Recent advances in imaging have revealed that false memories can be held by the very same cells that hold accurate ones, but we don't have much information about how false memories get there in the first place. A recent study published in PNAS provides some insight into this issue, finding that false memories may arise from similarities among the items being remembered.

In neuroscience, false memories don’t necessarily refer to a sensational memory that might land you on a daytime talk show. Typically, neuroscientists are more interested in banal false memories. For example, a classic experiment in false memories involves showing a subject a series of words related to the winter season, like ice, snow, wind, etc. In this paradigm, even if subjects aren’t shown the word “cold,” they are still likely to remember having seen it. This is a classic false memory.

Neuroscientists have suspected that this type of false memory arises because the word “cold” is similar conceptually to the list of winter words that the subject did see. Even though the cognitive mechanism that causes this phenomenon (called conceptual similarity) is theoretically understood, however, its neural underpinnings have not been widely explored. Using a combination of the word-recall experiment described above and fMRI scans that could track the brain activity of the participants, the authors of this paper have begun to identify some of what’s behind the false memory effect.

The researchers used an fMRI technique that compared various scans, looking for similarities in neural activity when subjects were thinking about the words on a list. They then analyzed the similarities between these neural firing patterns and the way that the brain fired when the subjects were thinking about the false memory word.

During this experiment, the researchers used several different lists of words, some of which are known to be more likely to produce a false memory than others. The researchers hypothesized that they’d see more overlap in neural activity for the lists that are more likely to produce false memories. As predicted, they found a high level of correlation between neural activity in response to a word and the likelihood that word would produce a false memory.

Each subject completed the memory recall fMRI task several times, with different sets of words. This allowed researchers to compare different false memories within the same subject. They found that neuron-firing patterns for different false memories were similar for each individual participant but were different when they compared the participants’ brain firing patterns to each other. This demonstrated that each individual has a memory coding for each group of words that’s at least partially unique. That’s most likely due to personal memories related to the concepts behind each list.

The data for this paper was collected over several weeks, which demonstrated that there was a high level of stability in the brain’s response to these concepts.

The researchers suggest that the use of similar firing patterns to code for similar words and concepts may be a mechanism that the brain uses to increase its efficiency—storing like with like. Their data could be interpreted as uncovering a potential cost of this otherwise-efficient system: the emergence of false memories. Perhaps the benefits outweigh the cost—our ancestors’ false memories would likely be very similar to real memories and may not have had many adverse consequences.

PNAS, 2016. DOI: 10.1073/pnas.1610686113 (About DOIs).