Prior studies have shown that stress reduces working memory capacity, and now a new study by researchers at the University of Wisconsin (Madison) sheds light on the neural processes behind this phenomenon. By observing individual neural activity while rats followed a maze, the team discovered how stress affected the firing of neurons and reduced the rats ability to focus and remember their way through the maze. The researchers discovered that stress doesn’t inhibit neural activity but instead changes it, making it less effective at staying on task.
The brain uses working memory (a function of the prefontal cortex) to hold pertinent information in the foreground, swapping vital data in and out of longer term storage as needed.
“You don’t need that part of the brain to hear or talk, to keep long-term memories, or to remember what you did as a child or what you read in the newspaper three days ago,” said Dr. Craig Berridge, UW–Madison psychology professor. But it’s essential for focusing attention and modulating emotions.
“People without a prefrontal cortex are very distractible,” Berridge said. “They’re very impulsive. They can be very argumentative.”
Using a novel statistical modeling method the researchers showed that rat prefrontal neurons fired and re-fired regularly to keep important information fresh.
“Even though these neurons communicate on a scale of every thousandth of a second, they know what they did one second to one-and-a-half seconds ago,” Devilbiss said. “But if the neuron doesn’t stimulate itself again within a little more than a second, it’s lost that information.”
When the researchers added a blast of white noise a rat’s ability to complete the maze dropped from 90% to 65%. Neural monitoring shows that the stressed rats couldn’t retain information about how to get to the next chocolate chip reward, reacting to distractions such as noises and smells around them instead.
“The literature tells us that stress plays a role in more than half of all workplace accidents, and a lot of people have to work under what we would consider a great deal of stress,” Devilbiss said.
“Air traffic controllers need to concentrate and focus with a lot riding on their actions. People in the military have to carry out these thought processes in conditions that would be very distracting, and now we know that this distraction is happening at the level of individual cells in the brain.”
“Based on drug studies, it had been believed stress simply suppressed prefrontal cortex activity,” Berridge said. “These studies demonstrate that rather than suppressing activity, stress modifies the nature of that activity. Treatments that keep neurons on their self-stimulating task while shutting out distractions may help protect working memory.”
