Intraoperative EEG-based monitors: are we looking under the lamppost?

PURPOSE OF REVIEW: While electroencephalogram (EEG)-based depth of anesthesia monitors have been in use clinically for decades, there is still a major debate concerning their efficacy for detecting awareness under anesthesia (AUA). Further utilization of these monitors has also been discussed vividly, for example, reduction of postoperative delirium (POD).It seems that with regard to reducing AUA and POD, these monitors might be applicable, under specific anesthetic protocols. But in other settings, such monitoring might be less contributive and may have a 'built-it glass ceiling'.Recent advances in other venues of electrophysiological monitoring might have a strong theoretical rationale, and early supporting results, to offer a breakthrough out of this metaphorical glass ceiling. The purpose of this review is to present this possibility. RECENT FINDINGS: Following previous findings, it might be concluded that for some anesthesia protocols, the prevailing depth of anesthesia monitors may prevent incidences of AUA and POD. However, in other settings, which may involve other anesthesia protocols, or specifically for POD - other perioperative causes, they may not. Attention-related processes measured by easy-to-use real-time electrophysiological markers are becoming feasible, also under anesthesia, and might be applicable for more comprehensive prevention of AUA, POD and possibly other perioperative complications. SUMMARY: Attention-related monitoring might have a strong theoretical basis for the prevention of AUA, POD, and potentially other distressing postoperative outcomes, such as stroke and postoperative neurocognitive disorder. There seems to be already some initial supporting evidence in this regard.

Association Between Risk of Stroke and Delirium After Cardiac Surgery and a New Electroencephalogram Index of Interhemispheric Similarity.

OBJECTIVES: Neurologic complications after surgery (stroke, delirium) remain a major concern despite advancements in surgical and anesthetic techniques. The authors aimed to evaluate whether a novel index of interhemispheric similarity, the lateral interconnection ratio (LIR), between 2 prefrontal electroencephalogram (EEG) channels could be associated with stroke and delirium following cardiac surgery. DESIGN: Retrospective observational study. SETTING: Single university hospital. PARTICIPANTS: A total of 803 adult patients without documentation of a previous stroke, who underwent cardiac surgery with cardiopulmonary bypass (CPB) between July 2016 and January 2018. INTERVENTIONS: The LIR index was calculated retrospectively from the patients' EEG database. MEASUREMENTS AND MAIN RESULTS: LIR was analyzed intraoperatively every 10 seconds and compared among patients with postoperative stroke, patients with delirium, and patients without documented neurologic complications, during 5 key periods, each lasting10 minutes: (1) surgery start, (2) before CPB, (3) on CPB, (4) after CPB, and (5) surgery end. After cardiac surgery, 31 patients suffered from stroke; 48 patients were diagnosed with delirium; and 724 had no documented neurologic complications. Patients with stroke demonstrated a decrease in LIR index between the start of surgery and the postbypass period of 0.08 (0.01, 0.36 [21]; median and [interquartile range {IQR}]; valid EEG samples); whereas there was no similar decrease in the no-dysfunction group (-0.04 [-0.13, 0.04; {551}], p < 0.0001). Patients with delirium showed a decrease in LIR index between the start of surgery and the end of the surgery by 0.15 (0.02, 0.30 [12]), compared with no such decrease in the no-dysfunction group (-0.02 [-0.12, 0.08 {376}], p ≈ 0.001). CONCLUSIONS: After improvement of SNR, it might be of value to further study the index decrease as an indication for risk for brain injury after surgery. The timing of decrease (after CPB or end of surgery) may provide hints regarding the injury pathophysiology and its onset.

Attentional Engagement During Mobile Application Skill Learning Among Patients With Memory Impairment: A Case Series Exploration.

