Frequencies Of Photic Stimulation Research Articles

Neuronal Ceroid Lipofuscinosis: Clinical and Laboratory Profile in Children from Tertiary Care Centre in South India.

Neuronal ceroid Lipofuscinosis (NCL), inherited disorders of lysosomal storage disorders, constitute the most common progressive encephalopathies with an incidence of 1.3 to 7 in 100,000 live births. We reported clinical, electrophysiological, radiological, ultrastructural, and molecular genetic features of NCL. This is a retrospective review, in a tertiary care center from January 2016 to December 2019. All children with clinical features of NCL and confirmed by pathogenic mutation and/or enzyme assay were included. A total of 60 children (male:female = 3:1) were studied. The commonest type was CLN 2 (41.7%). Neuroregression, seizures, and ataxia were present in all cases. Retinal arterial attenuation was seen in 38.33% cases. Magnetic resonance imaging (MRI) brain was abnormal in all patients, thalamic and caudate nucleus atrophy common in CLN1 (62%). Electroencephalography was abnormal in all children, but photoparoxysmal response at low intermittent photic stimulation frequencies was seen in four children of CLN2. Electron microscopy done in 43 children revealed abnormal inclusions in 20 (46.52%) children. Enzyme study showed low levels in 36 (78%) out of 46 cases. Of these, 21 had low tripeptidyl peptidase and 15 had low palmitoyl protein thioesterase levels. Molecular testing done in 26 cases showed pathogenic variant in 23 (88%) cases. Infantile onset with thalamic atrophy on MRI is common in CLN1 and refractory epilepsy, visual impairment and specific EEG changes are common in CLN2. These features are helpful in selecting enzyme assay for CLN1 versus CLN2. Electron microscopy helped in the diagnosis and genetic testing in subtyping. Thus, a multimode approach played a role in the diagnosis of NCL.

3. Polarized and lens color effects on photoparoxysmal response

Introduction Approximately 5% of epilepsy patients’ photosensitivity can be detected on EEG recordings. This photoparoxysmal response (PPR) may prevent patients from performing their daily activities and also can result in seizures and anxiety. The objective of this study is to optimize the use of Z1 and other polarized and colored lenses for reducing PPR in epileptics. Purpose We propose that by covering central and temporal visual fields with either Z1 lenses plus side guards or elongated polarized lenses may suppress the PPR by altering the luminance and/or wavelength. Methods 22 pediatric patients with Type 4 PPR (Waltz et al.) were tested with and without Z1 lenses using photic stimulation from 1 to 21 Hz. 19 patients had primary generalized epilepsy (5 JME & 14 Absence), 2 had reflex epilepsy and 2 had Dravet’s Syndrome. Results Responses were classified into 3 groups: PPR disappearance, persistence or attenuation. 14 patients had reduced PPR (64%) and in 5 patients PPR disappeared (23%). 3 patients (13%) demonstrated persistence of the PPR with Z1 lenses. Several patients tested with side guards plus cobalt blue tint polarized lens sunglasses showed marked PPR reduction. Several patients tested with elongated polarized sunglasses covering the temporal visual field showed PPR attenuation. Placing a red lens over the photic stimulation lamp augmented the PPR from 1 to 19 Hz stimulation in several patients. A blue lens over the photic lamp resulted in attenuation or disappearance of the PPR at several photic stimulation frequencies in several patients. Conclusions Z1 and other blue lenses reduced the PPR in nearly all patients. Possible mechanisms include polarization, reduction of luminance, and filtering of red light. Further testing of photosensitive patients will be performed. Comparisons will be made between Z1, elongated polarized, cobalt blue, red and green Coppola, 2006 , Jeavons and Harding, 1975 , Newmark and Penry, 1979 , Binnie and Jeavons, 1992 , Quirk et al., 1995 , Kasteleijn-Nolst Trenit’e et al., 2002 , Takahashi and Tsukahara, 1976 .

The evaluation of EEG response to photic stimulation in normal and diseased subjects

In this paper, our aim is to determine two photic stimulation frequencies, which would represent normal and diseased subjects, separately. Following features were extracted for this aim; linear prediction coefficients (LPC), subband wavelet entropy (SWE), subband wavelet variance (SWV), and relative power (RP). After extracting related features, analysis of variance (ANOVA) statistical test was used for the statistical evaluation of these features. According to the obtained results, wavelet transform-based entropy gave the best results to determine the representing stimulation frequencies. As a result, 29 Hz stimulation frequency was determined as the most representative frequency for normal subjects, whereas 8 Hz stimulation frequency was determined as the most representative frequency for diseased subjects.

