Intermittent Light Stimulation Research Articles

Generating fast-twitch myotubes in vitro with an optogenetic-based, quantitative contractility assay.

The composition of fiber types within skeletal muscle impacts the tissue's physiological characteristics and susceptibility to disease and ageing. In vitro systems should therefore account for fiber-type composition when modelling muscle conditions. To induce fiber specification in vitro, we designed a quantitative contractility assay based on optogenetics and particle image velocimetry. We submitted cultured myotubes to long-term intermittent light-stimulation patterns and characterized their structural and functional adaptations. After several days of in vitro exercise, myotubes contract faster and are more resistant to fatigue. The enhanced contractile functionality was accompanied by advanced maturation such as increased width and up-regulation of neuron receptor genes. We observed an up-regulation in the expression of fast myosin heavy-chain isoforms, which induced a shift towards a fast-twitch phenotype. This long-term in vitro exercise strategy can be used to study fiber specification and refine muscle disease modelling.

Sub-second timing irregularities in a simple motor task in autism spectrum disorder: Preliminary effects of intermittent light stimulation.

Several authors have contributed extensively to the neurocognitive understanding of timing. In Autism Spectrum Disorder (ASD) on the contrary, internal timing and its functioning is not well understood. In this study, we have adapted a simple finger-tapping motor task, with a timing component, as we aim at understanding whether the processing of time is preserved in this population. We have tested a group of people on the autism spectrum without intellectual disabilities and a control sample recruited from the general population, matched for age, sex, schooling and general cognitive abilities on this task with a learning and testing phase. In the testing phase, we have added two exploratory conditions where participants were exposed to intermittent light stimulation of 4 and 8 Hz. Results show that both in the learning and testing phase, besides troubles in the motor component encountered by the people on the spectrum, their timing component performance was also problematic. This reveals to be especially true for time intervals below the 1 s range, as hypothesized, whereas performance in longer intervals is clearly preserved. It was also observed that the exposure to intermittent light stimulation specifically overcomes the difficulties observed in the autistic group, at the timing components at this millisecond time range. The observed timing difficulties in this group seem to be restricted to the system responsible for the processing of time intervals in the milliseconds range, which helps accommodate disparate findings in the literature.

Abnormal brain function in photophobic patients with dry eye disease: An fMRI study

Background and objectivesPhotophobia, a frequent and disabling symptom observed in various neurological conditions and eye diseases, is thought to involve maladaptive brain functioning. We assessed this hypothesis, using functional magnetic resonance imaging (fMRI) in photophobic patients with minimal-to-severe dry eye disease (DED), as compared to healthy controls. MethodsThis prospective, monocentric, comparative, cohort study included eleven photophobic DED patients compared to eight controls. Photophobic patients had a complete evaluation of DED to exclude any other cause of photophobia. All participants were scanned with fMRI under intermittent light stimulation with a LED lamp (27s. ON, 27 s. OFF), and cerebral activations were studied with univariate contrasts between the ON and OFF conditions, and with functional connectivity methods. ResultsFirstly, stimulation activated the occipital cortex more strongly in patients than in controls. Moreover, stimulation deactivated the superior temporal cortex in patients less than in controls. Secondly, functional connectivity analysis showed that light stimulation induced lesser decoupling between the occipital cortex and the salience and visual networks in patients than in controls. DiscussionThe current data shows that DED patients with photophobia have maladaptive brain anomalies. There is hyperactivity in the cortical visual system, associated with abnormal functional interactions, both within the visual cortex, and between visual areas and salience control mechanisms. Such anomalies show similarities with other conditions such as tinnitus, hyperacusis, and neuropathic pain. Those findings support novel neurally oriented methods for the care of patients with photophobia.

