The IBIS project: data collection in London. Improved Monitoring for Brain Dysfunction during Intensive Care and Surgery.

The primary aim of the Improved Monitoring for Brain Dysfunction during Intensive Care and Surgery (IBIS) project was to create a unique and comprehensively annotated data library (DL) of multiple physiological, including neurophysiological, signals. Data collection was undertaken in Kuopio, Finland and London, UK, and comparable protocols were used at all the sites. In London, 43 patients were recruited at the Royal Brompton Hospital, followed by nine at St. Bartholomew's Hospital, all of whom underwent cardiac or combined cardiac and carotid artery surgery. Thirty-seven patients underwent a single operation, while 15 underwent two procedures. The protocols and equipment used, problems specific to the electrically hostile environment and preliminary results are described, including those of clinical interest. The DL is being used for the development of clinically applicable neurophysiological monitoring tools.

A SPECT study of the effect of vagal nerve stimulation on thalamic activity in patients with epilepsy.

The mechanism by which vagal nerve stimulation (VNS) exerts an anticonvulsant effect in humans is unknown. This study used (99m)Tc-HMPAO single photon emission tomography (SPECT) to examine the effects of VNS on regional cerebral activity in thalamic and insular regions. Seven subjects with epilepsy who had been receiving vagal nerve stimulation for at least 6 months underwent SPECT scanning with simultaneous scalp electroencephalographic (EEG) recording. Subjects were studied in two states; during VNS activity and during a comparison condition of VNS inactivity. A region of interest analysis demonstrated that rapid cycling stimulation (7 seconds on, 12 seconds off) was associated with relatively decreased activity in left and right medial thalamic regions. No systematic stimulation-related changes were observed on visual or spectral analysis of EEG data. The thalamus is involved in modulation of ongoing cortical EEG activity in animals. Our results support the hypothesis that VNS may exert an antiepileptic action by an effect on thalamic activity.

Possible roles for mismatch negativity in neuropsychiatry.

OBJECTIVE: This article reviews research on the main characteristics of mismatch negativity (MMN) and its applications in neuropsychiatry. BACKGROUND: Event-related potentials (ERPs) have been used to study many aspects of information processing. Mismatch negativity is an early auditory ERP that has been identified as an index of an automatic (preconscious) alerting mechanism stimulating an individual to attend to unexpected environmental events. Disturbances of MMN may relate to abnormalities of auditory information processing contributing to the pathophysiology of neuropsychiatric conditions. METHOD: The authors review (1) studies that have evaluated the electrophysiological aspects of MMN and (2) studies that have investigated the different applications of MMN in neuropsychiatry. RESULTS: The first part of this article describes the characteristics of MMN, its cerebral origins, and electrophysiological parameters. We then discuss the role of "echoic memory" as well as that of attention and vigilance. In the second part of the article, disturbances in MMN associated with schizophrenia, depressive illness, dementing processes, and other neuropsychiatric states are discussed. CONCLUSIONS: MMN is a preconscious cognitive ERP, the main generators and functions of which are well defined. Observations relating to the origins of MMN and its role in early auditory information processing together with its possible behavioral significance, combined with observations of MMN aberrations in psychiatric conditions, may provide novel insights into the pathophysiology of neuropsychiatric states.

Monitoring vigilance during single and serial visual evoked potentials.

Full- and half-field visual evoked potentials (VEPs) are used to evaluate functional effects of optic chiasm compression by pituitary tumours. Reduction in VEP amplitude, typically from the temporal fields of vision, can occur even without demonstrable clinical deficit. An inherent problem of prolonged or serial testing is that changing levels of vigilance may affect the VEP. Gradual decrease in vigilance during a test sequence or with serial testing may cause a reduction in amplitude of the response mimicking the abnormality sought. This has serious implications when monitoring the effect of medical treatment since it may give a false impression of tumour growth requiring urgent surgery to prevent blindness. This report illustrates the nature of the problem and describes techniques using electroencephalograms (EEG), which have been used in an attempt to monitor vigilance. The ultimate aim is to produce a system to automate such monitoring during VEP recording.

Effect of antecedent glucose control on cerebral function during hypoglycemia.

OBJECTIVE: The incidence of both severe and asymptomatic hypoglycemia is increased threefold in intensively treated diabetic patients. To examine whether this reflects cerebral adaptation to low blood glucose levels, we investigated the effect of preceding glycemic experience on hormonal, EEG, and evoked potential responses to experimentally induced hypoglycemia with the slow-fall clamp. RESEARCH DESIGN AND METHODS: Three groups were examined: well-controlled diabetic patients and patients with insulinoma (group 1), poorly controlled diabetic patients (group 2), and nondiabetic subjects (group 3). RESULTS: The glucose threshold for epinephrine release was lower in group 1 (2.3 +/- 0.1 vs. 3.0 +/- 0.3 and 3.1 +/- 0.1 mM, P less than 0.02), and the peak epinephrine response was reduced (1.29 +/- 0.36 vs. 5.48 +/- 1 and 5.62 +/- 1.2 nM, P less than 0.01) compared with groups 2 and 3, whereas symptoms were not perceived until a lower blood glucose level had been reached (2.0 +/- 0.2 vs. 3.3 +/- 0.4 and 2.6 +/- 0.2 mM, P less than 0.01). Other counterregulatory responses were similarly delayed and diminished. In contrast, EEG changes that were compatible with hypoglycemia were detected in all subjects in group 1 (blood glucose 1.9 +/- 0.1 mM) but in only two in group 2 and none in group 3, despite similar blood glucose nadirs. CONCLUSIONS: The glycemic threshold for hormonal responses to hypoglycemia falls in individuals with intensively treated diabetes or insulinomas, but these patients are more likely to develop EEG abnormalities during hypoglycemia. This disparity helps explain the increased vulnerability of intensively treated patients to severe hypoglycemia.