Intermittent Photic Stimulation Research Articles

The development of the electroencephalogram in normal children from the age of 1 through 15 years. Paroxysmal activity.

In cases of 1 through 15 year-old normal children the occurrence of paroxysmal activity with the exception of the 14 and 6 Hz positive spike phenomenon was studied. The children were considered normal as a result of 1: strict selection after thorough penetration of obstetric history, mental and physical development, diseases and injuries involving the CNS, and past and present behavior so as to exclude neurological and physical disorders; 2: physical examination to exclude actual somatic and neurological aberrations, and at the same time 3: routine observation to reveal overt psycho-pathology. The material comprised 743 children with successful records at rest. Hyperventilation was performed with 82.6 per cent; intermittent photic stimulation with 81.4 per cent; and sleep, either spontaneous or barbiturate-induced, with 80.5 per cent of the children.

Relation of occipital spikes evoked by intermittent photic stimulation to visual evoked responses in photosensitive epilepsy.

PATIENTS suffering from photosensitive epilepsy show generalized discharges in their electroencephalogram (EEG) during intermittent photic stimulation. In some patients, these discharges are preceded by occipital spikes, suggesting a focal onset. Hishikawa et al.1 have reported that the occipital spikes obtained in photo-sensitive epileptics have the same latency as some components of the visual evoked responses (VER), and suggested, that this might explain the origin of the occipital spikes in photosensitive epilepsy. The spikes were, however, obtained at flash rates of 10–16 s−1 (that is, the interval between the flashes was limited to a range of 63–100 ms) and the comparison of the occipital spikes was made not with the VER of the individual patient, but with VERs of a normal population. Further, the latencies for positive and negative components of the VER, as given by the authors, show a very wide range and in fact overlap. The relatively small interval between the flashes and the wide range of the VER components could result in a fortuitous relationship between occipital spikes and VER components. It has also been reported by Rodin et al.2 that spikes preceding generalized seizures, induced by ‘Megimide’ during intermittent photic stimulation, were related to normal VERs and consisted of a marked exaggeration of the secondary VER components. Their report, however, is concerned with normal animals (cats); and no details of the photic stimuli and the spikes are given. For these reasons we felt that we should re-examine the problem. The existence of a relationship between abnormal and “normal” responses would be critical to any theory attempting to explain the genesis of the occipital “epileptogenic” spikes.

Réponses évoquées visuelles chez les enfants voyants et mal-voyants

Thirty-one children aged 7–12 years received intermittent photic stimulation at a slow rate (768 msec between flashes) and a fast rate (83 msec), with eyes closed and with eyes open. Twenty-two of the subjects had normal vision, nine showed a considerable bilateral visual defect of peripheral (non-cortical) origin, the remaining vision in the better eye being less than 3/10. The responses to 200 or 100 flashes (depending on the rate used) were recorded from two montages, each consisting of a line of 9 equidistant electrodes, 2 cm apart: (1) posterior median longitudinal montage going from the vertex to the inion; (2) right-left transverse montage crossing the midline 8 cm in front of the inion. After analogue-digital conversion the responses were averaged with a computer and presented in the form of integrated chronograms (r.m.s.) and spatio-temporal maps; statistically significant differences were demonstrated: (1) between normal and poor vision considered over-all, and (2) between poorly-sighted subjects as a function of remaining visual acuity, using indices to measure the amplitude and the latency of each component, their topography (place of gradient phase reversal) and the energy of the whole response or of the after-discharge studied by itself. Compared to that in children with normal vision, the response in children with poor vision is characterized by: (1) a much weaker energy, either of the over-all response, or of the afterdischarge separated by mathematical filtering; (2) a much smaller amplitude of the positive wave which culminates at about 120 msec in the most posterior regions (wave IV of Cigánek); (3) a more anterior topography (parietal instead of occipital) of this positive wave; (4) increased latency of the negative wave which culminates at about 60 msec; (5) very small differences in amplitude as a result of opening and closing the eyes, such that the differences between subjects with normal vision and poorly sighted subjects are only statistically significant with the eyes closed. In the group of children with poor vision the amplitude of the response is seen to be least when the visual acuity remaining is smallest. The site of the lesion causing the sensory defect also plays a part. Some characteristics of the visual evoked response of subjects with poor vision (small amplitude, parietal rather than occipital topography) resemble those of the alpha activity of these children, particularly if it is studied in its average form. The problem of interpreting the peculiarities of the response evoked in subjects with poor vision is discussed in relation to a specific visual mechanism, underlying background activity and synchronizing mechanisms.