IMPORTANCE: Attentional engagement is essential for successful cognitive rehabilitation, but little is known about longitudinal interactions with skill learning. OBJECTIVE: To examine how attentional engagement is associated with mobile application skill learning for memory compensation. We hypothesized that patients with greater functional capacity would demonstrate faster learning and attentional engagement drop with skill acquisition, whereas patients with lesser functional capacity would have to maintain attentional engagement to progress throughout training. DESIGN: A case series approach was used with longitudinal skill learning and electroencephalographic (EEG) data recorded across multiple trials and sessions of mobile calendar application training. SETTING: The study was run in a hospital-based neuropsychology clinic. PARTICIPANTS: Seven participants (5 with acquired brain injury, 1 with mild cognitive impairment, and 1 healthy older adult) were recruited. INTERVENTION: Mobile application operation was trained for the purpose of memory compensation. Skill learning was facilitated through a structured rehabilitation protocol, including large amounts of guided practice with the integration of errorless learning. OUTCOMES AND MEASURES: We quantified learning using the proportion of application steps completed independently at each session. We measured attentional engagement using an EEG marker: the Brain Engagement Index. RESULTS: For fast learners, attentional engagement generally decreased as mobile application learning progressed. In contrast, slow learners exhibited stable engagement over time with consistent, yet much slower, progress in skill learning. CONCLUSIONS AND RELEVANCE: The present data indicate that when cognitive impairment is more substantial, skill learning may involve greater attentional engagement. What This Article Adds: Patients undergoing memory rehabilitation may benefit from methods to enhance attentional engagement during skill learning when executive dysfunction is a considerable element of their cognitive profile. Monitoring attentional engagement during cognitive rehabilitation may be useful in identifying and addressing barriers to learning in real time.

Identifying Recall Under Sedation by a Novel EEG Based Index of Attention-A Pilot Study.

Overview: Recall is an accepted consequence of sedation. But due to the very low prevalence of the more devastating awareness under anesthesia (AUA), it might be of value to assess first the efficacy of new markers for AUA by their efficacy in discovering the more prevalent recall under sedation (RUS). In this pilot study we assessed whether a novel index for attentional effort, the cognitive effort index (CEI), derived in real-time from one forehead EEG channel, could differentiate between patients with or without RUS. Methods: EEG was sampled from 2 groups: (1) Patients who underwent deep sedation (n = 25) (using drugs according to the anesthesiologist preference, but generally combining either Midazolam or Propofol together with either Fentanyl or Remifentanil). (2) Patients who underwent general anesthesia (GA, n = 13, a negative control for recall). In recovery, recall was assessed using the BRICE questionnaire. Results: Of the 25 sedated patients, 11 experienced recall. The CEI marker was high during significantly longer periods in patients with recall, compared to sedated patients, or patients under GA, without recall. Moreover, the increase in CEI was evident mainly toward the end of the procedure. Conclusion: RUS seems to associate with higher level of attention, which is identified in real-time by the easy-to-extract CEI marker.

Bedside patient engagement monitor for rehabilitation in disorders of consciousness - demonstrative case-reports.

AIM: A chronic disorder of consciousness (DOC) is a devastating condition for the patients and their families. Achieving improved communication with patients in this state is of utmost importance. Over recent years we have seen some progress in the development of rehabilitation protocols for patients with DOC by which the patient's limited actions impact the environment (e.g. activate music) based on the principle of contingent stimulation. However, one of the major factors, which hinders further progress, is the limited overt responsiveness of the patient, which poses a severe limitation on the ability of the therapists to evaluate whether specific interventions have an impact. In this work, we harness a novel electrophysiological marker the Brain Engagement Index (BEI), which enables simple monitoring of patient's engagement during interventions, intending to overcome this limitation. METHODS: We combine the BEI marker with the contingent stimulation principle, to propose a 4-levels protocol for advancing communication with DOC patients. RESULTS: The potential of the evolving protocol is demonstrated with 4 representative case reports. Each case report demonstrates one level of the protocol. CONCLUSIONS: The protocol seems to be both feasible and effective for better clarification of the communication abilities of DOC patients. We recommend its continued evaluation employing a more structured study.IMPLICATIONS FOR REHABILITATIONWe suggest a systematic method for rehabilitation of patients with disorders of consciousnessIt is based upon monitoring patient engagement in real-time and selecting interventions accordingly.

