Imagine that you are driving along at a safe speed. Suddenly, a stop sign appears where you didn't see one before and you quickly jam on the brakes.
Though it might seem that your response to the stop sign was automatic, your brain is actually processing a lot of information about this car ride.
According to researchers in the Hopkins Department of Psychological and Brain Sciences, led by Susan Courtney, the brain reacts to new information in working memory, which is a network of many brain regions.
Generally, working memory is involved with a person's current activities - it is the immediate record of what your brain is thinking about or working on over the last few seconds or minutes. When your mind switches to a new task, your working memory is essentially reset.
These researchers wanted to investigate how working memory can adapt to changes in information. Specifically, they examined the brain's response to certain "rules," or "if-then" scenarios. For instance, if you see a stop sign, then you press the brakes.
"The main purpose in conducting this research was to investigate how the brain switches between abstract 'rules' that are held in memory, which govern our behavior," said Caroline Montojo, a graduate student and the first author on the paper.
Courtney and her lab members discovered that the brain responded differently to the stimulus (the stop sign) and the rule (press the brakes).
"We found that rules that people must actively remember are controlled primarily through the prefrontal cortex, which is in the very front of the brain," Montojo said.
"Item information, such as numbers, are controlled primarily through parietal cortex, which is near the back of the brain."
Functional magnetic resonance imaging (fMRI) was used to look at the activation of these brain regions. Subjects in an fMRI study were told to perform certain tasks while in the scanner. The brain's response to these tasks can then be determined from the scanned images.
Courtney's research team asked subjects to memorize the numbers 47 and 53, which would act as stimuli, and the operations add and subtract, which served as rules. For each trial, the subject was told a number and rule to use. For example, the screen may have read "47 - Add."
Next, the screen showed another number, such as 11. The following screen showed four possible answers and the subject needed to pick the answer that equals "11 + 47."
Subjects performed a series of these types of trials, with the number or the rule changing periodically. People were much less accurate in guessing an answer if they were asked to switch both the rule and the number from the previous task.
So if they were told "47 - Add" in one trial and "57 - Subtract" in the next trial, subjects found it harder to choose the correct answer in the second trial.
This study showed that the subject can make both rule and stimulus updates in working memory. While previous speculation has suggested that stimulus and rule updates were managed by entirely different neural networks, this research indicates that the frontoparietal network is mostly responsible.
"These results are important for understanding how the human brain accomplishes complex, goal-directed behaviors that require remembering and switching between abstract rules," Montojo said.
"This research helps inform our broader research goals of determining how human beings are able to adjust behavior so elegantly and quickly under changing circumstances," Montojo said.
These findings may have clincal relevance as well. There are several psychiatric disorders that hinder a person's ability to make updates to new rules.
