Vanderbilt University researchers have discovered that early visual areas, long believed to play no role in higher cognitive functions such as memory, retain information previously hidden from brain studies.
The researchers made the discovery using a new technique for decoding data from functional magnetic resonance imaging or fMRI. The findings are a significant step forward in understanding how we perceive, process and remember visual information.
The results were published Feb. 18 online by Nature.
"We discovered that early visual areas play an important role in visual working memory," Frank Tong, co-author of the research and an associate professor of psychology at Vanderbilt, said. "How do people maintain an active representation of what they have just seen moments ago? This has long been a conundrum in the literature.
"Before, we knew that early visual areas of the cerebral cortex that are the first to receive visual information were exquisitely tuned to process incoming visual signals from the eye, but not to store this information," Tong said. "We also knew that the higher-order brain areas responsible for memory lack the visual sensitivity of early brain areas, but somehow people are able to remember a visual pattern with remarkable precision for many seconds, actually, for as long as they keep thinking about that pattern. Our question was, where is this precise information being stored in the brain?
"Using a new technique to analyze fMRI data, we've found that the fine-scale activity patterns in early visual areas reveal a trace or something like an echo of the stimulus that the person is actively retaining, even though the overall activity in these areas is really weak after the stimulus is removed," Tong continued.
"Visual cortex has always been thought to be more stimulus driven and has not been implicated in cognitive processes such as memory or active maintenance of information," Stephenie Harrison, lead author of the research and a graduate student in the Vanderbilt Psychology Department, said. "By using a neural decoding technique, we were able to read out what people were holding in their visual memory. We believe this sustained visual information could be useful when people must perform complex visual tasks in everyday life."
Research subjects were shown two examples of simple striped patterns at different orientations. They were then told to hold either one or the other of the orientations in their mind while being scanned using fMRI. Orientation has long been known to be one of the first and most basic pieces of visual information coded and processed by the brain.