fMRI default mode connectivity in vegetative state and locked-in syndrome patients

Abstract

Introduction: The aim of this study is to assess fMRI resting-state cerebral connectivity in vegetative state and locked-in syndrome patients by means of a user-independent method. Resting baseline (or default mode) activity is thought to be related to awareness of the internal world (that is, mind wandering, and so forth) and encompasses posterior cingulate/precuneal, anterior cingulate/mesiofrontal and posterior lateral parietal cortices. Methods: We here present a novel clinical application for a userindependent default mode network analysis. Resting state data were acquired for seven vegetative state patients (age range 16 to 87 years), one locked-in syndrome patient (aged 24 years) and seven healthy subjects (25 to 65 years). Patients' diagnosis was based on Coma Recovery Scale assessment prior and following scanning. Data were pre-processed and analyzed using independent component analysis as implemented in Brain Voyager. Connectivity studies employed 13 target regions of interest defined on an average default mode map calculated from an independent dataset of 20 controls (21 to 60 years). Resting state connectivity was assessed by calculating the number of functional connections within the default mode map for each subject. Next, Student t tests compared patients with controls at the group level (P <0.05). Results: Compared with controls, vegetative patients showed a lower total number of edges (that is, connections; 24 (plus or minus) 4, range 19 to 31 and 13 (plus or minus) 3, range 8 to 15, P <0.001) and less functional connections with the precuneus (6 (plus or minus) 1 and 2 (plus or minus) 2; P <0.001). The default mode network shows a reduced connectivity in vegetative patients as compared with controls mainly between the precuneus and medial prefrontal cortex ventral. Finally, for the locked-in syndrome patient the connectivity graph counted 21 total number of effective connections and five effective connections with the precuneus, which was not significantly different from healthy controls. Conclusions: The connectivity study showed no overlap between the number of effective connections or edges in vegetative state patients and in controls. Connectivity graph analysis identified anterior-posterior midline disconnections in the vegetative state, in line with previous studies emphasizing the critical role of the precuneus/PCC and mesiofrontal cortices in the emergence of conscious awareness.