Monday, April 25, 2005

fMRI and the Primary Visual Cortex

Improved Scanning Technique Uses Brain as Portal to Thought
By NICHOLAS WADE
The New York Times
Published: April 25, 2005

By peering not into the eyes but into the brain, an improved scanning technique has enabled scientists to figure out what people are looking at - even, in some cases, when they are not aware of what they have seen.

The advance, reported today, shows that the scanners may be better able than previously supposed to probe the border between conscious and unconscious thought and even, in certain circumstances, to read people's state of mind.

The scanning technique, known as functional magnetic resonance imaging, is a more powerful version of a technique widely used in hospitals. It can show which regions of the brain are actively performing some task, but until now has lacked the resolution to track specific groups of neurons, as the functional units of the brain are called.

The improvement lies not in the scanners themselves but in a new analytic technique developed by Dr. Frank Tong, a psychologist at Vanderbilt University. In today's issue of the journal Nature Neuroscience, he and a colleague, Dr. Yukiyasu Kamitani, report that they were able with the scanner to distinguish the orientation of a test pattern of lines being observed by their subjects.

The scanner was able to furnish the necessary data because it was looking into a region of the brain known as the primary visual cortex, where information from the eye is processed. One of the first relay stations from the retina, an area of the visual cortex called V1, holds columns of neurons that burst into activity when lines or edges are perceived, with each column responding to a specific angle of orientation.

Dr. Tong set the scanner to monitor the orientation columns in V1. Though the columns of neurons are too small for the scanner to see directly, he found a way to infer statistically which columns were active and hence which orientation the V1 area was responding to.

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