Maybe making a cup of coffee is a daily requirement for you. You like your cup of coffee in a specific way and you brew it the same way every day. Maybe you grind your own coffee beans and pour frothed milk over them.
“There’s a series of things you need to do that need to be done in the correct order,” said Edward Ester, assistant professor of psychology. “If you mess up, you get a bad cup of coffee.” And nobody wants that.
Ester studies the relationship between the information people receive from their environment that is dedicated to short-term memory and how they are able to act on this information.
“The way we conceptualize short-term memory is like a mental workspace where the brain can not only put information, but also process that information,” Ester said.
Short-term memory is the information that people hold in their minds. For example, doing a math problem in your head requires short-term memory. If you add two numbers, say 17 and 28, you probably separate the digits into the tens and ones. Maybe you add the digits in the ones place first, and you know that 7 and 8 add up to 15. But at the same time, you hold down the 1 and 2 in the tens place to add them (to get to 3) and any other number that comes out of the place of it (1). Keeping these numbers in your mind uses short-term memory.
“It sounds really simple and mundane, but there’s a lot of processing and a lot of things that have to go right before you can do something as simple as adding a few numbers together,” Ester said. There is some variability in how well people can retain information in short-term memory. Interestingly, people’s ability to retain information in short-term memory is completely independent of their ability to retain information in long-term memory.
Ester wants to understand how short-term memory interacts with the part of the brain that controls motor output. Researchers believe that memory systems exist to provide a basis or reason for action. But people can perform actions without having to retain the memories that originally triggered or inspired that action, and Ester wanted to know how well the brain’s motor and memory systems communicate. Rachel Weese, an undergraduate student in Ester’s lab with a major in psychology and a minor in biological anthropology, worked on this research question with Ester.
“It’s these types of goal-oriented behaviors that really interest Rachel and me, and how the information from this short-term memory system translates into how people interact with the world,” Ester said. We have a pretty good understanding of how the motor system is mapped. On the memory side, things are a little more opaque.
The researchers wanted to know if the brain networks controlling memory and actions can be active simultaneously or act in sequence. The real answer likely lies somewhere in between, and can provide researchers with insight into the degree of integration of motor and cognitive networks in the brain.
“We have some ideas about how different areas of the brain might be responsible for controlling these individual processes (motor and working memory),” Ester said. These ideas include a model that Ester describes as “the Psychology 101 thing that everyone learns” but also as “woefully incomplete”.
“This is the model that has dominated both psychology and cognitive neuroscience for at least 70 years,” he said. The model consists of three boxes: The first box represents perception or sensation, with an arrow pointing to a box representing memory and decision making. There is an arrow going from the memory box to a box representing the engine outputs and actions. The arrows show how information is processed in the brain.
“So there’s this nice linear output,” Esther said. But we know there are a million ways this model breaks down. For example, the things you act on inform the things you pay attention to, so the motor box may actually inform the perception box. We get these very impoverished views of how the brain actually solves problems in real-world tasks. Ester and Weese sought to determine how memory and action networks in the brain actually interact.
They recruited research subjects to sit in front of a computer screen with electrodes on their heads. Subjects were shown two pictures and asked to recall one of them. The experiment hinted at which the subjects were expected to remember, and they should respond at the end of the trial, with either their left hand or their right hand pointing to the correct image. The electroencephalogram or EEG electrodes captured information about which parts of the brain the subjects were using throughout the process. Monitoring active networks in the brain helped researchers determine whether they were being used in sequence or in parallel.
“The extent to which the timing of brain signals associated with stimuli processing and response planning overlap gives us insight into how closely brain networks are associated with cognition and action,” Ester said.
What Weese and Ester found was that the short-term memory and motor parts of the subjects’ brains could be active at the same time, showing that the motor and memory parts of the brain could act simultaneously. Now the researchers want to determine whether certain actions or decisions could be taken simultaneously (like making your cup of coffee) or sequentially. The lab is also interested in how different people land on the spectrum of simultaneous or sequential brain network activity.
For Ester, short-term memory appears to be “a fundamental part of how we think about and interact with the world.” But the “woefully incomplete” model isn’t useless, Ester said. “Eventually, and this is the way of science, all models are wrong, but some are useful.” Although neuroscientists have learned a great deal by following this model, it is an oversimplification of the relationship between memory and action.
It’s time to move beyond this model and consider a more holistic perspective on how cognitive and motor systems interact.
“There were a lot of people who came before us,” Ester said, referring to older research papers that pointed out the linear model was flawed but never got much attention. “It’s time to move beyond this model and consider a more holistic perspective on how cognitive and motor systems interact.”
The holistic perspective will be difficult to parse. The brain is still largely a mystery, and as Ester mentioned, memory is still a black box that scientists have yet to examine.
“Memory systems are closely related to motor systems,” Ester said, “but there is a degree of independence where memory systems can look ahead. One of the defining characteristics of the short-term memory system is that has a capacity limit.
Weese gave an example of a workaround for this limited ability using a technology metaphor. She said it’s like uploading memory from a thumb drive (your short-term memory) to a computer (the engine blueprint). You can discard the drive afterwards to avoid clutter.
Developing a better understanding of how these systems interact could be important for people learning to use a prosthesis using a neural implant. It takes some getting used to, but eventually motor plans become second nature.
This story was originally published in the College of Science’s 2022 “Live a Life of Discovery” magazine as “Thinking Ahead”.
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