Multi-frequency reference function to reduce noise in functional MRI

In functional MRI series of images of the brain are acquired, constructing pixels´ time courses. The common practice is to present stimuli over a block of images, a control condition over another equal block, and to repeat these two blocks for several times. This stimuli presentation, which is the basis for constructing a reference function, generally contains a single frequency. Under these conditions, noise, as well as aliases due to physiological fluctuations, that contain this single frequency can overlap with the signal, this results in detecting artifacts (false brain activity). The authors have designed a stimulus presentation containing a combination of frequencies such that the overlap with noise and any physiological fluctuations would be minimized. The results of the authors´ studies suggest that the multi-frequency stimuli presentation approach is effective in reducing the detection of noise and artifact