[show abstract][hide abstract] ABSTRACT: In recent decades, there has been a growing interest in the assessment of patients in altered states of consciousness. There is a need for accurate and early prediction of awakening and recovery from coma. Neurophysiological assessment of coma was once restricted to brainstem auditory and primary cortex somatosensory evoked potentials elicited in the 30 ms range, which have both shown good predictive value for poor coma outcome only. In this paper, we review how passive auditory oddball paradigms including deviant and novel sounds have proved their efficiency in assessing brain function at a higher level, without requiring the patient's active involvement, thus providing an enhanced tool for the prediction of coma outcome. The presence of an MMN in response to deviant stimuli highlights preserved automatic sensory memory processes. Recorded during coma, MMN has shown high specificity as a predictor of recovery of consciousness. The presence of a novelty P3 in response to the subject's own first name presented as a novel (rare) stimulus has shown a good correlation with coma awakening. There is now a growing interest in the search for markers of consciousness, if there are any, in unresponsive patients (chronic vegetative or minimally conscious states). We discuss the different ERP patterns observed in these patients. The presence of novelty P3, including parietal components and possibly followed by a late parietal positivity, raises the possibility that some awareness processes are at work in these unresponsive patients.
[show abstract][hide abstract] ABSTRACT: To investigate automatic event-related potentials (ERPs) to an auditory change in migraine patients.
Auditory ERPs were recorded in 22 female patients suffering from menstrually-related migraine and in 20 age-matched control subjects, in three sessions: in the middle of the menstrual cycle, before and during menses. In each session, 200 trains of tone-bursts each including two duration deviants were presented in a passive listening condition.
In all sessions, duration deviance elicited a mismatch negativity (MMN) showing no difference between the two groups. However, migraine patients showed an increased N1 orienting component to all incoming stimuli and a prolonged N2b to deviance. They also presented a different modulation of P3a amplitude along the menstrual cycle, which tended to normalise during migraine attacks. None of the studied ERP components showed a default of habituation.
This passive paradigm highlighted increased automatic attention orienting to auditory changes but normal auditory sensory processing in migraineurs.
Our observations suggest normal auditory processing up to attention triggering but enhanced activation of attention-related frontal networks in migraineurs.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 11/2013; · 3.12 Impact Factor
[show abstract][hide abstract] ABSTRACT: Transcranial electric stimulation elicited muscle motor evoked potentials (TESmMEPs) is one of the best methods for corticospinal tract's function monitoring during spine and spinal cord surgeries. A train of multipulse electric stimulation is required for eliciting TESmMEPs under general anaesthesia. Here, we investigated the best stimulation parameters for eliciting and recording tibialis anterior's TESmMEPs during paediatric scoliosis surgery.
Numbers of pulses (NOP), inter-stimulus intervals (ISI) and current intensities allowing the best size tibialis anterior muscle's TESmMEPs under general anaesthesia, were tested and collected during 77 paediatric scoliosis surgery monitoring procedures in our hospital. Individual pulse duration was kept at 0.5ms and stimulating electrodes were positioned at C1 and C2 (International 10-20-EEG-System) during all the tests.
The NOP used for eliciting the best tibialis anterior TESmMEPs response was 5, 6, and 7 respectively in 21 (27%), 47 (61%) and 9 (12%) out of the 77 patients. The ISI was 2, 3 and 4 ms respectively in 13 (17%), 55 (71%) and 9 (12%) of them. The current intensity used varied from 300 to 700V (mean: 448±136 V).
Most patients had 6 as best NOP (61%) and 3ms as best ISI (71%). These findings support that a NOP of 6 and an ISI of 3 ms should be preferentially used as optimal stimulation settings for intraoperative tibialis anterior muscle's TESmMEPs eliciting and recording during paediatric scoliosis surgery.
[show abstract][hide abstract] ABSTRACT: To investigate long-term (LTH) and short-term (STH) habituation of auditory event-related potentials (ERPs) during a migraine cycle, using a classic habituation paradigm.
In 22 patients suffering from menstrually-related migraine and in 20 age-matched control subjects, auditory ERPs were recorded in 3 sessions: in the middle of the menstrual cycle, before menses, and during menses. In 12 patients, a migraine attack occurred during one of the peri-menses sessions. In each session, 200 trains of stimuli were presented, with an average of 10 stimuli per train.
In response to the first stimuli of the trains, migraineurs exhibited in all sessions a larger orienting component of N1 than matched controls and a larger P3a in the interictal session, which normalized during attacks. They also showed a residual orienting component in response to the subsequent stimuli inside the trains. In contrast, the sensory component of N1 showed no difference between the two groups, with similar STH and LTH.
Migraineurs show an exacerbated attention orienting to auditory stimulation, without any habituation deficit.