Clinical observations on photosensitive epilepsy : H. Gerken (Kiel, West Germany)

The ‘Photosensitivity Model’ uses a standardized stimulation protocol of repeated intermittent photic stimulation (IPS) over a three-day period, with administration of a single dose of an investigational antiepileptic drug (AED) after a baseline IPS day in photosensitive patients, followed by a third IPS day to determine duration of effect. This ‘Photosensitivity Model’ has shown its value in the development of new AEDs. Levetiracetam (LEV), currently a first-line AED in new-onset focal epilepsies, was not effective in classical animal models, but showed dose-dependent efficacy in the human ‘Photosensitivity Model’. Nevertheless, concerns have been expressed that AEDs selectively suppressing focal seizures might not suppress generalized photoparoxysmal EEG responses (PPR), the pharmacodynamic outcome measure in the Model. Herein, the following questions have been addressed: I. Can patients with generalized epileptiform discharges, evoked by IPS, so-called PPR, have focal epilepsy (focal seizures)? II. Are the photosensitive patients with focal epilepsy, who have participated in the photosensitivity trials, non-responsive to a new AED under investigation, as compared to those with generalized epilepsies? III. Are “focal epilepsy” AEDs effective both in the ‘Photosensitivity Model’ and in real life in photosensitive patients? We performed a systematic literature review of PPR in focal seizures and focal epilepsy and we analyzed data (published and unpublished) from 20 different potential AEDs studied prospectively in the ‘Photosensitivity Model’. Finally, the PPR effects of Na+ channel-blocking AEDs (considered as the most typical AEDs for focal epilepsy) are discussed with unequivocal examples given of the focal nature of a patient’s PPR. Based on the entire data evidence, we conclude that: 1. PPRs certainly exist in focal epilepsy (17% on average); 2. Clinical signs and symptoms of PPRs can be focal and 3. PPRs can definitely be used to identify or to prove efficacy of new AEDs for patients with focal epilepsy.

Lengthening of time estimates in four different temporal patterns of visual light stimulation

Lengthening in time estimates has been described by several authors. Thirty-six Ss produced estimates of a 10~sec interval over 29 sequential trials under one of four environmental conditions, steady illumination (SI), darkness (D), intermittent photic stimulation with a dark background (IPSD), and intermittent photic stimulation with ambient light (IPSA). Differences from zero trend and other trend differences were produced for all pairs except SI and IPSA. Results were interpreted as evidence favoring Treisman ’s model of the internal clock.

Electrophysiological analysis of the mechanisms underlying critical flicker frequency

The effect of intermittent photic stimulation on cortical activity was studied with rabbits on which psychophysical determinations of CFF had been made. In all cases photic following was clearly detectable at frequencies well above the flicker fusion threshold. The average amplitude of the evoked potentials at various frequencies relative to the amplitude at 5 c/s was calculated to determine the per cent of attenuation in the response as the frequency of stimulation was increased. It was found that CFF always occurred when the response had attenuated 10–20 per cent of the maximum. These results coupled with recent findings on the effects of intermittent photic stimulation on single cells in the visual system were used to formulate an account of the mechanism underlying CFF.

A test of the effectiveness of intermittent photic stimulation on hypnotic performance

Abstract An attempt was made to confirm the previously reported finding of Hammer and Arkins (1964) of a significantly greater improvement in hypnotic performance as a result of 11 cps intermittent photic stimulation than with frequencies outside the range of EEG alpha activity. Using the Brain Wave Synchronizer, three groups of Ss were given stimulation at 5 cps, 11 cps, and 30 cps. Tests of hypnotic performance were made during stimulation, immediately after stimulation, and a week or more later. No evidence of frequency-specific effect was obtained, and the original finding was considered not confirmed.

