The cerebral cortex is folded into a complex pattern of ridges (gyri) and grooves (sulci) that is broadly conserved across humans but varies in detail from one brain to the next. The major sulci define the lobes; the minor sulci and gyri within each lobe define the functional subregions. Knowing this surface anatomy is essential for interpreting MRI scans, for localizing lesions, for understanding the patterns of cortical syndromes, and for any serious discussion of higher cortical function. A patient with a small infarct in the foot of the central gyrus has a different deficit from a patient with a small infarct in the inferior frontal gyrus, and the bedside difference is intelligible only if the underlying anatomy is intelligible.

This page covers the macroscopic anatomy of the cerebral hemispheres: the four classical lobes plus the insula and limbic regions, the major sulci that define them, the major gyri within each lobe, and the functional significance of each subregion. The cytoarchitecture (Brodmann areas, layered cortex) and the underlying white matter pathways are covered on dedicated pages.

The Major Sulci

Three sulci dominate the lateral surface of the brain and define the boundaries of the four classical lobes:

• Central sulcus (of Rolando): runs roughly from the superior medial surface downward and forward toward the lateral sulcus. Separates the frontal lobe (anterior) from the parietal lobe (posterior). The cortex immediately anterior is the primary motor cortex (precentral gyrus); the cortex immediately posterior is the primary somatosensory cortex (postcentral gyrus).
• Lateral sulcus (of Sylvius): deep horizontal groove on the lateral surface, running from the orbital region backward and slightly upward. Separates the temporal lobe (below) from the frontal and parietal lobes (above). The insula lies within its depth.
• Parieto-occipital sulcus: best seen on the medial surface, running from the superior border downward to meet the calcarine sulcus. Separates the parietal lobe (anterior) from the occipital lobe (posterior). On the lateral surface, the parieto-occipital boundary is arbitrarily drawn from the parieto-occipital sulcus down to the preoccipital notch.

The medial surface also features the cingulate sulcus, separating the cingulate gyrus from the rest of the medial cortex, and the calcarine sulcus, separating the cuneus (above) from the lingual gyrus (below) — both highly relevant for the limbic and visual systems.

The Frontal Lobe

The frontal lobe occupies about a third of the cerebral cortex. It extends from the central sulcus posteriorly to the frontal pole anteriorly, and from the medial surface (cingulate sulcus) downward to the orbital surface above the eye sockets. Major subdivisions:

Precentral Gyrus (Primary Motor Cortex)

The strip of cortex immediately anterior to the central sulcus. Contains the primary motor cortex (Brodmann area 4), with a topographic map of contralateral body movements — the motor homunculus, with the face at the lateral end (near the lateral sulcus), the hand and arm in the middle, and the foot at the medial end (extending onto the medial surface as the paracentral lobule). The face, hand, and tongue occupy disproportionately large cortical territory, reflecting the precision of voluntary movement in these regions.

Superior Frontal Gyrus

The most superior gyrus of the lateral frontal surface, running from the precentral gyrus to the frontal pole. Contains the supplementary motor area on its medial extension, important for motor planning, bimanual coordination, and movement initiation.

Middle Frontal Gyrus

The middle of the three lateral frontal gyri. Contains the frontal eye field posteriorly (which generates contralateral saccades) and dorsolateral prefrontal cortex anteriorly (executive function, working memory, set-shifting, abstraction).

Inferior Frontal Gyrus

The most inferior gyrus on the lateral frontal surface, subdivided into pars opercularis (most posterior), pars triangularis, and pars orbitalis (most anterior). The pars opercularis and pars triangularis in the dominant hemisphere together constitute Broca area (Brodmann areas 44 and 45), the principal motor speech area. Lesions here produce non-fluent (Broca) aphasia.

Orbitofrontal Cortex

The inferior surface of the frontal lobe, sitting above the orbits. Involved in social judgment, emotional regulation, impulse control, and decision-making. Lesions produce disinhibition, emotional lability, and the personality changes classically described in Phineas Gage.

Medial Frontal Cortex

Including the anterior cingulate, the supplementary motor area, and the medial prefrontal regions. Mediates motivation, drive, and the initiation of action. Lesions produce abulia, akinetic mutism, and (with bilateral involvement) urinary incontinence and gait apraxia — the classical features of normal pressure hydrocephalus and bifrontal disease.

