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PubMedDate not supplied

[The induction of seizures in "Papio papio" following allylglycine alone or in combination with intermittent photic stimulation (author's transl)].

Allylglycine, an inhibitor of GABA synthesis, produces increased sensitivity to photic stimulation and in convulsant doses spontaneous seizures arising occipitally in the baboon (Horton and Meldrum, 1973). In this study, convulsant doses of allylglycine induced either sharp wave and polyspike frontorolandic discharges (FR) or critical posterior discharges which then reinforce the fronto-rolandic spikes. A seizure may then arise from the fronto-rolandic region and secondarily spread to the rest of the cerebral cortex. Intermittent photic stimulation produces a reinforcement of the fronto-rolandic sharp waves and can also induce self-maintaining mechanisms similar to those just described. In this situation, however, and with the animals paralysed with Flaxedil no seizures arising occipitally have been observed. The role of the occipital cortex as the sensory visual and somatic afferent in photosensitive epilepsy in the baboon is discussed in the light of these results.

Allyl Compounds↗
PubMedDate not supplied

[Off-effect in visual cortex evoked potentials of humans under several conditions of photic stimulation].

Visually evoked potentials (EP) to light were recorded from the occipital cortical area under conditions of changes in stimulus duration and of different intensity of retinal illumination. The work was aimed at establishing the appearance and development of the EP off-effect in humans at these conditions of photic stimulations. This was necessitated by the large dispersion of data obtained in establishing the conditions of photic stimulation, which many authors consider essential for recording the off-effect. The off-effect was studied in greater detail also to elucidate its role in EP generation to a high-frequency photic stimulation. The data recorded are discussed and compared with those of other authors, obtained in studying electrical responses of the retina and the cerebral cortex.

Adolescent↗
PubMed1995

Photic stimulation study of changing the arterial partial pressure level of carbon dioxide.

To investigate the effect of the level of baseline cerebral blood flow (CBF) on local CBF augmentation by activation, we have used positron emission tomography to measure regional CBF (rCBF) in 12 normal volunteers with and without photic stimulation during hypocapnia, normocapnia, and hypercapnia. The increase in rCBF in the primary visual cortex by photic stimulation was 10.8 +/- 3.1, 18.6 +/- 9.3, and 19.5 +/- 6.1 ml 100 ml-1 min-1 in hypo-, normo-, and hypercapnia, respectively. The increase was significantly smaller in hypocapnia than in normocapnia (p < 0.005). The fractional CBF increase caused by the photic stimulation was the same in all breathing conditions. This result indicates that the magnitude of the CBF increase induced by neuronal activity correlates proportionally with the level of baseline CBF.

Adult↗
PubMed1990

The effects of photic stimulation and private self-consciousness on the complexity of visual imagination imagery.

Three levels of photic stimulation (6, 10, 18 Hz) were employed to induce visual imagination imagery in 40 female undergraduates, half of whom had been selected because they had an habitual interest in their own internal states and half because they had no such interest (high and low on a Private Self-conscious (PSC) scale). It was predicted, and found, that more complex images would be reported (1) under the averaged 6 and 10 Hz condition than under the 18 Hz condition, (2) under the 6 than under the 10 Hz condition, and (3) under the high PSC than under the low PSC condition. An interaction effect was also obtained such that the complexity of visual imagination imagery was greatest for the high PSC group, compared with the low PSC group, under the 6 Hz condition and least under the 18 Hz condition. Additional analyses were undertaken on the types of colour, form and movement reported by the high and low PSC groups under combined conditions of photic stimulation. The results of the complexity scores were discussed in terms of West's (1962) 'perceptual release' theory and several suggestions were made for future research.

Adolescent↗
PubMed2003

Sequential EEG analysis during intermittent photic stimulation in never-medicated patients with schizophrenia.

