Our brain is made up of two hemispheres joined by a bundle of nerve fibers that make up the corpus callosum. Thanks to this structure both hemispheres can exchange information and, together with the action of other brain areas, we can be aware of our own body.

However, when this structure fails or is injured a rare disorder known as stranger’s hand syndrome can occur whereby the person is unable to control the movements of their own arm and hand which may be experienced as alien or even possessed.

What is the syndrome of the hand of others?

Also known as “strange hand syndrome”, “alien hand syndrome” or “Dr. Strangelove’s syndrome”, this strange disorder of neurological origin is distinguished by causing in the person who suffers it all kinds of involuntary and uncontrolled movements in one of the upper extremities .

In addition, another of the particularities of the syndrome of the hand of others is the sensation of strangeness that the person feels with respect to this extremity. That is, the patient experiences a personification of the arm and hand, which seem to have a life of their own .

The first time this syndrome was described was in 1908. The famous German doctor Kurt Goldstein discovered these strange symptoms in patients who had undergone a commissure. This intervention consists of making a cut in the corpus callosum and was typical of treatments for very serious epilepsies, with the aim of preventing such attacks from spreading from one brain hemisphere to another.

Clinical classification

There are two different types of foreign hand syndrome, which differ in terms of the causes and anatomical correlates of this syndrome.

1. Acute variant of the syndrome

One of the forms in which the syndrome manifests itself is the acute variant, which is due to damage to the corpus callosum that causes temporary changes in the supplementary motor area . It is hypothesized that this damage is due to hemispheric retraction during commissure.

This acute variant is characterized by more intense and exaggerated movements, but of short duration.

2. Chronic variant

The second form that the foreign hand syndrome takes is the chronic variant. This is caused by injury to the corpus callosum, as well as injury to the extra motor area, which is located in the medial frontal lobe.

What symptoms appear?

The clinical picture of foreign hand syndrome has two main symptoms. These symptoms are:

Dissociation

Sensation of dissociation of the affected limb. The person firmly believes that this arm is not part of his/her body and therefore cannot exercise any control over the movements of the body. However, tactile sensitivity is retained so that, although the person cannot control it, he or she can feel everything that happens to the limb.

Absence of movement control

The patient is not aware of the acts performed by the affected arm and hand . That is, the person is not aware when the limb is performing any kind of movement, no matter how complicated or exaggerated it is.

In many cases, the movements made by the limb considered to be foreign cause interference with the movements or actions performed by the healthy limb. In addition, this neurological disorder dissociates the intention of the action so that the impulses of the other hand are totally opposite to those of the healthy hand.

Context Influences

After observation of cases, it has been found that these “foreign limbs” tend to react in response to nearby stimuli such as flashing objects that are within their reach. Hence, it is hypothesized that the behaviour of these limbs is guided by contextual stimuli.

The intensity of the symptoms may vary in a fluctuating manner. In highly stressful or anxious situations , the clinical picture of someone else’s hand syndrome tends to increase in both quantity and intensity.

Eventually, these symptoms can lead to a large number of psychological and emotional side effects. This associated symptomatology can range from feelings of confusion and anxiety, to experiencing fear and panic attacks . However, the psychological consequences can vary greatly between patients since many of them learn to live with this type of disorder.

What causes it?

As mentioned above, the origin of foreign hand syndrome is found in a lesion of the corpus callosum . This structure is in charge of joining and transmitting information between both cerebral hemispheres, as well as making sure that both work in a coordinated way.

However, there is a lot of research that points to the idea that this syndrome cannot be explained by this type of injury alone, but that it is probably also due to some type of cortical damage or frontal lobe injury.

These brain injuries can be due to numerous incidents , such as tumour masses, brain aneurysms, head injuries or by brain surgery such as the aforementioned commissary.

What’s the diagnosis?

Because the syndrome of the hand of others has exclusively organic causes, its diagnosis is based almost exclusively on the elaboration of a clinical history and an exhaustive physical examination .

Tests that your doctor should perform for an effective diagnosis of this disorder include neuroimaging tests , such as computerized axial tomography (CT) or nuclear magnetic resonance (NMR) scans. These techniques allow the state of the nervous system and the severity of brain damage to be assessed.

Is there a treatment?

No effective treatment protocol has yet been developed for SHS. When this condition is caused by brain lesions associated with tumors or aneurysms, the treatment of these should decrease the symptoms of this syndrome .

However, symptomatic treatment for psychological symptoms can be performed. In addition, the patient can undergo training by which he or she can keep the affected limb occupied and thus reduce the amount of unwanted movements .