A Theoretical Comprehensive Framework for the Process of Theories Formation.

Scientists rely more and more upon computerized data mining and artificial intelligence to analyze data sets and identify association rules, which serve as the basis of evolving theories. This tendency is likely to expand, and computerized intelligence is likely to take a leading role in scientific theorizing. While the ever-advancing technology could be of great benefit, scientists with expertise in many research fields do not necessarily understand thoroughly enough the various assumptions, which underlie different data mining methods and which pose significant limitations on the association rules that could be identified in the first place. There seems to be a need for a comprehensive framework, which should present the various possible technological aids in the context of our neurocognitive process of theorizing and identifying association rules. Such a framework can be hopefully used to understand, identify, and overcome the limitations of the currently fragmented processes of technology-based theorizing and the formation of association rules in any research field. In order to meet this end, we divide theorizing into underlying neurocognitive components, describe their current technological expansions and limitations, and offer a possible comprehensive computational framework for each such component and their combination.

Real-time monitoring of barriers to patient engagement for improved rehabilitation: a protocol and representative case reports.

PURPOSE: There is ample evidence that patient engagement is of major clinical importance in rehabilitation, and it seems this engagement is based upon effective allocation of attention to the tasks during the rehabilitation session. It is possible to discern two types of barriers which hinder attentive engagement: (1) dysfunctional affective coping and (2) limited cognitive recruitment and specifically attention deficit. These barriers might be general for a given patient, due to pre-morbid or co-morbid dysfunctions. But more often they are evoked by tasks or challenges during the rehabilitation session which might be too complicated or stressing for the specific patient who copes with potentially grave impairments. These barriers hinder rehabilitation progress and should be monitored and overcome, by the therapist, throughout the session. METHODS: We have developed an easy-to-use tool for monitoring a patient's attentive engagement in real-time throughout a rehabilitation session based on analysing the electrophysiological signal sampled from a simple headset. The tool then analyzes the dynamics of the marker over time to identify cognitive and affective barriers during the session. It enables the therapist to insert feedback regarding the patient's functional performance and to combine it with the analysed barriers, in order to derive automatic recommendations for overcoming the cognitive and affective barriers (if identified) for significant enhancement of the rehabilitation session. RESULTS AND CONCLUSIONS: In this work we present the principles of the tool as well as three detailed case reports to demonstrate its potential usefulness.IMPLICATIONS FOR REHABILITATIONCognitive and affective barriers hinder patient engagment and rehabilitation success.In this work we present an easy to use electrophysiology-based tool which monitors these barriers.Based on the measured barriers and patient's performance, the tool derives treatment suggestions.

The Effects of Anesthetics on the Cortex-Lessons From Event-Related Potentials.

Consciousness while under general anesthesia is a dreadful condition. Various electroencephalogram (EEG)-based technologies have been developed, on the basis of empirical evidence, in order to identify this condition. However, certain electrophysiological phenomena, which seem strongly related with depth of anesthesia in some drugs, appear less consistent with those of other anesthetic drugs. There is a gap between the complexity of the phenomenon of consciousness and its behavioral manifestations, on the one hand, and the empirical nature of the reported electrophysiological markers, which are associated with it, on the other hand. In fact, such a gap might prevent us from progressing toward unified electrophysiological markers of consciousness while under anesthesia, which are applicable to all anesthetic drugs. We believe that there is a need to bridge this conceptual gap. Therefore, in this work, we will try to present a theoretical framework for such bridging. First, we suggest focusing on neuropsychological processes, which seem to have a clear role in the behavioral manifestations of consciousness while under anesthesia but seem, nevertheless, better defined than consciousness itself-such as perception and attention. Then, we suggest analyzing the effects of anesthesia upon these neuropsychological processes, as they are manifested in the EEG signal. Specifically, we will focus on the effects of anesthesia on event-related potentials (ERPs), which seem more easily associable with neuropsychological modeling.

