Corazzol M, Lio G, Lefevre A, Deiana G, Tell L, André-Obadia N, Bourdillon P, Guenot M, Desmurget M, Luauté J, Sirigu A. Restoring consciousness with vagus nerve stimulation. Curr Biol. 2017 Sep 25;27(18):R994-R996.
Patients lying in a vegetative state present severe impairments of consciousness caused by lesions in the cortex, the brainstem, the thalamus and the white matter. There is agreement that this condition may involve disconnections in long-range cortico-cortical and thalamo-cortical pathways. Hence, in the vegetative state cortical activity is 'deafferented' from subcortical modulation and/or principally disrupted between fronto-parietal regions. Some patients in a vegetative state recover while others persistently remain in such a state. The neural signature of spontaneous recovery is linked to increased thalamo-cortical activity and improved fronto-parietal functional connectivity. The likelihood of consciousness recovery depends on the extent of brain damage and patients' etiology, but after one year of unresponsive behavior, chances become low. There is thus a need to explore novel ways of repairing lost consciousness. Here we report beneficial effects of vagus nerve stimulation on consciousness level of a single patient in a vegetative state, including improved behavioral responsiveness and enhanced brain connectivity patterns.
From the manuscript
Following the hypothesis that vagus nerve stimulation functionally reorganizes the thalamo-cortical network, we tested its effects on the cortical activity of a patient lying in a vegetative state for 15 years following traumatic brain injury. Behavioral, electroencephalographic (EEG) and 18F-FDG PET recordings were performed before and after surgical implantation of a vagus nerve stimulator. Stimulation was gradually increased to a maximum intensity of 1.5 mA, and its effects were monitored over six months post-implantation. After one month of stimulation, when intensity reached 1 mA, clinical examination revealed reproducible and consistent improvements in general arousal, sustained attention, body motility and visual pursuit. Scores on the Coma Recovery Scale-Revised (CRS-R) test improved, mostly in the visual domain, as stimulation increased, from a score of 5 at baseline (last exam) to 10 at highest intensities (1.00–1.25 mA), indicating a transition from a vegetative to minimally conscious state…
These findings show that stimulation of the vagus nerve promoted the spread of cortical signals and caused an increase of metabolic activity leading to behavioral improvement as measured with the CRS-R scale and as reported by clinicians and family members. Thus, potentiating vagus nerve inputs to the brain helps to restore consciousness even after many years of being in a vegetative state, thus challenging the belief that disorders of consciousness persisting after 12 months are irreversible. The direct connection between the NTS where the vagus nerve originates and the thalamus may be at the origin of the significant increase in theta signal recorded at the cortical level. In particular, the parietal cortex appears to be a major player in guiding the expansion of neural activity across brain areas. The enhanced neural activity might also be mediated by neurotransmission changes given that vagus nerve projections target key regions important for the liberation of norepinephrine and serotonin. Finally, since the vagus nerve has bidirectional control over the brain and the body, reactivation of sensory/visceral afferences might have enhanced brain activity within a body/brain closed loop process. Our study demonstrates the therapeutic potential of vagus nerve stimulation to modulate large-scale human brain activity and alleviate disorders of consciousness.
Courtesy of Medscape