Origin and plastic properties of late components evoked in the rat's but not in the armadillo's prepyriform cortex

Following ipsilateral olfactory bulb (IOB) stimulation long-latency (62-89 ms) gross and unit responses were evoked in the prepyriform cortex of rats prepared under urethane or pentobarbital, but were absent in 23 armadillos explored under the same anesthetics. Depth profile and current source density analysis revealed that generators of early and late components (LC) lie within cortical layers Ia-Ib, suggesting that LC may represent a compound depolarizing excitatory postsynaptic potential, generated by recurrent excitation of pyramidal cells. LC satisfied, in addition, several parametric requirements for habituation, favoring the hypothesis that late response waning following a period of predictable, repetitive and invariant stimulation, might be related to behavioral habituation to odors.