From Nose to Memory: The Involuntary Nature of Odor-evoked Autobiographical Memories in Alzheimer’s Disease

Abstract

Research suggests that odors may serve as a potent cue for autobiographical retrieval. We tested this hypothesis in Alzheimer's disease (AD) and investigated whether odor-evoked autobiographical memory is an involuntary process that shares similarities with music-evoked autobiographical memory. Participants with mild AD and controls were asked to retrieve 2 personal memories after odor exposure, after music exposure, and in an odor-and music-free condition. AD participants showed better specificity, emotional experience, mental time travel, and retrieval time after odor and music exposure than in the control condition. Similar beneficial effects of odor and music exposure were observed for autobiographical characteristics (i.e., specificity, emotional experience, and mental time travel), except for retrieval time which was more improved after odor than after music exposure. Interestingly, regression analyses suggested executive involvement in memories evoked in the control condition but not in those evoked after music or odor exposure. These findings suggest the involuntary nature of odor-evoked autobiographical memory in AD. They also suggest that olfactory cuing could serve as a useful and ecologically valid tool to stimulate autobiographical memory, at least in the mild stage of the disease.

Emotional and Phenomenological Properties of Odor-Evoked Autobiographical Memories in Alzheimer’s Disease

“…Autobiographical memory is an essential part of the human memory system as it allows the construction and maintenance of self-awareness, personal knowledge and self-image [1], and can be defined as the ability to relive past personal events. Autobiographical memory has been found to be impaired in Alzheimer’s disease (AD) [2,3,4,5,6]. Autobiographical memory compromise in AD is characterized by an overgenerality, i.e., a reduced ability of AD patients to produce specific memories [4,7,8,9,10,11,12,13,14].…”

“…Decline of autobiographical memory in AD is also associated with changes in the strength and the quality of the sense of identity in patients [15]. As a result of autobiographical memory impairment, AD patients demonstrate difficulty in mentally reliving past events with the perceptual, sensory and conceptual details of the original event, replaced by a general feeling of knowing or familiarity [2,16,17,18,19,20].…”

Could Self-Consciousness Be Enhanced in Alzheimer’s Disease? An Approach from Emotional Sensorial Stimulation

“…Moreover, olfactory memory has two kinds of perceptual-cognitive processing, the olfactory explicit memory which lets the identification of the odor and the olfactory implicit memory which lets odor-evoked memories which are involuntary, spontaneous, with high emotional content, and without effortful cognitive process [80,118,[121][122][123][124]. The Autobiographical Memory [80,87] proposes that personal events can be evoked by a direct and indirect way.…”

“…To our knowledge, only five studies have examined the impact of odor on autobiographical remembering in AD [123,[160][161][162][163]. All studies have demonstrated the positive effects of odor on personal event memories.…”

“…All studies have demonstrated the positive effects of odor on personal event memories. In 2017, El Haj et al [123] investigated the involuntary nature of autobiographical memory in AD triggered by music and odor. They showed that AD patients improved specificity, emotional experience, retrieval time, and mental time travel when memories were cued by odor compared to an odor-free condition.…”