The supplemental motor area is a region located in the frontal lobe of the brain, in charge of functions such as the initiation, preparation and coordination of motor actions, as well as other processes related to language.

When a part of this brain area is removed or injured, supplemental motor area syndrome may occur. In this article we explain what it is and what are the main features of the motor supplemental area syndrome and the brain region that is affected by it. We also explain the clinical signs and symptoms it causes, and how to make a differential diagnosis of this disorder.

The supplementary motor area: characteristics, location and functions

To understand what Supplemental Motor Area Syndrome is, we must first look at the characteristics and main functions of such an important region of the brain as the supplemental motor area.

This brain region is located on the medial side of the frontal lobe . It extends, subsequently, to the primary motor cortex and, inferiorly, to the cingulate gyrus. It belongs to Brodmann area 6 and is part of the motor cortex, and more specifically, the secondary motor cortex (along with the premotor area).

The researchers have divided the supplementary motor area into at least two distinct parts: the budgetary motor area, which would be responsible for initiating movements in response to external and environmental stimuli; and the supplementary motor area itself, whose functions include managing the initiation of voluntary, internally generated motor sequences.

The supplementary motor area is, as we commented, a key region for initiating motor actions, but it also has an important role in the motivation necessary for movement to occur . This is also true of the processes involved in speech, since the activation of this area is also essential for initiating acts of verbal communication.

On the other hand, activation of the supplementary motor area occurs when complex motor sequences are carried out that require fine and precise movements (e.g. hand sewing or drawing). Moreover, several studies have shown that this area is also activated when we imagine that we are performing a particular movement, even if it is not carried out later.

In studies carried out with subjects who have suffered injuries in this brain area, it has been proven that when the damage occurs in the left supplementary motor area, a transcortical motor aphasia tends to occur, which is characterized by a deficit in the comprehension of language, both verbal and written , although, on the other hand, the patient maintains a certain verbal fluency.

Another disorder related to damage in this region of the brain and which we will discuss throughout the article is supplemental motor area syndrome. Let’s see what it is.

What is Supplemental Motor Area Syndrome?

Supplemental motor area syndrome is a disorder that results from surgical resection or injury to the brain region that bears its name . It was Laplane, who in 1977 described the clinical evolution of supplemental motor area syndrome in patients who had such resective surgery.

This researcher observed that the lesions in the supplementary motor area produced a characteristic syndrome that evolves in three stages:

1. After surgery and resection of the supplemental motor area

The patient, immediately after surgery and resection of the supplementary motor area, experiences global akinesia (more pronounced on the contralateral side) and arrests of speech .

2. A few days after recovery

The patient, a few days after recovery from surgery, experiences a severe reduction in spontaneous motor activity on the contralateral side, facial paralysis and reduced spontaneous speech .

3. Time after surgery

Some time after the resective surgery, the patient will have long term sequelae that include the alteration of fine and precise hand movements, such as alternating movements, especially in complex tasks.

Characteristics and main symptoms

The main characteristic of the syndrome of the supplementary motor area is its transitory character and its complete reversibility, which can occur in a period of time that is usually less than 6 months . The patient recovers the automatic movements before the volunteers, which is logical if we take into account that in the supplementary motor area the management of internally generated movements (without external stimulation) predominates over the motor actions initiated from external stimuli.

The patient’s recovery is based on the mechanisms of neuronal plasticity that facilitate the transfer of information from the supplementary motor area to its contralateral counterpart. However, the patient will experience clinical signs and symptoms that will last as long as it takes to complete recovery .

Supplemental motor area syndrome generates comorbid crises, which cause tonic postures including contralateral elbow flexion, arm abduction with external shoulder rotation, as well as cephalic and ocular deviation. These epileptic seizures usually last a few seconds (between 5 and 30) and are characterized by being quite frequent, without auras, with a sudden beginning and end, as well as predominating during the patient’s sleep and when vocalizing.

Transcortical motor aphasia occurs in practically all cases where the lesion is in the dominant hemisphere , and several studies have shown that most patients also present severe hemiparesis with motor neglect.

Language disorders in people with supplemental motor area syndrome have the following characteristics:

  • Hypofluent language, with dysnomia and slowness (caused by transcortical motor anomie).
  • Repetition and understanding are preserved.
  • Telegraphic language.
  • Rarely, parafasia occurs.
  • Occasionally, there can be echolalia and perseveration.

Differential diagnosis

The differential diagnosis of patients with supplemental motor area syndrome (SAMS) is usually made with people who present motor deficits in the immediate postoperative period and injuries of the corticospinal tract , which is characterized by an increase in muscle stretching reflexes, unlike what occurs in SAMS.

In some cases, the motor deficit could be considered as a motor neglect, rather than a hemiparesis , since many times verbal stimuli obtain a motor response from the affected brain. Recovery from SAMS includes the participation of the uninjured hemisphere, in which SAMS takes on a preponderant role in beginning to relearn movement.

Bibliographic references:

  • Krainik A et al. Postoperative speech disorder after medial frontal surgery. Role of the supplementary motor area. Neurology 2003; 60: 587-94.
  • Nachev, P., Kennard, C., & Husain, M. (2008). Functional role of the supplementary and pre-supplementary motor areas. Nature Reviews Neuroscience, 9(11), 856.
  • Rajshekhar, U. B. V. (2000). Síndrome del área motora suplementaria postoperatoria: características clínicas y resultado. British journal of neurosurgery, 14(3), 204-210.