The Impact of Flashing on the Efficacy of Variable Message Signs: A Vehicle-by-Vehicle Approach

A great deal of research has examined the efficacy of variable message signs (VMS) to induce driver behavior changes, improve safety conditions, and decongest the traffic network. However, there is little literature regarding the most effective ways to display this information on VMS. Furthermore, none of the previous contributions have concentrated on analyzing what impact flashing VMS have on drivers by using real traffic data. This article seeks to bridge this gap, analyzing the effect of incorporating intermittent light stimulation to messages on drivers’ behavior on a Chilean highway, using vehicle-by-vehicle data obtained in a non-intrusive way. In order to do so, an experiment was carried out to measure the responses of drivers when faced with two types of messages: (1) those intended to induce a speed reduction and (2) those aimed at generating lane changes. From the statistical models we obtained several insights. Our results show that flashing messages may increase the effectiveness of VMS depending on environmental and traffic conditions. In particular, for speed moderation messages, we found 12 significant effects, showing, for example, that a flashing message is most effective in the hours of darkness, with low congestion, small spacing, and low average speeds. Additionally, it has a more significant impact on experienced drivers. On the other hand, for lane change messages, we found five significant effects, showing that flashing messaging reduces its effectiveness in situations where a high cognitive load is required, such as in high flow and high average speeds. No particular effects were identified in either case for specific vehicle types.

Photo-Dependent Reflex Seizures-A Scoping Review with Proposal of Classification.

Children and adolescents are the largest at-risk group for the appearance of reflex seizures or epilepsy syndromes with a photoparoxysmal response. The aim of this study was to present an overview of the literature regarding photo-dependent reflex seizures. Epilepsy with seizures provoked by intermittent light stimulation is a distinct group of epilepsies; therefore, we focused on reflex seizures provoked by different factors whose common feature is the patient’s response to intermittent photic stimulation. A qualitative search of PubMed/MEDLINE, Scopus, EBSCO, and Cochrane Library electronic databases for selected terms was carried out for scientific articles published up to May 2020 outlining the outcomes of control, observational, and case studies. This scoping review was developed and followed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews. The review of the qualitative evidence for the synthesis of photosensitive epilepsy allowed us to distinguish the following categories: light-induced seizures and light-deprived seizures. Differentiating between intermittent photic stimulation-related epilepsy syndromes and seizures is essential in order to determine the length of appropriate treatment. Photo-dependent reflex seizures make up the majority of this type of disorder among reflex seizures. Since there are many seizures provoking factors in the world around us, it is important to distinguish amongst them in order to be able to protect the patient exposed to this factor. It is recommended that the photostimulation procedure be performed during a routine electroencephalogram study.

Cerebral blood flow differences between high- vs low-frequency VNS therapy in the epileptic baboon

PurposeCerebral blood flow (CBF) tracks physiological effects of ictal or interictal epileptic discharges (IEDs) and neurostimulation. This study compared CBF changes between high-frequency (HF; 300 Hz) microburst, and standard, low-frequency (LF; 30 Hz) vagal nerve stimulation (VNS) Therapy in 2 baboons with genetic generalized epilepsy (GGE), including one with photosensitivity. MethodsThe baboons were selected based on video recordings and scalp EEG studies. They were both implanted with Sentiva™ 1000 devices capable of stimulating at standard and microburst frequencies. Nine H215O (10–20 mCi) positron emission tomographic (PET) scans were performed each session (two PET sessions acquired for each animal). The baboons were sedated with ketamine, paralyzed, and monitored with scalp EEG. CBF changes were compared between the two modes of stimulation and resting scans in the first study, while in the second, VNS Therapy trials were combined with intermittent light stimulation (ILS) at 25 Hz and compared to CBF changes induced by ILS alone. ResultsILS-associated IED rates were slightly reduced by HF- and LF-VNS Therapies in B1, while spontaneous IEDs were completely suppressed by HF-VNS Therapy in B2. Regional CBF changes were consistent between the two modes of therapy in each baboon, in particular with respect to the activation of the superior colliculus and cerebellum. Neither VNS mode suppressed the photoepileptic response in B1. In B2, IED suppression was associated with bilateral deactivations of the frontal and temporal cortices, cingulate and anterior striatum, as well as bilateral cerebellar activations. ConclusionsThis pilot study reveals similar activation/deactivation patterns between LF- and HF-VNS Therapies, but the most pronounced CBF differences between the two baboons and the two modes of stimulation may have been driven by the suppression of the epileptic network by HF-VNS Therapy in B2. Some therapeutic targets appear to be subcortical, including the putamen, superior colliculus, brainstem nuclei, as well as the cerebellum, all of which modulate corticothalamic networks, which is particularly reflected by CBF changes associated with HF-VNS Therapy. These findings need to be replicated in larger samples and correlated with long-term clinical outcomes.

