Optical recording of odor-evoked responses in the olfactory brain of the naive and aversively trained terrestrial snails

Regular spontaneous oscillations were recorded both electro- and optophysio logically using a voltage-sensitive absorption dye in the olfactory part of the brain (procerebral robe of the cerebral ganglia) of the gastropod moll usk Helix lucorum. Odor application caused transient changes in procerebral oscillations, and an odor-evoked potential was recorded in the procerebrum (PC). The wave of evoked potential originated near the place of olfactory nerve entrance into the PC and propagated via the procerebral neuropile tow ard the cell body layer. The spread of the odor-evoked potential correspond ed roughly to the neuropile area, whereas the spontaneous oscillations were recorded in the cell body layer of the PC and were not observed in the neu ropile. Evoked potential did not produce additional events intercalated int o the ongoing spontaneous oscillations. Changes in parameters of spontaneou s oscillations to the repeated presentations of the same odor were variable . To estimate the role of spontaneous oscillations in odor encoding, we tra ined the snail to avoid cineole, using paired presentations of cineole and electric shock. Elaboration of conditioned aversion to cineole applications resulted in distinct pairing-specific changes in behavior of the snails an d procerebral activity. Responses to odor (cineole) applications were not d ifferent in amplitude or frequency of spontaneous oscillations in control a nd trained snails, whereas ratio of amplitudes of the same oscillation wave in proximal and distal regions of the procerebrum was significantly differ ent in control and aversively trained snails, reflecting changes in neural firing in certain areas of the olfactory lobe.