Since the work of Steven Laureys’ team published in 2000 in The Lancet, we know that on a neuroanatomical level, consciousness particularly involves the activation of several nuclei in different areas of the association cortex, as well as thalamocortical loops, which consist of continuously ongoing neural signals between nuclei in the thalamus and neurons in all modular areas of the cortex. Consciousness seems to be indissociable from these feedback loops, which would appear to constitute a mechanism that increases attention allowing a given representation to enter into our conscious work space.

In 2006, an article by Nicholas Schiff from Cornell University (New York) was published in Nature. It informed us that the stimulation of the thalamus by implanted electrodes could be beneficial to patients in a minimally conscious state. “However, this invasive technique risks causing bleeding and infections”, Steven Laureys tells us. “Therefore, in the Coma Science Group, we decided to turn our attention to transcranial direct current stimulation (tDCS), a non-invasive method whose relevance had already been revealed in healthy subjects, where it improved attention, working memory and the language function.”

Healthy subjects were stimulated via two electrodes attached to their head, one positioned over the left prefrontal dorsolateral cortex and the other placed over the right supraorbital region. The Coma Science Group researchers chose the same two spots, since the electric stimulation distributed from these locations seemed to affect the regions previously defined as involved in the phenomenon of consciousness.

Signs of consciousness

Fifty-five patients in a vegetative state/unresponsive wakefulness syndrome or a minimally conscious state were administered tDCS for 20 minutes. Some of them were in a chronic phase, i.e. in a those states for more than three months after coming out of a coma; others were in an acute and subacute phase (less than three months). “Moreover, comas of both traumatic and non-traumatic origin (anoxia) were represented”, explains Steven Laureys.

During the first stage, researchers demonstrated the harmlessness of this type of stimulation. In particular, it didn’t cause epilepsy. The protocol of the actual experiment was double-blind placebo-controlled. The person leading the experiment, Aurore Thibaut, a physiotherapist and a doctoral student from the Coma Science Group, provided the stimulator with a code. Unaware of whether the code was activating the electrodes or not, this code determined whether or not the patients received a continuous current. Fort-eight hours passed between each session, at the end of which the codes were reversed for each patient so that those who had previously been stimulated, weren’t during the next session, and vice versa.

In each case, the patient’s state of consciousness was measured using a standardised tool, the Coma Recovery Scale-Revised (CRS-R), developed in the United Stated by Joseph Giacino’s team and validated in French by Caroline Schnakers, FNRS research associate at ULg, and by Steven Laureys. In total, four assessments were carried out on each patient: before and after the “real” stimulation, and before and after the “false” one (placebo).