fMRI and Data Filtering Provide Insights into Brain Activity

Imaging techniques that enable physicians to look through the human skull and right into the active brain have become an important tool for both research and medical diagnosis. However, the underlying data have to be processed in elaborate ways before a colorful image reveals information about brain activity. Swiss and German scientists were now able to demonstrate how the use of different filters may influence the resulting images and lead to contradictory conclusions.

In the April 2011 issue of Human Brain Mapping, Dr. Tonio Ball of the Bernstein Center Freiburg (Germany) and colleagues from the Carl von Ossietzky University Oldenburg (Germany), University of Basel (Switzerland), and the Otto von Guericke University of Magdeburg (Germany) demonstrated how variable the findings of imaging techniques such as functional magnetic resonance imaging (fMRI) can be depending on the way how the original data are filtered. The use of filtering algorithms is indispensable in order to separate meaningful information from inherent noise that is part of every data set. These filters have different "mesh sizes” or widths, and are indispensable in the first place to reveal activity patterns that span different scale sizes. In most instances, only a filter of one specific width, which differs from study to study, is employed.

Dr. Ball and colleagues systematically examined the influence of the mesh size of these filters on the resulting imagery of brain activity. They conducted an experiment during which test persons had to rate music by pressing a button while lying in an fMRI scanner. During this task, brain regions responsible for hearing, vision, and arm movements were active.
The scientists treated the gained data with filters of different widths and found surprising results: The filters had a noticeable influence on the outcome of the brain scan analyses, revealing increased brain activity in one region in one case, and in a different region--in the other. Even the smallest alterations in filter width led to areas of the brain appearing to be either active or inactive. This effect can ultimately lead to widely different interpretations of such a scan. Dr. Ball and his colleagues therefore stress the importance of taking into account the effect of filtering in future interpretations of fMRI studies. This way, scientists will not run the risk of inadvertently distorting their findings from the brain scans.

Related Links:
Bernstein Center Freiburg
Carl Von Ossietzky University Oldenburg
University of Basel
Otto von Guericke University of Magdeburg