Assessment of Neurovascular Coupling by Spectral Analysis of Cerebral Blood Flow Velocity With Transcranial Doppler

OBJECTIVE

Neurovascular coupling (NVC) represents the increase in regional blood flow associated with neural activity. The aim here was to describe a new approach to non-invasive measurement of NVC by spectral analysis of the cerebral blood flow velocity (CBFV) with transcranial Doppler.

METHODS

In a sample of 20 healthy participants, we monitored systolic CBFV in the left posterior cerebral artery (PCA) during off (eyes closed) and on (flickering checkerboard) periods. The contralateral middle cerebral artery was simultaneously monitored as a control. Each participant was submitted to three experiments, each having five cycles, with increasing duration of the cycles, from 10 s (0.1 Hz) to 20 s (0.05 Hz) and lastly 40 s (0.025 Hz), half the time for on and for off periods, constituting a total of 6 min. The successive cycles were expected to cause oscillation in CBFV in a sinusoidal pattern that could be characterized by spectral analysis. We also measured the classic CBFV overshoot as the relative increase in percentage of systolic CBFV from baseline. The relationship and agreement between the two methods were analyzed by linear regression and Bland-Altman plots. In every participant, a clear peak of amplitude in the PCA CBFV spectrum was discernible at 0.1, 0.05 and 0.025 Hz of visual stimulation.

RESULTS

On average, this amplitude was 7.1 ± 2.3%, 10.9 ± 3.5% and 17.3 ± 6.5%, respectively. This response contrasted significantly with an absent peak in middle cerebral artery monitoring (p < 0.0001). The spectral amplitude and classic overshoot were highly correlated and linearly related (p < 0.0001).

CONCLUSION

NVC can be quantified by the spectral amplitude of PCA CBFV at slower and higher frequencies of visual stimulation. This method represents an alternative to classic overshoot without the need for stimulus marking or synchronization.

Single-trial EEG analysis reveals burst structure during photic driving

OBJECTIVE

Photic driving in the human visual cortex evoked by intermittent photic stimulation is usually characterized in averaged data by an ongoing oscillation showing frequency entrainment and resonance phenomena during the course of stimulation. We challenge this view of an ongoing oscillation by analyzing unaveraged data.

METHODS

64-channel EEGs were recorded during visual stimulation with light flashes at eight stimulation frequencies between 7.8 and 23 Hz for fourteen healthy volunteers. Time-frequency analyses were performed in averaged and unaveraged data.

RESULTS

While we find ongoing oscillations in the averaged data during intermittent photic stimulation, we find transient events (bursts) of activity in the unaveraged data. Both resonance and entrainment occur for the ongoing oscillations in the averaged data and the bursts in the unaveraged data.

CONCLUSIONS

We argue that the continuous oscillations in the averaged signal may be composed of brief, transient bursts in single trials. Our results can also explain previously observed amplitude fluctuations in averaged photic driving data.

SIGNIFICANCE

Single-trial analyses might consequently improve our understanding of resonance and entrainment phenomena in the brain.

Light-emitting-diode and Grass PS 33 xenon lamp photic stimulators are equivalent in the assessment of photosensitivity: Clinical and research implications

The assessment of the effect of photic stimulation is an integral component of an EEG exam and is especially important in patients referred for ascertained or suspected photosensitivity with or without a diagnosis of epilepsy. A positive test result relies on eliciting a specific abnormality defined as the "photoparoxysmal response". Reliability of this assessment is strongly influenced by technical and procedural variables, a critical one represented by the physical properties of the stimulators used. Established clinical norms are based on data acquired with the "gold-standard" Grass PS stimulators. These are no longer commercially available and have been replaced by stimulators using light emitting diode (LED) technology. To our knowledge no comparative study on their efficacy has been conducted. To address this gap, we recruited 39 patients aged 5-54 years, referred to two specialized centers with confirmed of suspected diagnosis of photosensitive epilepsy or generalized epilepsy with photosensitivity in a prospective randomized single-blind cross-over study to compare two commercially available LED-bases stimulation systems (FSA 10® and Lifeline® stimulators) against the Grass PS 33 xenon lamp device. Our findings indicate that the LED systems tested are equivalent to the Grass stimulator both in identifying the PPR in affected individuals.

