Cluster sizes in interleaved silent steady state (ISSS) imaging

The effect of increasing the number of scans in the "cluster" of an interleaved silent steady state (ISSS) fMRI imaging scheme from 1 to 2, and then to 3 was examined by a fixed-effects analysis of an auditory short-term memory task with four subjects. Compared to a cluster size of 1, a cluster of 2 scans improved sensitivity at detecting brain activity and statistical power, while a cluster of 3 scans further improved statistical power but seemed not to improve sensitivity beyond that achieved with a cluster of 2 scans. The findings reveal that cluster size is a vital parameter for an ISSS imaging scheme.