Next time you're bickering with someone about the right way to get somewhere, because you're driving in circles on unfamiliar roads, or lost in a topiary maze (and you don't have access to a phone, I guess), how do you decide which one of you is the navigator-in-chief? Rock, paper, scissors? Fight about which way is north until someone gives in? Sure, those both seem like reasonable things to do in this underdeveloped hypothetical situation. But, you could also hand over the wayfinding responsiblities to the healthier sleeper between you. Losing sleep makes people vulnerable to losing their way, according to a recent study, published in the journal Sleep Science.
Spatial memory is memory of any information about geographic location, navigation or spatial orientation. And spatial memories fall under the category of declarative memory, meaning a fact or event we can consiously recall (or declare). Studies suggest that sleep enhances spatial-memory skills and that sleep loss takes a toll on them.
In most prior research on sleep and spatial memory, study participants have had to familiarize themselves with a new environment after skipping a night, or two, of sleep. This experimental set up, however, probably isn't an accurate reflection of sleep loss in real life. The average under-slept person isn't forgoing sleep entirely for two days; they're getting some, but not enough sleep for days, weeks or months at a time. So, in the current study, psychologists from the University of Calgary sought to see how people who sleep poorly, in real life, find their way around a new (virtual) environment, compared to naturally good sleepers.
For the study, 24 participants (college students) completed self-assessments of their sleep habits and problems, and filled out questionnaires on anxiety and depression symptoms. Based on these results, researchers divided participants into two groups: normal sleepers and people who don't sleep so good (and might have insomnia or something like it). Then, for a week, participants also kept sleep diaries and wore actigraphy trackers (e.g., fitbit).
Next came the navigation experiment: Researchers built a virtual environment consisting of four rooms connected by various hallways (so, basically, a maze). First, participants took a brief tour of the house, so they had a rough idea of where the four rooms were in relation to one another. Then, they returned to their starting point for the challenge: retrieving letters from designated rooms and dropping them off in other rooms, using the shortest routes possible. Researchers scored participants on their speed and rates of error, defined as instances of choosing longer-than-necessary pathways between rooms. As researchers predicted, the normal-sleep group finished the letter-delivery tasks faster and with fewer errors than their sleep-deprived counterparts.
While researchers assigned participants to the normal-sleep/poor-sleep groups based on participants' self-reports, they also collected actigraphy data to see if it echoed participants' own, subjective assessments. It did not. Does that mean participants didn't have a good sense of how well or how much they sleep? It's possible. Afterall, insomniacs are notoriously unreliable narrators when it comes to recounting their rest.
But, actigraphy may deserve blame, too. Clinical sleep tools (the mess of electrodes and sensors worn during sleep tests) offer a nuanced portrait of sleep, broken down in stages. Actigraphy trackers, on the other hand, just use motion as a proxy for wakefulness, meaning that lying still is interpreted as being asleep. So, actigraphy doesn't always tell the whole story, especially when it comes to insomniacs, who may spend a lot of time inert and awake.
Why would skipping sleep take a toll on spatial reasoning skills? Well, here's one hypothesis: Sleep loss has been linked to reduced volume in the hippocampus, which is thought to play a central role in spatial orientation and navigation. In this study, under-slept participants may have lacked the hippocampal capacity to encode (learn) new spatial information. So, while the normal-sleep group could use their brief tour of the virtual environment to get the lay of the land, the poor-sleep group didn't have the robust hippocampi necessary to get familiar. The study, researchers wrote, "provides the very first evidence that poor sleep quality affects learning of novel routes in virtual environments and influences subsequent performance in wayfinding."
But, there were limitations. For instance, researchers noticed that poor-sleepers scored higher, across the board, for anxiety and depression symptoms. It's not clear from the study if the cognitive impact of sleep loss was responsible for their slow, mistake-ridden performance. It's possible that they struggled with navigation because anxiety affected their ability to work under pressure, or even because depression caused their hippocampal shrinkage, rather than sleep loss. As usual, more research is needed.