A new study has found that contrary to popular scientific belief, remembering an event drives the production of memory-related brain waves more than actually engaging in the event does. The finding could improve the treatment of memory loss in people with brain damage or cognitive impairments.

When many neurons are activated, they create rhythmical electrical pulses just like a wave of spectators raising their arms in a packed stadium, and produce a detectable reflection of what’s going on inside our brains.

These brain waves, or neural oscillations, fall into five categories – gamma, beta, alpha, theta, and delta – depending on their amplitude and frequency. We exhibit gamma waves when we’re problem-solving or learning, beta when alert or excited, alpha when we’re physically and mentally relaxed, theta during moments of creativity and meditation, and delta waves during deep, dreamless sleep.

Previous research has shown that theta oscillations in the hippocampus, a complex structure deep in the brain’s temporal lobe, are linked to memory formation and spatial navigation. A new study led by researchers from the University of Arizona has examined what drives the production of these theta oscillations.

It was thought that compared to memory formation, a person’s external environment had a more important role in driving theta oscillations. That is, the oscillations produced while engaged in an event were greater than those produced when creating a memory of that event. However, the current study suggests this is not the case.

“Surprisingly, we found that theta oscillations in humans are more prevalent when someone is just remembering things, compared to experiencing events directly,” said Sarah Seger, lead author of the study.

The researchers recruited 13 patients being monitored for epileptic seizures using intracranial electrodes and recorded their hippocampal theta oscillations. The patients undertook a spatial navigation task on a laptop computer, using a joystick to navigate a virtual reality (VR) city to reach a particular store. When they reached the destination, the experiment was paused, and the patients were asked to imagine the location where they started their navigation and to mentally navigate the route they just took.

During the joystick-driven navigation process, theta oscillations were less frequent and shorter in duration compared to oscillations that occurred when patients were only imagining the route. Based on their findings, the researchers concluded that memory is the main driver of theta activity in humans.

They say their findings could be used to help improve memory in people with brain damage or cognitive impairments caused by stroke, seizures or diseases like Parkinson’s disease. Engaging in cognitive training and rehabilitation by having people actively create memories would drive theta oscillations, which has the potential to improve memory over time, the researchers say.

“Basically, you take a patient who has memory impairments, and you try to teach them to be better at memory,” said Arne Ekstrom, corresponding author of the study.

The researchers are planning to conduct further research with freely walking patients rather than patients who are in bed to see how actual navigation affects theta oscillations compared to memory.

The study was published in the journal Neuron.

Source: University of Arizona