Tracking the recovery of consciousness from coma

Abstract

Predicting the chances of recovery of consciousness and communication in patients who survive their coma but transit in a vegetative state or minimally conscious state (MCS) remains a major challenge for their medical caregivers. Very few studies have examined the slow neuronal changes underlying functional recovery of consciousness from severe chronic brain damage. A case study in this issue of the JCI reports an extraordinary recovery of functional verbal communication and motor function in a patient who remained in MCS for 19 years (see the related article beginning on page 2005). Diffusion tensor MRI showed increased fractional anisotropy (assumed to reflect myelinated fiber density) in posteromedial cortices, encompassing cuneus and precuneus. These same areas showed increased glucose metabolism as studied by PET scanning, likely reflecting the neuronal regrowth paralleling the patient's clinical recovery. This case shows that old dogmas need to be oppugned, as recovery with meaningful reduction in disability continued in this case for nearly 2 decades after extremely severe traumatic brain injury.

Figure 1. PET studies show that in the rare patients who recover consciousness after being in a chronic VS, glucose metabolism is partially restored in discrete cortical regions.

(A) The most significant restoration of glucose metabolism occurs in the posteromedial cortices (shown in white on a medial view of a 3D-rendered MRI). The arrows represent the corticocortical and corticothalamocortical functional disconnections observed in vegetative patients. MF, mesiofrontal cortex; P, precuneus; T, thalamus (nonspecific nuclei). (B) Metabolism in this area is significantly impaired during the VS (black) but resumes near-normal activity after recovery of consciousness (REC; gray). Normal resting metabolic rates of glucose as measured in healthy controls are shown for comparison (CON; white). In this issue of the JCI, Voss and coworkers report on their observation of intracortical connectivity changes in the same area of the brain, as assessed by diffusion tensor MRI, in an exceptional patient who emerged after spending 19 years in an MCS (12). This residual cerebral plasticity in chronic disorders of consciousness has been largely overlooked by the medical community and deserves further study to expose its underlying cellular mechanisms. Figure and data adapted with permission from the Journal of Neurology, Neurosurgery, and Psychiatry (22).