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The four lobes: textbook vs a real cortex
The 4 lobes of the brain: textbook diagram vs a real cortex. Same colours, very different picture.
- The textbook draws 4 smooth lobes. A real cortex is folded: about two-thirds of its surface is hidden inside the folds (sulci). Seen straight from the side, only ~18% of this hemisphere's cortex is visible (measured on this brain).
- Only some borders are real grooves: the central sulcus (frontal | parietal) and the lateral fissure. On the side of the brain, the occipital border and the parietal | temporal border are imaginary lines drawn by anatomists.
- The insula, often called the hidden 5th lobe, lies completely under the lips (opercula) of the lateral fissure.
- Clinical: the temporal lobe is the commonest source of focal epilepsy, and in ~80% of temporal lobe epilepsy the seizures start on its hidden inner (mesial) side, most often from hippocampal sclerosis.
- No two brains fold the same, not even the two hemispheres of one brain.
Sources and licence
Data: the 7 T MRI of one volunteer (Lüsebrink et al., Sci Data 2021, CC0): his FreeSurfer pial surface, with FreeSurfer DKT parcels grouped into lobes. The "textbook" shape is our smoothing of the same surface, not a scan; the 3D model is shown in the colours of our viewer. Facts: Van Essen & Drury, J Neurosci 1997; Kucukyuruk et al. 2012 and Flores 2002 (lobe borders); Radiopaedia (insula); StatPearls (mesial temporal lobe epilepsy); Téllez-Zenteno & Hernández-Ronquillo 2012.
Video licence: CC BY 4.0. To reuse it, credit “Cerebrarium (Aldo Spolaore)”, link to this page and name the data sources above.
Educational content, not medical advice.
