A comparison of recording modalities of P300 event-related potentials (ERP) for brain-computer interface (BCI) paradigm

AIMS OF THE STUDY

A brain-computer interface aims at restoring communication and control in severely disabled people by identification and classification of EEG features such as event-related potentials (ERPs). The aim of this study is to compare different modalities of EEG recording for extraction of ERPs. The first comparison evaluates the performance of six disc electrodes with that of the EMOTIV headset, while the second evaluates three different electrode types (disc, needle, and large squared electrode).

MATERIAL AND METHODS

Ten healthy volunteers gave informed consent and were randomized to try the traditional EEG system (six disc electrodes with gel and skin preparation) or the EMOTIV Headset first. Together with the six disc electrodes, a needle and a square electrode of larger surface were simultaneously recording near lead Cz. Each modality was evaluated over three sessions of auditory P300 separated by one hour.

RESULTS

No statically significant effect was found for the electrode type, nor was the interaction between electrode type and session number. There was no statistically significant difference of performance between the EMOTIV and the six traditional EEG disc electrodes, although there was a trend showing worse performance of the EMOTIV headset. However, the modality-session interaction was highly significant (P<0.001) showing that, while the performance of the six disc electrodes stay constant over sessions, the performance of the EMOTIV headset drops dramatically between 2 and 3h of use. Finally, the evaluation of comfort by participants revealed an increasing discomfort with the EMOTIV headset starting with the second hour of use.

CONCLUSION

Our study does not recommend the use of one modality over another based on performance but suggests the choice should be made on more practical considerations such as the expected length of use, the availability of skilled labor for system setup and above all, the patient comfort.

Hot water epilepsy: a benign and unrecognized form

Hot water epilepsy is a reflex epilepsy. Seizures are provoked by hot water, and result from the association of both cutaneous and heat stimuli. Described mainly in India and Japan, the condition seems to be rare in Europe, where it occurs in young children. We report five infants aged from 6 months to 2 years. They had brief seizures during bathing with activity arrest, hypotonia, and vasoactive modification; clonic movements were observed. A simple treatment-decreasing the bath temperature-can be sufficient. Sometimes an antiepileptic drug is required. Seizure course and psychomotor development are favorable. Hot water epilepsy is a benign form of epilepsy. Its incidence could be underestimated because of confusion with febrile convulsions, vagal fits, or aquagenic urticaria.

[Cerebral anoxia in near-drowning of children. The prognostic value of EEG]

The retrospective electroclinical evaluation of anoxia by near-drowning in 23 children observed between 1985 and 1989 revealed 2 groups, each with a distinct evolution: the first group, with good prognosis of 17 children, which recovered consciousness without neurological complications between 2 d and 1 wk after the accident. The second group of 6 children with a poor outcome--either i), death; or ii), state of permanent injury; or iii), a high level of clinical deficits. The gravity of the early clinical state, the estimated duration of cardiorespiratory arrest, the severity of the hypothermia, the seizures and the paroxysmic activity, do not determine the severity of near-drowning encephalopathy. The EEG patterns described in correlation with the group and the clinical outcome permitted determination of prognostic criteria. A good prognostic consisted of the following: moderate background activity, sleep patterns, response to auditory and painful stimulations, and numerous beta rhythms. A bad outcome was defined by: high voltage, rhythmic delta waves; biphasic sharp waves; monotonous EEG, "burst-suppression" pattern, absence of beta rhythms. The importance of EEG recordings is emphasized performed as early as possible and until 3 or 7 d after the near-drowning. Any modification in the EEG, with attenuation or disappearance of fast frequencies and painful reactivity, appearance or enhancement of slow and biphasic sharp waves, are ominous signs and may be accompanied by the appearance of cerebral oedema and decerebration.

Obstructive sleep apnoea syndrome: comparison between polysomnography and portable sleep monitoring based on jaw recordings

INTRODUCTION

Obstructive sleep apnoea syndrome (OSAS) constitutes a new major public health problem because of its several pathophysiologic consequences such as cognitive disorders, excessive daytime sleepiness with risks of traffic accidents, cardiovascular implications, and decrease of quality of life. The necessity of a gold-standard polysomnography to ensure an accurate diagnosis implies an expensive, technical and time-consuming examination. Thus, it seems logical to develop new systems so as to diagnose SAS and to make it possible to detect apnoeas/hypopnoeas easily during sleep even at home.

AIM OF THE STUDY

To assess a novel type-3 portable monitoring (PM) device, the Somnolter, and dedicated automatic analysis of several signals, one of which is the mandibular movement signal.

METHOD

We studied patients suffering from OSAS. For all the patients, a nocturnal diagnosis polysomnography (PSG) was recorded in hospital settings, based on six EEG channels, two EOG channels, chin EMG channel, EKG, and respiratory parameters. At the same time, the Somnolter PM device recorded the physiological parameters from its own nasal prongs, thoracic belt, pulse oxymeter, body position, and jaw movement sensors. A visual analysis of PSG recordings was made leading to the detection of apnoea/hypopnoea index (AHI-PSG) and an automatic analysis of the Somnolter traces was performed to get automatic apnoea/hypopnoea index (AHI-A). The added value of the mandible movement signals was the particular jaw movements related to arousals, to respiratory efforts and to sleep/wake state. A comparison was made between the automatic and gold AHIs standard and the correlation was calculated between them.

