In quantum theory of cognition, memories are created by the act of remembering

The way that thoughts and memories arise from the physical material in our brains is one of the most complex questions in modern science. One important question in this area is how individual thoughts and memories change over time. The classical, intuitive view is that every thought, or "cognitive variable," that we've ever had can be assigned a specific, well-defined value at all times of our lives. But now psychologists are challenging that view by applying quantum probability theory to how memories change over time in our brains.

"There are two lines of thought when it comes to using quantum theory to describe cognitive processes," James M. Yearsley, a researcher in the Department of Psychology at City University London, told Phys.org. "The first is that some decision-making processes appear quantum because there are physical processes in the brain (at the level of neurons, etc.) that are quantum. This is very controversial and is a position held by only a minority. The second line of thought is that basic physical processes in the brain at the level of neurons are classical, and the (apparent) non-classical features of some human decision-making arises because of the complex way in which thoughts and feelings are related to basic brain processes. This is by far the more common viewpoint, and is the one we personally subscribe to."

In their study, Yearsley and Emmanuel M. Pothos, also at City University London, have proposed that quantum probability theory may be used to assign probabilities to how precisely our thoughts, decisions, feelings, memories, and other cognitive variables can be recalled and defined over time. In this view, recalling a memory at one point in time interferes with how we remember perceiving that same memory in the past or how we will perceive it in the future, much in the way a measurement may change the outcome of something being measured. This act of recall is sometimes called "constructive" because it can change (or construct) the recalled thoughts. In this view, the memory itself is essentially created by the act of remembering.