Full Idea
If the operation of a brain implant inside the brain is a cognitive operation, why should it not count as a cognitive operation when it is outside the brain? There are many mechanisms which would count as cognitive if they were inside the subject.
Gist of Idea
A mechanism can count as 'cognitive' whether it is in the brain or outside it
Source
report of A Clark / D Chalmers (The Extended Mind [1998]) by Mark Rowlands - Externalism Ch.9
Book Reference
Rowlands,Mark: 'Externalism' [Acumen 2003], p.160
A Reaction
This argues for externalism of the vehicle of thought, rather than its content. The idea is that there is no significant difference between remembering a phone number and writing it on a bit of paper. I find it hard to disagree.