Connectivity as a marker for accurate diagnosis in Disorders of Consciousness (DOC)

Question:

Recent studies revealed differences in signal distribution inDOC-patients, depending on the diagnosis. We investigated systematic differences in transcallosal coherence. Greater coherence in healthy than in DOC-Patients and greater coherence in patients in a minimally conscious state (MCS) than patients with unresponsible wakefulness syndrome (UWS) was expected.

Methods:

Rest-EEG was recorded in 66 subjects (24 MCS, 30 UWS, 12 Healthy). The absolute value of coherence between each electrode of the left hemisphere and each electrode of the right hemisphere was computed (F3, F4, C7, F8, C3, C4, P3, P4, O1, O2). T-tests were calculated for each of 12 frequency bands (1 Hz up to 28 Hz) and for each electrode combination between MCS- and UWS-patients and between healthy subjects and DOC-patients.

Results:

The statistics did not reveal remarkable differences between the MCS- and the UWS-group. The comparison of DOC-patients and healthy subjects revealed statistical trends (p < 0.05, uncorrected) in about 32% of the computed tests, especially in higher frequencies (> 20 Hz).

Conclusions:

Since connectivity of MCS- and UWS-patients did not differ in a convincing extent, one might conclude that consciousness is not represented by the transcallosal connectivity. The results concerning differences between healthy subjects and DOC-patients did not allow a reasonable conclusion, either. We suggest that the use of connectivity measures such as coherence is dominated by a high inter-individual variance, making group comparisons unfeasible.