Photosensitive epilepsy: Relationships between the visual evoked responses and the epileptiform discharges induced by intermittent photic stimulation

In fifteen patients with photosensitive epilepsy the characteristics of the EEG epileptiform discharges induced by intermittent photic stimulation (IPS) were investigated. In all the patients generalized EEG epileptiform discharges were induced by IPS. In eight of them (1st group) the discharges appeared first in the occipital area, whereas in the remaining seven patients (2nd group) they occured simultaneously over all head regions or appeared earlier over the anterior areas of both sides. Averaged visual evoked responses (VERs) to single flashes of light in the patients were similar morphologically to those of normal subjects. In these, the VER recorded from the mid-occipital area consisted of 4–6 rhythmic wavelets occurring within 100 msec from the flash and of larger deflexions following such wavelets. The initial component of the response is positive and has a peak latency of 20–27 msec. In six patients of the 1st group certain components of the VER were extraordinarily augmented. The earliest spikes of the EEG epileptiform discharges appearing first over the occipital regions were interpreted as unusually augmented VERs. The photosensitivity of the patients decreased remarkably during drowsiness. No epileptiform discharges were induced during slow wave sleep. In the REM stage of sleep the discharges were on the contrary as promptly induced as in the waking state. This phenomenon did not seem to be due to pupillary miosis. Monocular stimulation markedly reduced the epileptogenic effect of IPS as compared to binocular stimulation. Background illumination appeared to modify the epileptogenic effects of IPS. Ophthalmological examination revealed incomplete red-green color blindness in one patient and quadrantic hemianopsia in another. In the remaining subjects no pathological conditions of the retina were found. Some considerations on the neural mechanisms involved in epileptic photosensitivity are presented.

Experimental epilepsy induced by cobalt powder in lower brain-stem and thalamic structures

In chronic unrestrained unanaesthetized cats metallic cobalt powder in the lower brain-stem induced, as early as 24h after introduction, marked EEG changes characterized by hypersynchronous potentials, high voltage spikes, spike and wave complexes, generally associated with myoclonic jerks involving facial, cervical and forelimb flexor muscles. These changes generally faded away within 5–6 days. Generalized attacks of myoclonic type were also observed. Sensory stimulation had a driving effect on the electroclinical manifestations. Hypersynchronous potentials were driven by intermittent photic stimulation. The convulsive threshold to Metrazol injection was also definitely lowered. Similar electro-clinical manifestations followed also the introduction of cobalt powder in some midline thalamic nuclei. The results suggest a functional interconnection between some midline thalamic nuclei and lower brain-stem structures in the production of the electro-clinical manifestations of subcortical origin.

The Study of Target Size in Production of Brightness, Hue, and Saturation for Intermittent Photic Stimulation in the Red End of the Visible Spectrum

The Study of Target Size in Production of Brightness, Hue, and Saturation for Intermittent Photic Stimulation in the Red End of the Visible Spectrum

Changes in sensory phenomena and observer criteria at low rates of intermittent photic stimulation.

Changes in sensory phenomena and observer criteria at low rates of intermittent photic stimulation.

Influence of low-rate flashing on optic nystagmus

In the rabbit, low-rate flashing (5–10/sec) of one eye enhances the response, evoked from the heterologous optic pathway by flashing, optokinetic or electrical stimulation. Central nystagmus, elicited by the third form of excitation, is improved by intermittent photic stimulation of either retina at low frequencies, but greater enhancement is obtained by flashing of the heterologous eye. It is assumed that low-rate flashing exerts essentially an unspecific, i.e., non-directional effect.

Effect of visual deprivation during postnatal maturation on the electroencephalogram of the cat

Electroencephalograms were obtained from cats which had been raised in continuous darkness from before eye opening to approximately 1 year of age, and compared to those obtained from a control group reared in the lighted laboratory. Rearing in darkness produced no detectable electrocortical abnormalities in the “spontaneous” record; however, when the response from the visual cortex of dark-reared animals to intermittent photic stimulation was investigated it was found that the flicker-induced potentials were reduced at all frequencies of stimulation utilized (1–50 flash/sec). All light-reared and no dark-reared animals demonstrated visually-mediated responses as judged by performance on five simple behavioral tests. When two dark-reared animals were placed in the experimenter's home their scores on all five behavioral tests changed from negative to positive within 10 days. Two additional dark-reared animals placed in a cage in the lighted laboratory required over 30 days of experience before positive scores were obtained on these tests. This research demonstrated that the behavioral deficits produced by the exclusion of the adequate stimulus from the retina during the postnatal developmental period does not necessarily produce electrophysiological abnormalities in the visual cortex and that these profound behavioral deficits may be very rapidly altered when the proper conditions are utilized.

