Passive versus active novelty detection: How volition shapes olfactory representations in the medial temporal lobe

Across animal species, novel stimuli elicit arousal and evoke sensory inspection and exploration. This type of spontaneous curiosity critically relies on the animals’ ability to identify the novelty of a sensory stimulus against previously experienced stimuli. However, since familiarity is characterized by the absence of a behavioural responses, passive novelty detection tasks involve asymmetric motor responses which can confound the analysis of neural signals. To address this limitation, I established a two alternative forced choice novelty detection task which offers the opportunity to investigate novelty detection in a volitional context with symmetric motor responses for novel and familiar stimuli. Mice were trained to report the familiarity of olfactory stimuli by collecting rewards at either of two reward port associated with novel or familiar stimuli. Mice learned the task, as indicated by the correct selection of the novelty-associated reward port on the first occurrence of a novel stimulus. Four mice which performed the operant task with above 70% success rate were recorded in the LEC, CA1, CA2 and SUB with Neuropixel probes. I further performed recordings in 5 mice in a passive task, in which they were exposed to familiar and novel stimuli. I used a classifier to determine when the information was present in the recorded regions and found time-dependent differences between the two tasks. In the passive task, novelty and odor identity could both be discriminated before the onset of the behavioral response. In the operant task, on the other hand, odor identity was delayed until after the decision.