Excitability Changes in Occipital Cortex After Continuous Theta-Burst Stimulation

OpenAlex İngilizce

The visual cortical system is the endpoint of many afferent visual pathways and has more neuronal connections than the other sensory modalities.In comparison with visual processing, it is known that auditory sensory is associated with 3%, and somatosensory processing is associated with 11% of the brain (1).The role of the visual system in neurological diseases and physiological processes is being investigated with increasing interest in view of this intense connectivity.The visual system evaluation of the neurophysiological activity by transcranial magnetic stimulation (TMS) and visual evoked potentials (VEP) responses are easily applicable research methodologies.Habituation is the observance of a decrease in the responses of VEPs while the number of consecutive and uninterrupted visual stimuli is increased (2).It is known that like all other sensory modalities, the short-term plastic change mechanism in visual habituation is a defense mechanism against repetitive stimulus (3).TMS, with its diagnostic and modulatory capabilities regarding the brain, can be used as a second non-invasive tool (4).The flashes of light and scotomas that occur in the visual field in a few seconds after stimulation of the visual system are known as the phosphenes (5), which are also an excitability parameter of the visual cortex.Depending on stimulation parameters, these can be applied to human brain cortical structures with inhibitory or excitatory effects.Although applying repetitive TMS (rTMS) stimuli on the cerebral cortical structures can induce temporary inhibition or facilitation in the brain (6), permanent neuroplasticity effects can be obtained with multiple sessions.In previous studies, 1 Hz rTMS over the habituation and phosphene thresholds were compared in sham and real cTBS sessions.Results: The phosphene threshold values increased to statistically significant levels after the real cTBS session.Visual evoked potential habituation was observed in both sham and real cTBS sessions in individuals without significant differences.Also, no difference between the P100 latencies and N75-P100 amplitude values in the sham and real cTBS sessions was observed.Conclusion: Phosphene threshold measurements demonstrated the modulation of the occipital cortex excitability via cTBS in healthy subjects.