Intermittent light stimulation in on-demand streaming television series, accuracy of information and seizure occurrence. The stream-light study

In about 3% of people with epilepsy (PWE), exposure to flashing light sequences (FLS) can trigger seizures. Exposure to FLS may as well induce other symptoms (i.e. headache and dizziness). On-demand streaming platforms (OSP) have become popular nowadays. Binge watching sessions involve the use of laptops and take place in conditions of low ambient light. The purpose our study is to identify the presence of FLS in the catalogues offered by the main OSP, and to assess any correlation to seizure or discomfort symptoms recurrence. The presence of adequate information addressed to PWE was evaluated.

Differences in visual information processing style between Idiopathic Generalized Epilepsy with and without photosensitivity

PurposeRecently, altered visual cortical processes i.e., lack of habituation to visual evoked potentials (VEP), has been highlighted in both photosensitive epilepsy and in a specific i.e., analytic mode of processing visual inputs. In this study we aimed at evaluating the relationship between photosensitivity (PS) and analytic style of processing visual information, in a sample of 30 patients with Idiopathic Generalized Epilepsy (IGE) and matched healthy controls. MethodsAt our Epilepsy unit of the Sapienza University of Rome, we consecutively enrolled 15 patients with IGE with PSand matched them with 15 patients with IGE without PS and 15 Healthy Volunteers. All patients underwent EEG recording in basal conditions during hyperventilation (3 Min), and intermittent light stimulation. The most effective frequencies comprised from 12 to 16 Hz.The instruments used to gather psychological cognitive behavioral data, consisted of participation in two tests: the Sternberg-Wagner Self-Assessment Inventory and the Mariani Learning Style Questionnaire. ResultsCompared to controls, both IGE groups show significantly higher scores for the analytic style (One-way ANOVA, F(2,44) = 110.3, p < 0.0001). Epilepsy groups thereby showed very distinctive cognitive styles as measured with the Sternberg test. In the visual style, scores of the photosensitive Individuals with IGE were significantly higher than the non-photosensitive individuals with IGE (p < 0.0001, Tukey’s post hoc test). ConclusionsAn association between analytic style of processing visual information and PS in IGE has been shown. The common neurophysiological features between these two factors, suggest the possibility to evaluate this cognitive behavior as a potential target for nonpharmacological therapeutic strategies in photosensitive epilepsy.

Epilepsy with eyelid myoclonias (Jeavons syndrome): An electro-clinical study of 40 patients from childhood to adulthood

PurposeTo describe the typical and atypical clinical and electroencephalographic (EEG) features of 40 patients with Jeavons syndrome (JS). MethodRetrospective analysis from two French tertiary centers. ResultsForty patients were enrolled (31 females and 9 males; sex ratio F/M = 3.44; mean age at epilepsy onset: 6.2 ± 3.4 years [range: 1–15 years]). A positive family history of generalized genetic epilepsy was reported by 13 patients (32.5 %). Eyelid myoclonias with or without absence were the seizure onset in 29 patients (72.5 %), and generalized tonic-clonic seizures in 11 (27.5 %). Over the course of the disease, all had absences. Intellectual disability and psychiatric disorders were reported in 14 (35 %) and 18 patients (45 %), respectively. Focal EEG abnormalities were observed in 65 % of patients, with a posterior (57.7 %) or anterior (30 %) distribution. Generalized EEG discharges were identified in 37 patients (92.5 %). Epileptiform abnormalities were activated during NREM sleep and increased upon awakening. Response to intermittent light stimulation (ILS) was observed in 34 patients (85 %), with an unusual pattern of epileptiform abnormalities at the same frequency of the flashes in 20 patients. Patients with all seizure types were more likely to have this response (p = 0.017). ConclusionJS is a lifelong genetic epileptic syndrome with onset in childhood, female preponderance, and a positive family history of epilepsy in one-third of the cases. Focal EEG abnormalities are frequent. Response to ILS appears different from other photosensitive syndromes, with an unusual pattern of photo-induced abnormal synchronization. Intellectual disability and psychiatric disorders are not rare.

Human Motion Driven Self-Powered Photodynamic System for Long-Term Autonomous Cancer Therapy.

