When bad things happen, we don't want to remember. We try to block, resist, ignore – but we should perhaps be doing the opposite, researchers say.
A new study led by scientists in Texas suggests the act of intentionally forgetting is linked to increased cerebral engagement with the unwanted information in question. In other words, to forget something, you actually need to focus on it.
"A moderate level of brain activity is critical to this forgetting mechanism," explains psychologist Tracy Wang from the University of Texas at Austin.
"Too strong, and it will strengthen the memory; too weak, and you won't modify it."
Trying to actively forget unwanted memories doesn't just help prevent your brain from getting overloaded.
It also lets people move on from painful experiences and emotions they'd rather not recall, which is part of the reason it's an area of active interest to neuroscientists.
"We may want to discard memories that trigger maladaptive responses, such as traumatic memories, so that we can respond to new experiences in more adaptive ways," says one of the researchers, Jarrod Lewis-Peacock.
"Decades of research has shown that we have the ability to voluntarily forget something, but how our brains do that is still being questioned."
Much prior research on intentional forgetting has focussed on brain activity in the prefrontal cortex, and the brain's memory centre, the hippocampus.
In the new study, the researchers monitored a different part of the brain called the ventral temporal cortex, which helps us process and categorise visual stimuli.
In an experiment with 24 healthy young adults, the participants were shown pictures of scenes and people's faces, and were instructed to either remember or forget each image.
During the experiment, each of the participants had their brain activity monitored by functional magnetic resonance imaging (fMRI) machines.
When the researchers examined activity in the ventral temporal cortex, they found that the act of forgetting effectively uses more brain power than remembering.
"Pictures followed by a forget instruction elicited higher levels of processing in [the] ventral temporal cortex compared to those followed by a remember instruction," the authors write in their paper.
"This boost in processing led to more forgetting, particularly for items that showed moderate (vs. weak or strong) activation."
Of course, forgetting specific images on demand in a contrived laboratory experiment is very different to moving on from painful or traumatic memories of events experienced in the real world.
But the mechanisms at work could be the same, researchers say, and figuring out how to activate them could be a huge benefit to people around the world who need to forget things, but don't know how.
Especially since this finding in particular challenges our natural intuition to suppress things; instead, we should involve more rather than less attention to unwanted information, in order to forget it.
"Importantly, it's the intention to forget that increases the activation of the memory," Wang says.
"When this activation hits the 'moderate level' sweet spot, that's when it leads to later forgetting of that experience."
The findings are reported in JNeurosci.