The results of a new University study suggest a link between an area of the brain called the rostrolateral prefrontal cortex and the ability to stay on track in a sequence of tasks.
The paper — published in the journal Neuron and authored by David Badre, associate professor of cognitive, linguistic and psychological sciences, Postdoctoral Fellow Theresa Desrochers and Christopher Chatham, a former postdoc in Badre’s lab — involved study participants recording the color and shape of objects. While they did this, their brains were scanned using functional magnetic resonance imaging to measure activity in specific parts of the brain.
The participants were asked to remember patterns — for example, color, color, shape, shape — and repeat these sequences, identifying objects in sets of four. The study found that the activity in the RLPFC specifically ramped up throughout the display of one sequence and reset before the start of a new one.
Desrochers said because participants did not receive cues as to which part of the sequence they were on, the RLPFC can be seen as resolving uncertainty by increasing activity throughout sequences.
Matt Nassar, a postdoctoral research associate in Associate Professor of Cognitive Linguistic and Psychological Science Michael Frank’s lab, who was not involved in the study, wrote in an email to The Herald that, according to the study’s results, activation of the RLPFC is consistent with amplification of a control signal that is related to “uncertainty about the current sequence position.”
While the task drew on participants’ ability to track where they were in the sequence, it also involved other cognitive control components such as naming the current shape or color and switching between task sets of color or shape identification, Chatham said.
For further evidence that the RLPFC deals with the ability to resolve uncertainty and keep on track, rather than other components of cognitive control, the researchers asked the participants to perform the sequential tasks while undergoing transcranial magnetic stimulation in the RLPFC and two other regions of the pre-frontal lobe. TMS sends a non-invasive pulse signal to briefly disturb the activity of the brain in the targeted area.
In two separate experiments, only stimulation of the RLPFC resulted in participants making more errors.
“In the face of the much publicized replication issue recently brought to the forefront of psychological and medical research, it is great to see that they performed a direct replication of their primary causal (TMS) result,” Nassar said. This pattern was parallel to the activation pattern that had also been observed using fMRI, Desrochers said.
The TMS technology enabled the researchers to conclude that the implications of the RLPFC were causal, not simply correlational, in staying on track, Chatham said. The use of both techniques, and correspondence between them, shows that the RLPFC was “playing a causal role in the task performance,” Nassar wrote.
This finding was unprecedented, according to Desrochers, in that previous research had shown that the more abstract something is, the farther forward into the frontal cortex it activates. Additionally, the frontal lobe has been thought to be involved in static rather than sequential tasks.
But according to the study, previous work that looked at the brain areas that control simple motor tasks or cued sequences do not fully illuminate the neural mechanisms involved in task sequences.
Going into the experiment, the team believed this region was performing this task, Chatham said. But “you can only say so much from the fMRI,” he said. Seeing this effect displayed in the two TMS trials was “a real triumph,” Chatham said.
These results are important, Desrochers said, because they distinguish the RLPFC from the other parts of the frontal cortex. Nassar noted that the work “highlights a new role for prefrontal circuitry in organizing the efforts of more basic motor planning circuits according to higher order task sequencing.”
Chatham said it underscores the region’s importance in how the frontal lobe controls behavior, helping decode hierarchical cognitive control — the ability to put effort into immediate goals while still keeping larger ones in mind.
Sarah Master ’17, an undergraduate research assistant who assisted with the study, said it is groundbreaking to see that the RLPFC is responsible for controlling tasks in humans. It is hard to know how this research will fit into the larger understanding of the brain, as it is “a small piece of a very large puzzle,” Master said.
Desrochers said this region makes us very human.
RLPFC is one of the regions that almost certainly does not serve the same function in other animals as in humans, and it illuminates where intelligent behavior, specifically the ability to regulate behavior, comes from, Chatham said.
The compromised ability to regulate behavior is a common factor in disorders which reduce the quality of life, Chatham said. Frontal lobe dysfunction plays a role in head trauma, stroke and diseases, Desrochers said. Though people with frontal lobe dysfunction may perform well on classical tests of functions, they can’t perform sequences and thus can’t live independently, she added.
Desrochers said basic science can lead to the development of therapies. A search for therapies that would target this function can begin to narrow its focus, Chatham said, adding that people had reached out about therapeutic implications, and this study gives a direction of where to go.
Three follow-up studies have begun, Desrochers said. The first study relates to uncertainty and provides subjects with clues while they are doing the sequences, to see how this affects the results. The assumption had been that the clues will help reduce uncertainty, Desrochers said. But the preliminary answer is that it is not that clear cut, he added.
The second study asks whether the learning process is similar in both physical motor sequences — such as pressing a series of keys — and mental sequences. The third study examines the brain’s activation when keeping track of a visual set of images.