To investigate sequential changes in electroencephalograms (EEGs) during intermittent photic stimulation (IPS), quantitative EEG analysis for the alpha band (related to stimulus frequency) was performed in 18 drug-naïve schizophrenic patients and 18 sex- and age-matched control subjects. IPS consisted of white flickers at 10 flashes/sec, lasting 10 sec and repeated six times at 10 sec intervals. The differences between the two groups were assessed for two conditions (i.e., during photic stimulation (PS) and inter-PS). During stimulus, the absolute 9-11 Hz band power of the patient group was higher at the posterior than that at the anterior sites throughout the 10 sec periods. However, this difference between sites was not seen during the first 1 sec in the control group. During the nonstimulus period, posterior dominance of 9-11 Hz band power was prominent in the patient group throughout. In the control group, however, this difference was minor, especially during the latter half of the period. These results suggest that schizophrenic patients show fewer changes in posterior alpha activity during both stimulus and nonstimulus, and this continuity of posterior dominance may reflect hyperarousal, which counteracts any decrease in vigilance throughout the IPS.

Adolescent↗
PubMed1978

Intermittent photic stimulation. Clinical usefulness of non-convulsive responses.

The clinical usefulness of non-convulsive responses induced by intermittent photic stimulation (IPS) was studied in 46 patients whose evaluation included both electroencephalography (EEG) and computerized cranial tomography (CT scan). Three patterns of photic responses were identified and related to background EEG activity and type of lesion seen on CT scan. An asymmetry in photic driving manifested only by a consistent amplitude difference greater than 50% was rarely associated with other EEG changes such as focal slowing or significant asymmetry in the alpha rhythm. In contrast, an asymmetry in development of the photic response correlated well with ipsilateral focal slowing and CT scan evidence of parenchymatous brain disease. Bilateral, symmetrical high amplitude single spikes evoked by individual light flashes were seen only in patients with diffuse encephalopathies. In no patient with structural brain disease as judged by CT scan was an abnormality in IPS the only EEG finding. There was also no apparent relationship between the anatomical site of a focal cerebral lesion and the type of response induced by IPS. Photic stimulation is of limited value in non-epileptic patients. Little clinical significance can be attached to nonconculsive responses in the absence of associated EEG changes which by themselves are generally more informative.

Adult↗
PubMed2002

Impact of intravenous nicotine on BOLD signal response to photic stimulation.

Functional magnetic resonance imaging (fMRI) is increasingly being applied in the study of brain effects of nicotine. In addition, because tobacco smoking is common, many subjects studied with fMRI for other reasons may have appreciable levels of nicotine in plasma and brain during scanning. However, there is concern that the vascular effects of nicotine may alter the coupling between blood oxygen level dependent (BOLD) signal and neuronal activity. The objective of this study was to test for evidence of alteration of BOLD signal response of occipital cortex, a region with a relatively low concentration of neuronal nicotine receptors, to photic stimulation during intravenous infusion of nicotine. Nine nicotine dependent healthy smokers were withdrawn from nicotine under controlled conditions and then scanned while receiving photic stimulation and successive intravenous infusions of saline and nicotine. No evidence for an effect of nicotine on BOLD signal response to photic stimulation was detected at the doses studied. This observation suggests that nicotine does not alter the coupling between BOLD signal and neuronal activity in the visual cortex.

Humans↗
PubMed2000

Alteration of motor cortex excitability in response to intermittent photic stimulation.

OBJECTIVE: To measure the duration of cortical silent period (C-SP) in response to different frequencies of intermittent photic stimulation (IPS). METHODS: Ten normal volunteers without a history of seizures were studied. First, using a magnetic stimulator we determined the resting motor threshold (RMT). The C-SP produced by a single magnetic shock at 120% of RMT was measured in the maximally contracted abductor pollicis brevis. C-SP was then measured while subjects were exposed to IPS at 5, 10, 15, 20, 30, 50, and 60 Hz with closed eyes. RESULTS: The average duration of C-SP was 135+/-33. 2 ms with no photic stimulation. This did not change significantly when subjects were exposed to IPS at 5, 10, 15, 20, and 30 Hz. The duration of C-SP, however, decreased significantly at higher frequencies. At 50 Hz it was 116.2+/-43 ms (P=0.003) and at 60 Hz it was 112.7+/-44.6 ms (P<0.001). CONCLUSION: Our findings suggest that motor cortex inhibition is altered in response to IPS at 50 and 60 Hz.

