packed into the limited space of the skull. Some sulci are consistent across individuals (e.g., central sulcus, lateral sulcus) and serve as anatomical landmarks dividing the cortical lobes.

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Brain Divisions

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Frontal lobeParietal lobeTemporal lobeOccipital lobeCerebellumBrainstem

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Brain Anatomy & Function

10 questions · ~12 min · Beginner

AmygdalaCerebellumBasal ganglia

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Brain Structure & Organisation — Flashcards

Self-test on key terms. 10 cards to work through.

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Frequently asked questions

Why does the brain have so many folds (gyri and sulci)?+

Folding (gyrification) allows a very large surface area of cortex to fit inside the skull. The human cortex has a surface area of roughly 2,500 cm² — about the size of a large pizza — but can fold to fit within a skull of ~1,400 cm³. A flat, unfolded cortex of the same area would require a much larger skull, which would create problems for childbirth and upright locomotion. The degree of gyrification correlates broadly with brain complexity: smooth-brained (lissencephalic) mammals such as rats have small cortices, while highly gyrified (gyrencephalic) brains like those of humans, dolphins, and elephants have proportionally larger cortices.

Is the left brain really "logical" and the right brain "creative"?+

This is a popular myth that oversimplifies genuine hemispheric differences. The "left brain = logical, right brain = creative" characterisation comes partly from real findings in split-brain patients (Roger Sperry's Nobel Prize-winning work) and from stroke research showing different deficits from left vs right hemisphere damage. The left hemisphere does show specialisation for language, sequential processing, and fine motor control for the right hand. The right hemisphere shows advantages in visuospatial processing, holistic perception, and prosody (the emotional tone of language). However, virtually all complex cognitive tasks — including creative and analytical thinking — involve both hemispheres working together through the corpus callosum. Imaging studies consistently show bilateral activation for reasoning, music, and creative tasks.

Sources

Last reviewed July 2025

1.
Kandel, E. R., Schwartz, J. H., Jessell, T. M., Siegelbaum, S. A., & Hudspeth, A. J. (2021). Principles of Neural Science (6th ed.). McGraw-Hill.
+About this source
Comprehensive reference for brain structure and organisation, cortical lobes, hemispheres, cerebellum, and brainstem.
2.
Bear, M. F., Connors, B. W., & Paradiso, M. A. (2020). Neuroscience: Exploring the Brain (4th ed.). Jones & Bartlett Learning.
+About this source
Undergraduate neuroscience textbook covering gross brain anatomy, sulci and gyri, and major brain regions.
3.
Penfield, W., & Rasmussen, T. (1950). The Cerebral Cortex of Man: A Clinical Study of Localization of Function. Macmillan.
+About this source
Foundational clinical mapping of the motor and sensory homunculi through direct cortical stimulation during epilepsy surgery.