Supplementary motor area

Details
Synonyms
Pronunciation
Carnegie stage
Days
Precursor
Gives rise to
Part of

The supplementary motor area (SMA) is a part of the cerebral cortex that contributes to the control of movement. It is located on the medial surface of the frontal lobe, anterior to the primary motor cortex and superior to the cingulate cortex.

Anatomy

The SMA is divided into two regions: the pre-SMA and the SMA proper. The pre-SMA is located more anteriorly and is involved in higher-order aspects of motor control, such as the planning and initiation of movement. The SMA proper is located more posteriorly and is involved in the execution of movement sequences.

Function

The SMA plays a crucial role in the planning and coordination of complex movements. It is particularly involved in the initiation of movements that are internally generated rather than triggered by external stimuli. The SMA is also implicated in the coordination of bimanual movements, where both hands are used simultaneously.

Connections

The SMA has extensive connections with other motor-related areas of the brain. It receives input from the prefrontal cortex, which is involved in higher cognitive functions, and the parietal lobe, which processes sensory information. The SMA sends output to the primary motor cortex, which directly controls voluntary movements, and to the basal ganglia and cerebellum, which are involved in the regulation of movement.

Clinical Significance

Damage to the SMA can result in a variety of motor deficits. One common condition associated with SMA damage is akinesia, a lack of voluntary movement. Patients may also experience difficulty in initiating movements or in performing complex motor tasks. In some cases, SMA damage can lead to alien hand syndrome, where one hand acts independently of conscious control.

Research

Recent research has focused on the role of the SMA in motor learning and the reorganization of motor functions following brain injury. Studies using functional magnetic resonance imaging (fMRI) have shown that the SMA is activated during the learning of new motor skills and that it may play a role in the recovery of motor function after a stroke.

See also

• Primary motor cortex
• Premotor cortex
• Basal ganglia
• Cerebellum
• Frontal lobe