RESULTS

Ninety patients, aged between 47 and 70 years (mean age: 55.4±8.7) took part in the study. The linear regression and the correlation coefficient between AHI-PSG and AHI-A showed the good reliability of the automatic method. The Bland Altman analysis shows a correlation of 0.95 with a sensitivity of 83.6 and specificity of 81.8.

CONCLUSION

The dedicated automatic analysis based on mandibular movements presents a good potential for the diagnosis of OSAS. The AHI computed by the automatic method is correlated with the AHI-PSG and the Somnolter could easily be used both in hospital, and in ambulatory settings.

Indications de l'électroencéphalogramme en période néonatale

The electroencephalogram (EEG), an easy-to-use and non invasive cerebral investigation, is a useful tool for diagnosis and early prognosis in newborn babies. In newborn full term babies manifesting abnormal clinical signs, EEG can point focal lesions or specific aetiology. EEG background activity and sleep organization have a high prognostic value. Tracings recorded over long period can detect seizures, with or without clinical manifestations, and differentiate them from paroxysmal non epileptic movements. The EEG should therefore be recorded at the beginning of the first symptoms, and if possible before any seizure treatment. When used as a neonatal prognostic tool, EEG background activity is classified as normal, abnormal (type A and type B discontinuous and hyperactive rapid tracing) or highly abnormal (inactive, paroxysmal, low voltage plus theta tracing). In such cases, the initial recording must be made between 12 and 48 h after birth, and then between 4 and 8 days of life. Severe EEG abnormalities before 12 h of life have no reliable prognostic value but may help in the choice of early neuroprotective treatment of acute cerebral hypoxia-ischemia. During presumed hypoxic-ischemic encephalopathy, unusual EEG patterns may indicate another diagnosis. In premature newborn babies (29-32 w GA) with neurological abnormalities, EEG use is the same as in term newborns. Without any neurological abnormal sign, EEG requirements depend on GA and the mother's or child's risk factors. Before 28 w GA, when looking for positive rolandic sharp waves (PRSW), EEG records are to be acquired systematically at D2-D3, D7-D8, 31-32 and 36 w GA. It is well known that numerous and persistent PRSW are related to periventricular leukomalacia (PVL) and indicate a bad prognosis. In babies born after 32 GA with clinically severe symptoms, an EEG should be performed before D7. Background activity, organization and maturation of the tracing are valuable diagnosis and prognosis indicators. These recommendations are designed (1) to get a maximum of precise informations from a limited number of tracings and (2) to standardize practices and thus facilitate comparisons and multicenter studies.

[Monitoring of somatosensory evoked potentials during surgery for scoliosis in young adults: apropos of 33 cases]

The risk of serious neurologic complications in spinal surgery for scoliosis is not insignificant. The recording of cortical somatosensory evoked potentials (CSEP) is an electrophysiological method of monitoring during surgery. Measurement of CSEPs was carried out before, during and after surgery in a preliminary series of 33 patients. These recordings were made: after induction of anesthesia and exposure of the spine; after instrumentation but without correction; after maximum traction; and at termination of surgery. The aim of this work was to establish alarm criteria. Statistical analysis showed a significant increase in latencies after instrumentation without correction, and after maximum traction. The alarm criteria were determined as an increase of more than 5 msec in the first positive deflection associated with an unusual drop in amplitude (over 75%). If these anomalies persist, the "wake-up test" must be used. In practice, this monitoring has often aided in reducing the period of surgery by using the "wake-up test" in a few selected cases.

[Hot water epilepsy: a benign and underestimated form]

BACKGROUND

Hot water epilepsy belongs to the group of reflex epilepsies. Seizures are provoked by hot water, due to the association of both cutaneous and heat stimuli. Described mainly in India and Japan, it seems to be rare in Europe where it occurs in young children.

CASE REPORTS

Five infants aged between 6 months to 2 years had seizures during bathing with activity arrest, hypotonia and vasoactive modification. Sometimes clonic movements could be observed. The diagnosis was confirmed by EEG recorded during bath in the fives cases, with video for two of them. The course of the seizures and of the psychomotor development were favorable.

CONCLUSION

Hot water epilepsy is a benign epilepsy. Its incidence could be underestimated because seizures can be confused with febrile convulsions or vagal fits.

Continuous EEG monitoring in children in the intensive care unit (ICU)

Pediatric EEG in the intensive care unit (ICU) requires specific technical requirements in order to yield relevant data depending upon clinical scenario: diagnosis of electroclinical or subclinical seizures, their quantification before and after therapeutic changes and sometimes evaluation of severity of cortical dysfunction. The urgent nature of these indications implies the rapid set-up of the EEG system by qualified staff and possibility of maintaining the electrodes in place during long periods of time. Various techniques are available today for EEG monitoring, the interpretation of which depends on the contribution of an experienced physician. Among recent techniques, those most commonly used are trend curves obtained via signal analysis such as amplitude EEG (a-EEG) and density spectral array (DSA) or compressed spectral array (CSA). Trend curves enable the digital creation of a display graph containing several hours of transformed and compressed EEG recorded data. Visualized on one sole display graph, these trend curves can facilitate the identification of very slow changes in EEG background activity and their variation (alertness cycles, changes linked to treatment administrations) as well as seizure patterns and their quantification. In this chapter, we propose a brief overview of monitoring techniques, followed by a review of the various data yielded by EEG monitoring as well as the relevance of this type of management; finally, detailed clinical indications will be discussed after thorough analysis of the literature.