Cortical Dynamics of Phosphene Perception: A Study Using EEG Signals

Introduction: Scientific evidence has shown that the electrical stimulation of the primary occipital cortex can evoke luminous visual perceptions known as phosphenes. This finding has provided the basis for the development of cortical visual prostheses for blind individuals. In this context, understanding and unveiling the cortical perceptual dynamics evoked during the process of perceiving phosphenes is crucial in order to improve the interaction between this technology and the user.

Methods: In this study, we investigated the cortical perceptual dynamics of three blind subjects who were implanted with a 10x10 Utah microelectrode array in their visual cortices. Cortical responses during the perception and non-perception of evoked phosphenes were monitored using electroencephalographic (EEG) techniques. Processing methods included the quantification of event-related synchronization/desynchronization (ERS/ERD) and directed transfer function (DTF)-based connectivity analysis.

Results and Discussion: The analysis of EEG signals revealed significant differences in ERS/ERD within the 1-to-45 Hz range (specifically between 4 to 7.5Hz), predominantly in frontal and prefrontal regions, when subjects perceive phosphenes. These differences were observed between 250 and 750 ms following stimulus application. Connectivity analysis based on DTF determination showed that phosphene perception evokes directional connections from temporal regions to central and frontal regions.

Conclusions: In this study, we demonstrated that EEG signals allow the characterization of cortical dynamics during phosphene perception. It was observed that, in terms of evoked oscillation energy, frontal areas exhibit higher synchronization during phosphene perception, while in terms of directional connectivity, cortical directional information shows cross-modulation when the phosphene is perceived.