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Neurology. 2015 Jan 13;84(2):167-73. doi: 10.1212/WNL.0000000000001123. Epub 2014 Dec 5.

Thalamo-frontal connectivity mediates top-down cognitive functions in disorders of consciousness.

Author information

1
From the Department of Psychology (M.M.M., M.R.), University of California Los Angeles; the Department of Neurosurgery (M.M.M.), Brain Injury Research Center (BIRC), Geffen School of Medicine at UCLA, Los Angeles; the Cognition and Brain Sciences Unit (P.F.), Medical Research Council, Cambridge; the Division of Neurosurgery (P.F., E.K., J.D.P.), University of Cambridge, Addenbrooke's Hospital, Cambridge, UK; and the Natural Science Building (A.M.O.), Brain & Mind Institute, The University of Western Ontario, London, Canada. monti@psych.ucla.edu.
2
From the Department of Psychology (M.M.M., M.R.), University of California Los Angeles; the Department of Neurosurgery (M.M.M.), Brain Injury Research Center (BIRC), Geffen School of Medicine at UCLA, Los Angeles; the Cognition and Brain Sciences Unit (P.F.), Medical Research Council, Cambridge; the Division of Neurosurgery (P.F., E.K., J.D.P.), University of Cambridge, Addenbrooke's Hospital, Cambridge, UK; and the Natural Science Building (A.M.O.), Brain & Mind Institute, The University of Western Ontario, London, Canada.

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.

PMID:
25480912
PMCID:
PMC4336082
DOI:
10.1212/WNL.0000000000001123
[Indexed for MEDLINE]
Free PMC Article

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