Long-term and low-dose photodynamic therapy for treating tumors requires a sustainable energy supply. The power source technology of batteries and wireless charging for driving a light-emitting diode (LED) may cause inconveniences during treatment. In addition, the development of telemedicine and Internet medicine put forward higher demands on treatment methods, such as better patient compliance and autonomous management. Here, we show a self-powered photodynamic therapy (s-PDT) system with two different irradiation modes that can be autonomously managed by patients. The as-fabricated s-PDT system based on a twinning structured piezoelectric nanogenerator is powered by energy harvested from body motion and realizes effective tumor tissue killing and inhibition. As demonstrated at the cellular level, the s-PDT system can significantly suppress tumor cell growth with the pulsed light stimulation mode. When the miniature LED was implanted subcutaneously in mice with transplanted tumors, the s-PDT system led to significant antitumor effects by irradiation with intermittent continuous light stimulation mode for 12 days, and an 87.46% tumor inhibition rate was obtained. This innovative s-PDT system combined with two treatment modes may provide a great opportunity to develop wearable/implantable and self-controllable devices for long-term photodynamic therapy, which would be a promising method for clinical cancer treatment.

Development of an oyster shell and lignite modified zeolite (OLMZ) fixed bioreactor coupled with intermittent light stimulation for high efficient ammonium-rich anaerobic digestion process

A novel oyster shell and lignite modified zeolite (OLMZ) fixed bioreactor incorporated with intermittent light illumination process was developed for alleviating ammonia inhibition to improve efficiency of ammonium-rich anaerobic digestion (AD). The SEM morphology of the newly synthesized OLMZ showed porous structure and rough surface, with increased BET surface area compared to unmodified zeolite (UMZ). After modification with oyster shell and lignite, the metal cations content in OLMZ increased significantly and the ammonia adsorption capability of OLMZ improved by 1.3 folds compared to UMZ. Thus, the results suggested that OLMZ is a better adsorbent than UMZ for ammonia uptake. Furthermore, the pseudo-second-order kinetics and the isotherm results verified the adsorption of ammonia on OLMZ was dominated by ion exchange with high affinity for ammonia uptake. As for the anaerobic digestion, the light illuminated OLMZ fixed bioreactor process (OLMZ-I) resulted in the highest methane yield of 372 ± 30 mL/g-DOCremoved, which showed 300% increase compared to the control (124 ± 12 mL/g-DOCremoved). In addition, OLMZ-I showed higher ammonia removal capacity and stable pH which indicated that the ammonia inhibition was effectively mitigated. Correspondingly, metal cations supplementation and light stimulation in OLMZ-I showed increased ATP and coenzyme F420 implying high activation of methanogens leading to improved CH4 production. The large biomass quantity and SEM observation of microbes immobilized on the fixed OLMZ system aided by light further supported the enhanced performance of the reactor. Furthermore, the conductance of sludge in OLMZ-I bioreactor increased 3 folds compared to the control, reflecting a potential direct interspecies electron transfer (DIET) between the anaerobes was strengthened. The synergetic effects of ammonia removal, microbes immobilization, metal cations supplementation and accelerated electrical communication between methanogenic system combined with light stimulation on methanogen activation facilitated the enhancement of methanogenesis. Therefore, the OLMZ fixed bioreactor coupled with intermittent light stimulation shows great potential in practical application for bioconversion of ammonium-rich livestock waste.

Characteristics of visual evoked potentials related to the electro-clinical expression of reflex seizures in photosensitive patients with idiopathic occipital lobe epilepsy

Seizures provoked by visual stimuli may be induced by abnormal responses to light (photosensitivity) and structured patterns (patternsensitivity). In this study, we analysed visual evoked potentials (VEPs) in three different samples: i) 38 photosensitive patients (21 males, 17 females; mean age 10.0 ± 2.9 years) with idiopathic occipital lobe epilepsy and reflex seizures (RS); ii) 13 non-photosensitive patients (6 males, 7 females; mean age 11.7 ± 5.3) with idiopathic occipital lobe epilepsy; 20 healthy controls (12 males, 8 females; mean age 10.0 ± 3.4). After written informed consent, all subjects underwent a standard procedure of visual stimulation with intermittent light and pattern stimulation, under digital video-EEG recording. The EEG signal was processed off-line by averaging analysis for each stimulus to obtain the corresponding VEP. Comparisons among groups showed no significant differences for P100 latency. Higher P100 amplitude as well as higher after-discharge (AD) were found in photosensitive patients with RS. Thirty-seven of these patients had one or more RS during the procedure of stimulation for a total of 66 episodes. Significant increases of P100 amplitude and higher values of AD amplitude were found in relation to the occurrence of photoparoxysmal response (PPR) and/or seizures during full-field pattern stimulation. The increase in amplitude of the AD was higher when PPR was associated with seizures. The high amplitude of early VEP components confirms the abnormal hyperexcitability in the cortex of photosensitive patients with occipital lobe epilepsy. Moreover, the AD amplitude appears to be related to electro-clinical expression, being greater when PPR evolves into clinically evident seizures.

