NEURAL CODING IN ANTENNAL OLFACTORY CELLS OF TSETSE-FLIES (GLOSSINA SPP.)

Spike trains from individual antennal olfactory cells of tsetse flies (Glossina spp.) obtained during steady-state conditions (spontaneous a s well as during stimulation with 1-octen-3-ol) and dynamic stimulatio n with repetitive pulses of 1-octen-3-ol were investigated by studying the spike frequency and the temporal structure of the trains. In gene ral, stimulation changes the intensity of the spike activity but leave s the underlying stochastic structure unaffected. This structure turns out to be a renewal process. The only independently varying parameter in this process is the mean interspike interval length, suggesting th at olfactory cells of tsetse flies may transmit information via a freq uency coding. In spike records with high firing rates, however, the st ationary records had significant negative first-order serial correlati on coefficients and were non-renewal. Some cells in this study were ca pable of precisely encoding the onset of the odour pulses at frequenci es up to at least 3 Hz. Cells with a rapid return to pre-stimulus acti vity at the end of stimulation responded more adequately to pulsed sti muli than cells with a long increased spike frequency. While short-fir ing cells process information via a frequency code, long-firing cells responded with two distinctive phases: a phasic, non-renewal response and a tonic, renewal response which may function as a memory of previo us stimulations.