The Parietal Lobe

The parietal lobe lies behind the central sulcus and above the lateral sulcus, extending posteriorly to the parieto-occipital sulcus. Major subdivisions:

Postcentral Gyrus (Primary Somatosensory Cortex)

The strip of cortex immediately posterior to the central sulcus. Contains the primary somatosensory cortex (Brodmann areas 3, 1, 2), with a topographic map of contralateral body sensation — the sensory homunculus, with proportions similar to the motor homunculus (face, hand, and lips disproportionately large; trunk and proximal limbs compressed).

Superior Parietal Lobule

Above the intraparietal sulcus. Involved in spatial attention, sensorimotor integration, and the planning of movements toward visually guided targets.

Inferior Parietal Lobule

Below the intraparietal sulcus, subdivided into:

• Supramarginal gyrus: wraps around the end of the lateral sulcus. In the dominant hemisphere, involved in language (conduction aphasia from lesions here) and ideomotor apraxia.
• Angular gyrus: posterior to the supramarginal gyrus, surrounding the end of the superior temporal sulcus. In the dominant hemisphere, involved in reading, writing, calculation, and Gerstmann syndrome.

Non-Dominant Parietal Lobe

The right parietal lobe (in most people) is the seat of spatial attention. Lesions produce the classical right hemisphere syndrome: left neglect, extinction, anosognosia, constructional apraxia, dressing apraxia. The non-dominant parietal lobe is one of the most clinically distinctive cortical regions in neurology.

The Temporal Lobe

The temporal lobe lies below the lateral sulcus, extending forward to the temporal pole and back to merge with the parietal and occipital lobes. Major subdivisions:

Superior Temporal Gyrus

Contains the primary auditory cortex on its superior surface (Heschl’s gyrus) — Brodmann areas 41 and 42 — and the auditory association cortex on the lateral surface. The posterior portion in the dominant hemisphere constitutes Wernicke area, the principal language comprehension area. Lesions here produce fluent (Wernicke) aphasia.

Middle Temporal Gyrus

Inferior to the superior temporal gyrus. Involved in language comprehension, semantic memory, and (in its posterior portion) motion processing (area MT/V5).

Inferior Temporal Gyrus

The most inferior of the lateral temporal gyri. Involved in visual object recognition; lesions can produce visual agnosia, prosopagnosia (with bilateral involvement), and visual semantic deficits.

Medial Temporal Lobe

Includes the hippocampus, the entorhinal cortex (the gateway to the hippocampus), the amygdala (anterior), and the parahippocampal gyrus. This is the seat of episodic memory and emotional processing. Bilateral medial temporal lesions produce dense anterograde amnesia (as in the famous patient H.M.). The hippocampus is also exquisitely vulnerable to anoxic-ischemic injury, herpes simplex encephalitis, and the pathology of Alzheimer disease.

Fusiform Gyrus

On the inferior surface of the temporal lobe, extending forward from the occipital lobe. Contains the fusiform face area (FFA), critical for face recognition. Bilateral lesions produce prosopagnosia.

The Occipital Lobe

The occipital lobe is the most posterior division. Its major function is vision. Major subdivisions:

Calcarine (Striate) Cortex

Lies along the calcarine sulcus on the medial surface — Brodmann area 17, the primary visual cortex (V1). Has a topographic map of the contralateral visual field, with the macula disproportionately represented at the occipital pole. Damage produces homonymous hemianopia, often with macular sparing (because the macular representation has dual blood supply).

Extrastriate Cortex

The visual association cortex (Brodmann areas 18, 19) surrounds the primary visual cortex. Different regions process different aspects of vision: V2, V3, V4 (color), V5/MT (motion), the lateral occipital complex (objects), the fusiform face area, the parahippocampal place area. Lesions here produce specific visual agnosias.

Cuneus and Lingual Gyrus

The cortex above (cuneus) and below (lingual gyrus) the calcarine sulcus. The cuneus processes lower visual field; the lingual gyrus processes upper visual field. The classical “upper homonymous quadrantanopia” can result from lingual gyrus lesions (the “pie in the floor” complement to Meyer’s loop’s “pie in the sky”).

