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-na?ve 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.     

Photosensitive epilepsy: Spectral and coherence analyses of EEG using 14 Hz intermittent photic stimulation

ObjectiveTo evaluate the EEG recorded in photosensitive idiopathic generalised epilepsy (IGE) patients at rest and during 14 Hz IPS, frequency capable of inducing photoparoxysmal responses (PPRs).MethodsPower spectrum density and coherence profiles were estimated using a block autoregressive parametric model (AR) in 28 patients and 22 controls.ResultsAt rest, the intra- and inter-hemispheric coherence spectra showed a significantly larger number of coherence peaks in the gamma band in patients with respect to controls. During intermittent photic stimulation (IPS), coherent gamma activity is mainly presented as IPS frequency harmonics; moreover, the patients’ mean coherence values significantly increased. In six patients re-evaluated with IPS after putting on glasses with Z1 blue lens (which counteracts PPR) the spectral and coherence profiles tended to return to the resting ones.ConclusionsPatients are endowed with inherited EEG hyper-synchrony as shown by the large number of coherence peaks detectable under resting conditions, whereas IPS enhances intra- and inter-hemispheric mean coherence values in the gamma band. The persistence of alpha activity peaks during IPS in most controls but not in patients suggests that the alpha generating network plays a significant role in counteracting PPR.SignificanceBoth gamma and alpha EEG generators are involved in the PPR generation and in the widespread synchronisation characterising the IGE-associated photosensitivity.     

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.     

Cortical unit activity during intermittent photic stimulation in Papio papio. Relationship with paroxysmal fronto-rolandic activity

Extracellular records have been made in the fronto-rolandic (FR), parietal and occipital cortical areas in Papio papio injected with allylglycine and paralysed with a synthetic curarizing agent. The organization of the unit discharges in the absence of intermittent light stimulation (ILS) is normal. During ILS, unit discharges in the FR cortex are organized in bursts of high frequency that are synchronous with the spikes of the EEG paroxysmal discharges (PD) in the same territory; this burst-organized FR activity is reversible, and bursts disappear when the ILS stops. In addition, in the FR cortex, triple or single flashes induced paroxysmal visual evoked potentials (PVEP) whose spikes were accompanied by bursts identical to the preceding ones. The slow waves which constituted the PD and the PVEP corresponded to a transitory inhibition of the FR neuronal activity. From the unit discharge patterns, no difference was observed between the two EEG paroxysmal activities recorded. No pattern of discharge in bursts was ever observed in the parietal and occipital cortex. The synchronizing role of the light stimulation in the FR cortex in Papio papio under allylglycine is discussed and the results are used to compare the experimental model with the naturally highly photosensitive animal. The particular reactivity of the FR cortex with respect to other regions is also discussed. Finally, the results bring forth new information in favour of a similarity between PD and PVEP.     

The EEG response to photic stimulation is not increased in alcohol-related seizures

Objective

To investigate the occipital EEG response to 18 and 24 Hz photic stimulation (the H-response) in alcohol-related seizures (ARS).

Method

Twenty-two ARS patients, 15 of whom had a withdrawal seizure (WS) were compared with patients with recent seizures of other causes: 21 patients with epilepsy, and 30 Alcohol Use Disorders Identification Test (AUDIT) negative patients with other seizures. EEG from 37 out-patients with epilepsy and 79 sciatica patents served as patient-controls. The spectral amplitude around 18 and 24 Hz and a new photic H-ratio (24/18 Hz relative amplitude) was calculated.

Results

The H-ratio was significantly reduced in the ARS group compared to the sciatica group. H-ratio reduction correlated with the AUDIT score in ARS patients (p = 0.02). No differences between WS and non-WS patients were found for H-response variables.

Conclusion

A dose–response relationship between AUDIT and the photic response H-ratio was observed in ARS patients. The EEG-driving response to 24 Hz flashes was not increased in ARS.

Significance

The relative decrease in 24 Hz photic response in ARS reflected drinking severity. The H-ratio is a candidate biomarker for ARS on the group level, although the moderate effect size precludes its use in individual patients.     

Monosynaptic reflexes during generalized spike and wave activity, provoked by intermittent photic stimulation

Achilles tendon (T) and Hoffmann (H) reflexes were evoked during spike and wave activity (SWA) in 6 patients with generalized epilepsy, selected on the basis of their photosensitivity. SWA was provoked by intermittent photic stimulation (IPS). It was demonstrated that monosynaptic reflex amplitudes were larger during SWA than at rest. Although IPS caused by itself a slight increase in amplitudes, there was an obvious difference from the larger increase during SWA. T reflexes showed a more explicit increment than H reflexes. The activity changes in the spinal motor circuits were nearly always present in the absence of any clinical manifestation of motor activity. The possible mechanisms are discussed.     

The clinical significance of occipital spikes as a sole response to intermittent photic stimulation.

Forty-five patients who showed occipital spikes as a sole response to IPS have been studied over a 9 year period. Occipital spikes induced by IPS are non-specific, not constantly present and in themselves are not indicative of epilepsy. Occipital spikes alone are seen in a very small percentage of clinical photosensitive patients.     

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.     

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.     

Apnoea and bradycardia during epileptic seizures: relation to sudden death in epilepsy.

OBJECTIVE--To record non-invasively ictal cardiorespiratory variables. METHODS--Techniques employed in polysomnography were used in patients with epilepsy undergoing EEG-video recording at a telemetry unit. RESULTS--Apnoea (> 10, range > 10-63, mean 24 s) was seen in 20 of 47 clinical seizures (three secondary generalised, 16 complex partial, and one tonic) and 10 of 17 patients. Apnoea was central in 10 patients, but obstructive apnoea was also recorded in three of 10. Oxyhaemoglobin saturation (SpO2) dropped to less than 85% in 10 seizures (six patients). An increase in heart rate was common (91% of seizures). Bradycardia/sinus arrest was documented in four patients (mean maximum RR interval 5.36, range 2.8-8.6 s) but always in the context of a change in respiratory pattern. CONCLUSION--Ictal apnoea was often seen. The occurrence of bradycardia in association with apnoea suggests the involvement of cardiorespiratory reflexes. Similar mechanisms may operate in cases of sudden death in epilepsy.     

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.     

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.     

Clinical significance of EEG abnormalities during photic stimulation in patients with photosensitive epilepsy

PURPOSE: The continued presence of EEG abnormalities in patients with a history of photosensitive seizures is used to signify the persistence of photosensitive epilepsy. The extent to which this approach places patients at risk of seizures is unclear, however. We describe those EEG abnormalities that may be tolerated with low risk of further seizures, and those that are indicative of poor seizure control. METHODS: Fifty patients with EEG evidence of persistent photosensitive epilepsy underwent photosensitivity testing with diffuse and patterned light; 58% of patients continued to experience seizures, and 42% were seizure free. The incidence of EEG abnormalities to diffuse and patterned intermittent photic stimulation (IPS) was analysed as a function of recent seizures. RESULTS: All patients showed EEG abnormalities to patterned IPS; there was no significant association between patterned IPS and poor seizure control. EEG abnormalities to diffuse IPS occurred in 58% of patients, and 76% of these patients had experienced a seizure within the previous year. These patients were more than twice as likely to be poorly controlled than those who showed abnormalities only to patterned IPS. These results were consistent for both medicated and unmedicated patients. CONCLUSIONS: EEG abnormalities to patterned IPS can be used to signify the persistence of photosensitive epilepsy, but abnormalities to diffuse IPS are more likely to indicate the patient is poorly controlled and at risk of further seizures.