Retinal plasticity in retinopathy of prematurity, and phototherapy prospects

In premature babies, plastic changes develop in the neural retina, which, depending on the severity of retinopathy of prematurity (ROP), are a manifestation of adaptive or non-adaptive plasticity. In various experimental studies on animal ROP models, the conditioning effects of intermittent white light stimulation and various mechanisms of the positive effect of red and ultraviolet radiation on the plasticity of the retina have been demonstrated, which allows phototherapy to be considered as a promising modifying treatment for ROP supplementing the main therapy. Taking into account that light-dependent processes are involved in the pathogenesis of ROP, we also hypothesize that fractal phototherapy with complex-structured optical stimuli, as a method of activating adaptive neuroplasticity, can be most effective in the complex of methods for preventing and treating ROP.

Responses to Intermittent Light Stimulation Late in the Night Phase Before Dawn.

The circadian clock is comprised of two oscillators that independently track sunset (evening) and sunrise (morning), though little is known about how light responses differ in each. Here, we quantified the morning oscillator’s responses to 19 separate pulse trains, collecting observations from over 1300 Drosophila at ZT23. Our results show that the advances in activity onset produced by these protocols depended on the tempo of light administration even when total exposure was conserved across a 15-min window. Moreover, patterns of stimulation previously shown to optimize the evening oscillator’s delay resetting at ZT13 (an hour after dusk) were equally effective for the M oscillator at ZT23 (an hour before dawn), though the morning oscillator was by comparison more photosensitive and could benefit from a greater number of fractionation strategies that better converted light into phase-shifting drive. These data continue to build the case that the reading frames for the pacemaker’s time-of-day estimates at dusk and dawn are not uniform and suggest that the “photologic” for the evening versus morning oscillator’s resetting might be dissociable.

Long-Term Changes in Optical Properties (μa, μ's, μeff and DPF) of Human Head Tissue During Functional Neuroimaging Experiments.

Frequency-domain near-infrared spectroscopy (FD-NIRS) enables to measure absolute optical properties (i.e. the absorption coefficient, μa, and the reduced scattering coefficient, [Formula: see text]) of the brain tissue. The aim of this study was to investigate how the optical properties changed during the course of a functional NIRS experiment. The analyzed dataset comprised of FD-NIRS measurements of 14 healthy subjects (9 males, 5 females, aged: 33.4 ± 10.5years, range: 24-57years old). Each measurement lasted 33min, i.e. 8 min baseline in darkness, 10 min intermittent light stimulation, and 15 min recovery in darkness. Optical tissue properties were obtained bilaterally over the prefrontal cortex (PFC) and visual cortex (VC) with FD-NIRS (Imagent, ISS Inc., USA). Changes in μa and [Formula: see text] were directly measured and two parameters were calculated, i.e. the differential pathlength factor (DPF) and the effective attenuation coefficient (μeff). Differences in the behavior of the optical changes were observed when comparing group-averaged data versus single datasets: no clear overall trend was presented in the group data, whereas a clear long-term trend was visible in almost all of the single measurements. Interestingly, the changes in [Formula: see text] statistically significantly correlated with μa, positively in the PFC and negatively in the VC. Our analysis demonstrates that all optical brain tissue properties (μa, [Formula: see text], μeff and DPF) change during these functional neuroimaging experiments. The change in [Formula: see text] is not random but follows a trend, which depends on the single experiment and measurement location. The change in the scattering properties of the brain tissue during a functional experiment is not negligible. The assumption [Formula: see text] ≈ const during an experiment is valid for group-averaged data but not for data from single experiments.