A pilot study on the electrophysiological monitoring of patient's engagement in post-stroke physical rehabilitation.

Introduction: This study discusses the feasibility of an electrophysiological monitor for patient engagement during rehabilitation sessions. While patient engagement has a significant clinical role, it is not obvious how its real-time monitoring could be used.Objective: We designed this study to provide further support for the feasibility of such a tool based on the Brain Engagement Index (BEI), and to discuss clinical usefulness and its evaluation.Methods: The study involved 30 patients during post-stroke rehabilitation. Each patient underwent two sessions with BEI monitoring. In one session the therapist received real-time feedback from the monitor and in the other he did not. The BEI was compared to video-based evaluation of temporary functional change from the session start to its end and with a rater-based evaluation of the level of engagement evoked by the exercises in the session.Results: Irrespective of whether feedback is used, there is association between BEI and temporary functional change as well as with evaluated engagement. Furthermore, the contribution of the BEI monitor to rehabilitation may be demonstrated.Conclusions: It would be challenging to establish directly the monitor's contribution in large-scale studies. Nevertheless, it might be sufficient to demonstrate that the monitor provides important information regarding patient engagement.Implication for RehabilitationThis work presents an easy-to-use electrophysiological index for monitoring patient engagement in real-time.Enhanced engagement is of utmost importance for effective rehabilitation.The ability to identify in real-time barriers to engagement is expected to be of great contributive value.

A New Index of Coordinated Posterior and Anterior Evoked EEG to Detect Recall Under Sedation - A Pilot Study.

EEG-based technologies may be limited in identifying recall under sedation (RUS). We developed a novel index, posteriorization/anteriorization (P/A) index, based on auditory evoked EEG signal and assessed whether it could differentiate between patients with or without RUS. Methods: EEG and BIS were sampled from 3 groups: 1. Patients undergoing sedation (n = 26); 2. Awake volunteers (n = 13, positive control for recall) 3. Patients undergoing general anesthesia (GA, n = 12, negative control for recall). In recovery, recall was assessed using the BRICE questionnaire. Of the 26 sedated patients, 12 experienced recall. Both The P/A index and BIS differentiated between patients with recall and no recall. However, BIS differentiation may have been sensitive to the main drug used for sedation (midazolam vs. propofol) and the P/A index did not show similar drug-based sensitivity. Furthermore, only BIS results were correlated with EMG. Conclusion: This pilot study provided support for the association between P/A index and recall after sedation. Further research is needed in integrating the index into clinical use: (1) it should be derived by an easy-to-use EEG system with a better signal-to-noise ratio; (2) its applicability to other drugs must be shown.

Neuropsychiatric Disorders as Erratic Attention Regulation - Lessons from Electrophysiology.

Attention related electrophysiological waves, such as P300, often deviate from norm in various populations of neuropsychiatric patients. For example, the amplitude is often smaller and the latency is often longer in major depressive disorder, in bipolar disorder and in schizophrenia. On the other hand, in other neuropsychiatric populations, it is often possible to note the opposite phenomena of larger P300 amplitude and shorter latency in comparison with norm, but only for a specific subset of stimuli. This is often reported in various anxiety disorders, substance abuse and various chronic pain syndromes. These findings in the various clinical populations, on their commonalities and differences, are presented in this work. The prevalence of these two types of deviations in the electrophysiological markers of attention, shared by multiple neuropsychiatric populations, raise interesting questions regarding the role of attention deviation and regulation in neuropsychiatry. We present these questions and outline a possible hypothesis in this regard. Furthermore, such potential sensitivity of the attention-related markers to clinical dynamics suggests they could be candidates for monitoring and, potentially, early-sensing of clinical dynamics. Therefore, we discuss the potential usability of such markers.

