Deokwon Ko

Region and frequency specific changes of spectral power in Alzheimer’s disease and mild cognitive impairment

OBJECTIVES To find out whether healthy control (HC), amnestic mild cognitive impairment (aMCI), and Alzheimers disease (AD) subjects exhibit region and frequency specific spectral power differences and whether the spectral power changes correlate with domain-specific cognitive function. METHODS Forty-one AD, 38 aMCI, and 39 HC subjects underwent quantitative EEG and comprehensive neuropsychological tests. Repeated measures analysis of variance was performed to identify differences in EEG spectral power among the three groups by scalp region and EEG frequency. Correlations between region and frequency specific spectral powers and neuropsychological test scores were evaluated. RESULTS Temporal and parieto-occipital theta band powers were highest in AD. Whereas, parieto-occipital alpha and frontal and temporal beta 2 band powers were highest in HC and lowest in AD (p<0.05). Temporal and parieto-occipital theta powers negatively correlated with verbal and visuospatial memory recall, while parieto-occipital alpha and temporal beta 2 powers positively correlated with verbal memory recall (p<0.01). CONCLUSIONS Region and frequency specific oscillatory characteristics of EEG reflect domain-specific cognitive function in patients with aMCI and AD. SIGNIFICANCE Region and frequency specific spectral powers have clinical implications as additional markers differentiating AD, aMCI, and HC.

Theta Oscillation Related to the Auditory Discrimination Process in Mismatch Negativity: Oddball versus Control Paradigm

Background and Purpose The aim of this study was to identify the mechanism underlying the auditory discriminatory process reflected in mismatch negativity (MMN), using time-frequency analysis of single-trial event-related potentials (ERPs). Methods Two auditory tones of different probabilities (oddball paradigm) and the same probability (control paradigm) were used. The average dynamic changes in amplitude were evaluated, and the in-phase consistency of the EEG spectrum at each frequency and time window across trials, event-related spectral perturbations (ERSPs), and inter-trial phase coherence (ITC) were computed. Results Subtraction of the ERPs of standard stimuli from the ERPs of deviant stimuli revealed a clear MMN component in the oddball paradigm. However, no discernible MMN component was observed in the control paradigm. Statistical tests showed that in the oddball paradigm, deviant tones produced significant increases of theta ERSPs and ITC at around 250 ms as compared with the standard tone, while no significant difference between the two stimuli was observed in the control paradigm. Conclusions Our results confirm that the auditory discriminatory process reflected in MMN is accompanied by phase resetting and power modulation at the theta frequency.

Electrophysiologic disturbances during daytime in patients with restless legs syndrome: Further evidence of cognitive dysfunction?

BACKGROUNDS It has been reported that patients with restless legs syndrome (RLS) may have cognitive deficit. The authors performed EEG and ERP analysis during daytime to identify electrophysiologic relations with cognitive dysfunction in unmedicated RLS patients. METHODS Seventeen drug naive RLS patients (53.7±9.6 years) and 13 age-matched healthy controls participated in the present study. EEG was recorded during the waking-resting state and during a visual oddball task. RLS severities were determined using the International RLS Severity Scale. Stanford sleepiness scale (SSS) and bothersomeness visual analog scale (VAS) scores were determined immediately after ERP sessions. EEG power spectra and P300 amplitude and latency were compared for patients and controls. Clinical variables were correlated with P300 findings. RESULTS Waking-resting EEG showed that RLS patients had significantly higher beta activity in frontocentral regions than controls. SSS scores were not different in the two groups. But the bothersomeness VAS scores of RLS patients were significantly higher than those of controls. Furthermore, P300 latency was significantly longer in patients, and patients had significantly lower P300 amplitudes in frontal and central locations. In addition, P300 latency was found to be significantly correlated with bothersomeness during the ERP test, whereas P300 amplitude showed no such tendency. CONCLUSIONS Our study supports the notion that RLS patients have an underlying cognitive dysfunction. Significant correlations found between P300 latency and bothersomeness, a lack of sleepiness during the ERP test, and increased beta activity in resting state EEGs suggest that a combination of inattention and cortical dysfunction underlie cognitive dysfunction in RLS.

Increased Corticomuscular Coherence in Idiopathic REM Sleep Behavior Disorder.