Previous migraine studies reported interictal habituation deficits of ERPs, but demonstrated in the auditory modality only in paradigms testing intensity dependence. Previous and current results can be interpreted as an increased attention orienting, possibly relying on an abnormal involvement of frontal cortex in auditory processing.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 03/2011; 122(9):1755-63. · 3.12 Impact Factor
[show abstract][hide abstract] ABSTRACT: The present retrospective cohort study compares the long-term functional outcome, improvement or deterioration, of patients considered in a vegetative state (VS) or a minimally conscious state (MCS) 1 year after coma onset, then yearly for up to 5 years.
We reviewed the clinical courses of 12 patients in VS and 39 in MCS. The outcomes were assessed at 2, 3, 4, and 5 years after injury using the 5 categories of the Glasgow Outcome Scale plus an additional category for patients in MCS. A logistic regression analysis investigated the relationships between each outcome and 10 predictor variables. Four of these variables were auditory evoked potentials recorded at the early stage of coma.
None of the patients in VS improved during the follow-up period: 1 was lost to follow-up, 9 died, and 2 remained in VS. Among patients in MCS, 3 were lost to follow-up, 14 died, 9 remained in MCS, and 13 emerged from MCS with severe disabilities. VS, age >39 years, and bilateral absence of cortical components of middle-latency auditory evoked potentials were significantly associated with deterioration.
In contrast to patients in VS, a third of patients in MCS improved more than 1 year after coma onset. This emphasizes the need to define reliable boundaries between VS and MCS using repeated clinical evaluations and all imaging and neurophysiologic tools available today.
[show abstract][hide abstract] ABSTRACT: To assess markers of cognition, if any, in patients in a permanent vegetative state (PVS).
Event-related potential (ERP) mapping was performed on 27 patients in permanent (4-261 months after coma onset) vegetative (PVS, n=16) or minimally conscious states (MCS, n=11) due to anoxia (n=18) or other aetiologies (n=9). Mismatch negativity (MMN) to duration-deviant tones and novelty P3 (nP3) to the subject's own name were recorded according to a paradigm previously validated in healthy volunteers and comatose patients. SEPs, MLAEPs and BAEPs were also recorded.
MMN was present in 5/27 and nP3 in 7/27 patients. ERPs were not related to the time from coma onset and not different in MCS and in PVS. Normal SEPs and MLAEPs, and present nP3s were less frequent in anoxia than in other aetiologies.
Irrespective of their clinical assessment, a few patients are likely to process sound deviance (MMN) or novelty (nP3), mainly when their state is not due to anoxia.
Some PVS patients may be able to put certain awareness marker processes to work. The diagnostic criteria for PVS or MCS, currently based on mere behaviour, should also include functional brain investigations, such as ERPs, related to the aetiology.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 03/2010; 121(7):1032-42. · 3.12 Impact Factor
[show abstract][hide abstract] ABSTRACT: Brainstem auditory evoked potentials (BAEP) monitoring is a useful tool to decrease the danger of hearing loss during pontocerebellar angle surgery, particularly in microvascular decompression (MVD). Critical complications arising during MVD surgery are the stretching of the VIII nerve – the main cause of hearing loss – labyrinthine artery manipulation, direct trauma with instruments, or a nearby coagulation, and at end of the surgery neocompression of the cochlear nerve by the prosthesis positioned between the conflicting vessel(s) and the VIIth–VIIIth nerve complex. All these dangers warrant the use of BEAP monitoring during the surgical team's training period. Based on delay in latency of peak V, we established warning thresholds that can provide useful feedback to the surgeon to modify the surgical strategy: the initial signal at 0.4ms is considered the safety limit. A second signal threshold at 0.6ms (warning signal for risk) corresponds to the group of patients without resultant hearing loss. The third threshold characterized by the delay of peak V is at 1ms (warning signal for a potentially critical situation). BAEP monitoring provides the surgeon with information on the functional state of the auditory pathways and should help avoid or correct manoeuvres that can harm hearing function. BAEP monitoring during VIIth–VIIIth complex surgery, particularly in MVD of facial nerves for HFS is very useful during the learning period.
[show abstract][hide abstract] ABSTRACT: For patients with pharmaco-resistant temporal epilepsy, unilateral anterior temporal lobectomy (ATL) - i.e. the surgical resection of the hippocampus, the amygdala, the temporal pole and the most anterior part of the temporal gyri - is an efficient treatment. There is growing evidence that anterior regions of the temporal lobe are involved in the integration and short-term memorization of object-related sound properties. However, non-verbal auditory processing in patients with temporal lobe epilepsy (TLE) has raised little attention. To assess non-verbal auditory cognition in patients with temporal epilepsy both before and after unilateral ATL, we developed a set of non-verbal auditory tests, including environmental sounds. We could evaluate auditory semantic identification, acoustic and object-related short-term memory, and sound extraction from a sound mixture. The performances of 26 TLE patients before and/or after ATL were compared to those of 18 healthy subjects. Patients before and after ATL were found to present with similar deficits in pitch retention, and in identification and short-term memorisation of environmental sounds, whereas not being impaired in basic acoustic processing compared to healthy subjects. It is most likely that the deficits observed before and after ATL are related to epileptic neuropathological processes. Therefore, in patients with drug-resistant TLE, ATL seems to significantly improve seizure control without producing additional auditory deficits.