Sex influences the frequency of the posterior basic alpha rhythm in patients with epilepsy

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Sex influences the frequency of the basic alpha rhythm in patients with epilepsy.

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Women in this group have faster posterior basic alpha frequencies on average.

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Women with generalized epilepsy taking lamotrigine had the highest alpha frequency.

Objective

To determine effects of sex, epilepsy and epilepsy medication on the posterior basic alpha rhythm.

Methods

We reviewed the routine EEGs of 160 subjects, including 60 individuals with focal epilepsy, 60 with generalized epilepsy, and 40 healthy controls, measured the mean alpha frequencies of each person and applied a univariate three-factorial analysis of variance.

Results

Women have a significantly faster posterior basic rhythm as compared to men. Sex was the only independent factor influencing the posterior basic rhythm in this cohort. Additionally, we detected an interaction with intake of lamotrigine and idiopathic generalized epilepsy both increasing the basic alpha frequency in the group of female subjects only.

Conclusion

Sex was the main determinant of the posterior basic alpha frequency in our cohort.

Significance

Sex can influence the frequency of the posterior basic alpha rhythm.

[Influence of blue light from visual display terminals on human ocular surface]

Objective: To investigate the influence of blue light from visual display terminals (VDTs) on human ocular surface. Methods: Prospective intervention test Thirty volunteers were recruited to watch videos on the same VDT in a dark environment, about 40 cm from the screen. Volunteers were supposed to watch videos in the night shift mode that reduces the amount of blue light for 1 hour. At the same time of the second day, they watched the same videos on the VDT in the normal mode for 1 hour. Tear film break-up time (BUT), corneal fluorescein staining scores, lipid layer thickness (LLT), times of blinking in 19.1 seconds and the ratio of partial blinking in 19.1 seconds were measured before and after each watching. Meanwhile, volunteers were asked to complete a questionnaire about their subjective experience after watching. Results: BUT, corneal fluorescein staining scores and LLT showed no significant decreases in the volunteers after they watched videos on the VDT in the night shift mode [BUT before watching: (8.08±3.15)s, BUT after watching in the night shift mode: (5.31±2.49)s, t=-0.52, P>0.05], but there were significant decreases after they watched videos in the normal mode [BUT after watching in the normal mode: (3.35±1.95) s, t=2.40, P<0.05]. At the same time, there was a significant difference between night shift mode and normal mode[BUT after watching in the night shift mode (5.31±2.49)s, BUT after watching in the normal mode: (3.35±1.95)s, t=3.67, P<0.05). Times of blinking and the ratio of partial blinking in 19.1 seconds were increased modestly after watching in 2 different modes, but there was no significant difference(times of blinking after watching in the night shift mode were 5.55±3.27, times of blinking after watching in the normal mode were 5.93±3.59, t=-0.92, P>0.05). The questionnaire results showed that 70.0%(21) of the volunteers reported mild discomfort including eye dryness, itching, pain, foreign body sensation, redness and asthenopia, 46.7%(14) reported no difference between the 2 modes, 36.7%(11) preferred the night shift mode, 16.6%(5) felt better with the normal mode, and 80.0%(24) would like to try the night shift mode in their daily life. Conclusions: Use of VDTs for a short period of time can lower the stability of tear film. The night shift mode may cause less damage to the ocular surface than the normal mode. High-energy blue light from VDTs can be a risk factor in the ocular surface damage, but the damage is reversible. (Chin J Ophthalmol, 2018, 54: 426-431).

Four-dimensional map of the human early visual system

OBJECTIVE

We generated a large-scale, four-dimensional map of neuronal modulations elicited by full-field flash stimulation.

METHODS

We analyzed electrocorticography (ECoG) recordings from 63 patients with focal epilepsy, and delineated the spatial-temporal dynamics of visually-elicited high-gamma_{70-110 Hz} amplitudes on a standard brain template. We then clarified the neuronal events underlying visual evoked potential (VEP) components, by correlating with high-gamma amplitude measures.

