Abstract
We used electroencephalography (EEG) recordings to evaluate the cortical reactivity and effective connectivity during TMS in chronic VS or MCS patients. Moreover, the TMS-EEG data were compared with the results from standard somatosensory-evoked potentials (SEPs) and event-related potentials (ERPs). Thirteen patients with chronic consciousness disorders were examined at their bedsides. The amplitudes (reactivity) and scalp distributions (connectivity) of the cortical potentials evoked by TMS (TEPs) of the primary motor cortex were measured. Short-latency median nerve SEPs and auditory ERPs were also recorded. Reproducible TEPs were present in all control subjects in both the ipsilateral and the contralateral hemispheres relative to the site of the TMS. The amplitudes of the ipsilateral and contralateral TEPs were reduced in four of the five MCS patients, and the TEPs were bilaterally absent in one MCS patient. Five VS patients did not manifest ipsilateral or contralateral TEPs and three exhibited only ipsilateral TEPs with reduced amplitudes. The SEPs were altered in five VS and two MCS patients. ERPs were impaired in all patients and did not correlate with the clinical diagnosis. TEPs may add valuable information to the current clinical and neurophysiological assessment of chronic consciousness disorders.
Highlights
Since the first description of the vegetative state (VS) [1], both the medical community and laypeople have considered the diagnosis of a VS important because of the implications in the end-of-life decision-making processes [2]
event-related potentials (ERPs) Results The N1 was present in eleven patients (7 VS, 4 minimally conscious state (MCS)) and absent in two (1 VS, 1 MCS), but no significant correlation emerged between the presence/absence of the N1 and the clinical assessment of VS or MCS. (x2,0.001, p = 1.000) (Table 3 and Figure 4)
EEG Power Spectra Results The EEG frequency power spectra did no significantly differ between the MCS and VS patients for any of the frequency bands considered in the analysis
Summary
Since the first description of the vegetative state (VS) [1], both the medical community and laypeople have considered the diagnosis of a VS important because of the implications in the end-of-life decision-making processes [2]. In 2002, the term minimally conscious state (MCS) was introduced to describe patients who can be distinguished from VS patients by the presence of inconsistent cognitive behaviour that is either reproducible or sustained long enough to be differentiated from reflexive behaviour [3]. Despite these definitions, diagnosing a VS and distinguishing it from a MCS is a challenging task that is primarily based on the clinical history and the behavioural assessment of the patient. These difficulties have encouraged clinical researchers to develop diagnostic techniques to complement the behavioural evaluations
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