Auditory evoked potentials in sleep

AMAÇ: Bu çalısmanın amacı uykunun farklı evrelerinde uygulanan işitsel uyaranlara karşı verilen yanıtların değişimini irdelemektir. GEREÇ ve YÖNTEM: Çalısmaya 12 gönüllü birey alınmıştır (18-32 yas, ort: 24.5±4.1; 2 kadın). Kayıtlar, NuAmps 40 kanallı [Elektroensefalografi (EEG), Elektrookülografi (EOG), çene Elektromyografisi (EMG)] kayıt sistemi, ses uyarı modülü, video ve Bispektral indeks (BIS) monitorizasyonu kullanılarak gerçekleştirilmiştir. Uyku kayıtları sırasında (1500 Hz, 80 dB, 500 ms) işitsel uyaranlar kulak içine (etimotik) uygulanmıştır. Sürekli EEG, EOG ve EMG verileri, Rechtschaffen ve Kales (R&K) skorlama sistemine göre uyku evrelerine ayrılmıştır. Her bir evrede [Non-REM (N1, N2, N3 ve N4) ve REM] isitsel uyarılma potansiyelleri (IUP) incelenmiştir. Cz elektrotundan kayıtlı N100, P200, N300, P450, N550 ve P900 yanıtlarının uyku evrelerine göre değişimi araştırılmıştır. Istatistiksel analizlerde uyku evreleri ile IUP bileşenlerinin genlik ve latans ilişkileri tek yönlü varyans analizi (ANOVA) ile incelenmiştir. Ikili karşılaştırmalarda Bonferroni post hoc testi uygulanmıştır. BULGULAR: Uykunun derinleşmesi ile N100 bileseninin küçüldüğü, N300 ve P900 bileşeninin ise büyüdüğü gösterilmiştir. Dalga formlarında bulunan değişiklikler uykunun farklı evrelerinde (ve mikro evrelerde) dinamik bilgi işlemleme süreçleri olduğunu göstermektedir. SONUÇ: Isitsel uyarılma potansiyelleri, erken duyusal potansiyellerden geç işlemleme süreçlerine kadar beyin fonksiyonlarının çalışılmasında yararlı bir yöntemdir. Bu elektrofizyolojik ipuçları gelecekte uyku araştırmalarına ve klinik uygulamalara yararlı olabilirler.OBJECTIVE: The aim of the present study is to investigate the responses to auditory stimulations during different sleep stages. MATERIALS and METHODS: Twelve subjects (mean age: 24.5±4.1; 2 female) participated in the study. Data collection was performed with 40 channel NuAmps [Electroencephalography (EEG), electrooculography (EOG), chin electromyography (EMG)] recording system, auditory stimulation unit, video and Bispectral Index (BIS) monitorization. The records were scored according to Rechtschaffen and Kales (R&K) scoring system. Auditory evoked potentials (AEP) were analyzed in each sleep stage [Non-REM (N1, N2, N3 and N4) and REM]. N100, P200, N300, P450, N550 and P900 (P750) components were examined in Cz electrode. One-wayANOVA was applied to compare amplitudes and latencies of AEP components in different sleep stages. Post-hoc comparisons were conducted with Bonferroni method. RESULTS: The results showed that by deepening of sleep N100 decreased, N300 and P900 increased. The changes and interactions in the waveforms pointed at a dynamic information processing in the brain throughout different stages (and also microstates) of sleep. CONCLUSION: The auditory stimulations serve as a plausible study method providing a scope for brain functioning from early sensory potentials to very late processes (as late as 900 ms post-stimulus). These electrophysiological hints may be utilized for future sleep research studies as well as clinical applications

Brain function assessment in different conscious states

Background: The study of brain functioning is a major challenge in neuroscience fields as human brain has a dynamic and ever changing information processing. Case is worsened with conditions where brain undergoes major changes in so-called different conscious states. Even though the exact definition of consciousness is a hard one, there are certain conditions where the descriptions have reached a consensus. The sleep and the anesthesia are different conditions which are separable from each other and also from wakefulness. The aim of our group has been to tackle the issue of brain functioning with setting up similar research conditions for these three conscious states.Methods: In order to achieve this goal we have designed an auditory stimulation battery with changing conditions to be recorded during a 40 channel EEG polygraph (Nuamps) session. The stimuli (modified mismatch, auditory evoked etc.) have been administered both in the operation room and the sleep lab via Embedded Interactive Stimulus Unit which was developed in our lab. The overall study has provided some results for three domains of consciousness. In order to be able to monitor the changes we have incorporated Bispectral Index Monitoring to both sleep and anesthesia conditions.Results: The first stage results have provided a basic understanding in these altered states such that auditory stimuli have been successfully processed in both light and deep sleep stages. The anesthesia provides a sudden change in brain responsiveness; therefore a dosage dependent anesthetic administration has proved to be useful. The auditory processing was exemplified targeting N1 wave, with a thorough analysis from spectrogram to sLORETA. The frequency components were observed to be shifting throughout the stages. The propofol administration and the deeper sleep stages both resulted in the decreasing of N1 component. The sLORETA revealed similar activity at BA7 in sleep (BIS 70) and target propofol concentration of 1.2 μg/mL.Conclusions: The current study utilized similar stimulation and recording system and incorporated BIS dependent values to validate a common approach to sleep and anesthesia. Accordingly the brain has a complex behavior pattern, dynamically changing its responsiveness in accordance with stimulations and states. © 2010 Ozgoren et al; licensee BioMed Central Ltd

