I’m getting more and more intrigued by working memory. It is key to early academic achievement, it’s connected to the importance of prior knowledge for learning,…

A new study explains now how trouble with working memory makes a distinct contribution to the difficulty people with schizophrenia sometimes have in learning.

From the press release:

In the new study in the Journal of Neuroscience, cognitive scientists Collins and Frank collaborated with schizophrenia experts James Waltz and James Gold of the University of Maryland, to measure the effects of working memory and reinforcement in learning by applying these methods. They found that only working memory was a source of impairment.

Learning about learning’s components

To find that out, they marshaled 49 volunteers with schizophrenia and an otherwise comparable set of 36 people without the condition to participate in the specially designed learning task. In each round, participants were shown a set of images and then were asked to push one of three buttons when they saw each image. With each button push they were told whether they had hit the correct button for that image. Over time, through trial and error, participants could learn which picture called for which button. With perfect memory, one wouldn’t need to see an image more than three times to learn the right button to push when it appeared.

The task therefore explicitly involves employing the brain’s systems for working memory (keeping each image — button association in mind) and for reinforcement learning (wanting to repeat an action that led to the feedback of “correct,” and to avoid one that produced “incorrect”). But in different rounds while the degree of reinforcement remained the same, the experimenters varied the number of images in the sets the volunteers saw, from 2 to 6. What varied, therefore, was the degree to which working memory was taxed.

What the researchers found was that for both people with schizophrenia and for controls, the larger the image set size, the more trials it took to learn to press the correct button consistently for each image and the longer it took to react to each stimulus. People with schizophrenia generally performed worse on the task than healthy controls.

Those results show that as the task involved more images, it became harder to do — a matter of working memory, since the capacity to maintain information explicitly in memory is limited — but that alone didn’t prove that working memory was a source of learning problems for people with schizophrenia: they could also be doing worse because of a slower use of the reinforcement.

To determine that, the researchers used their computational models of how learning occurs in the brain to fit the experimental data. They asked what parameters in the models needed to vary to accurately predict the behavior they measured in people with and without schizophrenia.

That analysis revealed that varying parameters of working memory, such as capacity, but not parameters of reinforcement learning, accounted best for differences in behavior between the groups.

“With model-fitting techniques, I can look quantitatively, trial-by-trial and see that the model predicts subject’s choices,” she said. “The same model explains both the healthy group and the patient group, but with differences in parameters.”

That confirmed that working memory uniquely affected learning in people with schizophrenia, while reinforcement learning mechanisms did not, Collins said.

The study suggests that working memory could be a more important target than reinforcement learning among researchers and clinicians hoping to help improve learning for people with schizophrenia, Collins said.

Among mentally healthy people, as well, the study illustrates that the different components of learning can be understood individually, even as they all interact in the brain to make learning happen.

“More broadly it brings attention to the fact that we need to consider learning as a multiactor kind of behavior that can’t be just summarized by a single sytem,” Collins said. “It’s important to design tasks that can separate them out so we can extract different sources of variance and correctly match them to different neural systems.

Abstract of the research:

Previous research has shown that patients with schizophrenia are impaired in reinforcement learning tasks. However, behavioral learning curves in such tasks originate from the interaction of multiple neural processes, including the basal ganglia- and dopamine-dependent reinforcement learning (RL) system, but also prefrontal cortex-dependent cognitive strategies involving working memory (WM). Thus, it is unclear which specific system induces impairments in schizophrenia. We recently developed a task and computational model allowing us to separately assess the roles of RL (slow, cumulative learning) mechanisms versus WM (fast but capacity-limited) mechanisms in healthy adult human subjects. Here, we used this task to assess patients’ specific sources of impairments in learning. In 15 separate blocks, subjects learned to pick one of three actions for stimuli. The number of stimuli to learn in each block varied from two to six, allowing us to separate influences of capacity-limited WM from the incremental RL system. As expected, both patients (n = 49) and healthy controls (n = 36) showed effects of set size and delay between stimulus repetitions, confirming the presence of working memory effects. Patients performed significantly worse than controls overall, but computational model fits and behavioral analyses indicate that these deficits could be entirely accounted for by changes in WM parameters (capacity and reliability), whereas RL processes were spared. These results suggest that the working memory system contributes strongly to learning impairments in schizophrenia.