Mechanism and echo time dependence of the fast response in fMR

The fast response (FR) is an early reduction in the amplitude of the fMR signal occurring shortly after the onset of stimulation. Owing to its potential advantages in terms of temporal and spatial resolution, it may be of considerable significance in functional experiments. A model for the mechanism of the FR was developed which accounts for the fMRS finding that the amplitude of the dip decreases with increasing echo time. Two computer simulations that confirmed the predictions of the model and showed that it is possible to select optimal echo times for the detection of the FR were performed.