What makes a human enjoy gourmet foods, consistently respond to pleasurable smells, or simply be able to focus for long periods of time?
Our brains come into direct contact with many kinds of stimuli that encourage us to seek pleasure and find meaning in life. And these stimuli come in many varieties, such as subtle shocks, cosmic gusts, and even just the slightest crush of the heel of a boot on concrete. In their new book, “The Neuroscience of Everyday Life,” Scientific American talks to Harvard Medical School psychologist Arthur Aron about such confounding properties.
Just imagine how puzzling it must be for researchers to tease out how, exactly, any of these seemingly intriguing phenomena make us feel and think. For Aron, whose latest work explores the impact of maternal psychosocial influence on infant development, this obsession with analysis extends into what he calls “social neuroses,” such as depression. Among its “fascinating questions,” the author writes, “is it possible to link the hard-wiring of the fetus, born into a caring mother, with the hard-wiring of the adolescent and the adult?”
In the 1980s, French and German neuroscientists decided to try to answer this question by hunting for mechanisms that might explain how the visual cortex—a necessary hub of perception, learning, and perception—addresses different aspects of sensory stimulation and context. They thought they’d be able to locate the connections between the visual cortex and other brain regions, as they did in rat brains, by counting those synapses. In particular, they asked to see if increasing the number of connections between visual processing neurons in either the left or right sides of the visual cortex increased the activation of those neurons in the brainstem region. This was in an effort to find a particular type of neuron related to sensory input, they thought.
After several years of studies, however, the authors found that it was only the visual cortex that might respond to sensory stimulation; the left or right sides of the visual cortex didn’t seem to show the same responses. And while they expected to find one kind of cell—an acoustic or some other type of neural cell—between each eye and the visual cortex, this was not the case. Instead, researchers could find different kinds of brain cells at each of the eye sites, though their numbers varied from eye to eye. And by contrast to human neurons, those brain cells were more sensitive to novel stimuli, suggesting that there are regions in the visual cortex that do not directly fire when we see, which suggests that they come from another brain region. Instead, the researchers thought, they were studying the activity of “superbright” neurons in a part of the visual cortex located just behind the ear.