Mapping of the human visual cortex using image-guided transcranial magnetic stimulation

Area of Science:

• Neuroscience
• Visual Perception
• Neuroimaging

Background:

• The human visual system's organization and plasticity are not fully understood.
• Non-invasive methods are needed to assess visual cortex function, especially in visually impaired individuals.

Purpose of the Study:

• To develop and validate a protocol for systematically mapping visual sensations evoked by transcranial magnetic stimulation (TMS) of the occipital cortex.
• To assess the potential of TMS for understanding visual cortex organization and for evaluating functional vision in blind subjects.

Main Methods:

• A figure-of-eight coil delivered focal, non-invasive TMS to 28 grid positions over the occipital cortex.
• A digitizing tablet, custom software, and audio-video recording facilitated precise data collection and phosphene analysis.
• A frameless neuronavigational device precisely located stimulation sites relative to the cortical surface.

Main Results:

• Transcranial magnetic stimulation (TMS) reliably elicited phosphenes in most sighted subjects and some blind individuals.
• Evoked phosphenes exhibited a clear topographic organization across the occipital cortex.
• Mapping results were reproducible and demonstrated good inter-subject congruence, despite minor variations.

Conclusions:

• The developed TMS protocol provides a reproducible and accurate method for mapping the human visual cortex.
• This technique enhances understanding of visual system physiology and plasticity.
• It is crucial for assessing residual visual cortex function in blind individuals, aiding cortical visual prosthesis selection.