Abstract
What neural codes does the brain use to represent and process sensory information? Stimulus-evoked oscillatory synchronization of neuronal activity has been observed in many systems, yet the possible functions of such rhythmic synchronization in neural coding remain largely speculative. In the locust, odors appear to be represented by dynamic ensembles of transiently synchronized neurons. The experiments described here explored the design and function of the locust olfactory system, focusing on projection neurons in the antennal lobe. The first goal was to characterize, by means of intracellular and multiple extracellular recordings, the oscillatory synchronization and slow temporal patterns in PN odor responses in vivo. After the system had been characterized, specific coding hypotheses were tested. The results demonstrated that the cycle-by-cycle firing patterns across ensembles of PNs encode odor identity information, but that other response features (such as phase or frequency) do not. Finally the mechanisms for the generation of these dynamics were addressed. Odors do not evoke oscillatory synchronization in the population activity of olfactory receptor afferents, and non-specific, temporally unpatterned electrical stimulation of receptor axons can evoke both oscillatory synchronization and slow temporal patterns in PNs, similar to those evoked by natural stimulation with odors. Oscillatory synchronization of olfactory neurons therefore originates in the antennal lobe, and slow temporal patterns in projection neurons can arise in the absence of temporal patterning of the afferent input.
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