Primary Motor Cortex (Area 4)

Jared A. Nielsen, PhD

Key Facts

Location and Boundaries

Anterior surface of the central sulcus and superior portion of precentral gyrus
Caudal: Central sulcus
Rostral: Precentral gyrus

Function

Initiate voluntary body movements
Contralateral control of movement
Motor homunculus is somatotopic map of body represented in area 4

Structural Connections

Corticospinal tract: 1st tract in circuit that controls body muscles
Corticobulbar tract: 1st tract in circuit that controls face, mouth, and throat muscles
Corticopontine tract: 1st tract in circuit that communicates with cerebellum
Primary somatosensory cortex (areas 1, 2, 3) provides sensory input as feedback for motor output
Secondary somatosensory cortex (areas 5, 7) combines multimodal sensory information to inform motor output
Premotor and supplementary motor areas (area 6) plan motor output and execute complex motor tasks
Cerebellum and basal ganglia (via thalamus) are involved in motor learning and coordination

Area 4-Associated Disorders

Upper motor neuron syndrome results from injury (e.g., stroke or traumatic brain injury) to pyramidal neurons in primary motor cortex or the corresponding axons that project to the spinal cord
Amyotrophic lateral sclerosis
Phantom limb pain
Treatments include electrical stimulation, physical therapy, strength training, and pharmaceuticals

(Left) Coactivation map of the motor hand area shows that brain regions reliably activate with the hand motor function (seed region: × = −24, y = −32, z = 60) in over 4,000 studies from the NeuroSynth database.

(Right) Coronal and axial slices from a cytoarchitectonic map of primary motor cortex are shown. This quantitative probabilistic map was derived from postmortem human brains and is specific to cellular properties unique to area 4 (data source: SPM Anatomy toolbox).

LOCATION AND BOUNDARIES

Location

Anterior surface of the central sulcus and superior portion of precentral gyrus

Boundaries

Caudal: Central sulcus
Rostral: Precentral gyrus
Medial: Cingulate sulcus
Lateral: Lateral sulcus
Surrounded by primary somatosensory cortex (areas 1, 2, and 3), premotor cortex and supplementary motor area (area 6), superior parietal cortex (area 5), posterior cingulate cortex (area 31), and parainsular area (area 43)

FUNCTION

Movement

Initiate voluntary body movements
Contralateral control of movement
- For example, activity in left primary motor cortex results in right-sided body movement and vice versa
Motor homunculus
- Somatotopic map of body represented in area 4
- Body part maps overlap considerably
- Body parts may be represented in > 1 region