Exploring the Limits of the Brain
By Caperton Gillett
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Descartes's concept of how sensations travel from the extremities to the brain |
At least, that’s what most of us probably think. And many of the world’s most illustrious thinkers have agreed. The exact relationship between the human brain and the human mind has been debated by philosophers throughout the ages. Plato and Aristotle fought for dualism—the idea that the mind or spirit is independent of the physical brain. Their contemporary, Parmenides, argued the case for monism: that body and spirit are one and the same.
Over the years, Plato, Aristotle, and their dualistic successor, Descartes, have undoubtedly had the upper hand. But ever since the 1920s, when science began to take a keen interest in the subject, the tables have turned. Sort of.
A Beautiful Mind
“Philosophers have been thinking about it forever, even though they weren’t thinking about the physical substrate of the mind,” says UAB neurobiologist Robin Lester, Ph.D. “We knew there was this thing, the mind, before we understood anything to do with the brain.”
As scientists have gained in their understanding of the brain’s powers, however, many have become convinced that this wonder organ can pull off the amazing tricks we attribute to the mind. Lester notes that psychiatrist, neuroscientist, and Nobel Prize winner Eric Kandel, M.D., who has studied the brain and mind intently, has crafted his own definitions of the concept. In Kandel’s landmark 1981 book Principles of Neural Science, says Lester, the mind is defined as simply the entire set of operations of the brain. Kandel later refined that description further to “the mental processes by which we perceive, act, learn, and remember.”
As to exactly what those mental processes might be, “that’s what neurobiologists are trying to define,” Lester says. “What is it about the synaptic connections or the excitability of neurons in the brain that gives rise to the mind?”
Neurobiology doesn’t have the answer yet, but it can supply some intriguing evidence that mind and matter are tightly linked. Lester gives as an example the case of Phineas Gage, a railroad foreman who had an iron rod driven through his frontal lobe in a freak accident and went on to suffer such profound personality changes that his friends barely recognized him. Lester also mentions a famous neurology patient, H.M., who underwent bilateral temporal lobe removals to treat his epilepsy and afterward found himself unable to create new long-term memories. “He lost his sense of who he was,” says Lester. “He lost part of his mind.”
Getting Physical
But how could a lump of gray matter produce Gray’s Elegy? Can human genius really be reduced to a series of chemical reactions? According to UAB philosopher Jacqueline Sullivan, Ph.D., there are several strong arguments in favor of the idea. They relate to a philosophical position called physicalism, which argues that mental states arise from or simply are physical states.
Pain, for instance, starts with a physical stimulus and ends with the activation of brain structures that tell us we hurt. Fear, which is not always triggered by physical stimuli, nevertheless depends on the activation of neurons in a region of the brain known as the amygdala for its behavioral expression.
So far so good. But some philosophers hold a position known as reductive physicalism, which is far more controversial. Reductive physicalists argue that every mental state has a single corresponding physical state—although Sullivan says that proponents have a hard time finding creditable supporting examples. The physical structures seen in animal brains differ significantly from those in human brains, making direct experimentation difficult. Still, researchers have already identified the specific structures in our brains associated with learning, memory, and multitudes of other functions, offering support to at least some concept of physicalism.
Arguing from these findings, reductionists say that there’s clearly a story that can be told at the physical level as to how these “higher” brain functions work, Sullivan says. “And if you can make that known, they say, then why wouldn’t reductive physicalism be true? Why can’t physicalism shed light on all the natures of our consciousness?”
Mental Mysteries
Most neuroscientists agree that what we know as the mind—personality, emotion, creativity—is simply the higher functions of the brain, taking in and interpreting stimuli and filtering them through cognitive circuits powered by biochemical reactions. But that doesn’t mean that science is able to explain how these biological threads are knit together into the human tapestry. Some explanations are yet to be found, if they’ll ever be found at all.
“There’s a concern that physicalism can’t capture the subjective nature of our experience,” Sullivan says. “For example, in 1974 Thomas Nagel argued convincingly that even if physicalism could tell us everything about the physical structures and physiological processes involved in a bat’s echolocation, it’s never going to be able to tell us what it’s like to be a bat, what the qualitative features of that experience are.”
Another argument against physicalism, Sullivan adds, was offered by the philosopher Frank Jackson in 1986. “Jackson uses the example of Mary, a neurophysiologist who lives in a black-and-white room and sees the world on a black-and-white monitor,” Sullivan says. “She knows everything about the brain and how color vision works at the physical level. One day, however, she steps outside, and suddenly she knows something she didn’t know before. That’s enough evidential support for the idea that physicalism can’t tell us everything about what life is like. Physicalism can provide a lot of knowledge, but it can’t provide the knowledge that Mary has once she actually steps outside and experiences the colorful world firsthand.”