Can dopamine bend time to shape memory

Ever heard of getting a "dopamine hit" from something you enjoy? These exciting moments also appear to influence memory, although perhaps not in the way you'd expect.

New research by UCLA psychologists suggests your brain may use dopamine to distort and expand time between distinct events, separating the flow of experience into pieces that can be flexibly reconstructed in the future.

The study, published in Nature Communications, found that a key dopamine-producing area of the brain - the ventral tegmental area - was activated when volunteers participating in an MRI scan detected the start of a new event. Importantly, when this dopamine hub was strongly activated, people reported more time had passed. The researchers also found that when people blinked more during a new event - an action thought to be related to dopamine signaling - their memory for time once again expanded.

"Dopamine is often talked about in the media as a chemical that makes things feel rewarding. People say we get a burst of dopamine when we eat food that we like, or when we scroll on social media, for example," said first author and UCLA doctoral student Erin Morrow. "But the dopamine system in our brain also responds strongly to novelty and change. We found that activation of the dopamine system at the beginning of a new event is likely one of the ways that our brain segments experiences into memorable episodes.

How do we form durable memories from the steady flow of life's experiences?

When we summon a memory, we may recall events as having unfolded very quickly or having dragged on at unbearable slowness. But that's not actually how time elapsed in the moment. It's somewhat of a puzzle, then, how our brain adds or subtracts time from the original flow of our experiences. This question is important because how our brain constructs new memories is related to how we experience and represent time.

UCLA psychology professor David Clewett studies how the brain marks event boundaries, which are transitions between different noteworthy contexts, to segment experience into a more organized format that can be retrieved later as memory.

"Time is often treated as a physical dimension," said Clewett. "But in psychology, time isn't fixed. It's something the brain constructs and is shaped by experience. As my colleague, professor Dean Buonomano puts it, our sense of time is evolution's way of allowing us to understand change. Our findings suggest that this process also shapes memory. I think of it as inserting small wedges into an otherwise continuous stream, helping neighboring events stand apart."

"The purpose of memory is not always to reconstruct the past completely accurately," said Morrow. "It helps us remember past experiences in the most useful way possible so that we can change our future behavior."

The dopamine system is engaged when new events happen

Researchers asked 32 volunteers to look at pictures of neutral objects while inside an MRI scanner. In between each object, tones were played in either the right or left ear. The same tone was repeated in the same ear across eight consecutive items to create a sense of a coherent event. The tone then switched to the other ear and changed pitch to create an "event boundary," a meaningful change that signaled the current event had ended and the next had begun.

This repeat-switch pattern continued throughout the remainder of the sequence, creating the perception of four different auditory events. Functional magnetic resonance imaging (fMRI) revealed strong activation of the ventral tegmental area (VTA) when changes occurred, suggesting that dopamine signaling was taking place. Stronger VTA responses were also associated with increased blinking, consistent with other evidence linking dopamine signaling to blinking.

Participants were then presented with pairs of images from the earlier sequence and asked how far apart in time they appeared. However, the "secret" was that the images were all actually the same distance apart in time. Strikingly, participants remembered items that spanned tone switches as occurring farther apart. This finding suggested that the tone switch - and the VTA response accompanying it - had helped separate the objects into different memories. If people blinked more often across this window, they also remembered the items as occurring further apart.

"We think the time dilation effect we found is useful, even though it's not accurate, because it may help push those experiences farther apart in memory," said Morrow.

Morrow said that the literature on the relationship between blinking and dopamine is mixed. She pointed out that many studies focus on blinking at rest or in people living with disorders related to atypical dopamine levels. In contrast, the current study took the novel approach of looking at dopamine and blinking while people without diagnosed psychiatric disorders were actively perceiving events.

How does change mark time in human memory?

This study represents an important step toward understanding how dopamine shapes memory. However, there are a few important limitations. These brain scans can't directly measure dopamine release, nor whether it causes time dilation directly. More research is needed to see whether these laboratory-based effects also apply to more complex, real-world experiences.

Even so, these findings could begin to shed light on why time feels so flexible and why it can differ so drastically across people and situations. Alongside novel or rewarding experiences, dopamine is also pumped across the brain during stress. This may help explain our strange memories of time during the COVID-19 pandemic. For many people, lockdown felt slow in the moment, yet occupies surprisingly little space in memory. Long stretches of Zoom meetings or online learning at home offered few contextual changes, leading those periods to later be indistinguishable and compressed. By contrast, the early periods of the pandemic - marked by stress and upheaval - often feel expanded in memory. Together, these examples demonstrate that when experiences are more eventful, the brain has more information to work with.

"Perhaps most importantly, our findings suggest that we don't simply move through time," says Clewett. "It is something we help create. By embracing change and variety, we expand our memories and, in that sense, expand our lives."