Interaction of central and flash nystagmus

Central nystagmus is evoked in the rabbit by electrical stimulation of one optic pathway. The response is strongest in the dark and is depressed by illumination of the heterologous retina. Flash nystagmus results from intermittent photic stimulation of one eye. Combination of central nystagmus with synergistic flashing potentiates the response markedly. Combination with antagonistic flashing at a rate of 25–30/sec depresses central nystagmus strongly, but at 5–10/sec it breaks the inhibitory effect of illumination on central nystagmus and may raise the response to the level of the dark control.

BRIGHTNESS ENHANCEMENT AND HUE. II. HUE SHIFT AS A FUNCTION OF STEADY AND INTERMITTENT PHOTIC STIMULATION.

BRIGHTNESS ENHANCEMENT AND HUE. II. HUE SHIFT AS A FUNCTION OF STEADY AND INTERMITTENT PHOTIC STIMULATION.

Effect of Flicker-Periodicity upon Performance and Arousal during a Rotary-Pursuit Task

Intermittent photic stimulation, hereafter referred to as flicker, is classified as a stressor agent by Sines et al., and has been used as the stimulus in the investigation of a variety of problems.' It is believed by some investigators that aperiodic flicker is more disturbing or stressful than is periodic flicker.2 One purpose of the present study was to test this hypothesis by determining the effects of periodic and aperiodic flicker upon performance and arousal during a rotary-pursuit task.A A second purpose was to relate performance and arousal. The concept of arousal has been described by a number of authors as referring to the degree of activation and energizing of the organism.4 It has been found that level of performance is related to level of arousal.5 Skin-resistance and heart-rate, which Malmo stated were physiological indicants of arousal,6 were used in the present study. Some question has, however, been raised as to their equivalence in this respect.7 A third purpose of the present study was to compare heart-rate and skin-resistance as indicants of arousal.

Nystagmus evoked by intermittent photic stimulation of the rabbit's eye.

Monokuläre Reizung des Kaninchens durch Lichtblitze ruft einen Nystagmus hervor, dessen Richtung identisch ist mit der Richtung der Augenbewegungen, die durch elektrische Stimulierung des ipsilateralen Nervus opticus verursacht werden. Die anhaltende Beleuchtung des kontralateralen Auges hemmt die Nystagmusreaktion.

Responses of the isolated mammalian retina to intermittent and steady photic stimulation

The potential usually recorded from the isolated retina probably corresponds to the P-III component of Granit. It was found that during intermittent photic stimulation (IPS), all responses tended toward a set negative potential value but the response excursion was limited by the decay process of the potential. The rate of decay of the massed response was shown to change during the initial period of IPS, permitting greater excursions after the first few responses. Introduction of a steady light also induced a negativity which was maintained throughout the period of stimulation and would also limit the excursions of the individual responses to the IPS.

Contributions to the study of gamma-aminobutyric acid (GABA) in the hypothalamohypophyseal pathways

The hypothalamo-hypophyseal complex contains large amounts of GABA in the dog. The GABA content of the hypothalamo-hypophyseal pathways decreases in the animals under stress. A thirst diet increases and insulin-induced hypoglycemia lowers the amounts of both GABA and the neurosecretory material in the hypothalamo-hypophyseal pathways. In intraventricular injections GABA intensifies staining of the neurosecretory material in the hypothalamo-hypophyseal pathways and activates the electroencephalographic tracing, accompanied by improved driving to intermittent photic stimulation and increase in the frequency spectrum. The activating effects of intracerebral administration of GABA disappear in the animal treated with chlorpromazine, hydroxylamine or sodium malonate and become inhibitory under conditions of insulin-induced hypoglycenia or hypophysectomy. The double stimulating and inhibitory properties of this amino acid depend upon the degree and route of its metabolization. The metabolic, histochemical and functional data reported prove that GABA influences the excitability of the reticulo-hypothalamo-hypophyseal pathways by the mechanism of its utilization as an oxidative substrate and not as an inhibitory chemical mediator.

THE INFLUENCE OF ATTENTION ON THE OCCIPITO-CORTICAL RESPONSES TO LIGHTFLASHES IN MAN.

Human occipito-cortical responses to intermittent photic stimulation were studied. In the majority of the subjects the most obvious effect of image formation on the flickering screen was amplitude reduction in those components occurring more than approx. 100 msec after the beginning of the flash. It is argued that this effect is caused by the image formation on the retina as such and not by the activity of some “attention mechanism”.