Memory is one of the murkiest functions of the human brain when it comes to our understanding of it. We’ve got a grasp on some basics, but other, more important specifics are still missing. A team of researchers, however, has recently discovered one more piece of the puzzle, connecting the types of memories we have with the nature of our future encounters. Their findings demonstrate how different parts of the brain, associated with different types of memories, influence how we pay attention in new situations.

“We’ve long understood there are different types of memories, but what these findings reveal are how different kinds of memories can drive our attention in the future,” said Elizabeth Goldfarb, lead author of the study and a doctoral candidate in NYU’s Department of Psychology, in a press release.

Goldfarb’s co-authors included Elizabeth Phelps, a professor in NYU’s Department of Psychology, and Marvin Chun, a professor in Yale University’s Department of Psychology.

Scientists have determined two main types of memories we haveare episodic — recollections of details from events in our life— and habitual, memories invoked in daily life that are often reflexive in nature. An episodic memory could be remembering the layout of your childhood friend’s house, while a habitual memory includes knowing how to tie your shoe. Researchers determined the different types of memory invoke different brain systems, with the striatum being important for habitual memories and the hippocampus being crucial to episodic memories. They aren’t so sure, however, about the neurological processes that allow memories to guide our attention in new situations.

The team took on the uncertainty by conducting a series of experiments during which participants’ brain activity was monitored using fMRI. The first set of trials involved “contextual cueing,” a phenomenon linked to episodic memories. For this particular experiment, participants were instructed to pick out a target (a rotated “T”) from among other distracting visuals on a computer screen, pressing a button once they found it. The subjects were unaware that some of the computer screens repeated, allowing their memory to form a familiar context to guide their attention to the target. Somewhat unsurprisingly, the findings showed that context-guided attention was associated with activity in the brain’s hippocampus.

The second set of trials employed a “stimulus-response” mechanism instead — one playing off our habitual memory process. For example, the stop sign that prompts you to take a habitual right turn to work every day serves as a stimulus. This time, the shapes on the screen were presented in a different color, which served as the “stimulus,” analogous to the stop sign. Eventually, study subjects learned that when they saw this color, they should look at a particular area of the screen for the “T.”

Unlike the context-cued trials, which showed activity in the hippocampus, the striatum was at work instead. The brain structure has long been linked with stimulus-response associations, but this finding reveals it has a role in guiding attention in new situations as well.

“Even though subjects had no idea that they were forming these memories, the fact that they performed better when contextual or habitual cues were present shows us that their attention was driven by memory,” Goldfarb said. “What we found here is that each of these types of memory can inform your future behavior."

Source: Goldfarb E, Chun M, Phelps E. Memory guided attention: Independent contributions of the hippocampus and striatum. Neuron. 2016.