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Results for “Photic Stimulation”

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At least 73 records · Page 4Linked to original sources
PubMed1975

EEG responses to photic stimulation in persons experienced at meditation.

The EEG responses to intermittent photic stimulation were examined in a group of subjects experienced in meditation, and compared with those of a control group. The meditators exhibited a significantly smaller decrement in alpha activity and alpha blocking over the course of the experiment than did the control group, and alpha induction occurred earlier and more frequently in the meditators. These findings support the hypothesis that experienced meditators spontaneously enter the meditative state on closing the eyes, and also the view that physiologically the meditative state is one of prolonged drowsiness. An alternative interpretation, that meditation is a state of sustained attention, is discussed.

Adult↗
PubMed2002

Functional magnetic resonance imaging of the cortical response to photic stimulation in humans following optic neuritis recovery.

Recovery from optic neuritis has been shown to be associated with an abnormal functional MRI (fMRI) response following exposure of the eye to an epoch based (ON-OFF design) flickering photic stimulus. Visual cortex activation is reduced during photic stimulation, whilst extra-occipital areas are extensively activated with a peak blood oxygen level dependent response during the OFF phase of the stimulus paradigm. We performed a further fMRI experiment to determine whether the abnormal extra-occipital response is a phase-specific phenomenon or whether it results from a delayed haemodynamic response. A cohort of patients that recovered from optic neuritis was studied, this time using a longer photic stimulation epoch (40 s). The extra-occipital response again peaked during the baseline condition, indicating that the phenomenon is phase dependent. Our results also reinforce the important findings of extra-occipital activation following optic neuritis which may represent an adaptive reorganization of the cerebral response.

Adult↗
PubMed1999

EEG changes following scopolamine administration in healthy subjects. Quantitative analysis during rest and photic stimulation.

This study examined the effects of the anticholinergic drug, scopolamine (0.25 mg) in 16 right-handed healthy volunteers. EEGs were recorded before and 60 min after intramuscular administration, and spectral analysis was performed on EEGs recorded at rest and during photic stimulation. Each subject was also evaluated by the Wechsler Memory Scale (WMS; form 1 or 2) before and 90 min after drug administration. In the resting EEG, the scopolamine administration resulted in a significant increase in the absolute power on the delta band (2.0- 3.8 Hz) and in the relative power on the delta and theta-1 bands (4.0-5.8 Hz) mainly over the central and parieto-occipital regions. In contrast, scopolamine significantly decreased the relative alpha-2 band (9.2-12.8 Hz) power mainly over the frontal regions and the absolute alpha-2 band power at most of the recording sites. The analysis of stimulus data showed that scopolamine significantly decreased fundamental photic driving responses elicited by photic stimulation at 15 Hz, with significant effects confined to the occipital regions. These EEG changes occurred in association with a significant reduction in total WMS scores as well as in scores of logical and visual memory subtests. These findings suggest that, in addition to cognitive impairments, central cholinergic dysfunction can cause EEG changes under both nonstimulus and stimulus conditions.

Adult↗
PubMed1984

Inhibition in corticotrophin and corticosterone secretion following photic stimulation in rats with 6-hydroxydopamine injection into the medial forebrain bundle.

Changes in corticotrophin (ACTH) and corticosterone (CS) serum levels, were examined in rats in which either 6-hydroxydopamine or vehicle were injected into the medial forebrain bundle (MFB) and which were sacrificed by decapitation 14 days later. The injection of the neurotoxin, which depleted very significantly the norepinephrine (NE) content of the mediobasal hypothalamus, elevated significantly the basal levels of serum ACTH and CS, but inhibited the rise in the levels of these hormones following photic stimulation. These results would suggest that the hypothalamic NE system has normally an inhibitory effect on basal ACTH and CS secretion and that the hormonal response to photic stimulation is mediated by that system and possibly by NE MFB fibers.

Adrenocorticotropic Hormone↗
PubMed1998

Responses to photic stimulation in patients with occipital spikes.

