The Sensory and Motor Cortices

Sensory cortical areas contribute to processing information from the senses; motor cortical areas contribute to planning and controlling movement. There are several sensory systems, so “sensory cortex” is a broader term than “somatosensory cortex”. Vision, hearing and bodily sensation do not all enter one cortical area.

The primary somatosensory cortex lies in the postcentral gyrus of the parietal lobe, behind the central sulcus. It contributes to processing bodily information such as touch and position sense. Its organisation is broadly somatotopic: different body regions have different cortical representations, with substantial representation of the hands and face.

Perception also depends on other cortical and subcortical systems. Pain, for example, should not be reduced to the activity of one spot on a sensory map. Reaching for an object combines visual information, bodily feedback and motor planning across connected regions.

Video: the primary somatosensory cortex

2-Minute Neuroscience: Primary Somatosensory Cortex — Neuroscientifically Challenged, by neuroscientist Marc Dingman. This animation locates the cortex behind the central sulcus and explains its body map and processing of bodily sensations.

The primary motor cortex lies in the precentral gyrus of the frontal lobe, in front of the central sulcus. Premotor and supplementary motor areas also contribute to movement. Cortical output travels through descending pathways and interacts with brainstem and spinal circuits; lower motor neurons ultimately activate skeletal muscles.

The motor cortex works with the basal ganglia, cerebellum and sensory systems. A movement is therefore not explained by a single cortical point switching a muscle on. Motor maps are useful approximations within a distributed system. See Neuroscience: The Primary Motor Cortex for the descending pathways and their connections.

Video: the motor cortex

2-Minute Neuroscience: Motor Cortex — Neuroscientifically Challenged, by neuroscientist Marc Dingman. A complementary explanation of motor maps, descending motor pathways and the distinction between primary motor, premotor and supplementary motor areas.

Wilder Penfield (1891–1976) was a neurosurgeon whose work helped map human cortical function during epilepsy surgery. He studied at Princeton and Oxford and received his medical degree from Johns Hopkins University in 1918. He and William Cone established the Montreal Neurological Institute in 1934. These details are documented by McGill University's Maude Abbott Medical Museum.

Penfield and colleagues used electrical stimulation during operations to identify responses and help preserve important functions. His contribution was part of a longer history of cortical research; it should not be described as the single-handed discovery of the somatosensory cortex. McGill's Penfield archive biography provides further historical detail.

A sensory or motor homunculus is a stylised body diagram illustrating relative cortical representation. Enlarged hands or lips represent the map's proportions, not the physical size or personal importance of those body parts. Sensory and motor maps answer different questions and should not be treated as interchangeable.

The familiar diagram is a simplified teaching aid. Boundaries and responses overlap, differ between individuals and depend on how they are measured. It is not a chart for locating a person's memories or emotions.

Sensory and motor anatomy helps practitioners distinguish a description of bodily experience from a claim about its cause. A client reporting tingling, tension or a changed body sensation has described an experience; the report alone does not identify a cortical lesion or demonstrate that a cortical map has changed.

Use observable descriptions in formulation and review records. New neurological symptoms require appropriate medical assessment rather than an interpretation based solely on an IEMT session.