A neuroimaging study in Italy found that autobiographical memories are represented across the hippocampus and interconnected regions of the brain cortex in such a way that memories from periods closer together in a person’s life tend to have more similar neural representation than memories that are farther apart in time. They found that the right hippocampus codes both event identity and temporal distance, while frontopolar and retrosplenial cortices encode temporal structure of memory. The paper was published in NeuroImage.
Autobiographical memories are memories about a person’s own life and personal experiences. They include specific events that happened at a particular time and place, such as a birthday celebration, a school trip, or an important conversation. These specific recollections are called episodic autobiographical memories. They involve remembering sensory details, emotions, people, and the feeling of mentally re-experiencing the original event.
Autobiographical memory also includes more general knowledge about oneself, such as knowing where one went to school or what kind of work one has done. This broader personal knowledge is called semantic autobiographical memory because it does not necessarily involve reliving a single event. Together, these forms of memory help people maintain a sense of personal identity and continuity over time.
They also allow individuals to reflect on the past, make decisions in the present, and imagine possible future events. Autobiographical memories are supported by a distributed network of brain regions, including the hippocampus, medial temporal areas, prefrontal regions, posterior cingulate and retrosplenial cortices, and parts of the parietal and visual cortex.
Study author Andrea Adriano and her colleagues conducted a neuroimaging study in which they tested the hypothesis that autobiographical memories are organized in the brain according to their temporal distance. More specifically, they hypothesized that the temporal distance between personal past events constitutes the key metric that allows experiences to be incorporated and navigated within this mental representation space. This organization of memories would emerge from mechanisms involving the hippocampus and cerebral cortex brain regions that organize memories of past experiences based on their temporal relations.
Study participants were 20 healthy adult volunteers. Their average age was 25 years. 11 of them were women.
At the start of the study, participants complete the Autobiographical Fluency Task. In this task, for each of five defined lifetime periods (5-10 years of age, 11-14 years of age, 15-19 years of age, 20-24 years of age, and the past 12 months), participants were asked to list as many events as possible, in written format. Instructions emphasized that the events had to be personally experienced by the participant, and that he/she should have a clear recollection of being personally involved.
For each event, participants provided a short title that was meaningful to them. Participants were required to list a minimum of 30 events per period. Participants also completed a vividness questionnaire for each lifetime period in which they rated the vividness of the visual images they had generated during the task.
Next, they underwent functional magnetic resonance imaging of their brains. During these recordings, participants viewed a set of labels some of which referred to the life events participants listed earlier (personal events), while others were artificially created and not provided by the participant (non-personal events). There were 20 personal and 20 non-personal event labels used in this task. Each participant completed four runs of this experimental task, each lasting 8 minutes. The order of event presentations was randomized each time.
Results showed that autobiographical memories (i.e., memories of past personal events) are arranged in the brain along a cortical-hippocampal timeline. This means that autobiographical memories are represented across the hippocampus and interconnected regions of the brain cortex in such a way that memories from periods closer together in a person’s life tend to have more similar neural representation than memories that are farther apart in time.
Results also indicated that the right hippocampus codes both event identity and temporal distance, while frontopolar and retrosplenial cortices encode temporal structure of memory. In other words, activity patterns in these cortical regions captured during neuroimaging reflected how far apart autobiographical memories were in time, meaning that memories from closer periods of life were represented more similarly than memories from more distant periods.
When the researchers examined small regions across the entire brain without limiting the analysis to predefined areas, they found that the temporal organization of autobiographical memories was represented across a broad network including parietal, temporal, frontal, and other regions. However, different brain regions did not encode the timeline independently, but showed similar representational patterns, suggesting coordinated processing across different brain networks in the hippocampus, cerebellum, and the cortex.
“These findings support the existence of a temporally organized mnemonic schema, namely a neural “timeline”, that underlies our ability to situate and differentiate personal memories across the lifespan.”, study authors concluded.
The study contributes to the scientific understanding of neural underpinnings of autobiographic memories. However, it should be noted that the study was conducted on a small group of relatively young and healthy individuals. As people age, the functioning and organization of brain networks often change. Because of this, the findings on older adults might not be identical.
The paper, “Echoes of time: Organization of episodic autobiographical memories in the brain according to their remoteness,” was authored by Andrea Adriano, Alice Teghil, Valentina Sulpizio, Federico Maria Tamigi, Gaia Cartocci, Federico Giove, and Maddalena Boccia.