Automatic labelling and identification of cerebral structure, such as cortical sulci, are useful in neurology, surgery planning, etc... In this paper, a method to detect the valley of the cortical sulci is presented. The aim of the method is to achieve the sulci medial surface. The method applied on MRI data, is based on geometrical features (curvature) which doesn't require the accurate segmentation of the cerebral cortex. We use a sub-voxel precision tracking. The minimum curvature vector in each point allows successive displacement along the valley of sulci. Partial derivatives provide the differential characteristics.