A major part of my work in the team concerns the development of a so called frameless stereotaxy or neuronavigation system, the “Brainsight Primate”. This system makes it possible to perform very precise intracerebral injections of neuronal tracers or place probes, electrodes etc. in buried cortex. Instead of a stereotactic frame, this 3D coordinate system is based on anatomical images obtained in MRI. A position sensor is used in the surgical suite to monitor the location and orientation of tools then, software is used to map these locations to the pre-operative image space. The first step of the processus consists in implanting markers (the position sensors) on the skull of the animal. These markers are identified by the Brainsight system and the software yields a series of coordinates in image space. The software uses these markers to calculate the 3D coordinates of individual voxels. Then we define our target and perform the surgery. We use a pointer recognized by infrared camera, which allows us to define the optimal pathway to the target. After the injection of neuronal tracers, I take part in detection and counting of fluorescent-labelled cells, histological staining and immuno-histochimical reaction. An important part of the processing is segmentation: we determine according to histological staining the areal and laminar distribution of labelled cells.