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Abstract
Objective: We employed functional MRI (fMRI) to assess whether (1) patients with disorders of consciousness (DOC) retain the ability to willfully engage in top-down processing and (2) what neurophysiologic factors distinguish patients who can demonstrate this ability from patients who cannot.
Methods: Sixteen volunteers, 8 patients in vegetative state (VS), 16 minimally conscious patients (MCS), and 4 exit from MCS (eMCS) patients were enrolled in a prospective cross-sectional fMRI study. Participants performed a target detection task in which they counted the number of times a (changing) target word was presented amidst a set of distractors.
Results: Three of 8 patients diagnosed as being in a VS exhibited significant activations in response to the task, thereby demonstrating a state of consciousness. Differential activations across tasks were also observed in 6 MCS patients and 1 eMCS patient. A psycho–physiologic interaction analysis revealed that the main factor distinguishing patients who responded to the task from those who did not was a greater connectivity between the anterior section of thalamus and prefrontal cortex.
Conclusions: In our sample of patients, the dissociation between overt behavior observable in clinical assessments and residual cognitive faculties is prevalent among DOC patients (37%). A substantial number of patients, including some diagnosed with VS, can demonstrate willful engagement in top-down cognition. While neuroimaging data are not the same as observable behavior, this suggests that the mental status of some VS patients exceeds what can be appreciated clinically. Furthermore, thalamo-frontal circuits might be crucial to sustaining top-down functions.
GLOSSARY
- DOC=
- disorders of consciousness;
- eMCS=
- exit from minimally conscious state;
- FA=
- flip angle;
- fMRI=
- functional MRI;
- GLM=
- generalized linear model;
- MCS=
- minimally conscious state;
- MNI=
- Montreal Neurological Institute;
- PPI=
- psycho–physiologic interaction approach;
- ROI=
- region of interest;
- TE=
- echo time;
- TR=
- repetition time;
- VS=
- vegetative state
Footnotes
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Editorial, page 114
- Received January 26, 2014.
- Accepted in final form August 6, 2014.
- © 2014 American Academy of Neurology
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