The authors hypothesized that if locomotor drive increases along with rapid eye movement (REM) sleep without atonia in idiopathic REM sleep behavior disorder (RBD), then RBD patients would have greater corticomuscular coherence (CMC) values during REM sleep than at other sleep stages and than in healthy control subjects during REM sleep. To explore this hypothesis, we analyzed beta frequency range CMC between sensorimotor cortex electroencephalography (EEG) and chin/limb muscle EMG in idiopathic RBD patients. Eleven drug naive idiopathic RBD patients and 11 age-matched healthy control subjects were included in the present study. All participants completed subjective sleep questionnaires and underwent polysomnography for one night. The CMC value between EEGs recorded at central electrodes and EMGs acquired at leg and chin muscles were computed and compared by repeated measures analysis of variance (ANOVA). Sleep stages and muscle (i.e., chin vs. leg) served as within-subject factors, and group served as the between-subject factor. Repeated measures ANOVA revealed no significant main effect of group (F1,20 = 0.571, p = 0.458) or muscle (F1,20 = 1.283, p = 0.271). However, sleep stage was found to have a significant main effect (F2.067,41.332 = 20.912, p < 0.001). The interaction between group and sleep stage was significant (F2.067,41.332 = 3.438, p = 0.040). RBD patients had a significantly higher CMC value than controls during REM sleep (0.047 ± 0.00 vs. 0.052 ± 0.00, respectively, p = 0.007). This study reveals increased CMC during REM sleep in patients with RBD, which indicates increased cortical locomotor drive. Furthermore, this study supports the hypothesis that sufficient locomotor drive plays a role in the pathophysiology of RBD in addition to REM sleep without atonia.

Fronto-temporal interactions in the theta-band during auditory deviant processing

Mismatch negativity (MMN) is a negative component of event-related potential (ERP) that reflects auditory deviant detection. Previous studies repeatedly suggested that MMN is generated by the fronto-temporal network. However, it is still unclear how the frontal and temporal areas interact. To verify this, we observed the spatiotemporal pattern of inter-regional functional connectivity using phase synchrony and Granger causality, by analyzing event-related electroencephalograms (EEGs) elicited by standard and deviant tones in an oddball paradigm. Strong theta-band phase synchrony and bidirectional Granger causality were observed between the frontal and temporal areas during the processing of auditory deviants, especially at the temporal interval of MMN. Our results support the hypothesis that fronto-temporal interactions are crucial to the generation of MMN during auditory deviant processing.

Reduced Neural Synchrony in Patients with Restless Legs Syndrome during a Visual Oddball Task

Background Restless legs syndrome (RLS) is a sensorimotor neurological disorder characterized by an irresistible urge to move the legs. It has been reported that RLS patients show cognitive deficits, presumably due to hyperactivity causing loss of attention, or malfunctions in the frontal region resulting from sleep deprivation. However, the mechanism underlying cognitive deficits in RLS patients is mostly unknown. As an effort to clarifying this, we investigated the differences in neural activity and phase synchrony between healthy controls and RLS patients during cognitive task performances. Methodology/Principal Findings Seventeen female drug-naive RLS patients were enrolled in the study, and an age-matched group of thirteen healthy female volunteers served as controls. Multichannel event-related potentials (ERPs) were recorded from RLS patients and normal controls while performing a visual oddball task. In addition to conventional analyses of ERP waveforms and spectra, interregional gamma-band phase synchrony (GBPS) was investigated to observe the differences in interregional neural synchronies between normal and RLS patient groups. Strong GBPS was observed primarily between anterior and posterior regions along the midline for both groups. Along with significant reduction and delay of P300 ERP and induced gamma-band activity (GBA), the GBPS was considerably decreased in RLS patients compared to normal subjects, especially at frontal region. Conclusions Overall, our results support that cognitive dysfunction in RLS patients is associated with reduced interregional neural synchrony as well as alterations in local neural activity.

Cognitive functions and stereopsis in patients with Parkinson's disease and Alzheimer's disease using 3-dimensional television: a case controlled trial.

