Not long ago, my editor asked if I wanted to cover a lecture by a premier neuroscience researcher on the fascinating topic of “the deliberating brain,” preceded by cocktails at one of New York’s most elegant old hotels.
As decisions go, I thought, this was a no-brainer.
But I was wrong. One thing that Dana Alliance member Michael N. Shadlen, M.D., Ph.D., made very clear in his talk, hosted by the Columbia University Mind Brain Behavior Initiative and sponsored by the Dana Foundation, is that no decision is a no-brainer. “By understanding the building blocks of decision making,” he told his audience, “we can understand how the brain achieves cognition writ large.”
Because complicated decisions—whom to choose as a life partner or elect as president, whether to attend a lecture—are hard to study in the lab, Dr. Shadlen and his colleagues devised simple tasks to illuminate these building blocks. In his lecture, he summarized a series of experiments in his laboratory, which he recently moved from the University of Washington to Columbia, that showed how the brain weighs evidence to choose between alternatives.
He and his colleagues taught monkeys to identify five geometric shapes that supported the choice of “red,” five that suggested the right choice would be “green.” But the evidence was weighted: some shapes provided strong evidence in favor of their respective color, some weak, the same way some cues in the environment are more reliable than others. After seeing a sequence of four shapes, the animals chose one color or another, and were rewarded if correct.
The researchers taught the monkeys to signal their choice by moving their eyes toward a red or green spot, and placed an electrode to record activity in a single neuron in the “association cortex,” a region between brain areas that processes visual signals and those that direct eye movement. One feature of association cortex neurons, Dr. Shadlen explained, is “persistent activity”—the ability to keep firing while waiting to direct a response.
“Many of us feel that persistent activity holds the key to higher brain functions in general, not just decision making. To achieve our most cherished mental feats, the brain must use, represent, and compute with information that is not tied to immediate change in the sensory world.” On this basic level, he suggested, “cognition is an elaboration in evolution on a simpler brain that delivered sensation to the motor system directly; as we got a bigger brain, we were free from acting on information in the moment.”
In the videos that followed, we in the audience were privileged to see—and hear—the deliberating brain in action. A graph displayed the frequency of “spikes” of electrical impulses from the neuron in question as the monkey saw a sequence of shapes, while the audio played the crackle of electrical activity. In one trial, the line rose as more evidence for “red” was presented, and the sound reached a crescendo. In another, the electrical activity started out fast and loud, as the first shape strongly supported red, but then dwindled dramatically as successive shapes signaled green as the better choice.
“What we’re witnessing,” Dr. Shadlen said, “is a single cell, in a single decision, adding and subtracting, accumulating evidence and integrating it. We think this is the neural substrate for deliberating and reasoning… the building blocks of decision making and cognition.”
“I’m a neurologist, and twenty years from now I’d like to see the fruit of my labors make their way to the bedside”: these same building blocks, he believes, are fundamental in disorders of higher brain function. While the causes of schizophrenia, autism, and attention deficit disorder may prove genetic or toxic, “in the end they will manifest in failures of things like evidence accumulation, persistent activity, and the ability to know when to stop deliberating.”
Drugs to restore these core functions, Dr. Shadlen predicted, will come from an understanding of the brain in which his research will act in synergy with the work of others investigating synapses, genes, and proteins. The potential for such interdisciplinary progress, he said, “is why this decision maker chose to leave the beautiful Pacific Northwest for the mud near the 125th St. subway stop,” where the future home of Columbia’s Mind Brain Behavior Initiative is under construction.
Carl Sherman is a science writer in New York City.