RESULTS

The medial-occipital cortex initially revealed rapid neural activation followed by prolonged suppression, reflected by augmentation of high-gamma activity lasting up to 100 ms followed by attenuation lasting up to 1000 ms, respectively. With a number of covariate factors incorporated into a prediction model, the eccentricity representation independently predicted the magnitude of post-activation suppression, which was more intense in regions representing more parafoveal visual fields compared to those of more peripheral fields. The initial negative component on VEP was sharply contoured and co-occurred with early high-gamma augmentation, whose offset then co-occurred with a large positive VEP peak. A delayed negative VEP peak was blunt and co-occurred with prolonged high-gamma attenuation.

CONCLUSIONS

Eccentricity-dependent gradient in neural suppression in the medial-occipital region may explain the functional difference between peripheral and parafoveal/central vision. Early negative and positive VEP components may reflect neural activation, whereas a delayed negative VEP peak reflecting neural suppression.

SIGNIFICANCE

Our observation provides the mechanistic rationale for transient scotoma or mild flash-blindness, characterized by physiological afterimage preferentially formed in central vision following intense but non-injurious light exposure.

Automatic determination of EMG-contaminated components and validation of independent component analysis using EEG during pharmacologic paralysis

OBJECTIVE

Validate independent component analysis (ICA) for removal of EMG contamination from EEG, and demonstrate a heuristic, based on the gradient of EEG spectra (slope of graph of log EEG power vs log frequency, 7-70 Hz) from paralysed awake humans, to automatically identify and remove components that are predominantly EMG.

METHODS

We studied the gradient of EMG-free EEG spectra to quantitatively inform the choice of threshold. Then, pre-existing EEG from 3 disparate experimental groups was examined before and after applying the heuristic to validate that the heuristic preserved neurogenic activity (Berger effect, auditory odd ball, visual and auditory steady state responses).

RESULTS

(1) ICA-based EMG removal diminished EMG contamination up to approximately 50 Hz, (2) residual EMG contamination using automatic selection was similar to manual selection, and (3) task-induced cortical activity remained, was enhanced, or was revealed using the ICA-based methodology.

CONCLUSION

This study further validates ICA as a powerful technique for separating and removing myogenic signals from EEG. Automatic processing based on spectral gradients to exclude EMG-containing components is a conceptually simple and valid technique.

SIGNIFICANCE

This study strengthens ICA as a technique to remove EMG contamination from EEG whilst preserving neurogenic activity to 50 Hz.

Photic stimulation during electroencephalography: Efficacy and safety in an unselected cohort of patients referred to UK neurophysiology departments

PURPOSE

To determine efficacy and safety of photic stimulation (PS) during electroencephalography (EEG) in a large group of adult and paediatric patients.

METHODS

A prospective multicentre National Service Evaluation was performed organised by the joint audit committee of the two UK professional organisations (Association of Neurophysiological Scientists and British Society for Clinical Neurophysiology). Questionnaires about every EEG performed in the two-month study period were completed contemporaneously by physiologists at the time of the recording-reporting. The occurrence during PS of photoparoxysmal responses (PPRs), seizures and psychogenic non-epileptic attacks was noted from the EEG trace and contemporary clinical observation backed up by the video that was synchronised with the EEG. 5383 patients investigated with EEG and PS, mostly for possible epilepsy, were included in the study.

RESULTS

Seventy nine patients (1.5%) had a generalised PPR elicited by PS having had no generalised epileptiform discharges previously in the EEG. Thirty nine patients (0.7%) had seizures provoked by PS including two (0.04%) who had a generalised tonic clonic seizure (GTCS). Forty nine patients (0.9%) had non-epileptic attacks provoked by PS. Thus PS yielded potentially useful information (PPRs, seizures or non-epileptic attacks) in 167/5383 (3.1%) of patients. In a subset of 122/5383 (2.3%), PS provided the only useful information captured within the EEG.

CONCLUSION

PS contributes to the diagnosis of epilepsy and non-epileptic attack disorder in 3.1% of patients. It is a safe technique which produces GTCSs in only 0.04% patients. We conclude that PS is a moderately useful activation technique in diagnostic EEG, where the potential benefits out-weigh the risks; this information may assist the informed consent process.

