Neuroscientific implications of risk-optimized behavior in the mouse
(Medical Xpress) — Regardless of an organism’s biological complexity, every encephalized animal continuously makes under-informed behavioral choices that can have serious consequences. Despite its ubiquity, however, there’s a long-standing question about its neurological basis – namely, whether these choices are made through probabilistic world models constructed by the brain, or by reinforcement of learned associations.
Recently, however, scientists in the Department of Psychology at Rutgers University found that reinforcement cannot account for the rapidity with which mice modify their behavior when the chance of a given phenomenon changes.
The researchers say this indicates that mice may have primordially-evolved neural capabilities to represent likelihood and perform calculations that optimize their resulting behavior – and therefore that such genetic mechanisms can be investigated and manipulated by genetic and other procedures.
The scientists state that their findings suggest that neural mechanisms for estimating probabilities and calculating relative risk are phylogenetically ancient.
“Mice and humans have not shared a common ancestor since before the extinction of the dinosaurs,” “Thus, the fact that both mice and humans have well-developed brain mechanisms for calculating risk indicates that those mechanisms were present in their common ancestor.”This also suggests, he says, that this finding means that such mechanisms may be explored through genetic and other invasive procedures in genetically manipulated mice and other laboratory animals.
“A common strategy in modern mechanism-oriented biological research,” says Gallistel,” is to use the enormous power of combined classical and molecular genetics to discover the molecular, cellular and systems realization of basic mechanisms. A classic illustration of such use comes from the pioneering work of Seymour Benzer1 and his students on the circadian clock.
By the 1970s, a great deal of behavioral and physiological evidence had accumulated that organisms of all kinds, even bacteria, have an internal clock that regulates their physiology and, in animals, their behavior – for example, the sleep-wake cycle, the ingestion cycle, and, indeed, almost every aspect of physiology and behavior.”
However, until Benzer’s work, no one had the faintest idea what the actual mechanism of such a clock might look like or where to look for it. “What this mechanism might possibly be was so mysterious that many scientists did not believe that there really was a clock,” Gallistel points out. ”They thought it was an emergent phenomenon, which is scientific jargon for a phenomenon that does not have a mechanism in any simple sense of the term, but rather emerges from mysterious and ineffable interactions between many different mechanisms. Many contemporary neuroscientists see memory as such a phenomenon.”
“When I was a graduate student,” Gallistel recalls, “I became familiar with the extensive behavioral evidence of an internal clock in, for example, bees, and I argued to some of my fellow graduate students that there had to be an honest-to-God clock in the brain. I well remember one of them saying in sarcastic disbelief, ‘You mean if you took the top of the skull off, you could see the hands going around?’”
there are now techniques for inducing mutations in mice for the express purpose of finding mice with heritable malfunctions in any of the thousands of different physiological and behavioral processes about whose underlying mechanisms we’re still ignorant…..
Gallistel notes that this strategy only works if the phenomenon being investigated is robustly present and readily measured in animals like the mouse, the zebra fish, or the fruit fly – the species chiefly used in the pursuit of this strategy:
“If you think only humans – and maybe only college trained humans – can correctly estimate probabilities and correctly calculate risks, then there is no way you can use this strategyHowever, we’ve shown that mice can correctly estimate probabilities and correctly calculate risks – and that their ability to do so can be assessed in completely automated behavioral tests that require very little human labor, and that can be run on hundreds of mice simultaneously.
In other words, there is now a way to apply Benzer’s strategy to the mechanisms that mediate the brain’s ability to estimate probabilities and calculate risks – and the molecular and cellular bases of these abilities are as mysterious to us at this time, as were the molecular and cellular bases of the daily clock in the 1970s.”
Gallistel adds that other research and application areas might benefit from their findings. “Probabilities are simple quantities and the calculation of risk requires the application of arithmetic operations to these quantities,” he concludes. “The ability to represent quantities and apply arithmetic operations to them is a foundation of mental activity. Pursuit of these avenues could lead to an understanding of the physical bases for our ability to think.”