Brain Ability to Discern Own Name Tests Consciousness Level

Daniel M. Keller, PhD

July 17, 2012

July 17, 2012 (Prague, Czech Republic) — With a decreasing level of consciousness, a person's ability to distinguish between self and nonself referential stimuli also decreased, with concomitant changes in activity in certain areas of the brain.

Reporting study results here for a group from her laboratory, Vanessa Charland-Verville, a neuropsychologist in the Coma Science Group at the Cyclotron Research Centre and Neurology Department at the University and University Hospital of Liège in Belgium, said that the researchers hypothesized that the perception of one's own name when spoken depends on the level of consciousness, as revealed by the activation of self-related brain areas.

"The aim of the study was to specifically focus on these self-related brain areas, so I will talk to you about the medial prefrontal cortex and the posterior cingulate cortex," she told the delegates here at the 22nd Meeting of the European Neurological Society (ENS). The idea was to look for residual brain activation in these areas when a self-related stimulus — the participant's name — was given.

To test the hypothesis, the researchers recruited 12 healthy volunteers (11 women) with a mean age of 24 years and scanned them using functional magnetic resonance imaging (fMRI) while they were in 4 clinical states — normal wakefulness, mild sedation, deep sedation, and the recovery of consciousness. Sedation was achieved using computer-controlled intravenous infusion after a 6-hour fast.

The stimuli were the participant's own name or 8 other familiar names, given by 2 different voices in 3 intonations. The different intonations were used to avoid habituation to the voices.

The stimuli were delivered in 16 randomized blocks — 8 of the participant's name and 8 of the other names — with a 20-second silent/rest period between each 25-second block. fMRI and 64-electrode electroencephalogram (EEG) nets recorded brain activity.

Charland-Verville reported that all the names activated auditory cortices in all stages of anesthesia, "but what is interesting [during wakefulness] is that compared to other names, the own name elicits a greater activation that you don't see with other names in the medial prefrontal cortex area as well as the posterior cingulate cortex...and the thalamus, which are as well implicated in this...internal awareness."

In states of mild sedation, there was still "a little bit of activation" in this self-related brain area, and during unconsciousness, all the activation disappeared. But there was still residual activity in the primary auditory cortices and superior temporal gyri with all the stimuli.

The researchers found a significant correlation between medial prefrontal cortex activation in response to one's own name vs a different name and the level of consciousness.

"The more you're awake, the more you activate the self-related brain areas," Charland-Verville said. "We see that the more the subjects are aware of themselves, the more you see activation in the medial prefrontal cortex."

The EEG results showed high-frequency activation in the beta band about 150 msec after a participant heard his or her own name during wakefulness. All of this activity disappeared in a state of unconsciousness under complete anesthesia.

Charland-Verville concluded that when the level of consciousness decreases in healthy volunteers, "so does the brain decrease its ability to differentiate between external or internal stimuli" on fMRI or EEG, equating one's own name with an internal stimulus.

She said these results may be helpful in working with patients with disorders of consciousness. At present, stimuli often elicit only motor responses, but fMRI and EEG may give more clues as to patients' levels of consciousness. The higher the level of consciousness, the more activity will be seen in the anterior cingulate cortex, which is part of the intrinsic awareness system.

Charland-Verville advised always using patients' first names when interacting with patients with altered levels of consciousness "because it's really attention grabbing, and it's really robust because you see that there is still residual activity in mild-sedation volunteers."

She maintained that one's own name "is highly emotional." So session chairman Jacques De Reuck, MD, PhD, asked her what would happen if the experimenter used the name of someone's mother-in-law.

Dr. De Reuck, retired head of the Department of Neurology at Ghent University in Belgium and now working in neuroimaging at Lille University in France, who did not participate in the study, commented to Medscape Medical News, "The decrease in level of consciousness indeed decreases the self-referential stimuli, which is quite important." He said this research group has demonstrated that in comatose patients, some mental activity still exists, "and this is certainly a further extension of those kind of studies."

When asked whether the results seen under propofol-induced deep sedation can be extrapolated to comatose patients, Dr. De Reuck said, "They could respond differently. That's true." He said he supposed the researchers will carry out such studies on comatose patients.

One's own name may not necessarily be the ideal stimulus. "I think that you could use other paradigms than self-naming, perhaps something which is more emotionally linked," he said. "I don't personally feel that your first name is so emotionally linked, and [there could be] some other things which are perhaps more important."

He sees the study as providing a good method to pursue further work in comatose patients, in those who had undergone trauma, in those in vegetative states, and in persons with locked-in syndrome.

The study received no outside funding. Charland-Verville and Dr. De Reuck have disclosed no relevant financial relationships.

22nd Meeting of the European Neurological Society (ENS). Abstract O-236. Presented June 10, 2012.