Jan 27, 2008

Electrode implant stimulates consciousness

Researchers report in today's issue of Nature that they have improved brain function in a minimally conscious patient by implanting electrodes into his brain.

Schiff et al used deep brain stimulation (DBS), an experimental surgical technique that has previously been used to treat Parkinson's Disease and depression, to increase the level of arousal and motor control in the patient, who had been in a minimally conscious state for more than 6 years.

Neurologists define disorders of consciousness according to specific criteria based on behavioural responses. According to these criteria, levels of consciousness or arousal are thought of as existing in a continuum, from unconscious with eyes closed (coma), through unconscious with eyes open (the vegetative state) to conscious and intermittently responsive (the minimally conscious state).

The patient, a 38-year-old male, had been in a minimally conscious state for six and a half years following severe traumatic brain injury incurred during a violent attack. Since his injury, he occasionally tried to utter words and move his head, but was otherwise unable to communicate, and the doctors who performed the emergency surgery on him believed that he would not recover.

Neuroimaging studies had shown that although the patient sustained damage to much of his cerebral cortex, certain essential parts of the cortex remained intact. The researchers theorized that he had remained in the minimally conscious state because of an impairment in the brain's arousal system.

They therefore implanted the electrodes into the thalamus ("deep chamber"), which lies in the centre of the brain, and is involved in arousal, control of movements, and  relaying sensory information to the cerebral cortex. The thalamus is divided into a large number of nuclei, all of which contain a specific type of neuron. Little is known about the properties of these cells, but it is known that they project to diffuse areas of the cortex.

The researchers therefore reasoned that electrically stimulating these cells may activate the undamaged parts of the patient's cortex and lead to an improvement in his condition. Because the brain does not contain sensory receptors, implantation of the electrodes was completely painless

Within 2 days of having the electrodes implanted into his brain, the patient's condition had improved dramatically. He began opening his eyes for long periods of time, and responding to voices by turning his head in both directions.

In the months following the implantation, the researchers experimented to determine the most effective patterns of stimulation. During this time, the patient was able not only to name but also to use objects. He was, for example, capable of raising a cup to his mouth. He was also able to swallow food, so that he could be fed by mouth; beforehand, he was being fed via a tube inserted into his stomach.

To determine that it was the electrodes and not some other factor that led to an improvement in their patient's condition, the researchers then switched the electrical stimulation on and off periodically. They observed that the highest levels of arousal, as defined by the patient's ability to respond to his environment and perform limb movements, correlated with the stimulation. And, compared with before the surgery, some functions were improved during the periods at which there was no stimulation. This suggests that the stimulation had a beneficial carry-on even after the electrodes were switched off.

This is the first time that DBS has been used to treat such a condition, and the results provide a great deal of hope for a better prognosis for patients in the minimally conscious state. However, this study involved only one patient, so larger clinical trials are needed. And it is unlikely that such a treatment would be beneficial for patients who are in a persistent vegetative state or coma.