Scented memories of childhood

Objectives

It is often thought that no memories acquired before the age of three survive, but research shows this is not the case: these earliest memories do indeed exist, and are often older than we imagine. From the earliest years of life, autobiographical memory plays a central role in the construction of the self, as an entity situated in time and space. The five main senses (sight, hearing, touch, smell and taste) play a vital role in this function, as they are responsible for capturing sensory information, which is then transformed into lasting memories, thereby shaping each individual’s personality. Research shows that, among these senses, smell stands out: memories evoked by smells are often older and associated with a more positive emotional valence than those triggered by other sensory modalities. Nevertheless, the conditions under which these memories are formed, as well as the underlying brain mechanisms, remain poorly understood. Against this backdrop, the aim of this thesis was to explore the encoding conditions and subjective experience, in adulthood, of childhood olfactory memories in humans, as well as their neural basis in mice.

Project description

Initially, we conducted an online questionnaire survey of 647 participants to identify the parameters necessary for the formation of our earliest olfactory memory. The results indicate that these memories generally emerge from repeated associations between a pleasant smell and an environment that is both emotionally positive and multisensory. In adulthood, recalling these memories is accompanied by a strong positive emotional valence, a sense of nostalgia and the subjective impression of being transported back to the past.

Measurement method

To examine the mechanisms underlying this phenomenon, we developed an experimental model in mice that replicates this early olfactory imprinting. The association of a pleasant odour with an enriched and positive environment during the juvenile period induces a lasting preference for that odour in adulthood. We then studied the neural basis of this memory. We highlighted the role of the olfactory bulb, the first brain structure involved in odour processing, which has the unique ability to generate new neurons after birth. In particular, certain neurons generated early in life appear essential for the persistence of this olfactory memory: inhibiting their activity alters the memory associated with the odour. Furthermore, the smell associated with childhood activates a brain network involving regions linked to reward and memory, contributing to the persistence as well as the strong positive emotional valence of these memories.

Impact

These findings highlight how exposure to and attention paid to early sensory experiences – particularly olfactory ones – help shape our memory and identity through a positive emotional lens from the earliest years of life.