  Current theories hold that brain function is highly related to long-range
physical connections through axonal bundles, namely extrinsic connectiv-ity.
However, obtaining a groupwise cortical parcellation based on extrinsic
connectivity remains challenging. Current parcellation methods are
compu-tationally expensive; need tuning of several parameters or rely on ad-hoc
constraints. Furthermore, none of these methods present a model for the
cortical extrinsic connectivity of the cortex. To tackle these problems, we
propose a parsimonious model for the extrinsic connectivity and an efficient
parceling technique based on clustering of tractograms. Our technique allows
the creation of single subject and groupwise parcellations of the whole cortex.
The parcellations obtained with our technique are in agreement with structural
and functional parcellations in the literature. In particular, the motor and
sensory cortex are subdivided in agreement with the human ho-munculus of
Penfield. We illustrate this by comparing our resulting parcels with the motor
strip mapping included in the Human Connectome Project data.
