FEATURE

The Brain Trust

Columbia’s Mind, Brain, and Behavior Initiative is assembling the best thinkers in the world to study the most complex object in the known universe. How far can this neurological dream team go?

by David J. Craig Published Fall 2012
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Shadlen suspects that this mechanism operates in the brains of most animals, apart from those with the very simplest nervous systems. He hypothesizes that the “neural time integrator,” as he calls it, is duplicated throughout the brains of highly evolved organisms, even in areas responsible for complex functions like memory, language, emotion, and reason. “When this mechanism gets repeated, in layer upon layer of circuitry,” he says, “it eventually produces all different forms of cognition.”

Shadlen doesn’t know this for sure. The only neurons he has observed doing math are those involved in perceiving visual information. That’s because scientists who came before him were able to map the brain circuits for vision in unusual detail, making these circuits the easiest in the brain to monitor. Shadlen has devised clever ways to work around this limitation, though, such as by conducting experiments in which subjects play visual games that require them to keep a running tally of the likelihood that picking certain colors or shapes will bring rewards; the brain circuits for vision thus are made a testing ground for probabilistic reasoning.

“You can see the brain cells updating the probabilities over time, which strongly suggests that this phenomenon isn’t relegated to simple perception, but is a substrate for cognition more generally,” he says.

The idea that the brain uses statistical algorithms to formulate thoughts is not new. The English mathematician Thomas Bayes suggested as much 250 years ago, and scientists and philosophers have since wheeled out the notion periodically. Until now, though, no scientist had ever provided solid evidence for how it might work. Shadlen is regarded by his colleagues as the first to do so, and his work raises a classic philosophical question related to Descartes’s mind-body problem: if scientists can show that our thoughts are the result of pure computation, does this mean we lack free will?

Shadlen is clearly moved by this question, and he has written several papers aimed at philosophers to help them explore the implications of his work. In an essay published in Frontiers in Neuroscience in April, Shadlen and coauthor Adina Roskies, a Dartmouth philosopher, argue that his findings ought not diminish our sense of free will or moral responsibility. For starters, they say, scientists are still a long way from explaining how our most distinctly human traits, like self-awareness and moral thought, come about.

“Like nearly all neuroscientists, we accept physicalism,” they write. “All matters mental are caused by brains. But we leave open the possibility of emergent phenomena: properties that arise from simpler causes but which are not explained away by them.”

In his laboratory, meanwhile, Shadlen is trying to determine if the integrator may ever break down and what the ramifications are. He suspects that this happens quite commonly and that it contributes to a range of disorders that include schizophrenia, Alzheimer’s, and some forms of autism.

“Every neurologist has seen the symptoms, which include a general state of confusion,” says Shadlen. “I think it’s related to the deterioration of the integrator.”

Shadlen came to Columbia, he says, to collaborate with other top neuroscientists who might help him answer questions such as these: What would cause a person’s integrator to break? Are there genetic defects or chemical imbalances involved? Is this mechanism controlled by one part of the brain? Or is it, like consciousness itself, a phenomenon that involves the interaction of lots of brain areas? Can a broken integrator be fixed?

“I need to work alongside people who study the brain at its genetic, molecular, and cellular levels to make sure the principles my team has discovered find their way to the bedside,” he says. “That’s why I’m here.”

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