Keys discovered to unlock brain’s secrets of memory and time

Research is beginning to uncover how we put our memories in order.

More neuroscience research is focusing on time and memory.

Our bodies know when to fall asleep and when to wake up. Our brains can keep track of short bursts of time like a mental stopwatch. But in our memories, our sense of time is fuzzy. Now ­research is beginning to uncover how we put our memories in order.

These new insights into the workings of the brain, paired with other findings, could help in the understanding and early detection of diseases such as dementia and Alzheimer’s.

The idea we perceive time in our memory subjectively is well known in psychology, says Lila Davachi, a professor of psychology at Columbia University. People may feel as if a day flies by when it’s busy but later the memory stretches out because of the many recalled details.

Neuroscientists, however, have long had a limited understanding of how the brain marks this sense of time. Most research has pointed to the learning and memory hub of the brain, known as the hippo­campus, and the surrounding brain regions. Now neuroscientists are homing in on the lateral entorhinal cortex, which feeds into the memory hub, as a more specific time marker for memories.

“It’s not a clock in the way we think of a ticking metronome,” says James Knierim, a professor of neuroscience at Johns Hopkins University and a researcher on a recent study that broke ground in this area. “It’s a signal that changes over time as a result of the experience.”

In the study, published in the journal Nature, researchers allowed rats to roam in an open area while recording their brain ­activity. Each time researchers changed the surroundings by switching the wall colour, the LEC area of the rats’ brains responded more than anywhere else. Looking back at those signals, the researchers could create an accurate timeline of events.

When the rats ran laps on a figure-eight track, the same area of the brain marked specific movements, like left or right turns. But the signal was weaker in marking the laps themselves, says the first author on the study, Albert Tsao.

These animal findings can ­potentially be extrapolated to human experiences, says Edvard Moser, a Nobel laureate neuroscientist and senior researcher on the study. Similar to the rats running a figure-eight, if humans have a ­repetitive schedule, the time marker might start to repeat itself. “You may forget if this happens on a Monday, Tuesday or Wednesday, because the same thing is happening again,” says Moser, co-director of the Kavli Institute for Systems Neuroscience in Norway.

A study published in January in Nature Neuroscience added support to the idea that the LEC plays a role in time and memory. In the study, 19 college students watched an episode of the television show Curb Your Enthusiasm while ­researchers recorded their brain activity. Afterwards, the students were presented with images from the episode and asked to recall when they appeared. The most ­accurate guesses corresponded with the strongest LEC activity, says Michael Yassa, director of the Centre for Neurobiology of Learning and Memory at the University of California, Irvine, and senior ­researcher on the study.

Such results are causing neuroscience research, which has long focused on how the brain understands and remembers space and location, to increasingly focus on time and memory, experts say.

Many scientists believe the new findings could bolster research into Alzheimer’s and dementia.

Several studies on humans have pinpointed the entorhinal cortex, which consists of the LEC and the medial entorhinal cortex, an important part of the brain’s positioning system, as the starting point for the onset of dementia and Alzheimer’s disease. Some of the earliest symptoms for Alzheimer’s are losing track of the passage of time and dates, becoming disoriented and a weakening sense of smell — all cognitive processes linked to that part of the brain.

Studying that region in brains ageing typically and brains developing Alzheimer’s could help spot differences in brain development. If researchers can also pinpoint behavioural differences, physicians might be able to screen for signs of dementia or Alzheimer’s using time-based judgment tasks.

Yassa and his team recently launched a brain-imaging study in 150 healthy older adults with risk factors for Alzheimer’s disease. The participants, aged 60 to 85, completed a series of cognitive tasks and had their brains imaged. The team will follow up with participants every two years to see if they can link developments in the brain to specific cognitive impairments that could potentially lead to earlier detection, diagnosis or treatment, he says.

The Wall Street Journal