High-frequency burst vagal nerve simulation therapy in a natural primate model of genetic generalized epilepsy

PurposeSince the approval of Vagal Nerve Stimulation (VNS) Therapy for medically refractory focal epilepsies in 1997, it has been also reported to be effective for a wide range of generalized seizures types and epilepsy syndromes. Instead of conventional VNS Therapy delivered at 20–30Hz signal frequencies, this study evaluates efficacy and tolerability of high-frequency burst VNS in a natural animal model for genetic generalized epilepsy (GGE), the epileptic baboon. MethodsTwo female baboons (B1 P.h. Hamadryas and B2 P.h. Anubis x Cynocephalus) were selected because of frequently witnessed generalized tonic-clonic seizures (GTCS) for VNS implantation. High-frequency burst VNS Therapy was initiated after a 4–5 week baseline; different VNS settings (0.25, 2 or 2.5mA, 300Hz, 4 vs 7 pulses, 0.5–2.5s interburst interval, and intermittent stimulation for 1–2 vs for 24h per day) were tested over the subsequent 19 weeks, which included a 4–6 week wash-out period. GTCS frequencies were quantified for each setting, while seizure duration and postictal recovery times were compared to baseline. Scalp EEG studies were performed at almost every setting, including intermittent light stimulation (ILS) to evaluate photosensitivity. Pre-ILS ictal and interictal discharge rates, as well as ILS responses were compared between trials. The Novel Object test was used to assess potential treatment effects on behavior. ResultsHigh-frequency burst VNS Therapy reduced GTCS frequencies at all treatment settings in both baboons, except when output currents were reduced (0.25mA) or intermittent stimulation was restricted (to 1–2h/day). Seizure duration and postictal recovery times were unchanged. Scalp EEG studies did not demonstrate treatment-related decrease of ictal or interictal epileptic discharges or photosensitivity, but continuous treatment for 120–180s during ILS appeared to reduce photoparoxysmal responses. High-frequency burst VNS Therapy was well-tolerated by both baboons, without cardiac or behavioral changes. Repetitive muscle contractions involving the neck and left shoulder girdle were observed intermittently, most commonly at 0.5 interburst intervals, but these were transient, resolving with a few cycles of stimulation and not noted in wakefulness. ConclusionsThis preclinical pilot study demonstrates efficacy and tolerability of high-frequency burst VNS Therapy in the baboon model of GGE. The muscle contractions may be due to aberrant propagation of the stimulus along the vagal nerve or to the ansa cervicalis, but can be reduced by minimal adjustment of current output or stimulus duration.

Neurophysiological and clinical findings on Nodding Syndrome in 21 South Sudanese children and a review of the literature

PurposeTo describe the neurophysiological and clinical features of Nodding Syndrome (NS) in South Sudan. MethodsThe study was performed at the Epilepsy Service of “Usratuna” sited in Juba, South Sudan. The clinical history of each subject was collected along with an EEG tracing. ResultsTwenty-one children (10 females) were diagnosed with NS. Fifteen (72%) children were classified as Probable NS and six (28%) as Confirmed NS. They ranged in age between 6 and 14 years, and age at seizure onset ranged from 5 to 12 years. All the subjects presented with intellectual disability which was mild in severity in 12 (57%) cases, moderate in seven (33%) cases and severe in two (10%) cases. Interictal EEG was abnormal in 20 subjects. In 18 (85%) subjects, the EEG showed 2–3.5Hz spike-and-wave discharges often intermingled with sharp waves. Intermittent light stimulation was normal. In 12 (57%) children, interictal abnormalities were activated by hyperventilation. Ictal EEG was obtained in three patients. In all ictal EEGs head nodding episodes came in clusters during hyperventilation. None of the patients achieved good seizure control even if all of them received antiepileptic treatment (carbamazepine alone [43%] or in association with phenobarbitone or phenytoin). ConclusionThis study confirms that NS is an encephalopathy and intellectual disabilities are partially independent of seizure frequency and EEG pathological activity. Based on interictal and ictal EEG patterns and on the experience of other researchers, valproic acid would seem to be the first-choice antiepileptic drug. NS in South Sudan presents with clinical and neurophysiological features which are similar to those described in northern Uganda and more severe than in Tanzania.

Modeling the effective connectivity of the visual network in healthy and photosensitive, epileptic baboons.