The Insula

The insula lies buried within the lateral sulcus, covered by the opercula of the frontal, parietal, and temporal lobes. It is sometimes called the fifth lobe. It is involved in:

• Visceral and autonomic function: the anterior insula has been called the “interoceptive cortex,” processing internal body signals.
• Taste: primary gustatory cortex sits at the insular operculum.
• Pain and emotional processing: the insula is reliably activated by painful stimuli and by emotional experience.
• Cardiovascular regulation: insular lesions can produce arrhythmias, including atrial fibrillation, and contribute to autonomic instability after stroke.

Insular strokes produce variable syndromes including isolated dysarthria, taste abnormalities, swallowing difficulty, autonomic instability, and (with right insular involvement) cardiac arrhythmias.

The Cingulate Gyrus

The cingulate gyrus runs along the medial surface of the hemisphere, wrapping around the corpus callosum. It is the principal cortical component of the limbic system. Subdivided into:

• Anterior cingulate: involved in motivation, error detection, conflict monitoring, autonomic control. Lesions can produce abulia and akinetic mutism.
• Mid-cingulate: involved in motor control and pain processing.
• Posterior cingulate: involved in self-referential processing, autobiographical memory, and the default mode network. Often involved early in Alzheimer disease.
• Retrosplenial cortex: spatial navigation and memory.

The Functional Cortical Map: A Bedside Synthesis

The functional map of the cortex translates anatomical localization into clinical syndromes:

Lateralization

The two hemispheres have many overlapping functions but several important asymmetries:

• Language: dominant (usually left) hemisphere. Broca, Wernicke, arcuate fasciculus, angular gyrus, supramarginal gyrus all participate in language. Right-handers have left-hemisphere language dominance in about 95%; left-handers in about 70%, with 15% right-dominant and 15% bilateral.
• Spatial attention: non-dominant (usually right) hemisphere. The right hemisphere attends to both sides of space; the left attends mostly to the right. This asymmetry explains why left neglect from right-hemisphere lesions is far more common than the reverse.
• Praxis: dominant hemisphere. Ideomotor apraxia is a left parietal syndrome; the right hemisphere is less involved in skilled movement programming.
• Music processing, prosody, emotional comprehension: non-dominant hemisphere predominantly.

🔍 Did You Know?

The cerebral cortex covers about 2,500 square centimeters if unfolded — roughly the area of a square yard of fabric. Only about a third of this is visible from the outside; the remaining two-thirds is buried in the depths of the sulci. The folded arrangement allows the cortex to fit within the skull while preserving the enormous surface area required for cortical computation. Comparisons of cortical surface area between healthy adults reveal substantial individual differences, but the broad pattern of gyrification is highly conserved, allowing reliable use of major landmarks (central sulcus, lateral sulcus, calcarine sulcus) across patients.

Pitfalls and Pearls

• The central sulcus separates frontal from parietal lobes. Motor cortex is in front of it; sensory cortex behind.
• Broca area is in the dominant inferior frontal gyrus, specifically the pars opercularis and triangularis. Lesions produce non-fluent aphasia with preserved comprehension.
• Wernicke area is in the dominant posterior superior temporal gyrus. Lesions produce fluent aphasia with impaired comprehension and unawareness.
• The right (non-dominant) parietal lobe is the seat of spatial attention. Lesions produce the syndromes of left neglect, extinction, anosognosia, constructional apraxia.
• Bilateral medial temporal lesions produce dense anterograde amnesia. Unilateral lesions are usually less dramatic but specifically impair verbal memory (left) or visuospatial memory (right).
• Homonymous hemianopia with macular sparing localizes to the calcarine cortex; the macular representation has dual blood supply (MCA and PCA).
• The insula is often missed because it is buried in the lateral sulcus. Insular strokes can present with atypical syndromes including dysarthria with autonomic instability.
• The motor and sensory homunculi have similar proportions, with face, hand, and lips disproportionately large. The “foot” representation extends onto the medial surface as the paracentral lobule.
• The frontal eye fields produce contralateral saccades. Acute frontal stroke causes the eyes to deviate toward the side of the lesion (away from the side of the hemiparesis).
• Bilateral medial frontal lesions produce the triad of abulia, gait apraxia, and urinary incontinence — the classical NPH-like syndrome.

References

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