Stereopsis or depth perception is an awareness of the distances of objects from the observer, and binocular disparity is a necessary component of recognizing objects through stereopsis. In the past studies, patients with neurodegenerative disease (Alzheimer dementia, AD; Parkinson’s disease IPD) have problems of stereopsis but they did not have actual stimulation of stereopsis. Therefore in this study, we used a 3-dimensional (3D) movie on 3D television (TV) for actual stereopsis stimulation. We propose research through analyzing differences between the three groups (AD, IPD, and Controls), and identified relations between the results from the Titmus Stereo Fly Test, and the 3D TV test. The study also looked into factors that affect the 3D TV test. Before allowing the patients to watch TV, we examined Titmus stereo Fly Test and cognitive test. We used the 3D version of a movie, of 17 minutes 1 second duration, and carried out a questionnaire about stereopsis. The scores of the stereopsis questionnaire were decreased in AD patients, compared with in IPD and controls, although they did not have any difference of Titmus Stereo Fly Test scores. In IPD patients, cognitive function (Montreal cognitive assessment, MoCA) scores were correlated with the scores of the stereopsis questionnaire. We could conclude that Titmus fly test could not distinguish between the three groups and cognitive dysfunction contributes to actual stereopsis perception in IPD patients. Therefore the 3D TV test of AD and IPD patients was more effective than Titmus fly test.

Reduced Frontal P3a Amplitude in Migraine Patients during the Pain-Free Period

Background and Purpose Neuropsychological and neuroimaging studies both suggest that frontal lobe dysfunction is present in migraineurs. Since P3a abnormalities manifest in other diseases associated with attention problems, such as attention deficit hyperactivity disorder, we hypothesized that migraine patients have P3a abnormalities, particularly in the frontal region. Methods Event-related potentials were measured using a passive auditory oddball paradigm in 16 female migraineurs (aged 22.9±2.0 years, mean±SD) during the interictal period and in 16 age-matched healthy females (22.6±2.0 years). The amplitudes and latencies were analyzed independently using repeated-measures analysis of variance. Nonparametric statistical testing using a cluster-level randomization method was performed to localize the abnormalities. Results The mean P3a amplitude at frontal areas during the third trials was significantly lower in migraineurs (1.06 µV) than in controls (1.69 µV, p=0.026). P3a amplitudes were negatively correlated with the duration of the migraine history (r=-0.618, p=0.014). Cluster-based nonparametric statistical analysis showed that the amplitudes over left frontal areas were significantly lower in migraine patients than in controls. Conclusions A reduced P3a amplitude of migraineurs reflects attentional deficits and frontal dysfunction. The negative correlation between P3a amplitude and the duration of the migraine history suggests that attentional deficits and frontal dysfunction are either the cause or the result of headache.

The impact of 3D and 2D TV watching on neurophysiological responses and cognitive functioning in adults

BACKGROUND Watching three-dimensional television (3D TV) may strain the eyes. However, other potential harmful effects of 3D TV watching have been rarely investigated. The current study examined the impact of 3D TV watching on neurophysiological responses and cognitive functioning as compared with two-dimensional TV (2D TV) watching. METHODS A total of 72 individuals were randomly assigned to either a 3D TV watching group or a 2D TV watching group. Electroencephalography (EEG) was used to measure neurophysiological responses, and computerized neurocognitive tests were conducted immediately before and after TV watching. The Simulator Sickness Questionnaire (SSQ) was used to assess visual discomfort. RESULTS There was a significant change in visual discomfort between the two groups (SSQ score at baseline: 2.28 ± 3.05 for the 3D TV group and 3.69 ± 3.49 for the 2D TV group; SSQ score after watching TV: 4.6 ± 3.35 for the 3D TV group and 4.03 ± 3.47 for the 2D TV group), and this change was greater for the 3D TV watching group (P = 0.025). However, 3D TV watching did not have a differential impact on EEG responses. Furthermore, there were no significant differences between the groups in terms of changes in cognitive performance, except for a subtle difference in backward digit span performance. CONCLUSION Our findings suggest that 3D TV watching is as safe as 2D TV watching in terms of neurophysiological responses and cognitive functioning. Potential harmful effects of TV viewing might be similar regardless of whether 3D or 2D TV is viewed.

P24-22 Development of Polydimethylsiloxane (PDMS) and silver ball based dry type flexible EEG electrode for EEG recording

band, age-group under 30 has a smallest Z-score among three groups due to suppression by photic stimulus. The age-group from 30 to 60 showed the value intermediate between under 30 and over 60. Conclusions: We proposed the analysis method eliminating individual difference and then applied the method to photic driving response of normal subjects. Z-scores at frequencies such as the fundamental wave and higher harmonics is closely related to age. Significance: By using our statistical analysis method, the frequency characteristics of Z-score varied with advancing age drastically. Our method may be helpful to evaluate brain aging.