Left Posterior Orbitofrontal Cortex Is Associated With Odor-Induced Autobiographical Memory: An fMRI Study

Abstract

Autobiographical odor memory (AM-odor) accompanied by a sense of realism of a specific memory elicits strong emotions. AM-odor differs from memory triggered by other sensory modalities, possibly because olfaction involves a unique sensory process. Here, we examined the orbitofrontal cortex (OFC), using functional magnetic resonance imaging (fMRI) to determine which OFC subregions are related to AM-odor. Both AM-odor and a control odor successively increased subjective ratings of comfortableness and pleasantness. Importantly, AM-odor also increased arousal levels and the vividness of memories, and was associated with a deep and slow breathing pattern. fMRI analysis indicated robust activation in the left posterior OFC (L-POFC). Connectivity between the POFC and whole brain regions was estimated using psychophysiological interaction analysis (PPI). We detected several trends in connectivity between L-POFC and bilateral precuneus, bilateral rostral dorsal anterior cingulate cortex (rdACC), and left parahippocampus, which will be useful for targeting our hypotheses for future investigations. The slow breathing observed in AM-odor was correlated with rdACC activation. Odor associated with emotionally significant autobiographical memories was accompanied by slow and deep breathing, possibly involving rdACC processing.

Hippocampus and Parahippocampus Volume Reduction Associated With Impaired Olfactory Abilities in Subjects Without Evidence of Cognitive Decline

“…The para-HI is involved in processing memory of "where" events and is associated with the spatial contextual information of episodic memory (Eichenbaum et al, 2007). The para-HI is activated in parallel with the activity of the posterior OFC observed in odor-induced autobiographical memory (Watanabe et al, 2018), suggesting that the para-HI may function in relaying past memories and identification or recognition of memories. Anatomically, the para-HI is part of the medial temporal region, and the anterior part of the para-HI is closest to the ENT, which is the gateway to the dentate gyrus of the HI (Eichenbaum et al, 2007).…”

“…ROIs specifically associated with olfaction including the AMG, HI, para-HI, OFC, MFC, and rectus were analyzed. The AMG, HI, and para-HI were selected as ROIs based on the results of a previous study (Watanabe et al, 2018) where they were found to play key roles in olfactory memory and odorinduced emotional responses. In addition to these areas, the para-HI, MFC and rectus were examined, based on studies suggesting that these areas are involved in conscious awareness of olfactory stimuli (Delon-Martin et al, 2013;Watanabe et al, 2018).…”

“…Comparisons between these two groups might be helpful to clarify specific features of olfactory alteration in the brain. The HI, AMG, para-HI, OFC, rectus, and medial prefrontal cortex (MFC) were examined as regions of interest (ROI) based on a previous report (Watanabe et al, 2018). HI volume reduction has been reported in numerous conditions (Geuze et al, 2005), and volume reduction in the HI and AMG has been associated with olfactory recognition ability (Masaoka et al, 2020).…”

Heart Rate and Respiration Affect the Functional Connectivity of Default Mode Network in Resting-State Functional Magnetic Resonance Imaging

“…The pressure signals of both blood volume pulse waveform and inspiratory-expiratory flow were converted from an analog to a digital signal and stored in a control box using LabChart through PowerLab (ML846; ADInstruments, Aichi, Japan; Figures 1A,C). Further details about this method for monitoring RR and PR have been described previously (Masaoka et al, 2014a;Watanabe et al, 2018).…”

Odors Associated With Autobiographical Memory Induce Visual Imagination of Emotional Scenes as Well as Orbitofrontal-Fusiform Activation

“…Compared with other sensory input such as auditory and visual cues, memory retrieval induced by a specific odor can induce powerful visual imagery ( Herz, 2004 ). Brain imaging studies have indicated that AM-odors activate the hippocampus (HI) and amygdala (AMG) ( Herz, 2004 ; Masaoka et al, 2012a ), and in younger individuals, the posterior orbitofrontal cortex (POFC) as well ( Watanabe et al, 2018 ). Because olfactory information is directly transmitted to the piriform cortex, AMG, and entorhinal cortex (ENT), that is, centers of emotion and memory processing, olfactory input to these areas is directly associated with individual emotional past experiences ( Herz and Cupchik, 1992 ; Masaoka et al, 2012a ).…”