Altered resting state effective connectivity in long-standing vegetative state patients: an EEG study.
OBJECTIVE
Recent evidence mainly based on hemodynamic measures suggests that the impairment of functional connections between different brain areas may help to clarify the neuronal dysfunction occurring in patients with disorders of consciousness (DOC). The aim of this study was to evaluate effective EEG connectivity in a cohort of 18 patients in a chronic vegetative state (VS) observed years after the occurrence of hypoxic (eight) and traumatic or hemorrhagic brain insult.


METHODS
we analysed the EEG signals recorded under resting conditions using a frequency domain linear index of connectivity (partial directed coherence: PDC) estimated from a multivariate autoregressive model. The results were compared with those obtained in ten healthy controls.


RESULTS
Our findings indicated significant connectivity changes in EEG activities in delta and alpha bands. The VS patients showed a significant and widespread decrease in delta band connectivity, whereas the alpha activity was hyper-connected in the central and posterior cortical regions.


CONCLUSIONS
These changes suggest the occurrence of severe circuitry derangements probably due to the loose control of the subcortical connections. The alpha hyper-synchronisation may be due to simplified networks mainly involving the short-range connections between intrinsically oscillatory cortical neurons that generate aberrant EEG alpha sources. This increased connectivity may be interpreted as a reduction in information capacity, implying an increasing prevalence of stereotypic activity patterns.


CONCLUSIONS
Our observations suggest a remarkable rearrangement of connectivity in patients with long-standing VS. We hypothesize that in persistent VS, after a first period characterized by a breakdown of cortical connectivity, neurodegenerative processes, largely independent from the type of initial insult, lead to cortex de-afferentation and to a severe reduction of possible cortical activity patterns and states.
Dept. of Neurophysiology and Diagnostic Epileptology, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Giulia
G
Varotto
Dept. of Neurophysiology and Diagnostic Epileptology, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy; Dept. of Medical and Surgical Sciences of Communication and Behaviour, Neurology Section, University of Ferrara, Italy.
Patrik
P
Fazio
Dept. of Neurophysiology and Diagnostic Epileptology, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Davide
D
Rossi Sebastiano
Dept. of Neurophysiology and Diagnostic Epileptology, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Dunja
D
Duran
Dept. of Neuroradiology, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Ludovico
L
D'Incerti
Dept. of Cerebrovascular Diseases, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Eugenio
E
Parati
Unit of Neurology, Public Health, Disability Unit, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy; Coma Research Centre, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Davide
D
Sattin
Unit of Neurology, Public Health, Disability Unit, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy; Coma Research Centre, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Matilde
M
Leonardi
Dept. of Neurophysiology and Diagnostic Epileptology, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy.
Silvana
S
Franceschetti
Dept. of Neurophysiology and Diagnostic Epileptology, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy. Electronic address: panzica@istituto-besta.it.
Ferruccio
F
Panzica
D000328:Adult; D000368:Aged; D001921:Brain / Q000503:physiopathology; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000502:physiology / Q000503:physiopathology; D018458:Persistent Vegetative State / Q000503:physiopathology* / Q000523:psychology*; D012146:Rest / Q000502:physiology; D060685:Sense of Coherence
ABI; DOC; Disorders of consciousness; EEG; Effective connectivity; MVAR; PDC; Partial directed coherence; VS; Vegetative state; anoxic brain injury; disorders of consciousness; multivariate autoregressive; partial directed coherence; vegetative state