Somatotopi

Somatotopi, or somatotopy, is the orderly mapping of the body’s surface within the nervous system. It describes how different body parts are represented in specific neural structures, creating topographic maps that link anatomical location to a body region. The concept is foundational for both sensory and motor processing and is most famously illustrated by cortical body maps identified in the 20th century.

In the primary motor cortex (M1), the precentral gyrus contains a somatotopic map of voluntary movement, often depicted as the motor homunculus. Broadly, the legs are represented medially near the interhemispheric fissure, while the face and hands are represented laterally. The motor map is highly distorted and functionally interdependent, with representations overlapping and expanding for frequently used or precise motor actions. The map is dynamic and can reorganize after injury or training.

In the primary somatosensory cortex (S1) on the postcentral gyrus, the body is represented in a somatotopic map that corresponds to the surface of the body. S1 includes Brodmann areas 3, 1, and 2, and the sensory map tends to reflect the distribution of tactile and proprioceptive receptors. Compared with the motor map, the sensory representation is often more faithfully aligned with the body surface, though it varies among individuals and can be reshaped by experience.

Other parts of the nervous system also show somatotopy. The spinal cord’s dorsal columns organize information from the body's trunk and limbs into distinct fasciculi (gracile for the lower body, cuneate for the upper body). The thalamus (ventral posterior nuclei) and various brainstem and cerebellar regions exhibit their own somatotopic arrangements, contributing to integrated sensorimotor function.

Somatotopy underpins clinical localization, neurorehabilitation, and brain mapping, reflecting how the nervous system preserves body topology while supporting plasticity and learning.