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Somatosensation

Somatosensation

The somatosensory system relays sensory information from the skin, mucous membranes, limbs, and joints. Somatosensation is more familiarly known as the sense of touch. A typical somatosensory pathway includes three types of long neurons: primary, secondary, and tertiary. Primary neurons have cell bodies located near the spinal cord in groups of neurons called dorsal root ganglia. The sensory neurons of ganglia innervate designated areas of skin called dermatomes.

Motor and Sensory Areas of the Cortex

Motor and Sensory Areas of the Cortex

The cerebral cortex, the brain's outermost layer, is pivotal in processing complex cognitive tasks, emotions, and various sensory inputs and executing voluntary motor activities. This intricate structure is divided into three primary functional areas: the motor areas, sensory areas, and association areas.
Motor Areas
The motor areas located in the frontal lobe are central to controlling voluntary movements. This region is further subdivided into the primary motor cortex and the premotor cortex.

Association Areas of the Cortex

Association Areas of the Cortex

Association areas are regions of the cerebral cortex that do not have a specific sensory or motor function. Instead, they integrate and interpret information from various sources to enable higher cognitive processes such as memory, learning, and decision-making. Some key association areas include the following:
Prefrontal Association Area: This area is located in the frontal lobe and is involved in planning, decision-making, and moderating social behavior. It connects with primary motor areas,...

Overview of Somatic Sensory Pathways

Overview of Somatic Sensory Pathways

Somatic sensory or somatosensory pathways refer to the neural pathways that carry information related to touch, pressure, pain, temperature, and proprioception from the skin, muscles, tendons, and joints to the brain. These pathways involve several stages of processing and integration of sensory information.
The somatosensory system is divided into three main pathways: the dorsal (or posterior) column-medial lemniscus, spinothalamic (or anterolateral), and spinocerebellar pathways.
The dorsal...

Direct Motor Pathways

Direct Motor Pathways

The direct motor pathways, also known as the pyramidal tracts, are a group of neural pathways that originate in the brain and descend through the spinal cord. They control the voluntary movement of the body. There are two major direct motor pathways: the corticospinal and the corticobulbar tracts.
The corticospinal tract is responsible for the voluntary movement of the limbs and trunk. It originates in the cerebral cortex of the brain and descends through the cerebrum's internal capsule and the...

Somatosensory, Motor, and Association Cortex

Somatosensory, Motor, and Association Cortex

The somatosensory cortex in the parietal lobes is crucial for interpreting sensory data such as touch, temperature, and proprioception. The somatosensory cortex, situated in the parietal lobes, plays a vital role in interpreting sensory information like touch, temperature, and proprioception—awareness of body position. This specialized brain region features an organized structure wherein neurons at the top primarily process sensations originating from the lower body. In contrast, those at the...

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Related Experiment Video

Updated: Jun 29, 2026

Measuring and Manipulating Functionally Specific Neural Pathways in the Human Motor System with Transcranial Magnetic Stimulation

Measuring and Manipulating Functionally Specific Neural Pathways in the Human Motor System with Transcranial Magnetic Stimulation

Published on: February 23, 2020

Somatotopy in the ipsilateral primary motor cortex.

Hatem Alkadhi¹, Gerard R Crelier, Sabina Hotz Boendermaker

¹Institute of Neuroradiology, University Hospital Zurich, Zurich, Switzerland.

|November 20, 2002

Summary

This summary is machine-generated.

Ipsilateral primary motor cortex (M1) activation during movements is inconsistent and less pronounced than contralateral M1 activation. Its occurrence depends on overall motor network activity.

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Area of Science:

Neuroscience
Motor Control
Brain Imaging

Background:

The role and reliability of ipsilateral primary motor cortex (M1) activation during voluntary movements remain debated.
Previous studies have yielded conflicting results regarding the presence and localization of this activation.

Purpose of the Study:

To re-examine the occurrence, reliability, and somatotopic organization of ipsilateral M1 activation.
To investigate the relationship between ipsilateral M1 activation and global motor network activity.

Main Methods:

Functional magnetic resonance imaging (fMRI) was used in 12 healthy volunteers.
Participants performed various movements including hand, finger, wrist, elbow, foot, and tongue movements across two sessions.

Main Results:

Ipsilateral M1 activation was inconsistently observed across all movements (e.g., 54% for hand, 17% for foot).
When present, ipsilateral M1 activation showed smaller volumes and lower t-values compared to contralateral M1.
Somatotopic organization was observed in the ipsilateral M1, mirroring the contralateral representation.
Ipsilateral M1 activation was significantly correlated with higher global activation levels in other motor areas.

Conclusions:

Ipsilateral M1 activation during voluntary movements is unreliable and less robust than contralateral activation.
The presence of ipsilateral M1 activation is contingent upon the overall level of motor network engagement.
Somatotopic mapping confirms a structured representation within the ipsilateral M1.