Research correlates animal self-control with brain size

Michael Drummond/File
Michael Drummond/File

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If the campus squirrels seem overly eager to lunge for an unsuspecting student’s snack, new research suggests it may be because their small brains make it much harder for them to exhibit self-control than, for example, a baboon.

UC Berkeley psychology professor Lucia Jacobs and graduate student Mikel Delgado co-authored a large-scale study investigating self-control in animals, which found that absolute brain size is highly correlated to the ability to inhibit impulses or learned responses.

The study, published April 21 in the Proceedings of the National Academy of Sciences, was remarkable not only for its scale — the 58 co-authors represent 25 institutions that contributed data from 567 animals across 36 species — but also its implications for understanding the evolutionary processes that shape the human mind.

“We talk a lot about how we physically evolve, but what our brains actually do, across species, has not been examined in this level of detail,” Delgado said.

The study, organized largely by Evan MacLean, a researcher at Duke University, attempted to provide the first large-scale data set on cognitive abilities across species, investigating self-control — an important and easily-tested characteristic. Many labs study animal cognition, he said, but each tends to focus on a particular species or two and conduct research using its own individual methods.

“No one would be able to do this on their own; no lab would be able to study this many species,” Delgado said.

Researchers developed two tests for self-control; much of the challenge of the project was ensuring that each institution performed them the same way, MacLean said.

In the first test, called the “A-not-B task,” researchers repeatedly had test subjects retrieve food from container A. Then, subjects watched the researchers initially place food in container A but immediately move it to container B. If the subject still searched for the food in container A, it had failed to inhibit its learned response and failed to exhibit self-control.

In the second test, called the “cylinder task,” researchers familiarized subjects with finding food in an opaque cylinder by approaching the container from the side. Then, food was placed in a transparent cylinder. If the subject tried to approach the food head-on through the container, it had failed to inhibit its impulse to lunge for the food directly — another failure to exhibit self-control.

Jacobs and Delgado contributed the only data on rodents to the study, performing tests on captive Mongolian gerbils and campus fox squirrels.

The latter was the only species in the paper studied in the wild; the Jacobs lab often conducts studies with these squirrels.

“Some of them recognize me and will chase me across campus,” Delgado laughed.

Researchers compared the results of these tests, which were performed on subjects ranging from finches to coyotes to elephants, and found that the best predictor of performance was absolute brain size.

This was surprising, Jacobs said, as one might expect that brain size relative to a species’s body size would be a better indicator. Absolute brain size is associated with more cognitive networks, which could explain the correlation, according to the paper.

Moving forward, Jacobs said researchers intend to take a “bottom-up approach to brain evolution,” investigating basic structures and learning mechanisms using the methodology developed in this study.

Jacobs said investigating the evolutionary history of cognition is critical to understanding the development of human brains. As Delgado noted, “our behavior came from somewhere.”

Jacobs compared the complexity of the human brain to politics in the Middle East.

“You can’t understand that without understanding hundreds and thousands of years of history,” she said. “It’s a complex, nonlinear (situation) that’s arisen through historical events. The brain is the same way.”

Contact Sahil Chinoy at [email protected] and follow him on Twitter @sahilchinoy_dc.