Monitoring Migraine Cycle Dynamics with an Easy-to-Use Electrophysiological Marker-A Pilot Study.

Migraine attacks can cause significant discomfort and reduced functioning for days at a time, including the pre-ictal and post-ictal periods. During the inter-ictsal period, however, migraineurs seem to function normally. It is puzzling, therefore, that event-related potentials of migraine patients often differ in the asymptomatic and inter-ictal period. Part of the electrophysiological dynamics demonstrated in the migraine cycle are attention related. In this pilot study we evaluated an easy-to-use new marker, the Brain Engagement Index (BEI), for attention monitoring during the migraine cycle. We sampled 12 migraine patients for 20 days within one calendar month. Each session consisted of subjects' reports of stress level and migraine-related symptoms, and a 5 min EEG recording, with a 2-electrode EEG device, during an auditory oddball task. The first minute of the EEG sample was analyzed. Repetitive samples were also obtained from 10 healthy controls. The brain engagement index increased significantly during the pre-ictal (p ≈ 0.001) and the ictal (p ≈ 0.020) periods compared with the inter-ictal period. No difference was observed between the pre-ictal and ictal periods. Control subjects demonstrated intermediate Brain Engagement Index values, that is, higher than inter-ictal, yet lower than pre-ictal. Our preliminary results demonstrate the potential advantage of the use of a simple EEG system for improved prediction of migraine attacks. Further study is required to evaluate the efficacy of the Brain Engagement Index in monitoring the migraine cycle and the possible effects of interventions.

Simple Electroencephalographic Treatment-Emergent Marker Can Predict Repetitive Transcranial Magnetic Stimulation Antidepressant Response-A Feasibility Study.

OBJECTIVES: Prefrontal repetitive transcranial magnetic stimulation (rTMS) repeated daily for 4 to 6 weeks is used to treat major depressive disorder, but more than 50% of patients do not achieve significant response. Here we test the validity of a simple electroencephalographic (EEG) marker that predicts nonresponse to rTMS. Such a marker could potentially increase rTMS effectiveness by directing nonresponders to alternative treatments or by guiding early modification of stimulation parameters. METHODS: We retrospectively analyzed 2-channel EEG data captured in the OPT-TMS National Institute of Mental Health-sponsored, multicenter study. Cumulative Brain Engagement Index (cBEI), a measure derived from template matching that allows scoring EEG dynamics along treatment, was computed. RESULTS: Six hundred sixty-five EEG recordings were analyzed. In the rTMS group, the median cBEI was found to increase in the responder group but remained unchanged in the nonresponder group. The difference between the cBEI of the groups became statistically significant by the third valid EEG sample. Within 5 samples, 91% of the responders presented with a cBEI above a preset threshold. Within 9 samples, 17% of the nonresponders had a cBEI above the threshold. CONCLUSIONS: This study demonstrates the feasibility of a simple-to-capture EEG marker as a treatment-emergent marker of response to rTMS treatment of depression. In the OPT-TMS study, discontinuing treatment when the cBEI dropped below the threshold between the fifth to ninth treatment potentially could have avoided administration of 485 (63%) of 765 treatments. Because the marker can be generated online, it would be of interest to evaluate, in future studies, whether it could be used to tune treatment parameters and improve remission rates.

Monitoring Attention in ADHD with an Easy-to-Use Electrophysiological Index.

Attention deficit hyperactivity disorder (ADHD) involves characteristic electroencephalographic (EEG) activity. We developed a single-channel EEG marker for attention: the Brain Engagement Index (BEI'). In this study, we evaluated the use of BEI' for distinguishing between ADHD patients and controls, and for monitoring the effect of pharmacological treatment on ADHD patients. The BEI' values of 20 ADHD patients and 10 controls were measured using a 1-min auditory oddball paradigm and a continuous performance test (CPT) task. We showed that CPT BEI' is trait-specific and separates controls from ADHD patients. At the same time, oddball BEI' is state-specific and identifies differences in attention level within the two groups of ADHD participants and controls. The oddball BEI' also associates with response to treatment, after distinguishing between treatment effect and learning/time effect. The combined use of this marker with common computerized tests holds promise for research and clinical use in ADHD. Further work is required to confirm the results of the present study.