Investigation of sleep dynamics through multi-auditory stimuli

Amaç: Uykuda beyin yanıtlılığının, klasik uyku evreleme ve BİS sistemine göre farklı dönemlerde, işitsel uyaranlar aracılığıyla ve ?Uyarılma Potansiyelleri? yöntemi ile incelenmesi. Gereç ve Yöntem: Çalışmada 18 gönüllü bireyin uyku kayıtları incelendi (18-32 yaş, ort: 24.4 ± 3.6; 5 kadın). Uyku kayıtları sırasında basit işitsel uyaranlar (1500 Hz, 80 dB, 500 ms) kulak içine (etimotik) uygulandı. Klasik uyku skorlama ve BİS sistemine göre uyku dönemleri belirlendi ve her bir uyku döneminde işitsel uyarılma potansiyelleri (İUP) incelendi. N100, P200, N300, P450, N550 ve P900 yanıtlarının uyku dönemleri arasındaki değişimi araştırıldı. Bulgular: BİS sistemi ve klasik NREM uyku evreleri arasında, yüksek korelasyon olduğu saptandı. BİS sistemi ile uyku, klasik skorlama sistemlerine göre daha fazla sayıda dönemlerine ayrıldı ve İUP bileşenlerindeki değişim, daha fazla kademede incelendi. Özellikle, N100 bileşen genliğinde uyku derinleştikçe küçülme, N300 ve P900 bileşen genliklerinde ise büyüme görüldü. BİS ve NREM uyku evrelerinde elde edilen İUP arasında, yüksek korelasyon bulundu. Uykunun ilk ve ikinci yarısı arasında, İUP açısından farklılıklar olduğu gösterildi. İkinci yarı uykuda, yüzeyel uyku döneminde N100 genliğinin, derin uyku dönemlerinde ise P200 ve P900 genliklerinin küçüldüğü görüldü. Sonuç: Bu çalışma, BİS sistemi ile uykuda IUP'nin birlikte incelendiği ilk çalışma olma özelliğini göstermektedir. Bulgular, BİS sisteminin uyku dinamiğinin çalışılmasında, yararlı olabileceğini göstermiştir. Ayrıca uyku, BİS sistemi ile daha fazla alt dönemde incelenebildiği için İUP altında yatan süreçler, daha detaylı çalışılabilmiştir. Bu çalışmada BİS sistemi, klasik uyku evreleme sistemleri yerine değil, beraberinde kullanılmak üzere önerilmektedir. Uyku İUP bileşenlerinin altında yatan süreçleri anlayabilmek için daha çok kapsamlı çalışmaya ihtiyaç vardır. Dinamik İUP yöntemi ile BİS sisteminin birlikte kullanıldığı yeni çalışmalar, farklı uyku bozukluklarının altındaki patolojik süreçlerin aydınlatılmasında da fayda sağlayabilir. Objective: The aim of the present study is to investigate the brain responsiveness during different stages of sleep, which are scored according to classical sleep scoring and BIS systems, via auditory stimulations and ?Evoked Potentials?. Materials and Methods: In the study sleep recordings of 18 volunteer subjects were analyzed (18-32 year old, mean age: 24.4 ± 3.6; 5 females). During sleep recordings, auditory stimuli were applied into the ear channel (etymotic). Sleep stages were scored according to conventional sleep scoring systems and BIS system and in each of these stages Auditory Evoked Potentials (AEP) were analyzed. The alterations of N100, P200, N300, P450, N550 and P900 waveforms were investigated in different sleep stages. Results: A very high correlation factor was obtained between BIS system and classical NREM sleep stages. Sleep recordings were scored into more levels according to BIS system than conventional scoring systems. Deepening of sleep were followed by the decrease of N100 component amplitude, whereas N300 and P900 components? were found to be increased. Also, it has been found that, there was a very high correlation between AEPs which were scored according to classical methods and BIS system. Furthermore, it has been shown that, there was prominent differences in the first and second halves of sleep AEPs. In the second half of the sleep, N100 amplitude was higher in the light sleep and the amplitudes of P200 and P900 were higher in deep sleep stages. Conclusion: The present research is the first in studying BIS and AEPs together in sleep. The results showed that, BIS system may serve as a fruitful method in studying sleep dynamics. Furthermore, with the usage of BIS system, sleep could be analyzed in more stages which will in turn be useful studying the underlying processes of AEPs. In the present study, it was not the intention to claim that BIS system can replace classical staging methods, rather it is recommended as an accompanying method to sleep staging. Understanding the processes underlying the sleep AEPs needs further comprehensive researches. Future studies with dynamic AEPs and BIS system might also be beneficial in clarifying the pathological processes underlying sleep disorders