Hyperventilation and photic stimulation are useful additions to a placebo-based suggestive seizure induction protocol in patients with psychogenic nonepileptic seizures

The early and definitive diagnosis of psychogenic nonepileptic seizures is a common challenge in epileptology practice. Suggestive seizure induction is a valuable tool to aid the differentiation between epileptic and psychogenic nonepileptic seizures, especially when long-term video-EEG monitoring is inconclusive or unavailable. In this retrospective analysis, we compared the diagnostic yield of a classical, placebo-based induction protocol with that of an extended protocol that includes hyperventilation and photic stimulation as means of suggestion while also implementing more open, standardized patient information. We investigated whether the diversification of suggestive seizure induction has an effect on diagnostic yield and whether it preempts the administration of placebo. Data from 52 patients with confirmed psychogenic nonepileptic seizures were analyzed. While suggestive seizure induction using only placebo-based suggestion provoked a typical event in 13 of 20 patients (65%), the extended protocol was positive in 27 of 34 cases (84%); this improvement was not significant (p=0.11). Noninvasive suggestion techniques accounted for 78% of inductions, avoiding placebo administration in a majority of patients. Still, placebo remains an important part of suggestive seizure induction, responsible for 22% (6 out of 27) of successful inductions using our extended protocol. Our study demonstrates that the diversification of suggestive seizure induction is feasible and beneficial for both patients and diagnosticians.

Visual distraction alone for the improvement of colonoscopy-related pain and satisfaction

AIM: To evaluate the effect of a relaxing visual distraction alone on patient pain, anxiety, and satisfaction during colonoscopy.

METHODS: This study was designed as an endoscopist-blinded randomized controlled trial with 60 consecutively enrolled patients who underwent elective colonoscopy at Yokohama City University Hospital, Japan. Patients were randomly assigned to two groups: group 1 watched a silent movie using a head-mounted display, while group 2 only wore the display. All of the colonoscopies were performed without sedation. We examined pain, anxiety, and the satisfaction of patients before and after the procedure using questionnaires that included the Visual Analog Scale. Patients were also asked whether they would be willing to use the same method for a repeat procedure.

RESULTS: A total of 60 patients were allocated to two groups. Two patients assigned to group 1 and one patient assigned to group 2 were excluded after the randomization. Twenty-eight patients in group 1 and 29 patients in group 2 were entered into the final analysis. The groups were similar in terms of gender, age, history of prior colonoscopy, and pre-procedural anxiety score. The two groups were comparable in terms of the cecal insertion rate, the time to reach the cecum, the time needed for the total procedure, and vital signs. The median anxiety score during the colonoscopy did not differ significantly between the two groups (median scores, 20 vs 24). The median pain score during the procedure was lower in group 1, but the difference was not significant (median scores, 24.5 vs 42). The patients in group 1 reported significantly higher median post-procedural satisfaction levels, compared with the patients in group 2 (median scores, 89 vs 72, P = 0.04). Nearly three-quarters of the patients in group 1 wished to use the same method for repeat procedures, and the difference in rates between the two groups was statistically significant (75.0% vs 48.3%, P = 0.04). Patients with greater levels of anxiety before the procedure tended to feel a painful sensation. Among patients with a pre-procedural anxiety score of 50 or higher, the anxiety score during the procedure was significantly lower in the group that received the visual distraction (median scores, 20 vs 68, P = 0.05); the pain score during the colonoscopy was also lower (median scores, 23 vs 57, P = 0.04). No adverse effects arising from the visual distraction were recognized.

CONCLUSION: Visual distraction alone improves satisfaction in patients undergoing colonoscopy and decreases anxiety and pain during the procedure among patients with a high pre-procedural anxiety score.

Montage matters: the influence of transcranial alternating current stimulation on human physiological tremor

BACKGROUND

Classically, studies adopting non-invasive transcranial electrical stimulation have placed greater importance on the position of the primary "stimulating" electrode than the secondary "reference" electrode. However, recent current density modeling suggests that ascribing a neutral role to the reference electrode may prove an inappropriate oversimplification.

