In the mouse, in the medial part of the ventrobasal complex of the thalamus (VBm), an array of rod-shaped domains, poor in perikarya and with a diameter of about 70 microm, is embedded in a lattice of high cell packing-density. Each domain forms the core of a 'barreloid'. The arrangement of barreloids is topologically equivalent to that of the large barrels in the cortical somatosensory area (SI).