Abstract
Although neurons operate more slowly than transistors, the brain can process information with impressive speeds. Our psychophysical studies in rats showed a single sniff of 150 ms can provide precise information about an odor (Uchida and Mainen, 2003). These findings suggested that the sniff cycle may be a fundamental unit of odor information coding and processing, and raised the question of how olfactory information is encoded on such a time scale. In an attempt to identify underlying mechanisms of rapid odor coding, we performed multi-electrode recordings in the olfactory cortex while rats performed an odor discrimination task. The rats were trained to perform a two-alternative olfactory discrimination task using 2-3 odor pairs. Sniffing was simultaneously recorded using a temperature sensor implanted in the nostril. Olfactory cortical responses were robust and widely distributed. For neurons tested with >= 6 odors, over half showed a significant response to at least one odor. For responsive neurons, spikes were tightly locked to the sniff cycle. Typical responses constituted of a fast transient (–50 ms duration) with a fixed latency (<100 ms) from the inhalation onset. To quantify the time course of the development of piriform odor representations, the ability of single neurons to discriminate between odor pairs was quantified. These analyses showed discriminability developed rapidly, usually peaking or saturating within 100 ms of the onset of the first odor inhalation. [J Physiol Sci. 2007;57 Suppl:S40]
