A conversation with the neuroscientist.
Question: Why is statistics so important for the realm of neuroscience?
Adam Kepecs: So 500 years ago Galileo said that the book of nature is written in a language of mathematics and this really turned out to be true for physics. It was really incredibly powerful in understanding physical phenomena and for some strange reason that really nobody understands it just turned out to be not very powerful in describing biological phenomena. In fact, we have a lot of mathematical tools now we use to understand biological phenomena in general, but we have not been successful in finding a sort of universal language and I think that our study really adds to a growing body of evidence that the language of the brain is statistics, that the brain operates at a statistical engine. It’s not a logical engine based on reason, but a statistical engine based on evidence and if you think about it your legs couldn’t tell you Newton’s laws, but they still obey them and of course your brain might not be able to explain the laws of statistics, but it still obeys them.
Question: If the brain can be reduced to statistics, can it also be replicated by computers?
So I don’t believe there is any theoretical reason why our brain cannot be simulated in a computer. The problem is right now that we have 100 billion neurons in the brain—perhaps fewer if you count some relevant ones in the neocortex—and we don’t understand how they’re connected. We don’t understand the tricks of the architecture and we don’t fully understand what's relevant about it that we need to simulate. But what we understand already, the piecemeal is that there is nothing mysterious that needs to be added, so,, on a small scale... when we ask the question on a smaller scale, not can you simulate the brain, but can you simulate a particular process we’re getting better and better at it and better and better at accounting for how our brain functions.
Question: How does dopamine help us learn adaptive behaviors?
Adam Kepecs: So dopamine is a very interesting neurotransmitter and what is really unique about it, it’s a handful of neuromodulators which are special in the sense that they’re neurons. The source of the signal is localized to specific brain areas and from these brain areas they project all across the brain. There is a handful of other ones like serotonin, acetylcholine and these are very interesting because you can think of them as broadcast systems. Some small area functionally computing something very simple perhaps can send this information across the brain and we understand a lot about dopamine. It turned out to be incredibly interesting and there is a very simple summary of what we understand about dopamine, which is that these neurons are active when your expectations are violated. They suddenly send a burst of dopamine when you’re expecting something and you’re not getting it and if you think about it this is exactly the right kind of signal for learning. If you’re expecting something and you’re getting there is nothing to change about your behavior, whereas if you’re expecting something and you’re not getting it and you have a burst of dopamine now it is a great signal for learning.
Question: What role does dopamine play in addition?
Adam Kepecs: So addiction is really interesting. It turned out that essentially all of the addictive drugs that we know of end up activating the dopamine circuitry. They end up releasing dopamine. So an emerging idea is that what happens during addiction is that you have a normal computational process whereby dopamine sends signals out precisely what is the degree to which you violated your expectations and that allows you to precisely learn in proportion to what you need to.
And, on top of this an addictive drug ends up releasing extra dopamine, so what happens is that when you get those drugs you might feel happy. Let’s say you’re happy about a great chocolate ice cream. Over time you learn to expect that the chocolate ice cream is really great and you have no more dopamine released in expectation of that when you receive it, whereas, if you take an addictive drug you can never learn to expect it because the drug itself will release an extra kick of dopamine and when that happens the value of that drug keeps increasing because now you’re learning that "Wow my expectations were violated, therefore this must be much more valuable than what I thought before." So basically what ends up happening, the dopamine system gets hijacked by these drugs, so it’s a normal process of learning that gets hijacked by addictive drugs.
Question: Why is Phineas Gage so important to psychology?
Adam Kepecs: So there is this very interesting story about Phineas Gage. He lived in the 1800’s and the horrible accident happened to him during construction. A very large iron rod just went through and pierced his skull and he miraculously survived and what was amazing about it, not just his survival, but that he was still human. He could reason. His intellect didn’t seem to change, but something changed. His personality was different and his decision making skills and that was one of the first pieces of evidence that scientists had about the localization of these different functions and today with much more evidence and much more specific lesion studies we actually have a lot of evidence pointing to the fact that a part of the frontal lobe that was damaged in Phineas Gage, the orbital frontal cortex is key to decision making.
Recorded August 20, 2010
Interviewed by Max Miller