OBJECTIVE: To determine the effect of intermittent photic stimulation (IPS) and frequency of asymmetric driving responses in patients with occipital spikes. METHODS: The amplitude of the driving response at 4 flash frequencies was measured from a referential montage in 60 patients with occipital spikes and in 60 normal EEG records from age-matched patients. Responses were classified as asymmetric if the amplitude at one occipital area was less than 50% of the amplitude at the other. RESULTS: A measurable photic response occurred significantly less frequently in patients with occipital spikes (48%) compared to the control group (70%; Fisher's test P < 0.05). The driving response was asymmetric in 7/36 patients (37%) with unilateral spike foci versus none in the control group (Fisher's test, P < 0.001). The amplitude was suppressed ipsilateral to the focus in 5 patients, all of whom had an ipsilateral structural lesion or focal slowing. In two cases the amplitude was higher ipsilateral to the focus, neither having slowing or a structural lesion. CONCLUSIONS: Patients with occipital spikes have an increased frequency of asymmetric driving response. An attenuated response ipsilateral to the focus seems to be related to an underlying lesion while the presence of an epileptiform focus in some cases with no slowing on EEG and normal imaging studies may lead to an accentuation of this response.

Adolescent↗
PubMed1994

[Suppression of myoclonus associated with intermittent photic stimulation (IPS) in a case of Creutzfeldt-Jacob disease: with special reference to the specificity of IPS frequency].

The present study deals with electrophysiological findings 3 months after the patient fell into an apallic state during the course of Creutzfeldt-Jacob disease (CJD), when periodic limb myoclonus synchronizing with periodic synchronous discharge (PSD) began to diminish. The findings were as follows: On 2 Hz intermittent photic stimulation (IPS), myoclonus and the diffuse bisynchronous high amplitude sharp wave showed dissociation; the myoclonus was completely suppressed, while the high amplitude sharp wave was elicited. On 3 Hz IPS, myoclonus was incompletely suppressed, corresponding to every other high amplitude sharp waves which were induced synchronous to IPS. On 1 Hz IPS, the high amplitude sharp waves were scarcely induced while neither PSD nor the myoclonus were suppressed. The frequency of the PSD was about 1.2 Hz. Based on these findings, we propose that in addition to the cortical refractory period after PSD or the giant response to photic stimulation, there must be another refractory period in the distal impulse pathway longer than the cortical one. Although the exact electrophysiological mechanism involved in the present findings remains unknown, the possible mechanism responsible for the suppression of myoclonus by IPS and the specificity of IPS frequency in the suppression could be due to competitive suppression of the impulse between periodic myoclonus and the cortical reflex myoclonus through the interaction of the two independent refractory periods in the transmission pathway of the impulse.

Aged↗
PubMed1983

Photosensitive epilepsy and photoconvulsive responses to photic stimulation in Africans.

Three hundred sixty-two epileptic patients were examined clinically and electroencephalographically to determine the proportion with photosensitive epilepsy or showing photoconvulsive responses to intermittent photic stimulation (IPS). Also, 102 nonepileptic patients had an EEG done to find out the proportion showing photoconvulsive responses to IPS. Ten epileptic patients (2.76%) had photosensitive epilepsy, and six patients (1.6%) showed photoconvulsive responses to IPS. The nonepileptic patients showed no photoconvulsive responses to IPS. The relative rarity of photosensitive epilepsy and the greater incidence of nonreaction to photic stimulation in black African epileptics and nonepileptics compared with Caucasians indicate that black Africans are less photosensitive than Caucasians.

Adolescent↗
PubMed1976

The EEG response to repetitive photic stimulation in various regions of the chicken brain.

The EEG response in the chicken to repetitive photic stimulation was studied by frequency analysis and by the averaged response. Evoked responses were observable not only in stations along the visual pathway but also in broad areas apart from the visual pathway. The electrical activity in the archistriatum showed a marked response to flickering stimuli, indicating that this area is involved in the visual function in the chicken. In other telencephalic areas, photically evoked potentials could not be clearly demonstrated in the EEG records. In the hypothalamus and the nucleus rotundus of the diencephalon and in the nucleus reticularis superior of the mesencephalon, sinusoidal waves appeared during stimulation at 8-13/sec. No rhythmic after-discharge was observed following termination of photic stimulation. These finding are indicative of the difference of the visual response in the chicken from previously reported responses in other species.