Adult↗
PubMed2000

Hemodynamic responses to photic stimulation in neonates.

A three-channel near-infrared monitoring system was used to evaluate the regional hemodynamic responses to photic stimulation during spontaneous sleep in seven healthy neonates. Three pairs of parallel light guides, separated by 15 mm each, were placed over a 450-mm(2) occipital region of the head. Increases in oxygenated and total hemoglobin were observed during photic stimulation only in one channel, and no change or decreases in oxygenated, deoxygenated, and total hemoglobin were observed in the other two channels. The change in the direction of deoxygenated hemoglobin accompanying the increases in oxygenated and total hemoglobin (usually a decrease in adults) differed in each subject and also varied with each measurement even in the same subject. An increase, decrease, and no change were observed. The results imply that an increase in regional cerebral blood flow occurs because of stimulation specific to the visual cortex and that the increase in deoxygenated hemoglobin observed in the visual cortex of the neonatal brain is attributable to venous dilation.

Cerebrovascular Circulation↗
PubMed1998

Effects of flash frequency and repetition of intermittent photic stimulation on photoparoxysmal responses.

The protocol used for intermittent photic stimulation (IPS) may determine the likelihood of evoking a photoparoxysmal response (PPR). One-hundred and thirty-five electroencephalograms (EEGs) presenting PPRs, from 125 patients were studied in order to identify the most effective stimulation frequency to evoke a PPR and the effects of repetition of IPS on the occurrence of a PPR. Two stimulation protocols were used: protocol I (starting at 18 Hz and then testing at 2, 6, 8, 10, 15, 20, 30, 40, 50, 60 Hz) and protocol II (stimulating at 2, 6, 8, 10, 15, 18, 20, 30, 40, 50, 60 Hz). Protocol I was used for patients not known to be photosensitive whereas protocol II was used for patients known to be photosensitive before recording. Both latency and PPR grade for frequencies which evoked PPR were measured in all records. The most epileptogenic frequencies (those evoking grade 4 PPRs at the shortest latency) were within the range 15-18 Hz for both protocols. In the records where the IPS was repeated at the same frequency, the PPR latency and grade seen during the first and second stimulation trial were studied in order to establish habituation or potentiation of responses. Repetition of IPS at the same frequency induced habituation more often than potentiation, but only if trials were repeated consecutively which suggests that habituation is frequency specific and trials repeated during EEG recordings to confirm photosensitivity to a particular frequency should be separated in time or be non-consecutive. Five patients studied with protocol I (10.6%) showed a grade 4 PPR only during the initial trial at 18 Hz. Thus, as a general screening procedure for testing for photosensitivity commencing stimulation at 18 flashes/s appears to be justified. The combination of two different protocols delivered to patients with and without a history of photosensitivity appears to achieve a sensible compromise having a high likelihood of demonstrating photosensitivity with a minimum risk of precipitating seizures.

Adolescent↗
PubMed1985

Electrophysiological studies of myoclonic jerks provoked by photic stimulation.

A patient with a type of myoclonus produced by somatosensory and photic stimuli was studied electrophysiologically. Jerk-locked averaging showed cortical spikes in association with the spontaneous myoclonus. High amplitude somatosensory evoked potentials and high amplitude visual evoked potentials were observed. Somatosensory and photic stimuli produced 2 or 3 successive electromyographic (EMG) discharges. The time interval from the onset of the preceding EMG discharge to that of the following EMG discharge produced by photic stimulation corresponded to the latency of a long-loop reflex. It also corresponded to the time interval from the onset of the preceding EMG discharge to that of the following EMG discharge produced by somatosensory stimulation. Not only somatosensory but also photic stimuli might excite the loop of a long-loop reflex and cause myoclonic jerks.

