Odor specificity of habituation in the rat anterior piriform cortex.

Exposure to odorants results in a rapid (<10 s) reduction in odor-evoked activity in the rat piriform cortex despite relatively maintained afferent input from olfactory bulb mitral cells. To further understand this form of cortical plasticity, a detailed analysis of its odor specificity was performed. Habituation of odor responses in anterior piriform cortex single units was examined in anesthetized, freely breathing rats. The magnitude of single-unit responses of layer II/III neurons to 2-s odor pulses were examined before and after a 50-s habituating stimulus of either the same or different odor. The results demonstrated that odor habituation was odor specific, with no significant cross-habituation between either markedly different single odors or between odors within a series of straight chain alkanes. Furthermore, habituation to binary 1:1 mixtures produced minimal cross-habituation to the components of that mixture. These latter results may suggest synthetic odor processing in the olfactory system, with novel odor mixtures processed as unique stimuli. Potential mechanisms of odor habituation in the piriform cortex must be able to account for the high degree of specificity of this effect.