Seizure triggered by flicker electroretinogram in a patient with no history of epilepsy

Purpose It is well known that repetitive flash stimulation may trigger seizures in susceptible individuals. Nevertheless, reports of such incidents occurring during recording of a flash electroretinogram (ERG) are extremely rare. Here, we describe the case of a photic-induced seizure triggered during an ERG recording in the absence of a history of epilepsy or other paroxysmal events. Methods A 14-year-old male patient presented with reduced visual acuity and impaired mesopic vision. Ophthalmological exams confirmed the patient’s complaints but were inconclusive as to the underlying pathophysiology. An ERG recording was performed, during which the 30-Hz flicker stimulus triggered a seizure. Results The ERG was essentially normal, with the exception of a 7-Hz rhythm superimposed onto the flicker ERG response that was recorded when the seizure developed. Conclusions The present case highlights the possibility that the 30-Hz ERG flash stimulus triggers a seizure in patients with no previous paroxysmal events. Literature evidence suggests that the likelihood of such an incident could be reduced by stimulating monocularly.

Simultaneous Decoding of Eccentricity and Direction Information for a Single-Flicker SSVEP BCI

The feasibility of a steady-state visual evoked potential (SSVEP) brain–computer interface (BCI) with a single-flicker stimulus for multiple-target decoding has been demonstrated in a number of recent studies. The single-flicker BCIs have mainly employed the direction information for encoding the targets, i.e., different targets are placed at different spatial directions relative to the flicker stimulus. The present study explored whether visual eccentricity information can also be used to encode targets for the purpose of increasing the number of targets in the single-flicker BCIs. A total number of 16 targets were encoded, placed at eight spatial directions, and two eccentricities (2.5° and 5°) relative to a 12 Hz flicker stimulus. Whereas distinct SSVEP topographies were elicited when participants gazed at targets of different directions, targets of different eccentricities were mainly represented by different signal-to-noise ratios (SNRs). Using a canonical correlation analysis-based classification algorithm, simultaneous decoding of both direction and eccentricity information was achieved, with an offline 16-class accuracy of 66.8 ± 16.4% averaged over 12 participants and a best individual accuracy of 90.0%. Our results demonstrate a single-flicker BCI with a substantially increased target number towards practical applications.

Conscious perception of flickering stimuli in binocular rivalry and continuous flash suppression is not affected by tACS-induced SSR modulation

The content of conscious perception is known to correlate with steady-state responses (SSRs), yet their causal relationship remains unclear. Can we manipulate conscious perception by directly interfering with SSRs through transcranial alternating current stimulation (tACS)? Here, we directly addressed this question in three experiments involving binocular rivalry and continuous flash suppression (CFS). Specifically, while participants (N=24) viewed either binocular rivalry or tried to detect stimuli masked by CFS, we applied sham or real tACS across parieto-occipital cortex at either the same or a different frequency and phase as an SSR eliciting flicker stimulus. We found that tACS did not differentially affect conscious perception in the forms of predominance, CFS detection accuracy, reaction time, or metacognitive sensitivity, confirmed by Bayesian statistics. We conclude that tACS application at frequencies of stimulus-induced SSRs does not have perceptual effects and that SSRs may be epiphenomenal to conscious perception.

Fast cyclic stimulus flashing modulates perception of bi-stable figure

Many experiments have demonstrated that the rhythms in the brain influence an initial information processing. We investigated whether the alternation rate of the perception of a Necker cube depended on the degree of synchronization between two streams of spikes, one stemming from an external flashing image and the other from the action of an internal impulse stream. Knowing how a flickering stimulus with a given frequency and duration affects the alternation rate of bi-stable perception we could estimate properties of the internal signal. As the internal spike frequency is difficult to control, we varied the frequency of the flicker stimulus. Our results show that the duration of the dominant stimulus perception depends on the frequency or duration of the flashing stimuli. The values of the stimuli, at which the changes of the duration of the perceived image was maximal, we have called ‘extremal’. While changing the flash duration, the extremal parameters repeated periodically at 4ms intervals. Increasing the duration of the extremal stimuli by less than 4 ms shortens the duration of the dominant stimulus perception. Hence we may conclude that it is not the stimulus duration but the accurate coincidence (timing) of the moments of switching on of external stimuli to match the internal stimuli which explains our experimental results.

