When people look for something to pop into view at a particular spot—a baseball batter looking to a pitcher, for example—evidence has suggested that the visual centers of the brain can prepare themselves to respond more quickly and efficiently when the anticipated stimulus appears.
Now researchers have provided experimental confirmation of how this happens: a shift in the brainwave patterns in the visual cortex.
“We’re starting to get to the core of the neural mechanisms that underlie attention, and that could be important for helping us understand and treat a variety of cognitive disorders and brain injuries,” says senior author Maurizio Corbetta, M.D., Ph.D., the Norman J. Stupp Professor of Neurology at Washington University School of Medicine in St. Louis.
Corbetta and researchers at the University of Chieti in Italy published their results in the May 8 issue of The Journal of Neuroscience.
In earlier studies, Corbetta and others used functional brain imaging to establish that a network in the frontoparietal (the front and top) regions of the brain becomes active when a subject is anticipating the appearance of a visual stimulus.
The fact that this frontoparietal network activates when subjects were focusing on a certain part of their visual field suggested that it might be controlling the visual cortex, the area at the back of the brain where visual data from the optic nerves is processed. But brain scanners weren’t quick enough to prove this.
To test the theory, Corbetta and his colleagues in Italy first obtained precise fixes on the frontoparietal network in 16 volunteers. They did so using a neuronavigator system similar to one used for brain surgeries and based on previous studies performed in St. Louis.
Next, researchers used rapid transcranial magnetic stimulation (rTMS) to apply magnetic pulses to the frontoparietal network, temporarily disabling the brain cells there. Meanwhile, subjects looked for the brief appearance of a figure they had to identify on a computer screen. The subjects were given hints to where the figure might appear to draw their attention to a particular area of the screen. rTMS briefly disrupted the volunteers’ ability to direct their attention, increasing the time it took to respond by 10 percent and causing correct responses to drop by 6 percent.
“In general, rTMS made the subjects’ responses less efficient, proving that these regions are responsible for the control of visual attention,” says Corbetta, head of stroke and brain injury neurorehabilitation at the School of Medicine, Barnes-Jewish Hospital and the Rehabilitation Institute of St. Louis.
During the tests, scientists also used electroencephalography to monitor brain waves, which are produced by many neurons firing at the same time, a phenomenon called neural synchrony. Before volunteers were cued to where the stimulus might appear, the visual cortex was dominated by alpha waves, a frequency often associated with relaxation and the earliest phases of sleep. But when subjects received a cue to expect a stimulus, visual cortex neurons shifted into a higher-frequency wave band. When scientists used rTMS to temporarily disable the frontoparietal network, the brain wave shift in the visual cortex did not occur. Subjects in whom the brainwave shift was more impaired also had longer response times and more errors.
According to Corbetta, there are many neurological conditions, such as schizophrenia, traumatic brain injury and Parkinson’s disease, that may involve irregularities in brain wave patterns and the ability of one region to exert control over the brain waves of another region.
“By understanding how neural synchrony is important for simple processes like spatial attention, we’re laying the groundwork for understanding and correcting problems with synchrony in the more complex functions affected by these disorders,” he says.
Capotosto P, Babiloni C, Romani GL, Corbetta M. Frontoparietal cortex controls spatial attention through modulation of anticipatory alpha rhythms. The Journal of Neuroscience, May 6, 2009.
Funding from the European Community’s Seventh Framework Programme, the National Institute of Neurological Disorders and Stroke and the National Institute of Mental Health supported this research.
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