While it has long been known that humans and other primates consciously control their brain activity in order to produce and regulate movement, recent studies of ADHD patients and others revealed that people can also consciously control activity in movement-related brain areas without moving at all. Now, the same ability has been discovered in monkeys: Macaque monkey can actively increase the neural activity of certain brain regions to improve their concentration and better identify visual targets, according to research published yesterday (May 26) on Science Express.
This is the first example of "direct" neural control in these animals, said Robert Schafer, a neuroscience postdoc at the Massachusetts Institute of Technology and lead author on the study. The monkeys were able to alter their brain activity "without eye movements, visual stimulation, or training of any behavioral response," he said.
"In the past, functional MRI studies have shown that humans can modulate brain activity when they are given instant feedback about their brain activity. These kinds of studies have not been done in monkeys until now," Joshua Brown, director of the Cognitive Control Lab at Indiana University who was not involved with the research, told The Scientist in an email. "The advantage of studying monkeys in this way is that it is possible to see how the individual nerves are being controlled" by inserting probes directly into the brain regions of interest.
When primates move their eyes or even just prepare to move them, the brain's activity increases in the frontal eye field (FEF), a region in the frontal lobe of the brain that is responsible for rapid, synchronized eye movements. "We make [these eye movements] about four times each second, such as when we read this text," said Tirin Moore, a Stanford University neuroscientist and coauthor on the study.
In the new study, Schafer (previously a graduate student in Moore's lab at Stanford) and Moore, recorded the activity of 94 neurons within the FEF of two live macaque monkeys. To determine if monkeys can learn to control their brain activity in this region, the animals were trained to stare at a black dot on a screen so that they would not move their eyes. The researchers played a musical tone that increased in pitch as FEF activity went up, and became deeper as the neurons fired more slowly, and rewarded the monkeys with drops of apple juice for maintaining their FEF activity at either an increased or a decreased rate. Within around 3 months, the monkeys learned to associate the reward with the desired tone and would voluntarily adjust their FEF activity level accordingly.
The researchers further found that when the monkeys increased the neural activity in their FEF, the animals could more accurately find a search target. During the FEF activity exercise, the researchers would occasionally flash objects on the screen, and reward the monkeys for directing their gaze toward a rectangle, but not toward other shapes. At times when the monkeys were consciously increasing their FEF activity, they could detect the rectangular shape with 16.5 percent greater accuracy than when they were consciously decreasing their FEF activity.
"When monkeys learned how to control their brain activity, the nerves in a part of the brain that controls attention and eye movements were more able to detect visual signals in the environment," Brown said.
Though the research did not identify exactly how the monkeys manage to increase FEF neural activity, it did rule out that eye movement is responsible. The researchers propose that by focusing attention on a single location, a subject can voluntarily increase FEF activity, which in turn enables better identification of a visual target in later tests.
This is the first study to suggest that in addition to eye movement, the FEF is important for focusing attention, and that improvements in focus can result in increased cognitive abilities. "This could eventually lead to new kinds of treatment for attention deficit hyperactivity disorders," Brown said, by teaching patients to increase activity in a targeted area of their brain known to be responsible for the ability to concentrate.
R.J. Schafer and T. Moore, "Selective attention from voluntary control of neurons in prefrontal cortex," Science Express, doi: 10.1126/science.1199892, 2011.