Frontiers in Human Neuroscience 01/2009; 3:42. · 2.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Hemodynamic studies have shown that the auditory cortex can be activated by visual lip movements and is a site of interactions between auditory and visual speech processing. However, they provide no information about the chronology and mechanisms of these cross-modal processes. We recorded intracranial event-related potentials to auditory, visual, and bimodal speech syllables from depth electrodes implanted in the temporal lobe of 10 epileptic patients (altogether 932 contacts). We found that lip movements activate secondary auditory areas, very shortly (approximately equal to 10 ms) after the activation of the visual motion area MT/V5. After this putatively feedforward visual activation of the auditory cortex, audiovisual interactions took place in the secondary auditory cortex, from 30 ms after sound onset and before any activity in the polymodal areas. Audiovisual interactions in the auditory cortex, as estimated in a linear model, consisted both of a total suppression of the visual response to lipreading and a decrease of the auditory responses to the speech sound in the bimodal condition compared with unimodal conditions. These findings demonstrate that audiovisual speech integration does not respect the classical hierarchy from sensory-specific to associative cortical areas, but rather engages multiple cross-modal mechanisms at the first stages of nonprimary auditory cortex activation.
Journal of Neuroscience 01/2009; 28(52):14301-10. · 6.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: To assess patterns of novelty P3 elicited by the subject's own name (SON) in comatose patients and to compare SON novelty P3 prognostic value with that of mismatch negativity (MMN).
A passive oddball paradigm, previously validated in healthy subjects, including duration deviants and SON presented as a novel was applied in 50 severe comatose patients on average 20 days after coma onset. The outcome was assessed 3 months after coma onset.
MMN to deviants was found in 14/50 patients and a central-parietal P3 to SON was found in 21/50 patients. In 12 patients, a parietal component (P3b) was also clearly present in the late part of P3. Four patients showed an MMN but no P3. Eleven patients had a novelty P3, with a late parietal component for 5 of them, but no MMN. The presence of a P3 was highly correlated with awakening. Compared to MMN, P3 showed as large a specificity for awakening (0.85). It showed a much higher sensitivity (0.71 versus 0.42). All but one patient with P3b woke up.
The use of novelty P3 elicited by SON increases the prognostic value of MMN alone and improves the assessment of comatose patients by demonstrating the activation of higher-level cognitive functions in some of them. It shows that unconsciously perceived stimuli are processed and activate brain areas similarly to consciously perceived stimuli.
SON as a novel in an MMN design can be used to increase the prognostic value of ERPs in comatose patients and to assess unconscious cognitive processes in uncommunicative patients.
[show abstract][hide abstract] ABSTRACT: Indication of gamma-knife surgery (GKS) in temporal lobe epilepsy (TLE) remains a matter of debate. Either positive or negative results have been reported in studies with a maximum follow-up of 24 months. No long-term data have been published yet.
We collected data from 15 TLE patients who underwent GKS and whose follow-up was longer than 24 months. Localisation and extension of the epileptogenic zone (EZ) were assessed by SEEG in eight patients. Ten patients were presenting with mesial TLE (mTLE) while in the other five SEEG showed that the EZ was extending beyond mesio-temporal structures. GKS procedure was targeted to the EZ at a dose of 21.1+/-2.6Gy at the margin.
The mean duration of the follow-up was 60+/-22.3 months. At last follow-up, seven patients (46.7%) were free of disabling seizure. The last seizure following GKS occurred on average after a delay of 19.75+/-20.62 months. No patient suffered recurrent seizures after a long period free of disabling seizures. No significant prognostic predictor could be individualized in this population. However, 6 of the 10 patients with mTLE (60%) were seizure free whereas only 1 of the 5 (20%) whose EZ was more extended exhibited the same seizure outcome.
When a positive outcome is achieved, the risk of seizure recurrence remains low at long term. In patients with typical mTLE, long-term GKS results may be closed to those observed after conventional surgery. Conversely, this procedure should not be proposed to patients in whom SEEG results suggest that the EZ is not restricted to mesial temporal structures.
Epilepsy Research 08/2008; 80(1):23-9. · 2.24 Impact Factor