Abnormal cortical functional connections in Alzheimer’s disease: analysis of inter- and intra-hemispheric EEG coherence

To investigate inter- and intra-hemispheric electroencephalography (EEG) coherence at rest and during photic stimulation of patients with Alzheimer's disease (AD). Thirty-five patients (12 males, 23 females; 52 to approximately 64 y) and 33 sex- and age-matched controls (12 males, 21 females; 56 to approximately 65 y) were recruited in the present study. EEG signals from C3-C4, P3-P4, T5-T6 and O1-O2 electrode pairs resulted from the inter-hemispheric action, and EEG signals from C3-P3, C4-P4, P3-O1, P4-O2, C3-O1, C4-O2, T5-O1 and T6-O2 electrode pairs resulted from the intra-hemispheric action. The influence of inter- and intra-hemispheric coherence on EEG activity with eyes closed was examined, using fast Fourier transformation from the 16 sampled channels. The frequencies of photic stimulation were fixed at 5, 10 and 15 Hz, respectively. The general decrease of AD patients in inter- and intra-hemispheric EEG coherence was more significant than that of the normal controls at the resting EEG, with most striking decrease observed in the alpha-1 (8.0-9.0 Hz) and alpha-2 (9.5-12.5 Hz) bands. During photic stimulation, inter- and intra-hemispheric EEG coherences of the AD patients having lower values in the alpha (9.5-10.5 Hz) band than those of the control group. It suggests that under stimulated and non-stimulated conditions, AD patients had impaired inter- and intra-hemispheric functional connections, indicating failure of brain activation in alpha-related frequency.

Topographic aspects of photic driving in the electroencephalogram of children and adolescents.

The electroencephalogram amplitude spectra at 11 fixed frequencies of intermittent photic stimulation of 3 to 24 Hz were combined into driving "profiles" for 14 scalp points in 8 male and 7 female normal subjects aged 9 to 17 years. The driving response varied over frequency and was detected in 70 to 100% of cases in the occipital areas (maximum) and in 27 to 77% of cases in the frontal areas (minimum) using as a criterion peak amplitude 20% higher than those of the neighbors. Each subject responded, on average, to 9.7 +/- 1.15 intermittent photic stimulation frequencies in the right occipital area and to 6.8 +/- 1.97 frequencies in the right frontal area. Most of the driving responses (in relation to the previous background) were significant according to the spectral F-test (alpha = 0.05), which also detected changes in some cases of low amplitude responses not revealed by the peak criterion. The profiles had two maxima in the alpha and theta bands in all leads. The latter was not present in the background spectra in the posterior areas and was less pronounced in the anterior ones. The weight of the profile theta maximum increased towards the frontal areas where the two maxima were similar, while the profile amplitudes decreased. The profiles repeated the shape of the background spectra, except for the theta band. The interhemispheric correlation between profiles was high. The theta driving detected in all areas recorded suggests a generalized influence of the theta generators in prepubertal and pubertal subjects.

Stability of resonance EEG reactions to flickering light in humans

In order to study resonance phenomena in the EEG response to flickering light, 10 subjects were exposed to intermittent photic stimulation with the frequency of flashes linearly changing from 1 to 15 Hz and vice versa. Spectral analysis of occipital electrical activity revealed the occurence of peaks of spectral density in those frequency components which coincide with the frequency of flashes. Such resonance peaks were observed at individually specific frequencies of stimulation. To assess the stability of the characteristics of the resonance phenomena, a repeated trial with 4-fold higher rate of changing the flash frequency was performed 3 months later. In a repeated trial the resonance phenomena were less pronounced, but were registered at the same frequencies as in the initial trial, showing significant test-retest reliability. The data obtained are interpreted in terms of provoking the activity of multiple brain oscillators having a narrow tuning to individually specific frequencies of photic stimulation by flickering light with the changing frequency of flashes.

Effects of caffeine on resting EEG and response to sine wave modulated light

A double blind, placebo controlled study was designed to assess transient caffeine effects on spontaneous and evoked brain activity in man. Twelve normal males received 200 mg caffeine citrate or placebo on separate occasions. EEG from left and right occipital regions was recorded in the absence of stimulation and during the response to sine wave modulated light (SML). The photic stimulation frequencies were 5, 10, 15, 18 and 24 c/sec. EEG power at frequencies corresponding to fundamental and selected harmonics of stimulation frequencies was obtained. The time course of response to SML was studied over a period of 2 min. Caffeine reduced the EEG power under resting conditions and during SML stimulation. This reduction was statistically significant at 10 and 15 c/sec. At 24 c/sec, caffeine reduced the fundamental SML response, but not the resting EEG power. Evaluation of the SML response time course did not reveal any consistent tendencies. It appears that the response is sustained in a stable way over the period of 2 min.