Researchers from the University of Ottawa investigating the shared and unique neural processes that underlie different types of long-term memory have found these all use the same network of the brain rather than relying on different areas of the brain altogether.
The international study – published in eLife – calls into question a previous theory that characterises general semantic and episodic memory as two distinct systems instead suggesting different long-term memory types could be viewed as a spectrum, where they rely on activating the same areas of the brain at differing magnitudes.
“Personal semantics, despite its importance, remains an understudied area of long-term memory,” says lead author Annick Tanguay, who conducted the study both at uOttawa’s Faculty of Social Sciences’ School of Psychology and the University of East Anglia in Norwich (UK). “Even though remembering past events and our general knowledge about the world may feel quite different, they do rely on many common brain regions and thought processes, but to a different extent.”
Long-term memory can be classified into different categories of semantic and episodic memory. Semantic memory refers to an individual’s non-personal, general knowledge of the world, while episodic memory concerns the recollection of contextually specific events from their personal past.
“All these memory types seem to involve the same ingredients but to a variable extent.”
Annick Tanguay
— PhD and lead author
Tanguay and colleagues used a neuroimaging technique called functional magnetic resonance imaging (fMRI) to record the brain activity of 48 participants whilst they answered yes/no questions designed to involve either memory for general knowledge (semantic memory), unique events (episodic memory), autobiographical knowledge or memory for repeated events (two types of personal semantic memory). The team then used a multivariate analysis method to compare the participants’ brain activity across the four memory conditions. The neuroimaging data was collected at the Brain Imaging Centre at the University of Ottawa Institute of Mental Health Research (IMHR) at The Royal.
Their results indicated that personal semantic, general semantic and episodic memory had both shared and unique neural correlates. When they contrasted four memory conditions –autobiographical facts, repeated events, general semantics, and episodic memory– with a control condition, they identified the shared neural correlates, finding that all four types of memory involved activity within several regions of the brain’s ‘core memory network’.
Another 106 participants made ratings on the same statements to gain additional insights into what might explain similarities and differences between memory types. In sum, the neural activity in many regions of the ‘core memory network’ seemed to coincide with an increase in personal relevance, an increase in the visual details people perceived in their mind’s eye, and whether the memory involved a scene.
“Few studies have directly compared personal semantics to semantic or episodic memory, and even fewer have compared different types of personal semantics to one another. With our study, we were able to do so.” added senior author Patrick Davidson, Associate Professor at the School of Psychology and member of uOttawa’s Brain and Mind Research Institute.
This study is expected to be of great interest to memory researchers and could become a benchmark for future studies of autobiographical memory.
“A better comprehension of how several memory types fit together could help orient future research in a way that could have far-ranging implications,” says Davidson who worked with Louis Renoult (senior author), Associate Professor, School of Psychology, University of East Anglia and Daniela Palombo (co-author), Associate Professor, Department of Psychology, University of British Columbia.
‘The shared and unique neural correlates of personal semantic, general semantic, and episodic memory’ is published in eLife, November 21, 2023. DOI: 10.7554/eLife.83645
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