Electrophysiological and Bispectral Indeks Applications in REM Sleep

The goal of this study is to scrutinize the changes in electrophysiological responses to simple and complex auditory stimulations in REM sleep using Bispectral index (BIS) system besides Rechtschaffen and Kales (R&K) scoring system

Sleep Electrophysiology Via the Scope of Bispectral Index

Objective: The goal of this study was to investigate the changes in the responses to auditory stimuli, which were sorted according to the Bispectral Index (BIS) during sleep. This is the first known research study that incorporated full-scale analysis of sleep auditory evoked potentials (AEP) under the scope of BIS. Material and Methods: The measurements were conducted in twelve subjects (18-32 ages, mean: 24.5 +/- 4.1; 2 female). Recordings were done by using NuAmps 40 channel system [electroencephalography (EEG), electrooculography (EOG), and chin electromyography (EMG)], auditory stimulation unit, video and BIS monitor. Sleep data was acquired while (1500 Hz, 80 dB and 500 ms) auditory stimulations were applied into the ear channels (etymotic). The continuous EEG data were grouped according to the BIS index. In this sub-group of recordings, AEPs were analyzed. The evolution of N1, P2, N300, P450, N550 and P900 waveforms recorded from Cz electrode were investigated with regard to correlation of BIS and sleep stages. Results: The reduction of BIS values were followed by the decrease of NI component, whereas N300 and P900 components were found to be increased (Wilcoxon, p<0.05). AEPs dynamically evolved according to the changes in BIS values. The present findings support and advance the outcome of classical designs, which are based solely on the system Rechtschaffen & Kales (R&K) system. Conclusion: The present study investigated sleep states in extended number of levels with the BIS system, which provided higher time resolution. Based on the results, BIS may be suggested as a useful tool for sleep dynamic research studies also in pathological states

Analysis of non-REM sleep staging with electroencephalography bispectral index

The present study provides results in an early sleep period for non-REM stage correlation with bispectral index (BIS) values. The purpose of the study was to assess the applicability of an objective procedure to monitor sleep. Nine healthy subjects (mean age: 25.0 +/- 4.4; 1 female) were recruited for the study without history of any neurological, psychiatric, or sleep-related disorders. Electroencephalography (EEG) signals from 30 electrodes referenced to linked earlobe electrodes, and electrooculography (EOG) and electromyography (EMG) activities were recorded. BIS recording was performed simultaneously with EEG recording. Because that the current study is related to non-REM sleep, corresponding to the first sleep cycle, approximately 90 min of data was processed both for BIS and EEG data pools. The sleep staging was done using traditional Rechtschaffen and Kales scoring (R&K) and BIS scores were acquired online. The BIS values corresponded well to sleep depth, decreasing in accordance with sleep stages. Overall BIS correlation with sleep scores in the non-REM was found to be r = 0.86 (Spearman analysis, n = 9, r(2) = 0.75). Accompanying the traditional scoring, BIS and BIS-like tools can be useful for information processing and for psychophysiological applications in neurology, psychiatry, and further studies on consciousness

Synchronization Analysis of EEG Epilepsy by Visibility Network Graph and Cross-correlation

Epilepsy is a chronic neurological disorder affects people of all ages; this paper presents cross-correlation and state transfer network method to analyze synchronization between EEG data-channels from subjects with epilepsy seizures. The datasets are in two phases, preictal and ictal phase. All EEG segments are mapped into a corresponding state network graph to obtain the corresponding motifs and then the cross-correlation is applied to exhibit the synchronization changing during epilepsy seizures. The results showed that ictal phase presented high synchronization between channels, where low synchronization level is observed within preictal phase

Interhemispheric Correlation and Epileptic Seizures: Are They Related? A Preliminary Retrospective Study

Objectives: For the purpose of predicting seizure activities in focal temporal lobe epilepsy we examined interhemispheric correlation coefficients in pre-ictal EEG data