The baboon provides a model of photosensitive, generalized epilepsy. This study compares cerebral blood flow responses during intermittent light stimulation (ILS) between photosensitive (PS) and healthy control (CTL) baboons using H 2 (15) O-PET. We examined effective connectivity associated with visual stimulation in both groups using structural equation modeling (SEM). Eight PS and six CTL baboons, matched for age, gender and weight, were classified on the basis of scalp EEG findings performed during the neuroimaging studies. Five H 2 (15) O-PET studies were acquired alternating between resting and activation (ILS at 25Hz) scans. PET images were acquired in 3D mode and co-registered with MRI. SEM demonstrated differences in neural connectivity between PS and CTL groups during ILS that were not previously identified using traditional activation analyses. First-level pathways consisted of similar posterior-to-anterior projections in both groups. While second-level pathways were mainly lateralized to the left hemisphere in the CTL group, they consisted of bilateral anterior-to-posterior projections in the PS baboons. Third- and fourth-level pathways were only evident in PS baboons. This is the first functional neuroimaging study used to model the photoparoxysmal response (PPR) using a primate model of photosensitive, generalized epilepsy. Evidence of increased interhemispheric connectivity and bidirectional feedback loops in the PS baboons represents electrophysiological synchronization associated with the generation of epileptic discharges. PS baboons demonstrated decreased model stability compared to controls, which may be attributed to greater variability in the driving response or PPRs, or to the influence of regions not included in the model.

Subdural electrode recording of generalized photoepileptic responses.

We evaluated the spatiotemporal distribution of photic driving (PDR), photoparoxysmal (PPR), and photoconvulsive (PCR) responses recorded by intracranial electrodes (ic-EEG) in a patient with generalized photosensitivity and right frontal lobe cortical dysplasia. Intermittent light stimulation (ILS) was performed thirteen times in nine days. Cortical responses to ILS recorded by ic-EEG were reviewed and classified as PDRs, PPRs, and PCRs. Photic driving responses were restricted to the occipital lobe at ILS frequencies below 9 Hz, spreading to the parietal and central regions at > 9 Hz. Photoparoxysmal responses commonly presented as focal, medial occipital, and parietal interictal epileptic discharges (IEDs), the latter propagating to the sensorimotor cortices. Generalized IEDs were also generated in the setting of PPRs. Photoconvulsive responses, characterized by repetitive bilateral upper extremity myoclonus sustained until the end of the stimulus, were associated with propagation of the medial parieto-occipital discharge to the primary sensorimotor and supplementary area cortices, while generalized myoclonic seizures were associated with a generalized spike-and-wave discharge with an interhemispheric posterior cingulate onset sparing the sensorimotor cortices. Both types of PCR could occur during the same stimulus. Regardless of the pathway, PCRs only occurred when PDRs involved the parietal cortices. While there may be more than one pathway underlying PCRs, parietal lobe association cortices appear to be critical to their generation.

EEG activation by neuropsychological tasks in idiopathic generalized epilepsy of adolescence.

To evaluate the effects of neuropsychological activation (NPA) tasks on epileptiform discharges in adolescents with idiopathic generalized epilepsy (IGE) and their possible relationship to clinical epilepsy-related factors, also to compare the effects of the NPA to the habitual methods of electroencephalographic (EEG) activation. Fifty-nine patients with IGE aged 14-17 years underwent baseline video-EEG recording with habitual activation procedures followed by NPA tasks, and sleep EEG after sleep deprivation on the next day. At least one task of NPA showed provocative effect in 18.6% of cases. There was no difference between the provocative effects of action-programming and thinking NPA task groups as well as among individual NPA tasks. The provocative effects of NPA tasks were more prevalent in photosensitive cases, especially the tasks of action-programming type (p=0.04). The provocative NPA effects showed no relationship to gender, age, age at seizure onset, duration of epilepsy, treatment status, presence of myoclonias, recent generalized tonic-clonic seizures, family history of epilepsy. The provocative effects of NPA were comparable to those of hyperventilation (23.7%) and intermittent light stimulation (30.5%) (p>0.05). Although the provocative effects NPA tasks on epileptiform discharges on EEG did not outweigh the effects of the habitual activation procedures, NPA activation might be helpful as an additional diagnostic tool in adolescents with IGE in selected cases when routine EEG is not informative enough or when sleep EEG is readily unavailable, also in photosensitive cases. It may also help in providing advice for patients on safety issues.