Anatomical basis for the "one barrel – one vibrissa" hypothesis.

Each peripheral axon in the trigeminal nerve (N.V.) innervates one whisker follicle. Centrally the axons are aggregated in whisker-related bundles that terminate in several nuclei in the brainstem. Illustrated top to bottom these are: principal sensory nucleus and spinal trigeminal complex subnuclei oralis, interpolaris and caudalis. Barrelettes are present in all but subnucleus oralis. Whisker-related aggregations of afferent fibers and cell bodies are also observed in the contralateral thalamus and cerebral cortex.. Inset: cauterization of the middle row of whiskers on the day of birth - postnatal day 0 (PND 0) – leads to an abnormal cortical barrel field.

Adapted (by DJ Simons and T Prigg) from TA Woolsey, "Barrels, vibrissae and topographic representations," pp.111-113 in Encyclopedia of Neuroscience, G. Adelman ed., Birkhauser, Boston (1987).