Online Lecture by Cagatay Aydin

Stimulus novelty differentially modulates activity in the Anterior Olfactory Nucleus and Piriform Cortex

When humans or animals encounter novel sensory stimuli in their environment, they perform distinct orienting and exploratory behaviours. This intrinsic tendency to explore unknown stimuli is also referred to as perceptual curiosity. Behavioural responses to novel stimuli occur very rapidly, in often less than 100ms after stimulus onset. In order to accomplish such rapid reaction, the brain needs to perform a remarkably efficient computation involving a memory-based classification of incoming sensory stimuli into novel and familiar categories. To investigate the algorithm behind this classification, we have previously established a spontaneous olfactory novelty detection paradigm in head-restrained mice. Here, we used this paradigm to study how stimulus novelty affects neural activity in the olfactory cortex, specifically in the anterior olfactory nucleus (AON) and piriform cortex (PCx). We used multielectrode recordings to systematically characterize single-unit responses to novel and familiar odorants. At the population level, the AON but not the PCx appears modulated by novelty. A functional classification of odorant responses revealed three distinct response types among neurons in the AON and PCx. One of these response types in the AON accounts for the modulation by stimulus novelty observed at the population level. To identify the cellular identity of novelty-modulated neurons we performed optogenetically identified recordings of glutamatergic and GABAergic neurons in the AON and PCx. Collectively, our results support the hypothesis that specific AON projections but not PCx projections play a major role in olfactory novelty detection.