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Why some brains may be better at tracking tasks than others

Stanford Medicine researchers discovered that short-term memories are stored in “distributed” neural patterns in the brain.

I'm infamous in my household for being found with my head in the refrigerator, frozen as I wonder what it was I went to get. This doesn't seem to happen to my wife, who can keep five separate tasks running in her head without forgetting a thing.

So I was interested to speak recently with Shaul Druckmann, PhD, a neurobiologist at Stanford Medicine and member of the Wu Tsai Neurosciences Institute who recently published a study on exactly this type of forgetfulness -- in mice.

To study short term memory in the brain, Druckmann and collaborators at Baylor College of Medicine trained mice to recognize a signal indicating which of two spouts they could lick to get a drop of water -- one on the left and one on the right. Then they trained the mice to wait a couple seconds after this signal before licking, forcing them to create a short-lived memory that the researchers could study.

In line with prior studies of short-term memory, the mouse stored this information in patterns of electrical activity spread across thousands of neurons in the prefrontal cortex, a region at the front of the brain involved in planning and other so-called executive functions. These activity patterns, which stayed active throughout the memory task, seemed to be stored in a "distributed" fashion -- spread across both the left and right sides of the prefrontal cortex.

Theoretically, storing important information in several independent locations in the brain should be helpful in ensuring that neural misfirings in one part of the circuit or another can't disrupt the memory as a whole. It's similar to how computer data is "distributed" across server networks to make sure that a single drive failure doesn't erase valuable files. But the researchers wanted to see if this is what was really happening in the brain.

Lighting up the brain

So the team used optogenetics -- a technique that lets neuroscientists control the activity of brain cells with targeted beams of light -- to disrupt part of the distributed memory while the animal was trying to remember which side to lick. Predictably, this caused some mice to lose track of which side to lick, but other mice proved remarkably resistant to getting pieces of their memory circuits temporarily scrambled.

Here's where the research speaks to my own situation, with my head aimlessly stuck in the fridge: The scientists found that the animals whose memories were most resistant to optogenetic disruption had actually stored the memory differently than their more hapless brethren. Specifically, they appeared to store the information more independently in multiple locations, walled off from one another such that disruption of one part of the pattern didn't spread and disrupt the whole memory.

It's one thing to see some mice withstand an artificial laboratory manipulation better than others, but the same mice also did better on the memory task normally -- in the absence of any experimental tinkering with their memories. In other words, animals who stored their memories in a more secure, distributed fashion appeared to be better at blocking out natural distractions in the environment and from within their own skulls as well.

The study is one of the first examples showing differences in individual animals' brain activity that directly explain their cognitive performance, says Druckmann, who recently received a McKnight Scholar award to advance this work. It certainly helps me understand what may be going on in my own head when thoughts about the movie I watched last night displace my focus on deciding what to eat for breakfast.

These findings epitomize one of the fundamental questions Druckmann's lab tries to ask: Why is the brain organized the way it is, and not some other way?

"So far, all our efforts to build artificial systems are still quite simplistic in what they can accomplish, particularly compared to the remarkably flexible calculations an animal does as it navigates the world," he said. "It would be great to be able to reverse engineer the specific design principles built into all brains that allow animals to do such amazing things."

Photo by That's Her Business

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