The olfactory bulb coordinates the ventral hippocampus–medial prefrontal cortex circuit during spatial working memory performance

Abstract

Neural oscillations synchronize the activity of brain regions during cognitive functions, such as spatial working memory. Olfactory bulb (OB) oscillations are ubiquitous rhythms that can modulate neocortical and limbic regions. However, the functional connectivity between the OB and areas contributing to spatial working memory, such as the ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC), is less understood. Hence, we investigated functional interaction between OB and the vHPC–mPFC circuit during the spatial working memory performance in rats. To this end, we analyzed the simultaneously recorded local field potentials from OB, vHPC, and mPFC when rats explored the Y-maze and compared the brain activities of correct trials vs. wrong trials. We found that coupling between the vHPC and mPFC was augmented during correct trials. The enhanced coherence of OB activity with the vHPC–mPFC circuit at delta (< 4 Hz) and gamma (50–80 Hz) ranges were observed during correct trials. The cross-frequency analysis revealed that the OB delta phase increased the mPFC gamma power within corrected trials, indicating a modulatory role of OB oscillations on mPFC activity during correct trials. Moreover, the correlation between OB oscillations and the vHPC–mPFC circuit was increased at the delta range during correct trials, exhibiting enhanced synchronized activity of these regions during the cognitive task. We demonstrated a functional engagement of OB connectivity with the vHPC–mPFC circuit during spatial working memory task performance.

Olfactory bulb stimulation mitigates Alzheimer’s-like disease progression

“…A prior study involving healthy animals demonstrated that coherency between the OB and the PFC-HPC circuit increased during correct task performance. 11 This indicates that OB electrical stimulation brought the working memory circuit’s activity closer to that of healthy animals. This impact of olfactory pathway stimulation was also evident in comatose patients.…”

“…The OB plays a significant role in working memory performance. 11,12 A significant mechanism through which the OB potentially impacts working memory is nasal breathing. 38,39 The OB acts as a gateway, allowing nasal respiration to dynamically modulate brain activity.…”

“…We have previously reported that functional connectivity in the network between OB, mPFC and HPC is necessary for making the correct decision during working memory performance. 11,12 Therefore, after addressing the effect of OB stimulation on the activity of the network regions, here we intended to find the strength of coherency between OB, mPFC, vHPC, dHPC and EC due to applying OB stimulation in Aβ animals. As shown in figure 6, the network between the five mentioned brain regions was more strongly connected in the OB stimulated Aβ animals especially in higher frequency bands during working memory task.…”

“…15 OB plays a coordinating role in the cross-talk in this circuit particularly during working memory tasks. 11 Disruptions in the OB-EC-HPC-mPFC network, such as plaque accumulation and changes in cell viability during MCI, can impair memory performance. [16][17][18] Considering early AD biomarker presence in the OB and its vital role in this network, targeting the OB holds promise for preventive interventions.…”

The olfactory striae: A historical perspective on the inconsistent anatomy of the bulbar projections

“…A recent study shows stronger activation in the dorsal taenia tecta than in the ventral taenia tecta in response to an odorant, which could be explained by an indirect projection from the entorhinal cortex (Cousens, 2020). Research is underway to learn more about the role of the taenia tecta (Salimi et al, 2022; Shiotani et al, 2020).…”