Full Idea
The pattern of brain activation during, say, a word retrieval task is usually similar enough among the dozen or so participants who typically take part in such studies for their scans to be overlaid and still show a clear pattern.
Gist of Idea
Scans of brains doing similar tasks produce very similar patterns of activation
Source
Rita Carter (Mapping the Mind [1998], p. 17)
Book Reference
Carter,Rita: 'Mapping the Mind' [Phoenix 2000], p.17
A Reaction
This doesn't surprise me, though it could be interpreted as supporting type-type identity, or as supporting functionalism. Armstrong and Lewis endorse a sort of reductive functionalism which would fit this observation.