The olfactory piriform cortex (PC) is thought to participate in olfactory associative memory. Like the hippocampus, which is essential for episodic memory, it belongs to an evolutionally conserved paleocortex and comprises a three-layered cortical structure. During slow-wave sleep, the olfactory PC becomes less responsive to external odor stimuli and instead displays sharp wave (SPW) activity similar to that observed in the hippocampus. Neural activity patterns during hippocampal SPW have been intensively studied in terms of memory consolidation; however, little is known about the activity patterns of olfactory cortical neurons during olfactory cortex sharp waves (OC-SPWs). In this study, we recorded multi-unit neural activities in the anterior PC in urethane-anesthetized mice. We found that the activity patterns of olfactory cortical neurons during OC-SPWs were non-randomly organized. Individual olfactory cortical neurons varied in the timings of their peak firing rates during OC-SPW events. Moreover, specific pairs of olfactory cortical neurons were more frequently activated together than expected by chance. On the basis of these observations, we speculate that coordinated activation of specific subsets of olfactory cortical neurons repeats during OC-SPWs, thereby facilitating synaptic plasticity underlying the consolidation of olfactory associative memories.

The basolateral amygdala (BLA), a region critical for emotional processing, is the limbic hub that is connected with various brain regions. BLA neurons are classified into different subtypes that exhibit differential projection patterns and mediate distinct emotional behaviors; however, little is known about their presynaptic input patterns.In this study, we employed projection-specific monosynaptic rabies virus tracing to identify the direct monosynaptic inputs to BLA subtypes. We found that each neuronal subtype receives long-range projection input from specific brain regions. In contrast to their specific axonal projection patterns, all BLA neuronal subtypes exhibited relatively similar input patterns. This anatomical organization supports the idea that the BLA is a central integrator that associates sensory information in different modalities with valence and sends associative information to behaviorally relevant brain regions.

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Running title: activity patterns of olfactory cortical neurons 27 pages, 4 figures 190, 487, 4684 words for abstract, introduction, and whole manuscript, respectively Keywords: olfactory piriform cortex, multi-unit recording, spontaneous neural activity, olfactory cortex sharp wave, memory replay 2 ABSTRACT The olfactory piriform cortex is thought to participate in olfactory associative memory. Like the hippocampus, which is essential for episodic memory, it belongs to an evolutionally conserved paleocortex and comprises a three-layered cortical structure. During slow-wave sleep, the olfactory piriform cortex becomes less responsive to external odor stimuli and instead displays sharp wave (SPW) activity similar to that observed in the hippocampus. Neural activity patterns during hippocampal SPW have been intensively studied in terms of memory consolidation; however, little is known about the activity patterns of olfactory cortical neurons during olfactory cortex sharp waves (OC-SPWs). In this study, we recorded multi-unit neural activities in the anterior piriform cortex in urethane-anesthetized mice. We found that the activity patterns of olfactory cortical neurons during OC-SPWs were non-randomly organized. Individual olfactory cortical neurons varied in the timings of their peak firing rates during OC-SPW events. Moreover, specific pairs of olfactory cortical neurons were more frequently activated together than expected by chance. On the basis of these observations, we speculate that coordinated activation of specific subsets of olfactory cortical neurons repeats during OC-SPWs, thereby facilitating synaptic 3 plasticity underlying the consolidation of olfactory associative memories.

No abstract