When making simple decisions, neurons in the brain apply the same statistical trick used by Alan Turing to help break Germany’s Enigma code during World War II, according to a new study in animals by researchers at Columbia University’s Zuckerman Mind Brain and Behavior Institute. Results of the study were published Feb. 5 in Neuron.
As depicted in the film “The Imitation Game,” Alan Turing and his team of codebreakers devised the statistical technique to help them decipher German military messages encrypted with the Enigma machine. (The technique today is called Wald’s sequential probability ratio test, after Columbia professor Abraham Wald, who independently developed the test to determine if batches of munitions should be shipped to the front or if they contained too many duds.)
Finding pairs of messages encrypted with the same Enigma settings was critical to unlocking the code. Turing’s statistical test, in essence, decided as efficiently as possibly if any two messages were a pair.
The test evaluated corresponding pairs of letters from the two messages, aligned one above the other (in the film, codebreakers are often pictured doing this in the background, sliding messages around on grids). Although the letters themselves were gibberish, Turing realized that Enigma would preserve the matching probabilities of the original messages, as some letters are more common than others.
The codebreakers assigned values to aligned pairs of letters in the two messages. Unmatched pairs were given a negative value, matched pairs a positive value.
Starting at different points in the messages, the codebreakers began adding and subtracting. When the sum reached a positive of negative threshold, the two messages were deemed a pair from machines with the same setting, or not.
Neurons in the brains of rhesus monkeys do the same thing when faced with decisions, says Michael Shadlen, MD, PhD, professor of neuroscience at Columbia and an HHMI investigator.
In his study, Dr. Shadlen and co-first authors Shinichiro Kira, a former member of Dr. Shadlen’s lab and currently at Harvard Medical School, and Tianming Yang, of Shanghai Institutes for Biological Sciences, recorded the activity of neurons in the brains of two monkeys as they made a simple decision: look at a sequence of symbols on a computer screen, one after another, and whenever ready, choose between two spots for a reward.
To make the correct decision—the one that brought a reward—the monkeys had to weigh different clues encoded in the symbols that flashed onto the screen. Some of the eight symbols were unreliable clues about the reward’s location; others were more dependable.
And the monkeys had to think fast. Each symbol appeared for only 250 milliseconds.
As the monkeys watched the symbols, recordings of their neurons revealed how they came to a decision. Each symbol contributed a positive value (reward is in the left spot) or negative value (reward is in the right spot) to the accumulated evidence, which was represented in the neuron’s firing rate. More reliable symbols had a larger impact on the firing rate than less reliable symbols.
Just as in the Turing’s code breaking, once a positive or negative threshold was reached, the decision was deemed complete and the monkey indicated its choice.
Assuming that humans have the same capabilities—and that’s a good bet, says Dr. Shadlen—it means our brains are weighing probabilities and making rational decisions in very short periods of time. “It’s the basis of a very basic kind of rationality,” he says.
These types of decisions are mostly unconscious on our part. “They’re decisions like, ‘I’m going to pick up a book,’ or ‘I’m going to walk toward the left of the coffee table, not the right,’” Dr. Shadlen adds.
“We make lots of these decisions every day, and it turns out, we’re making them by using the laws of probability in a way that statisticians think is optimal.”
The paper is titled "A neural implementation of Wald's sequential probability ratio test."
The work was supported by the National Institutes of Health (EY011378, RR000166, and P30EY01730) and the Howard Hughes Medical Institute. S.K. was supported by a predoctoral fellowship from the Nakajima Foundation.
Columbia University Medical Center provides international leadership in basic, preclinical, and clinical research; medical and health sciences education; and patient care. The medical center trains future leaders and includes the dedicated work of many physicians, scientists, public health professionals, dentists, and nurses at the College of Physicians and Surgeons, the Mailman School of Public Health, the College of Dental Medicine, the School of Nursing, the biomedical departments of the Graduate School of Arts and Sciences, and allied research centers and institutions. Columbia University Medical Center is home to the largest medical research enterprise in New York City and State and one of the largest faculty medical practices in the Northeast. For more information, visit cumc.columbia.edu or columbiadoctors.org
Science Media Relations Officer
Lucky Tran | newswise
Staying in Shape
16.08.2018 | Max-Planck-Institut für molekulare Zellbiologie und Genetik
Chips, light and coding moves the front line in beating bacteria
16.08.2018 | Okinawa Institute of Science and Technology (OIST) Graduate University
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur
What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...
08.08.2018 | Event News
27.07.2018 | Event News
25.07.2018 | Event News
16.08.2018 | Life Sciences
16.08.2018 | Earth Sciences
16.08.2018 | Life Sciences