A neuroimaging study conducted in Italy found that autobiographical memories are represented across interconnected regions of the hippocampus and cerebral cortex, and that memories from closer periods in life tend to have more similar neural representations than memories that are more distant in time. They found that the right hippocampus encodes both event identity and temporal distance, and that the frontopolar and retrosplenial cortices encode the temporal structure of memory. The paper is neuroimage.
Autobiographical memories are memories about a person’s own life and personal experiences. These include specific events that happened at a specific time and place, such as a birthday celebration, a school trip, or an important conversation. Such specific memories are called episodic autobiographical memories. They include remembering sensory details, emotions, people, and the sensation of mentally re-experiencing the original event.
Autobiographical memories also include more general knowledge about ourselves, such as where we went to school and what jobs we’ve had. This broader personal knowledge is called semantic autobiographical memory because it does not necessarily involve reliving a single event. These forms of memory help people maintain a sense of personal identity and continuity over time.
It also allows individuals to reflect on the past, make decisions in the present, and imagine possible future events. Autobiographical memory is supported by a distributed network of brain regions, including the hippocampus, medial temporal cortex, prefrontal cortex, posterior cingulate and retrosplenial cortices, parietal cortex, and parts of the visual cortex.
Study author Andrea Adriano and her colleagues conducted a neuroimaging study testing the hypothesis that autobiographical memories are organized in the brain according to temporal distance. More specifically, they hypothesized that the temporal distance between personal past events constitutes an important indicator that allows experiences to be incorporated and navigated within this mental representation space. This memory organization is thought to result from mechanisms involving brain regions of the hippocampus and cerebral cortex that organize memories of past experiences based on temporal relationships.
Study participants were 20 healthy adult volunteers. Their average age was 25 years. Eleven of them were women.
At the beginning of the study, participants complete an autobiographical fluency task. In this task, participants were asked to list in written form as many events as possible for each of five defined life periods (5–10 years, 11–14 years, 15–19 years, 20–24 years, and the past 12 months). The instructions emphasized that the event must be experienced personally by the participants and must clearly remember having personally participated.
For each event, participants gave a short title that was meaningful to them. Participants were required to list at least 30 events per time period. At each lifetime period, participants also completed a vividness questionnaire that assessed the vividness of the visual images they produced during the task.
Next, they underwent functional magnetic resonance imaging of the brain. During these recordings, participants viewed a series of labels. Some of the labels referred to the participants in the previously listed life events (personal events), while others were artificially created and not provided by the participants (non-personal events). In this task, 20 personal event labels and 20 non-personal event labels were used. Each participant performed this experimental task four times, each lasting 8 minutes. The order of presentation of the events was random each time.
The results showed that autobiographical memories (i.e., memories of past personal events) are arranged in the brain along a cortico-hippocampal timeline. This means that autobiographical memories are represented across interconnected regions of the hippocampus and cerebral cortex, and that memories from closer periods in life tend to have more similar neural representations than memories that are more distant in time.
Results also showed that the right hippocampus encodes both event identity and temporal distance, and frontopolar and retrosplenial cortices encode the temporal structure of memory. In other words, the activity patterns in these cortical areas captured during neuroimaging studies reflect how far apart autobiographical memories are in time, meaning that memories from closer periods in life are more similarly represented than memories from more distant periods.
When the researchers looked at small regions across the brain without limiting their analysis to predefined regions, they found that the temporal organization of autobiographical memories is expressed across a broad network that includes parietal, temporal, frontal, and other regions. However, different brain regions did not independently encode timelines but showed similar representation patterns, suggesting coordinated processing across different brain networks in the hippocampus, cerebellum, and cortex.
“These findings support the existence of temporally organized memory schemas, or neural ‘timelines,’ that underlie our ability to locate and differentiate personal memories across the lifespan.” ” concluded the study authors.
This study contributes to the scientific understanding of the neural basis of autobiographical memory. However, it should be noted that this study was conducted on a small group of people who were relatively young and healthy. As people age, the function and composition of brain networks often change. Therefore, findings regarding older adults may not be the same.
The paper, “Echoes of Time: The organization of episodic autobiographical memories in the brain according to remoteness,” was written by Andrea Adriano, Alice Tegil, Valentina Sulpizio, Federico Maria Tamigi, Gaia Cartucci, Federico Giove, and Maddalena Boccia.
