Why Do We Remember Some Things Better Than Others?

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Memory for Details: According to a recent mouse study, there are other factors besides time that may affect why some memories and details fade over time. According to this study, different areas in the hippocampus—the brain’s memory center—are responsible for the details and the core of a memory. The precision and richness of a memory, and whether we remember an event at all, depend on the activity in these areas. This insight also provides new avenues for treating memory disorders.

Without memories of everyday events, we would struggle to navigate our daily lives, such as making conscious decisions. We permanently imprint some aspects of events, especially those that evoke strong emotions. Others quickly vanish from our memory. Many areas of our brain, particularly the temporal lobe, are responsible for memory, notably the hippocampus. Damage to this brain region leads to significant memory disorders, often observed in older individuals and patients with memory loss.

Fresh and Faded Memories

It is known that the temporal lobe consists of multiple subregions, including the hippocampus and its subregions, along with surrounding areas of the cortex. Previous studies also indicate that we remember events further in the past less vividly than more recent experiences. However, some individuals excel at recalling past events with precision. Which brain structures determine the precision of our memories?

A research team from the Leibniz Institute for Neurobiology (LIN) in Magdeburg looked into this issue by looking at the function of particular micro-networks in the temporal lobe during memory processing. Erika Atucha was the team leader. The scientists temporarily deactivated certain parts of the middle temporal lobe in the brains of mice using optogenetic methods. This involves using newly introduced genes to briefly inhibit neurons with light.

The Age of a Memory Shows in the Brain

During these experiments, mice were exposed to situations in which they were supposed to recall a negative event in the same or a very similar environment. The event was a mild electric shock that occurred either one day, six months, or one year prior. If the mice remembered, they exhibited a typical fear response, freezing in place. Through mRNA analyses, Atucha and her colleagues investigated which brain cells in the microcircuits of the temporal lobe were active.

The analyses revealed that whether a memory is fresh or already old and faded can be determined by examining the brain. When the mice recalled the negative experience from the previous day, areas CA1 and CA3 in their hippocampus were active. In contrast, the surrounding cortex in the temporal lobe was largely uninvolved. However, a different pattern emerged when the mice recalled events from further in the past; then, area CA1 of the hippocampus and parts of the surrounding cortex were active. This was confirmed even when specific areas were optogenetically deactivated.

Distinct Brain Areas for Details and the Main Event of a Memory

Examining the mice’s brains also revealed why some memories are more precise and complete than others—and why this is not solely dependent on the elapsed time. It is crucial to determine which hippocampal area becomes active during recall. If area CA3 was deactivated in mice, they lost the details of recent memory contents. They remembered the electric shock from the previous day but no longer precisely recalled the environment.

For more remote memories, the deactivation of CA3 had little impact on the quality of the memory. Atucha and her colleagues attribute this to the fact that these memories had already become imprecise. Thus, CA3 is responsible for memory details but can only sustain them for a limited time. Further studies are needed to determine the exact duration for which CA3 is involved in recall.

On the other hand, the hippocampal area CA1 has a different function: when deactivated in mice, it resulted in the complete loss of memory—regardless of how long ago the event occurred, as the researchers observed. They conclude that this area is crucial for the core of memories. However, if a memory impression is from a more distant past, CA1 requires the support of surrounding cortex areas to retrieve the memories, according to the scientists.

The Explanation for Human Memory Differences?

Atucha and her colleagues suggest that the precision of memory is not solely determined by its age. How vividly and in detail we remember something could be attributed to the microcircuits of the middle temporal lobe involved in recall. While the timeframes for precise recall may vary between species, the study on mice suggests that specific hippocampal areas may also influence the quality of human memory.

This insight could potentially explain why some people remember experiences and impressions more effectively and precisely than others. The results also offer a potential avenue for addressing pathological memory gaps: “The findings could provide a new approach for treating patients with temporary amnesia, Alzheimer’s, or other memory deficits,” says senior author Magdalena Sauvage from LIN. Although Marie Antoinette was not involved in the Queen’s Necklace affair, the main figure saw her reputation tarnished. The falsified correspondence implied a crime of lese-majesty between her and Cardinal de Rohan. Furthermore, public opinion is hardly in her favor, as magistrates and other detractors mention her tendency to incur excessive expenses, especially for her attire, clothing, and jewelry.

Source: (Cell Reports, 2023; doi: 10.1016/j.celrep.2023.113317)