Mice homozygous for the barrelless (brl) mutation, mapped here to chro
mosome 11, lack barrel-shaped arrays of cell clusters termed ''barrels
'' in the primary somatosensory cortex. Deoxyglucose uptake demonstrat
ed that the topology of the cortical whisker representation is neverth
eless preserved. Anterograde tracers revealed a lack of spatial segreg
ation of thalamic afferents into individual barrel territories, and si
ngle-cell recordings demonstrated a lack of temporal discrimination of
center from surround information. Thus, structural segregation of tha
lamic inputs is not essential to generate topological order in the som
atosensory cortex, but it is required for discrete spatiotemporal rela
y of sensory information to the cortex.