Cerebral Lobes and Cortical Areas

The cerebral cortex is the brain's folded outer sheet of grey matter, divided by major sulci into the frontal, parietal, temporal and occipital lobes, with the insula lying buried within the lateral sulcus. Within these lobes, smaller cortical areas defined by their cellular architecture and function carry out specialised roles in movement, sensation, language and higher cognition.

Definition

The cerebral lobes are the four (or five, counting the insula) anatomically defined regions of each cerebral hemisphere; cortical areas are subdivisions of the cortex distinguished by cytoarchitecture, connectivity and function, classically catalogued as Brodmann areas.

Scope

This topic covers the gross lobar organisation of the cerebral hemispheres, the principal functional regions within each lobe (such as primary motor, somatosensory, visual and auditory cortices and the association areas), and the architectonic mapping of cortex into numbered areas. It is anatomical and methodological reference material, not clinical guidance.

Core questions

• How are the cerebral hemispheres divided into lobes, and by which landmarks?
• What principal functional regions does each lobe contain?
• How is cortex parcellated into areas by cellular architecture, connectivity and function?

Key concepts

• Frontal, parietal, temporal and occipital lobes
• Insular cortex
• Primary versus association cortex
• Cytoarchitecture and Brodmann areas
• Functional localisation
• Hemispheric asymmetry and lateralisation
• Cortical parcellation

Mechanisms

The cortex is folded into gyri and sulci, and the deepest, most consistent sulci (the central and lateral sulci, the parieto-occipital sulcus) divide each hemisphere into lobes. Within the cortex, regions differ in the thickness and cellular composition of their six layers; Brodmann (1909) used these cytoarchitectonic differences to divide the cortex into numbered areas that align broadly with function, such as the primary motor (area 4) and primary visual (area 17) cortices. Beyond such primary areas, large expanses of association cortex integrate information and participate in distributed neurocognitive networks rather than single localised functions (Mesulam, 1990). Modern atlases parcellate the cortex automatically from MRI into named gyral regions (Desikan et al., 2006), and the two hemispheres show systematic structural and functional asymmetries (Toga & Thompson, 2003).

Clinical relevance

Lobar and cortical-area maps give a shared vocabulary for localising functions and describing where structural or imaging findings lie. This entry presents that anatomical framework for reference; it does not provide diagnostic criteria or treatment advice.

History

Gross lobar anatomy was established in classical anatomy, while the internal parcellation of cortex into areas is associated with Korbinian Brodmann, whose 1909 cytoarchitectonic map remains a reference framework. Twentieth-century work extended localisation into the concept of distributed association networks (Mesulam, 1990), and in-vivo MRI parcellation later made cortical regions measurable in individual brains (Desikan et al., 2006).

Debates

How sharply can the cortex be divided into discrete areas?

Cytoarchitectonic and functional boundaries do not always coincide, and individual brains vary, so whether cortex is best described as a mosaic of discrete areas or as graded transitions within networks remains an open framing question.

Key figures

• Korbinian Brodmann
• Marsel Mesulam
• Arthur Toga

Seminal works

• brodmann-1909
• mesulam-1990
• desikan-2006

Frequently asked questions

How many lobes does each cerebral hemisphere have?

Four are classically named — frontal, parietal, temporal and occipital — with the insula often counted as a fifth lobe lying hidden within the lateral sulcus.

What is a Brodmann area?

It is one of the numbered cortical regions Brodmann defined in 1909 on the basis of differences in the cellular architecture of the cortex; many correspond broadly to functional regions such as the primary motor or visual cortex.