There is rather a lot of inter-subject variability not only in
gross brain anatomy, but in functional mapping (electrical). On the
face of it, you propose to measure what cannot be measured.
Variability in tertiary, and even secondary, gyration is evident
to the naked eye. Most individuals in neuroscience, however, have
little hands-on experience with autopsies and gross brain dissection.
On the functional side, topographic mapping oflanguage cortex
in an individual subject is much wider than that indicated in classical
maps. Language is discretely localized within this zone, but with
different sites VARIABLY committed to naming, stop consonants, etc. See
Ojemann & Whitaker, Brain & language 6:239-260, and Whitaker & Ojemann
Nature 270:50-51. Additionally, there are GRADED effects within an
area as small as 5 mm.
Similar results were obtained with the ill-fated visual prosthesis
project in the early 70s. Electrically stimulated phosphene maps were
stable within subjects,but varied greatly between subjects -- and this
in one of the cortical areas considered the most "hard wired." (see
dobelle & Mladejovsky Journal of physiology 243:553-576.
A longer discussion of the above is found in Cytowic RE. 1989
Synesthesia: A Union of the senses, pp 188-189, and 155-1660. Springer
Whoever told you that movement and somesthesis are restricted
to the pre-and post-central gyrii is misinformed. In
marsupials (eg wallably and oppossum) there is CONSIDERABLE overlap of
motor and sensory areas; overlap is also seen in cats and other
mammals; multimodal neuron pools are found in humans too.
Richard E. Cytowic