HYPOTHESIS

We set out to test the hypothesis that the behavioral effects of transcranial electrical stimulation are critically dependent on the position of the return ("reference") electrode.

METHODS

We examined the effect of transcranial alternating current stimulation (sinusoidal waveform with no direct current offset at a peak-to-peak amplitude of 2000 μA and a frequency matched to each participant's peak tremor frequency) on physiological tremor in a group of healthy volunteers (N = 12). We implemented a sham-controlled experimental protocol where the position of the stimulating electrode remained fixed, overlying primary motor cortex, whilst the position of the return electrode varied between two cephalic (fronto-orbital and contralateral primary motor cortex) and two extracephalic (ipsilateral and contralateral shoulder) locations. We additionally controlled for the role of phosphenes in influencing motor output by assessing the response of tremor to photic stimulation, through self-reported phosphene ratings.

RESULTS

Altering only the position of the return electrode had a profound behavioral effect: only the montage with extracephalic return contralateral to the primary stimulating electrode significantly entrained physiological tremor (15.9% ± 6.1% increase in phase stability, 1 S.E.M.). Photic stimulation also entrained tremor (11.7% ± 5.1% increase in phase stability). Furthermore, the effects of electrical stimulation are distinct from those produced from direct phosphene induction, in that the latter were only seen with the fronto-orbital montage that did not affect the tremor.

CONCLUSION

The behavioral effects of transcranial alternating current stimulation appear to be critically dependent on the position of the reference electrode, highlighting the importance of electrode montage when designing experimental and therapeutic protocols.

Independent component analysis-based method for electroencephalogram analysis during photic stimulation

BACKGROUND

Intermittent photic stimulation (IPS) leads to phase- and time-locked activities in the electroencephalogram (EEG). While the first are easily obtained by means of averaging techniques (the evoked response), this latter reflects changes in the ongoing EEG that are important in event-related synchronization/desynchronization (ERS/ERD) studies. Techniques have been proposed for assessing such changes but they only provide the spectral estimate of the time-locked activities.

NEW METHOD

An independent component analysis-based method is proposed for the EEG analysis during IPS. Artificially generated sinusoidal functions at the stimulation frequency and harmonics are used together with the acquired EEG signal to build the observed vector that is presented to the ICA algorithm.

RESULTS

The proposed method was evaluated with simulated data and applied to EEG signals acquired on two electrodes placed over the occipital region showing that this method is capable of providing a suitable estimation of the ongoing EEG activities in both time and frequency domains.

COMPARISON WITH EXISTING METHOD(S)

The results were compared with a coherence-based method, showing that the proposed method can estimate the power spectrum of the ongoing EEG activity as precisely as the coherence-based method with the advantage of allowing the ongoing EEG activity in time domain to be also obtained.

CONCLUSIONS

The application of the proposed method could be used for ERS/ERD studies, since it separates evoked responses, which are phase-locked to the stimuli, from those that change the ongoing EEG in a time-locked manner to the external stimulation.

Informing patients about the impact of provocation methods increases the rate of psychogenic nonepileptic seizures during EEG recording

Observation of psychogenic nonepileptic seizures (PNESs) during video-EEG represents the diagnostic gold standard for PNESs. Different provocative techniques have been used to increase PNES frequency during EEG. These techniques include placebo administration, suggestion strategies, or both. In order to avoid the appearance of deception, we investigated the following hypothesis: If patients with PNESs were informed about the possible reduction of seizure threshold caused by hyperventilation and photic stimulation prior to EEG without any other suggestive strategies, PNESs would occur more frequently. In total, 34 inpatients with a diagnosis of PNESs, who had been informed prior to EEG about the increased seizure risk during hyperventilation and photic stimulation (study group), and 80 "noninformed" patients (control group) were enrolled. Psychogenic nonepileptic seizures occurred significantly more often in the study group compared to controls (38% vs. 10.0%, p=0.001). Our results imply that simply providing correct and explicit information about provocation techniques substantially increased the PNES rate.