Aged↗
PubMedDate not supplied

Dynamic MR imaging of human brain oxygenation during rest and photic stimulation.

Dynamic FLASH (fast low-angle shot) magnetic resonance (MR) imaging was used to monitor changes in brain oxygenation in the human visual cortex during photic stimulation. The approach exploits the sensitivity of the gradient-echo signal to susceptibility changes induced by varying concentrations of paramagnetic deoxyhemoglobin in the cerebral blood pool. After the onset of binocular photic stimulation (10 Hz, red light, checker-board), there was a distinct increase in the MR signal in the calcarine cortex within 6-9 seconds, indicating a decrease in the total deoxyhemoglobin concentration. After the stimulation was switched off, the MR signal returned to a basal value within a similar period of time. Assuming enhanced blood flow and only a minor increase in oxygen consumption (production of deoxyhemoglobin) during physiologic activation, the results reflect an enhanced supply of diamagnetic oxyhemoglobin and an increase in the partial oxygen pressure in the capillary and venous blood pools. In addition, a decrease in the basal MR signal in the calcarine cortex was observed during the first 60-90 seconds of persistent activation, which may be understood as an autoregulatory adaptation to increased overall brain activity associated with information processing due to continuous perception of visual stimuli.

Adult↗
PubMed1994

Quantitative EEG analysis at rest and during photic stimulation in drug-naive patients with first-episode paranoid schizophrenia.

In the present study, quantitative EEG analysis was performed at rest and during 10 Hz photic stimulation in 14 drug-naive patients with first-episode paranoid schizophrenia and 20 sex- and age-matched control subjects. Compared with the normal controls, the patients had significantly lower alpha-2 band amplitude in the resting EEG over all recording regions. No significant group differences were found in other frequency bands. In addition, EEG analysis during photic stimulation demonstrated that the patients had a rather uniform topographic profile in EEG amplitude for the alpha band, with significant group differences being confined to the posterior regions in the left hemisphere. There were no significant group differences in the amplitude for the frequency bands harmonically related to the stimulus frequency. These findings provide further evidence that schizophrenic patients have abnormal EEG activity in both non-stimulus and stimulus conditions, and suggest a dysfunction in the mechanisms underlying EEG alpha generation in schizophrenia.

Adult↗
PubMed2006

Transient decreases in Bispectral Index without associated changes in the level of consciousness during photic stimulation in an epileptic patient.

This case report describes a patient with a history of epileptic seizures who showed unusual decreases in the Bispectral Index (BIS) attributable to the induction of abnormal slow electroencephalographic (EEG) waves by photic stimulation, without any associated decrease in his level of consciousness. After starting anticonvulsive therapy, photic stimulation no longer induced abnormal EEG activity nor decreased BIS values. These findings suggest that BIS values may not accurately reflect a patient's actual level of consciousness in the presence of epilepsy-related abnormal EEG activity and that the BIS monitor may be able to track such EEG changes.

Adult↗
PubMed1990

Abnormal EEG responses to photic stimulation in schizophrenic patients.

Numerous studies have differentiated schizophrenic patients and normal controls in electroencephalography (EEG) spectral patterns recorded at rest. We replicated the resting EEG spectral differences between these groups and observed significant differences in periodic photic stimuli on the EEG spectra. Drug-free schizophrenic male patients (n = 8, mean age = 23.9) and normal male controls (n = 11, mean age = 24.3) were studied. Eighty seconds of EEG were collected from each subject for each of four experimental conditions: one resting and three photic-driving conditions (2.38, 4.54, and 8.33 Hz). Eye movement and other movement artifacts were minimized by use of an automatic amplitude threshold filter. Although large eye movements could be excluded as confounding factors, the filter could not for certain exclude small eye movements. Subjects were instructed to keep their eyes closed throughout. A significant difference was found between the groups both at rest and following photic stimulation in EEG activity. This result was characterized by increased delta activity and decreased alpha activity in schizophrenic patients at rest. The EEG activity following the photic driving also differentiated the groups. Schizophrenic patients had decreased sensitivity to the photic stimulation in the alpha range for spectra derived from both fundamental and harmonic analysis.

