A stranger in half your body

An amazing study has just been published online in Consciousness and Cognition about a patient with epilepsy who felt the left half of his body was being “invaded by a stranger” when he had a seizure. As a result, he felt he existed in one side of his body only.

The research is from the same Swiss team who made headlines with their study that used virtual reality to make participants feel they were in someone else’s body, and one where brain stimulation triggered the sensation of having an offset ‘shadow body’ in patients undergoing neurosurgery.

The researchers suggest that having an integrated sense of our own bodies involves three types of perception: self-location – the area where we experience the self to be located; first-person perspective – the perceived centre of the conscious experience; and self-identification – the degree to which we identify sensations with our own bodies.

They report two case studies of patients with neurological disorders where self-identification goes haywire. This is the first:

Patient 1 is a 55 year old, left-handed male patient suffering from epilepsy since the age of 14 years. His simple partial sensorimotor seizures [where he remained ‘awake’ throughout] affected his left hand had been well controlled under anti-epileptic medication until the onset of paroxysmal episodes of vertigo 9 years before the current hospitalization.

At that time he additionally started to experience the following, highly stereotypical pattern of symptoms: without any prior warning he would first have the impression of an increasing pressure in the entire left hemi-body. This sensation increased progressively in strength leading eventually to the sensation that he was invaded by a stranger in his left hemi-body.

At this time he also sensed that the left half of his head, the upper part of his left trunk, his left arm and his left leg were no longer belonging to him (no misattribution), that these parts were disconnected from the rest of his body, and that his body was divided into two parts (Fig. 1A [see image above]). Sometimes this was followed by the impression that the left arm was moving unintentionally and would disappear behind the patient’s back. During these episodes he never experienced any deformation or other changes of his body or the environment.

Furthermore, no autoscopic hallucinations, no sensation of floating or disembodiment, no change in visuo-spatial or first-person perspective, no disturbance of language or vision and no loss of contact or consciousness were noted. During these sensations the patient localized the self as within the right side of his body (shown in grey in Fig. 1 [above]). He managed to remain calm and was able to continue standing, walking, and even give oral presentations while in front of audiences at work (surrounding persons usually did not notice his seizure manifestations). These simple partial seizures occurred on a daily basis and lasted about 1 min.

These sorts of cases are useful because they help us understand whether theories about the brain and its relation to our experience are realistic.

For example, one test of the idea that body self-consciousness has three components (self-location; first-person perspective; and self-identification) would be to see if there are any patients who show disturbances to only one of these experiences due to a neurological problem.

This patient shows exactly this, giving us some additional evidence that the three-component idea is useful. It is not the only evidence we need of course, but it is still makes an important contribution.
 

Link to PubMed entry for study.
Link to DOI entry.