Animals↗
PubMed2001

Spatial structure of brain electric fields during intermittent photic stimulation.

EEG changes in 27 young healthy male right-handed volunteers on intermittent photic stimulation (IPS) were estimated using global field power (GFP), EEG microstate modeling and analysis (EMMA), and low-resolution electromagnetic brain tomography (LORETA). The GFP significantly increased at flashing frequency and high harmonics. Three model maps were extracted with the EMMA procedure, from which high alternation rates of each microstate were observed. Moreover, two of the three model maps contributed very highly, occurring most frequently. LORETA imaging of the three model maps obtained from the EMMA procedure showed that both visual dominant cortical areas were activated, especially in the left hemisphere. These results suggest that IPS does not cause peculiar spatial configurations of the brain electric field, but does cause acceleration and deviation of the microstate alternation. Also, a functional laterality between hemispheres might be enhanced by symmetric IPS.

Adult↗
PubMed1996

Effect of photic stimulation on energy metabolism in the human brain measured by 31P-MR spectroscopy.

Effect of photic stimulation (PS) on energy metabolism in the human occipital cortex was examined by using phosphorus-31 magnetic resonance spectroscopy in 9 normal subjects. Phosphocreatine (PCr)/total phosphorus signal peak area ratio significantly decreased from 12.3% to 10.9% during the 12 minutes of PS (P < 0.05). PCr once returned to a normal level after PS (11.9%) but significantly decreased again 12-18 minutes after PS (10.8%; P < 0.05). Intracellular pH increased from 7.08 to 7.16 during PS, although this increase was not significant. These results suggest that functional alteration of energy metabolism in the brain is different from that in muscles.

Adult↗
PubMed1979

Interaction between intermittent photic stimulation and auditory stimulation on the human EEG. Preliminary investigation through power spectral analysis.

The effects of flicker photic stimulation (6, 8, 9, 10, 11, 12, 14, 16 flashes/sec) and of white noise (80 dB SPL) on the EEG of man were investigated with the aid of power spectral analysis. In order to evaluate both the alpha attenuation response (AAR) and the 'driving' reaction induced by flicker as well as the effect of noise, the analysis was carried out on broad (delta, theta, alpha, beta) and on narrow (bandwidth: 1 Hz) spectral bands. A significant correlation between the amount of AAR induced by noise and a measure of the tendency to exhibit photic driving was found, though there was no clear-cut interaction between the photic stimuli and noise when delivered stimultaneously.

Acoustic Stimulation↗
PubMed2000

Effect of normal aging upon interhemispheric EEG coherence: analysis during rest and photic stimulation.

The present study was conducted to examine and compare interhemispheric EEG coherence at rest and during photic stimulation (PS; 5, 10 and 15 Hz) in 30 younger subjects aged 22.1 +/- 2.2 (mean +/- S.D.) and 25 elderly subjects aged 56.8 +/- 4.9. The elderly subjects had significantly lower coherence in the resting EEG for the delta, theta, alpha-3, beta-1 and beta-2 frequency bands. In contrast, EEG analysis during PS showed that elderly subjects had significantly higher coherence in the frequency corresponding to PS at 15 Hz. In addition, when we examined the changes in coherence from the resting state to the stimulus condition (i.e., coherence reactivity), elderly subjects had significantly higher coherence reactivity to PS at 15 Hz. These findings suggest a low interhemispheric functional connectivity in elderly subjects under non stimulus conditions and a high connectivity during photic stimulus.

Adult↗
PubMed1983

The treatment of congenital idiopathic nystagmus by intermittent photic stimulation.

An analysis is presented of the results obtained by treating 54 patients with congenital nystagmus using intermittent photic stimulation. The major beneficial effect has been to improve the visual acuity, though the nystagmus itself is sometimes reduced in amplitude or even eliminated; an unexpected bonus, in certain cases, is the improvement in stereoscopic acuity.

Adolescent↗
PubMedDate not supplied

[Interhemispheric interrelationships in the visual cortex of cats following unilateral polarization and photic stimulation of different intensity].

