You are mistaken. They use ECoG which is intracranial electroencephalography. These are electrodes placed on exposed surface of the brain. https://en.wikipedia.

You are mistaken. They use ECoG which is intracranial electroencephalography. These are electrodes placed on exposed surface of the brain. https://en.wikipedia.org/wiki/Electrocorticography https://en.wikipedia.org/wiki/Electrocorticography