An EEG Tool for Monitoring Patient Engagement during Stroke Rehabilitation: A Feasibility Study.

OBJECTIVE: Patient engagement is of major significance in neural rehabilitation. We developed a real-time EEG marker for attention, the Brain Engagement Index (BEI). In this work we investigate the relation between the BEI and temporary functional change during a rehabilitation session. METHODS: First part: 13 unimpaired controls underwent BEI monitoring during motor exercise of varying levels of difficulty. Second part: 18 subacute stroke patients underwent standard motor rehabilitation with and without use of real-time BEI feedback regarding their level of engagement. Single-session temporary functional changes were evaluated based on videos taken before and after training on a given task. Two assessors, blinded to feedback use, assessed the change following single-session treatments. RESULTS: First part: a relation between difficulty of exercise and BEI was identified. Second part: temporary functional change was associated with BEI level regardless of the use of feedback. CONCLUSIONS: This study provides preliminary evidence that when BEI is higher, the temporary functional change induced by the treatment session is better. Further work is required to expand this preliminary study and to evaluate whether such temporary functional change can be harnessed to improve clinical outcome. CLINICAL TRIAL REGISTRATION: Registered with clinicaltrials.gov, unique identifier: NCT02603718 (retrospectively registered 10/14/2015).

A Pilot Study of Possible Easy-to-Use Electrophysiological Index for Early Detection of Antidepressive Treatment Non-Response.

INTRODUCTION: The evaluation of response to pharmacological treatment in MDD requires 4-8 weeks. Therefore, the ability to predict response, and especially lack of response to treatment, as early as possible after treatment onset or change, is of prime significance. Many studies have demonstrated significant results regarding the ability to use EEG and ERP markers, including attention-associated markers such as P300, for early prediction of response to treatment. But these markers are derived from long EEG/ERP samples, often from multiple channels, which render them impractical for frequent sampling. METHODS AND RESULTS: We developed a new electrophysiological attention-associated marker from a single channel (two electrodes), using 1-min samples with auditory oddball stimuli. This work presents an initial evaluation of the ability to use this marker's dynamics between repetitive measures for early (<2 weeks) differentiation between responders and non-responders to antidepressive treatment, in 26 patients with various levels of depression and heterogeneous treatment interventions. The slope of change in the marker between early consecutive samples was negative in the non-responders, but not in the responders. This differentiation was stronger for patients suffering from severe depression (p < 0.001). CONCLUSION: This pilot study supports the feasibility of the EEG marker for early recognition of treatment-resistant depression. If verified in large-scale prospective studies, it can contribute to research and clinical work.

A Possible Common Neurophysiologic Basis for MDD, Bipolar Disorder, and Schizophrenia: Lessons from Electrophysiology.

There is ample electrophysiological evidence of attention dysfunction in the EEG/ERP signal of major depressive disorder (MDD), bipolar disorder, and schizophrenia. The reduced attention-related ERP waves show much similarity between MDD, bipolar disorder, and schizophrenia, raising the question whether there are similarities in the neurophysiologic process that underlies attention dysfunction in these pathologies. The present work suggests that there is such a unified underlying neurophysiologic process, which results in reduced attention in the three pathologies. Naturally, as these pathologies involve different clinical manifestations, we expect differences in their underlying neurophysiology. These differences and their subtle manifestation in the ERP marker for attention are also discussed. MDD, bipolar disorder, and schizophrenia are just three of multiple neuropsychiatric disorders, which involve changes in the EEG/ERP manifestations of attention. Further work should expand the basic model presented here to offer comprehensive modeling of these multiple disorders and to emphasize similarities and dissimilarities of the underlying neurophysiologic processes.

Migraine as dysfunctional drive reduction: Insight from electrophysiology.

