Multi-site optical recording of the rat piriform cortex activity.

Optical signals were recorded in the in vivo rat piriform cortex (PC) in response to olfactory bulb (OB) electrical stimulations delivered at 4 different sites. Afferent activity had a relatively wide (26.6% of the recorded area) but nonhomogeneous distribution on the PC surface. The different patterns of afferent activity observed in response to the 4 OB stimulations were intermixed with an overlap of only 38.5%. This activity was redistributed to the whole PC by intrinsic association fibres. The increase in the delay (from 4 ms to 12 ms) between afferent and redistributed activities along the antero-posterior axis indicated that the rostral to caudal association fibre system originating in the anterior PC was mainly responsible for the redistribution.