Postmortem investigation of a human cortical visual prosthesis that was implanted for 36 years

Area of Science:

• Neuroscience
• Biomedical Engineering
• Ophthalmology

Background:

• Cortical visual prostheses aim to restore sight in blind individuals.
• Long-term studies are crucial for understanding device performance and biological interactions.

Purpose of the Study:

• To analyze the postmortem brain of a patient with a 36-year-implanted cortical visual prosthesis.
• To identify design requirements for successful human cortical visual prostheses.

Main Methods:

• Postmortem histological analysis of the brain.
• Examination of the implanted electrode array and surrounding cortical tissue.
• Correlation of electrode location with elicited phosphenes.

Main Results:

• The electrode array rotated 25–40 degrees from the midsagittal plane, likely due to cable torque.
• Platinum electrodes showed degradation over 36 years.
• The array covered only the anterior 45% of the primary visual cortex (V1), missing foveal representation.
• More electrodes outside V1 elicited phosphenes than those inside V1.
• No significant neuronal loss was observed in the surrounding cortex.

Conclusions:

• Long-term efficacy of cortical visual prostheses necessitates detailed consideration of material-tissue interactions.
• Optimizing electrode array design to match cortical anatomy is critical.
• Advanced imaging techniques like MRI and PET can aid in pre-implant planning for future devices.