Adult↗
PubMed1994

Gender differences in quantitative EEG at rest and during photic stimulation in normal young adults.

In the present study quantitative EEG analysis was performed in 20 male and 20 female healthy adults in order to examine the gender differences in EEG activity at rest and during photic stimulation. The females generally showed a higher amplitude in the resting EEG than the males, with significant differences observed for the delta, theta, alpha 2 and beta bands at the limited electrode sites. The gender differences were more pronounced in EEG activity during photic stimulation, and the females had a higher EEG amplitude in the frequency band identical or harmonically related to the stimulus frequency. These findings provide further evidence that the gender differences exist in EEG activity in both stimulus and nonstimulus conditions.

Adult↗
PubMed1999

Brain activation during intermittent photic stimulation: a [15O]-water PET study on photosensitive epilepsy.

PURPOSE: Intermittent photic stimulation (IPS) is an activation procedure used during electroencephalogram (EEG) recording to elicit paroxysmal discharges in individuals with photosensitivity. Specific responses on EEG recording may be provoked by IPS at different frequencies of flickering in normal individuals and in patients with photosensitive epilepsy. METHODS: Changes in regional cerebral blood flow (rCBF) were studied during IPS in two groups of subjects by using [15O]-water positron emission tomography (PET): a control group consisting of eight healthy adults with photic driving response during IPS on EEG recording (mean age, 25 +/- 10.5 years) without history of neurologic or psychiatric abnormalities and a patient group consisting of four adults (mean age, 33 +/- 7.5 years) with history of photosensitive epilepsy. [15O]-water PET scanning with concomitant EEG monitoring was performed during baseline and IPS at 4-, 14-, and 30-Hz frequencies. RESULTS: The control group showed photic driving response at 14-Hz IPS frequency. The patient group showed photoparoxysmal response at 14 and 30 Hz, but not at 4 Hz. Changes in rCBF were determined by means of statistical parametric mapping. Increases in rCBF in occipital cortex (Brodmann's areas 17, 18, and 19) were observed in both groups. In addition, during photic driving responses, the control group showed rCBF increases in the insula and in the thalamus, on the right side. The patient group showed a significant rCBF increase in the hypothalamic region inferior to the left caudate nucleus during photoparoxysmal response. This activation was not found in the control group. Increased rCBF also was observed in the patient group in the head of the left caudate nucleus, in the left hippocampus, and in left insula during IPS without photoparoxysmal response. No activations in these regions were observed during photoparoxysmal response. CONCLUSIONS: These data may indicate involvement of the hypothalamus in photosensitive epilepsy and may suggest a modulatory function of the caudate nucleus, which might be associated with an inhibition of epileptic discharges during IPS in patients with photosensitive epilepsy.

Adult↗
PubMed2003

Perfusion changes with photic stimulation during two phases of the menstrual cycle: a pilot study comparing controls and true menstrual migraine patients.

This pilot study investigated the effect of menstrual cycle phase (late luteal and mid-follicular) on cerebral perfusion changes during photic stimulation in both controls (n = 5) and true menstrual migraine patients (n = 5). No significant differences in resting baseline perfusion were observed between the two groups during either phase of the menstrual cycle. During the late luteal phase, changes in perfusion within the occipital lobe due to photic stimulation were similar for both groups. However, during the mid-follicular phase, occipital perfusion during visual stimulation decreased for controls but significantly increased for true menstrual migraine patients (P < 0.05). A two way repeated measures anova also demonstrated a significant difference between menstrual migraine patients and controls for photic activation (P < 0.05).

Adult↗