How vegetative is the vegetative state? Preserved semantic processing in VS patients – Evidence from N 400 event-related potentials1

Abstract

Event-related potentials (ERPs) can provide valuable information about cognitive capabilities in severely braindamaged patients. This study examined 120 patients with severe brain damage using event related potentials ERPs (N 400) to gain information about their remaining semantic processing capabilities and to contribute to differential diagnosis. Patients were classified into three diagnostic groups: patients in vegetative state (VS), patients in near vegetative state (NEVS) and patients not in vegetative state (NOVS). N400 ERPs were analyzed on an individual basis. All three groups could be differentiated by N400. While VS-patients as a group were least likely to show N400, some VS-patients (approx. 12%) showed clear semantic N400 potentials as an indication of semantic processing capabilities. Patients in NEVS showed significantly more intact semantic capabilities (76.74%) than the VS-group despite little clinical differences between the two groups. Thus, ERPs provide valuable information about patients with brain injury whose clinical conditions often do not allow a true assessment of their cognitive capabilities. Given these findings, we would espouse that both ethical and legal debate should take into account results of ERP studies of such patients.

N400 predicts recovery from disorders of consciousness

“…For the N400, present numbers are similar to those of Kotchoubey et al and Schoenle and Witzke, who found an N400 in 14 to 39% of UWS patients, with the rates depending on assessment criteria and stimulus complexity. In line with the present pattern, across studies, more patients are identified with late ERPs when computerized analysis techniques are used, suggesting, perhaps contrary to common intuition, that clinicians use more conservative assessment criteria than current implementations of automated algorithms. This may be due to human raters taking into account overall data quality, discounting local differences even if they might be statistically significant, if they occur for example in the context of continuous high‐voltage discharges.…”

“…This wide range has been ascribed to variations in stimulus complexity or emotionality, heterogeneity in patients' etiology, current diagnosis, and different ERP analysis techniques . For the N400, present numbers are similar to those of Kotchoubey et al and Schoenle and Witzke, who found an N400 in 14 to 39% of UWS patients, with the rates depending on assessment criteria and stimulus complexity. In line with the present pattern, across studies, more patients are identified with late ERPs when computerized analysis techniques are used, suggesting, perhaps contrary to common intuition, that clinicians use more conservative assessment criteria than current implementations of automated algorithms.…”

“…In previous reports, the percentage of patients having a P300 ranged from 18 18 to 100% . This wide range has been ascribed to variations in stimulus complexity or emotionality, heterogeneity in patients' etiology, current diagnosis, and different ERP analysis techniques . For the N400, present numbers are similar to those of Kotchoubey et al and Schoenle and Witzke, who found an N400 in 14 to 39% of UWS patients, with the rates depending on assessment criteria and stimulus complexity.…”

“…A much brighter picture emerges for the N400 recorded from largely the same patients. Only one of the two previous studies examining N400 in UWS or MCS patients looked at prognosis. Kotchoubey reported a tendency for N400 presence to correlate with a better short‐term outcome in a mixed group of UWS and MCS patients .…”

“…It has long been known that brain event‐related potentials (ERPs) offer a means to assess information processing capabilities in the absence of overt behavior . Some studies have already demonstrated preserved ERPs in coma, UWS, and MCS, but due to the small number of investigated cases and frequent lack of outcome documentation, their clinical and prognostic significance is currently unclear. However, ERPs could be a powerful and efficient tool to assess information processing and perhaps even cortical correlates of command following in behaviorally unresponsive patients.…”