Metadata language
Kublik, Ewa (1968– ) : Supervisor ; Waleszczyk, Wioletta (1962-2020) : Supervisor
Publisher:Nencki Institute of Experimental Biology PAS
Place of publishing: Date issued/created: Description:207+21 pages : illustrations ; 30 cm ; Supplement: 21 pages Corrigenda to the doctoral dissertation ; Bibliography ; Summary in Polish
Degree name: Degree discipline : Degree grantor:Nencki Institute of Experimental Biology PAS ; degree obtained 27.06.2025
Type of object: Subject and Keywords:EEG ; Neuromodulation ; Periorbital pulsed current stimulation ; Phosphene perception ; Visual evoked potential ; Visual information processing
Abstract:
Noninvasive current stimulation is increasingly used to support the brain function and recovery from trauma or disease. The dissertation focused on the stimulation paradigm aimed to concentrate the effect within initial stages of the visual system. Periorbital pulsed current stimulation (pPCS) in the form of single biphasic pulses of sinusoidal waveform applied with electrodes below and above the eyes were tested with simulation approach and during in vivo experiments with healthy volunteers. The specific aims of the dissertation were to evaluate the concentration of induced electric field (IEF) in the brain, to characterize the behavioral and electrophysiological (EEG) responses to visual and electric stimulation, and to analyze the potential of pPCS in modulating information processing in the visual system in a paired pulse stimulation (PPS) paradigm, in which a current pulse is applied prior to a visual stimulus, allowing its effects on excitability and neural processing to be assessed. Computer simulations have shown that pPCS with electrodes located above and below the eyes concentrates the IEF mainly within the eyeballs, minimizing the impact on the optic nerves and other areas of the brain. In comparison, a configuration with electrodes over the eyes and one electrode placed on the occipital area generates a more diffuse IEF, covering also the optic nerve and the occipital cortex. IEF analyses indicated that the electric field concentration at the electrode’s edges depended on current density and curvature of the electrode edge. The simulations also showed that the default tissue conductivity values used in SimNIBS – popular software used to model IEF, are inaccurate. The Swiss ITIS Foundation database was proposed as more accurate. In the in vivo experimental study a periorbital electrodes’ arrangement was tested. The current pulses were shown to effectively induce phosphenes of retinal origin, with a detection threshold (of about 5%) at about 10 ms at an amplitude of 300 µA and cortical electrically evoked potentials (EEP). The increase of the pulse amplitude and duration resulted in nonlinear increase of phosphene detection and EEP amplitude, which were described using a customized three-factor Naka-Rushton model, taking into account the total pulse charge, amplitude and duration. The model revealed that the effect of total charge on the response decreases with increasing pulse intensity and length, leading to a saturation effect. The importance of parameters such as total charge, amplitude and pulse duration in the induction of phosphenes and the characteristics of the responses given was also highlighted. The second experimental study used the pPCS protocol, in which pulses of different lengths and amplitudes were applied before a checkerboard pattern reversal (CPR) visual stimulus. It was found that in the experimental group, current stimulation reduced the amplitude of early visual evoked potential (VEP) components, such as P1N1 and P1N2, compared to the placebo group, indicating its potential inhibitory effect on visual cortex excitability. This effect was cumulative over time, such that no differences in the strength of the effect were observed depending on the parameters of the stimulus, and its effect also extended to trials in which CPR was not preceded by the application of a current pulse. In addition, the effect of the stimulation increased with time, and clearly disappeared after its termination. In conclusion, the simulation and experimental studies conducted indicate that it is possible to precisely induce an electric field in the eyeballs using single biphasic sinusoidal current pulses applied in a periorbital configuration. This makes it possible to study phosphenes at both the behavioral and electrophysiological levels, and to apply this method to modulate information processing in the visual system of healthy humans. (…)
Copyright-protected material. May be used within the limits of statutory user freedoms
Copyright holder:Publication made available with the written permission of the author
Digitizing institution:Nencki Institute of Experimental Biology of the Polish Academy of Sciences
Original in:Library of the Nencki Institute of Experimental Biology PAS
Access: