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A new study provides more evidence that functional magnetic resonance imaging (fMRI) can provide additional insight into the cognitive status of patients with disorders of consciousness who show minimal or no signs of awareness based on conventional behavioral examination. "Conventional bedside assessments of consciousness rely on motor responses to indicate awareness. However, overt behaviors may be absent or ambiguous in patients with consciousness disorders, resulting in underestimating capacity for cognition," Joy Hirsch, PhD, director, Functional MRI Research Center, Columbia University Medical Center, in New York City, told Medscape Medical News.

"Our findings suggest that fMRI may provide additional objective options that 'give a voice' to an unresponsive patient or valuable assessment information to the family and medical team," she added.

The study involved 10 patients with and without conventional evidence of awareness who met diagnostic criteria for the minimally conscious state (MCS; n = 5), vegetative state (n = 3), emerged from MCS (EMCS; n = 1), and locked-in syndrome (n = 1). All patients underwent fMRI of the brain during an object-naming (command-following) task; they were instructed to silently "name to themselves" objects pictured in drawings.

Picture naming, the investigators note in their report, is considered a "complex process that recruits both stimulus-driven (bottom-up) and purpose-driven (top-down) pathways including visual input, language, short-term memory, and motor and executive functions."

The investigators observed hemodynamic responses in some or all of the areas constituting the network activated in normal subjects in 9 of 10 participants. These areas are the dorsal inferior frontal gyrus, ventral inferior frontal gyrus, presupplementary motor area, and superior temporal gyrus.

Specifically, the patient with locked-in syndrome, the patient with EMCS, 2 of the 5 patients with MCS, and 1 of the 3 patients in a vegetative state engaged a "complete network" of essential language-related brain regions on fMRI during the object-naming task; 4 of the 5 the remaining patients demonstrated partial preservation of the object-naming network. Patients who engaged a complete network of language-essential areas achieved the highest scores on the Revised Coma Recovery Scale.

"This study," Dr. Hirsch said, "found that an instruction to name objects can elicit brain activity in patients with consciousness disorders — in some cases similar to those observed in healthy subjects.

"These findings suggest that it may be possible to classify disorders of consciousness based on regions of the brain that are included in, or excluded from, the network of responsive areas," she added.

The study by Dr. Hirsch and colleagues follows several recent reports suggesting that fMRI may reveal signs of willful brain activation during cognitive task execution in brain-injured patients, Serge Goldman, MD, from Erasme Hospital in Brussels, Belgium, notes in a commentary published with the new study.

Based on accumulating research, Dr. Goldman told Medscape Medical News, "Our vision of patients considered in a 'vegetative state' or in a 'minimally conscious state' should now integrate the fact that these patients might have residual mental activities that are sufficiently organized and structured to be evidenced by neuroimaging technologies."

However, it remains unknown, Dr. Goldman said, what proportion of patients with disorders of consciousness retain some mental capacity, "and to which extent cognition in these noncommunicative patients are restricted to 'spots' within specific domains or cover crucial properties of human consciousness such as self-awareness and decision-making."

Dr. Goldman said caution is necessary in the interpretation of these neuroimaging data obtained in noncommunicative patients.

"In particular, before considering that brain functional changes seen on images result from voluntary command-following, it is necessary to ascertain that such changes might not be passively elicited by the stimulation used," he noted.

"Of major ethical importance," he added, is that "the prognostic value of residual cognitive activity demonstrated by neuroimaging remains totally unknown."

Source: Medscape

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