Brain structure is changed in congenital anosmia

We found subjects with congenital anosmia to exhibit larger gray matter volumes in the left entorhinal and piriform cortices. Further, they had thicker orbitofrontal cortices bilaterally. Their left piriform cortex was also thicker than that of controls. These findings are in contrast to those observed in acquired anosmia, where reduced olfactory function is associated with reduced volumes and thickness. However, they fit well with observations from other sensory systems, e.g., vision, where congenital sensory loss is associated with a thicker primary cortex. This finding has been attributed to reduced or absent synaptic pruning as a result of missing peripheral sensory input. Our findings suggest that similar mechanisms take place in the olfactory system.