Fast cyclic stimulus flashing modulates perception of bi-stable figure

Many experiments have demonstrated that the rhythms in the brain influence an initial information processing. We investigated whether the alternation rate of the perception of a Necker cube depended on the degree of synchronization between two streams of spikes, one stemming from an external flashing image and the other from the action of an internal impulse stream. Knowing how a flickering stimulus with a given frequency and duration affects the alternation rate of bi-stable perception we could estimate properties of the internal signal. As the internal spike frequency is difficult to control, we varied the frequency of the flicker stimulus. Our results show that the duration of the dominant stimulus perception depends on the frequency or duration of the flashing stimuli. The values of the stimuli, at which the changes of the duration of the perceived image was maximal, we have called ‘extremal’. While changing the flash duration, the extremal parameters repeated periodically at 4ms intervals. Increasing the duration of the extremal stimuli by less than 4 ms shortens the duration of the dominant stimulus perception. Hence we may conclude that it is not the stimulus duration but the accurate coincidence (timing) of the moments of switching on of external stimuli to match the internal stimuli which explains our experimental results.

Abstract 3802: Retinal Vasoreactivity as a Marker of Impaired Cerebral Function in Diabetes

The eye and the brain share embryological, anatomic and physiological similarities, which suggest that the retinal microvasculature may be an ideal surrogate marker of cerebrovascular function. This is intriguing, as the cerebral vasculature cannot be directly measured in a non-invasive manner. In epidemiological studies abnormal retinal Arteriovenous Ratios (AVR) are associated with an increased risk of stroke and cerebrovascular disease. However, the association between retinal vasoreactivity measurements and cerebral blood vessel function remains unknown. An attenuated retinal vasoreactivity may indicate endothelial dysfunction in the eye and brain and may prove to be useful as a marker of cerebrovascular disease in high risk populations such as in diabetics. STUDY GOALS: To examine 1) the impact of diabetes at different disease stages on measures of cerebrovascular function and 2) the relationship between retinal blood vessel reactivity, retinal AVRs and measures of cerebral small vessel function. METHODS: This cohort study included 29 type 2 diabetics, 14 pre-diabetics, and 14 healthy controls (ages: 37 to 75 years). Retinal vasoreactivity was measured with the Dynamic Vessel Analyzer (Imedos, Jena, Germany) following high frequency flicker light stimulation. Cerebrovascular blood flow velocity of the Middle Cerebral Artery (MCA) was assessed by Transcranial Doppler Ultrasound (TCD) (Siemens, USA). RESULTS: Progression of diabetes was found to be significantly associated with attenuation of light flicker stimulus response (P=0.0009 artery, P=0.0001 vein, CI 95%), AVR (P=0.0070, CI 95%), PI (P=0.0202, CI 95%), RI (P=0.0033, CI 95%) and hyperventilation-breath hold (P≤0.0001, CI 95%). Across all groups, attenuated retinal arterial and venous diameter responses to the light flicker stimulus were associated with an increase in MCA RI (P=0.02, r=-0.30 artery, P=0.06, r=-0.24 vein, CI 95%). An attenuated venous diameter response was associated with an increase in PI (P=0.02, r=-0.29 vein, CI 95%). In addition, attenuated retinal diameter responses were also associated with a decrease in MCA mean flow velocities following hyperventilation-breath hold (P=0.05, r=0.26 artery, P=0.01, r=0.34 vein, CI 95%). Attenuated retinal responses were also correlated with a reduction in AVR (P=0.05, r=0.26 artery, P=0.15, r=0.19 vein, CI 95%). CONCLUSION: Impairment of retinal vasoreactivity is associated with cerebrovascular dysfunction across the continuum of diabetes, possibly indicating that the eye reflects changes in cerebral blood vessel function and stroke risk.

Apparatus and Method for Establishment of Differential Avoidance Conditioning in the Cat

A technique and apparatus are described for the establishment of differential hurdle jump avoidance behavior in cats. Shock was used to condition a right vs left differentiation conditional upon the positions of conditioned stimuli. These conditioned stimuli were then used as secondary reinforcers to condition a right vs left differentiation conditional upon the frequency of non-positional flicker, conditioned stimuli. Random presentation of either flicker stimulus initiated a conditioned response with right cued by one frequency and left cued by the other frequency.