Cerebral Hemispheres and Lobes
The cerebral hemispheres are the paired, convoluted masses that form the largest part of the human brain. Their outer mantle of gray matter, the cerebral cortex, is folded into gyri and sulci and is divided into frontal, parietal, temporal, and occipital lobes, with the insula lying buried within the lateral sulcus.
Definition
The cerebral hemispheres are the two halves of the telencephalon, each covered by the cerebral cortex and conventionally partitioned into frontal, parietal, temporal, and occipital lobes (plus the insula) by major sulci.
Scope
This topic covers the gross subdivision of the cerebrum into hemispheres and lobes, the layered and columnar microstructure of the cortex, and the broad functional regions associated with each lobe. It is reference anatomy, not clinical localization guidance for patient care.
Key concepts
- Frontal, parietal, temporal, and occipital lobes
- Gyri and sulci
- Six-layered neocortex
- Cortical columns
- Hemispheric lateralization
- Corpus callosum and interhemispheric connections
Mechanisms
The cortex is organized into horizontal laminae (classically six layers in the neocortex) and into vertical functional units. Mountcastle's microelectrode recordings in somatosensory cortex demonstrated that neurons in a vertical column share modality and receptive-field properties, leading to the columnar hypothesis of cortical organization that he later generalized. Lobes are demarcated by landmark sulci — the central sulcus separating frontal from parietal lobe, and the lateral sulcus bounding the temporal lobe — and the two hemispheres communicate principally through the corpus callosum.
Clinical relevance
Because functions such as voluntary movement, somatic sensation, vision, and language map onto particular lobes and regions, lobar anatomy informs how clinicians reason about the location of lesions. This entry is educational reference material and is not intended to guide individual diagnosis or treatment.
History
Brodmann's early twentieth-century cytoarchitectonic maps parcellated the cortex into numbered areas on the basis of cellular structure. Mid-twentieth-century single-unit physiology, especially Mountcastle's somatosensory recordings, established the functional column as a fundamental unit, reconciling architectural and functional views of the cortex.
Key figures
- Vernon Mountcastle
- Korbinian Brodmann
Related topics
Seminal works
- mountcastle-1957
- mountcastle-1997
Frequently asked questions
- How many lobes does each cerebral hemisphere have?
- Each hemisphere is conventionally divided into four lobes — frontal, parietal, temporal, and occipital — named after the overlying skull bones; the insula is sometimes counted as a fifth, hidden lobe.
- What connects the two cerebral hemispheres?
- The hemispheres are joined mainly by the corpus callosum, a large commissure of white-matter fibers, along with smaller commissures such as the anterior commissure.