Working memory is the place we hold temporary information that we're using to handle ongoing tasks, like dialing a phone number or following a set of directions. We often forget these after we're done—unless it's going to be your daily commute, you don't need to permanently recall that you make a left at the third traffic light—but working memory plays an essential role in many processes, and a person's working memory capacity seems to correlate with their performance on a variety of tests. So, what happens if you wipe a bit of working memory out?

Scientists have now found out what happens in mice, although it probably wasn't what they intended to do. A team at the University of Aberdeen were focusing on a specific type of neuron that's damaged in people with schizophrenia, as well as those who abuse ketamine and PCP. (These neurons express a protein called parvalbumin.) They bred mice in which they could selectively stop these neurons by injecting a virus into specific areas of the brain. The virus would only be active in the cells of interest, and ensure the production of a tetanus toxin, which prevents the nerves from firing signals to their neighbors.

They found that they could use the virus to paralyze over 80 percent of the parvalbumin-positive neurons in a specific area of the brain, the CA1 region of the hippocampus, a brain structure associated with memory. The mice were then subjected to a battery of tests where, for the most part, they were surprisingly normal, with no signs of problems with locomotion or anxiety. They also learned to navigate a maze just as well as their unaltered peers, showing that spatial reference memory was intact.

But they couldn't navigate their way very smoothly. Instead, they had a strong tendency to revisit arms of the maze that they had been in previously, and the numbers of errors they made correlated with the extent of viral infection. Making random lesions in the same area of the brain didn't have the same effect, indicating that the problem really was specific to these cells. It was also specific to that area of the brain, since injections of virus elsewhere in the hippocampus had more general effects on memory.

If you had to simplify these results, it appears that the mice that lacked working spatial memory knew where they were trying to go, but didn't quite manage to figure out how to get there, since they couldn't keep track of where they'd been. There are a number of working memory systems beyond spatial memory, though—humans have dedicated systems for images and words, for example—but it will be tough to use mice to determine whether these neurons are a general feature of working memory.

Nature Neuroscience, 2011. DOI: 10.1038/nn.2751 (About DOIs).