Abstract: Event-related fMRI allows estimation of the hemodynamic response associated with transient brain activation evoked by various sensory, motor and cognitive events. Choosing a sequence of events that maximizes efficiency of estimating the Hemodynamic Response Function (HRF) is essential for conducting event-related brain imaging experiments. This paper presents a comparative analysis of two different paradigms of event-related fMRI using MATLAB platform. The distinction between random and periodic stimulus trial is used to distinguish between designs that are specified in terms of the occurrence that an event will occur at a series of time points (random) and those in which events always occur after a fixed interval of time or pre-specified time (periodic). These designs can be parameterized using General Linear Model (GLM) in terms of design matrix that embodies constraints and the model of HRF. This analysis shows that statistical efficiency falls off dramatically as the Inter-Stimulus Interval (ISI) gets sufficiently short, if the ISI is kept fixed for all trials. However, if the ISI is properly randomized from trial to trial, the efficiency improves with decreasing mean ISI. The results demonstrate the feasibility of using randomized experimental design for event-related fMRI thereby facilitating imaging modalities.

Keywords: Event-Related fMRI, General Linear Model, Functional Neuro-imaging, Efficiency, Hemodynamic response function.