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This case report describes a 38-year-old man in a minimally conscious state (MCS) after closed head injury, who improved after deep-brain stimulation (DBS) of the midline and adjacent thalamic nuclei.
The initial injury left the patient unresponsive for 2 months, after which he gradually improved over 6 years to the MCS. When the investigators encountered the patient (6 years post-injury), he could localize stimuli, follow commands inconsistently (occasionally including go, no-go), and mouth single words infrequently, but could not communicate yes-or-no responses consistently. MRI showed right frontal encephalomalacia and a right thalamic infarct. Functional MRI showed preservation of language areas despite a global reduction in cerebral metabolism on PET.
The DBS research protocol was complicated and included an empiric “titration” phase to establish optimal electrode settings. Optimized DBS produced longer periods of eye opening, some functional use of objects, and intelligible speaking. For the first time since the injury, the patient could swallow food and bring a cup to his mouth. During a 6-month, double-blind, crossover period with neuropsychological tests, arousal scale subscores were significantly higher with the DBS turned on than they were with it off. However, motor and communication scores did not improve; the investigators attributed this to a ceiling effect of the measurement scales. According to supplemental information, the patient continued to improve with 12 hours of DBS each day.
Schiff ND et al. Behavioural improvements with thalamic stimulation after severe traumatic brain injury. Nature 2007 Aug 2; 448:600.
Comment
Although use of brain stimulation for coma and related states is not novel, the procedure in this case was very carefully designed to replace the arousing and cohering effects on the cortex of the thalamic reticular neurons. This was not a miraculous awakening, as portrayed in some of the popular press, but a slight, and nonetheless convincing, improvement in arousal and in some complex behaviors. The patient was not vegetative, and large areas of his language cortex were preserved. It is unclear whether the authors have treated additional patients, and whether they have had less favorable outcomes. The authors acknowledge that their findings may not be generalizable, but their work opens a remarkable opportunity to study and treat acquired disorders of consciousness and arousal. Patients with diffuse axonal injury might not be capable of transmitting thalamic signals to the cortex, but this and other possibilities can now be tested.