High visual demand following theta burst stimulation modulates the effect on visual cortex excitability

Area of Science:

• Neuroscience
• Visual Neuroscience
• Cognitive Neuroscience

Background:

• Modulatory effects of repetitive transcranial magnetic stimulation (TMS) are influenced by the activity of the stimulated cortical area.
• Understanding these effects is crucial for optimizing neuromodulation techniques.

Purpose of the Study:

• To investigate the impact of continuous and intermittent theta burst stimulation (TBS) on visual cortex excitability.
• To examine the role of post-stimulation visual demand on TBS-induced changes in excitability.

Main Methods:

• A between-group design was employed, applying continuous or intermittent TBS at 100% of individual phosphene threshold (PT) intensity.
• Visual demand was manipulated post-stimulation, with participants performing either a high-demand acuity task or a low-demand task (looking at a wall).
• Phosphene thresholds (PTs) were measured to assess visual cortex excitability.

Main Results:

• No immediate changes in PTs were observed directly after TBS application.
• Continuous TBS led to increased PTs exclusively when participants engaged in high visual demand tasks post-stimulation.
• Low visual demand following continuous TBS, and any visual demand following intermittent TBS, did not alter PTs.
• Intermittent TBS showed no significant effect on visual cortex excitability.

Conclusions:

• The intensity of TBS is critical when applied to the visual cortex, as evidenced by the differing results compared to studies using subthreshold intensities.
• Neuronal activity both before and after TBS significantly influences its modulatory effects, underscoring the need for strict control of cortical activity throughout experimental sessions.