The olfactory bulb modulates entorhinal cortex oscillations during spatial working memory

Abstract

Cognitive functions such as working memory require integrated activity among different brain regions. Notably, entorhinal cortex (EC) activity is associated with the successful working memory task. Olfactory bulb (OB) oscillations are known as rhythms that modulate rhythmic activity in widespread brain regions during cognitive tasks. Since the OB is structurally connected to the EC, we hypothesized that OB could modulate EC activity during working memory performance. Herein, we explored OB–EC functional connectivity during spatial working memory performance by simultaneous recording local field potentials when rats performed a Y-maze task. Our results showed that the coherence of delta, theta, and gamma-band oscillations between OB and EC was increased during correct trials compared to wrong trials. Cross-frequency coupling analyses revealed that the modulatory effect of OBs low-frequency phase on EC gamma power and phase was enhanced when animals correctly performed working memory task. The influx of information from OB to EC was also increased at delta and gamma bands within correct trials. These findings indicated that the modulatory influence of OB rhythms on EC oscillations might be necessary for successful working memory performance.

Disrupted connectivity in the olfactory bulb-entorhinal cortex-dorsal hippocampus circuit is associated with recognition memory deficit in Alzheimer’s disease model

“…The EC-dHPC is a critical circuit for object recognition 17 , 32 . Moreover, the OB is closely connected with hippocampal formation, particularly EC, a hub for the hippocampus 28 , 33 , 34 . Initially, we found that coherence and synchrony of the EC-dHPC circuit are decreased in Aβ animals compared to the control group at theta and gamma bands during NOR task performance.…”

“…Firstly , OB rhythmic activity dynamically modulates other brain areas, notably the EC-dHPC, during a cognitive performance 28 . Thus, disrupted coupling due to Aβ in this circuit, probably via its direct effect on OB synapses and regardless of neural loss, may be responsible for impaired recognition memory.…”

“…Therefore, OB could be considered a pivotal regulator of neural activity in the brain during cognitive performances 26 , 27 . On the other hand, the OB is closely connected with the EC-HPC circuit, which has synchronized oscillatory activity during spatial recognition 22 , 28 . Hence, exploring the OB network in recognition memory can provide useful information about dynamic functional connectivity alterations in AD.…”

Olfactory bulb stimulation mitigates Alzheimer’s-like disease progression

“…Signals were preprocessed using the EEGLAB toolbox for noise rejection and baseline correction. 12 Power spectral density (PSD) was computed using the Welch's periodogram function in MATLAB. 30 To plot connection edges within five brain regions, we first calculated the coherence using mscohere function in MATLAB, and then any pairwise regions that passed the designated threshold of coherence were connected.…”

“…8,9 The OB is intricately connected to limbic regions and plays a role in memory control within a network involved memory-related functions. [10][11][12] The EC acts as the gateway for information entering and exiting the hippocampus. 13 It also serves as an interface between the medial prefrontal cortex (mPFC) and HPC for the rapid encoding of new memories.…”