How do you transfer the password #498jOp_9@W4jjiLL from a paper to your screen?
Have you ever wondered how your brain manages to keep information like a complicated password or an address in mind while you’re typing it out? New work from a former NIMy group member Megan Roussy (led by Julio Martinez-Trujillo and Lyle Muller at the Robarts) suggests that a relay race may be happening at lightning speed inside your head!
Working memory is our ability to hold and manipulate information in our minds temporarily. For instance, we use our working memory when we are remembering a phone number while looking it up to dial or keeping a tricky email address or password in mind when copying it from a paper to our laptop. But how exactly does our brain pull off this mental ‘holding’ act?
Two leading theories suggest that either (1) some neurons persistently fire to retain the information, or (2) periodic bursts of activity occur during the holding period to keep the ‘engram’ (memory trace) active and protected from decay. However, the first theory is metabolically expensive, and the second hasn’t been conclusively proven, especially for complex, real-world tasks like navigating your neighbourhood or holding a conversation.
A New Way to Hold Memories
In a fascinating study conducted as part of Megan’s thesis work, a third mode of ‘holding’ information in working memory has been demonstrated. Julio’s team recorded the activity of hundreds of neurons in the lateral prefrontal cortex, a brain region involved in working memory, in two (adorable) macaque monkeys. The monkeys performed a task where they had to remember a location in a virtual 3D environment, similar to remembering where a destination is in a video game world, and then navigate to that remembered location.
The Brain’s Relay Baton
Here’s where it gets interesting: Alexandra Busch (first author, a BrainSCAN scholar) found that the neurons in this brain region encoded the remembered locations using a series of sequential neuronal activations, called neuronal activation sequences (NASs). This NAS code was better at representing the remembered locations during the virtual reality task compared to the classical way of representing memories through the persistent firing of neurons. But wait, there’s more! When we blocked a specific neurotransmitter receptor (NMDA receptor) using low doses of the drug ketamine, it selectively impaired the NAS code and the monkeys’ performance on the working memory task in the virtual environment. It was like impairing someone’s ability to remember a location in a video game world.
The Flexible Coding
Brain has many tricks – it can flexibly employ different neural codes, like NASs, to represent working memories when engaged in complex, dynamic environments like virtual realities, and video games – and thus for many other real-world phenomena.
NAS is a bit like passing the baton in a relay to keep the key message intact.
To succeed in a relay race, we may need a good grip (persistent firing), periodic tightening of this grip (bursts), as well as passing it to the right team member (NAS). Of course, you got to run pretty fast too!
The brain’s ability to flexibly encode and retrieve information is truly remarkable, and this study sheds light on one of the fascinating ways it accomplishes this feat.
So, the next time you see a super-secure password like #498jOp_9@W4jjiLL and try to type it onto your screen, remember there’s a lightning-fast relay race happening in your brain to keep that information active and accessible.
Image – Based on the prompts from the text above in OpenArt SDXL