Anodic polarization of the parastriate area in the right hemisphere causes in symmetric regions of cat's visual cortex dynamic changes in EPs, interhemispheric functional asymmetry and interhemispheric relations, depending on the intensity of photic stimulation. The sequence of phases of interhemispheric callosal relations and characteristics of interaction between callosal and extracallosal influences were traced in different periods of polarization excitation. It was found that interhemispheric callosal and extracallosal influences lead either to stabilization of initial EP levels and interhemispheric asymmetry or to their change depending on conditions of photostimulation and on the stage in the formation of polarization site.

Animals↗
PubMed1976

The involvement of the preoptic-suprachiasmatic region in the photosexual reflex in quail: Effects of selective lesions and photic stimulation.

Small bilateral lesions of the preoptic and anterior hypothalamic regions completely suppressed the light-induced testicular growth in quail. Photic stimulation was selectively applied to this region using a small pellet of radioluminous paint (RLP). This local photostimulation induced no testicular growth in short day quail. On the contrary, testes were markedly enlarged after RLP was implanted in the tuberal or in the dorsal area of the infundibular complex of short day quail. This response was as large as in controls reared under 18L-6D. It is therefore confirmed that neuronal populations located in the infundibular complex are directly photosensible. No direct photosensitivity was observed in the preoptic and anterior hypothalamic regions and it is suggested that these areas can serve as a relay for retinal information.

Animals↗
PubMed1992

Effect of photic stimulation on human visual cortex lactate and phosphates using 1H and 31P magnetic resonance spectroscopy.

Previous animal and human studies showed that photic stimulation (PS) increased cerebral blood flow and glucose uptake much more than oxygen consumption, suggesting selective activation of anaerobic glycolysis. In the present studies, image-guided 1H and 31P magnetic resonance spectroscopy (MRS) was used to monitor the changes in lactate and high-energy phosphate concentrations produced by PS of visual cortex in six normal volunteers. PS initially produced a significant rise (to 250% of control, p less than 0.01) in visual cortex lactate during the first 6.4 min of PS, followed by a significant decline (p = 0.01) as PS continued. The PCr/Pi ratios decreased significantly from control values during the first 12.8 min of PS (p less than 0.05), and the pH was slightly increased. The positive P100 deflection of the visual evoked potential recorded between 100 and 172 ms after the strobe was significantly decreased from control at 12.8 min of PS (p less than 0.05). The finding that PS caused decreased PCr/Pi is consistent with the view that increased brain activity stimulated ATPase, causing a rise in ADP that shifted the creatine kinase reaction in the direction of ATP synthesis. The rise in lactate together with an increase in pH suggest that intracellular alkalosis, caused by the shift of creatine kinase, selectively stimulated glycolysis.

Adenosine Diphosphate↗
PubMed1991

Paroxysmal choreoathetosis precipitated by movement, sound and photic stimulation in a case of arterio-venous malformation in the parietal lobe.

A patient is presented with paroxysmal choreoathetosis precipitated by movement, sound and photic stimulation associated with an arterio-venous malformation (AVM) who responded to carbamazepine treatment. Hemodynamic circulatory disorder of the sensory-motor cortices having AVM may alter striatal function and produce paroxysmal choreoathetosis. This finding supports the concept that paroxysmal choreoathetosis results from an abnormality at the connections between basal ganglia and cerebral cortices.

Acoustic Stimulation↗
PubMed1987

Photosensitive patients: symptoms and signs during intermittent photic stimulation and their relation to seizures in daily life.

Thirty six patients were studied with a classical photoparoxysmal EEG response to intermittent photic stimulation (IPS). Clinical observations and complaints reported by patients during standardised IPS were recorded and compared with historical data. Twenty seven patients experienced impaired consciousness or showed motor phenomena such as involuntary opening of the eyes or jerking on one or both sides of the body. Twenty five patients had sensations such as pain in the eyes, jerking etc. There existed no relation between the duration of the evoked discharges (0.5-3 seconds) and observed signs or complaints. In 11 instances the clinical features found during IPS were not reported in a history taken from the patient and relatives.

Adolescent↗