Migraine is a prevalent disease, which may cause significant discomfort and reduced functioning for days, including the preictal and postictal periods. During the interictal period, however, migraineurs seem to function normally. It is puzzling, therefore, that event-related potentials (ERPs) of migraine patients often differ at the group level also in the asymptomatic, interictal phase, both in early and later ERP waves. Furthermore both types of ERP waves demonstrate changes, which are often noticed 12-48h before a migraine attack and continue throughout it. On the basis of previous work, it might be possible to associate these ERP differences and their dynamics with changes in patient attention, which might be further associated with stress. This paper suggests that such stress-related dynamics can explain both the ERP findings as well as the dynamics in clinical symptoms throughout the migraine cycle. It further suggests that migraine can be viewed as a (dysfunctional) stress-reducing solution. In this sense migraine can be viewed as a representative case for other stress-related and psychopathological disorders, which are also stress-reducing solutions.

Intracarotid Etomidate Decreases the Interhemispheric Synchronization in Electroencephalogram (EEG) During the Wada Test.

BACKGROUND: The Wada test is a diagnostic method to anesthetize 1 cerebral hemisphere and assess the language and memory functions of awake contralateral hemisphere before temporal lobectomy in patients with epilepsy. The effects of an ipsilateral injection of etomidate on the functional properties of contralateral hemisphere are not known. Our aim was to characterize the electroencephalographic (EEG) effects after intracarotid injection of etomidate and to determine the changes in synchronization between the ipsilateral and contralateral hemispheres. MATERIALS AND METHODS: We retrospectively analyzed EEG data from 15 patients who underwent Wada test with etomidate. Continuous EEG data from 4 electrodes (2 anterior [F3, F4] and 2 posterior [P3, P4]) were analyzed. After artifact rejection, we measured the amplitudes of delta (1 to 4 Hz) and alpha (7 to 13 Hz) waves and the changes in the interhemispheric synchronization before, during, and after etomidate injection. RESULTS: Ipsilateral injection of etomidate causes EEG changes in both hemispheres with increased amplitude of delta waves anteriorly and the alpha waves posteriorly. However this effect of etomidate is not uniform. Although there was a decrease in the interhemispheric synchronization of delta waves, there was no change in the synchronization of the alpha waves. CONCLUSIONS: Our study showed that the EEG effects of intracarotid ipsilateral injection of etomidate is not uniform in both hemispheres. Decrease in the interhemispheric synchronization of delta waves might serve as an indicator of ipsilateral effect of etomidate on the brain. Additional studies are needed to confirm our findings.

Thorough specification of the neurophysiologic processes underlying behavior and of their manifestation in EEG - demonstration with the go/no-go task.

In this work we demonstrate the principles of a systematic modeling approach of the neurophysiologic processes underlying a behavioral function. The modeling is based upon a flexible simulation tool, which enables parametric specification of the underlying neurophysiologic characteristics. While the impact of selecting specific parameters is of interest, in this work we focus on the insights, which emerge from rather accepted assumptions regarding neuronal representation. We show that harnessing of even such simple assumptions enables the derivation of significant insights regarding the nature of the neurophysiologic processes underlying behavior. We demonstrate our approach in some detail by modeling the behavioral go/no-go task. We further demonstrate the practical significance of this simplified modeling approach in interpreting experimental data - the manifestation of these processes in the EEG and ERP literature of normal and abnormal (ADHD) function, as well as with comprehensive relevant ERP data analysis. In-fact we show that from the model-based spatiotemporal segregation of the processes, it is possible to derive simple and yet effective and theory-based EEG markers differentiating normal and ADHD subjects. We summarize by claiming that the neurophysiologic processes modeled for the go/no-go task are part of a limited set of neurophysiologic processes which underlie, in a variety of combinations, any behavioral function with measurable operational definition. Such neurophysiologic processes could be sampled directly from EEG on the basis of model-based spatiotemporal segregation.