Feasibility Of Measuring Functional Connectivity In Task FMRI Block Design

In recent years,researchers have begun to study the changes of functional connectivity(FC)between different conditions in cognitive tasks.However,the duration of a single condition is generally short in task-state functional magnetic resonance imaging(fMRI)studies.And,FC is derived from low-frequency(generally 0.01-0.1 Hz)fluctuations(LFFs)and needs several minutes to achieve the stable state.It is possible that FC has not yet reached a stable state during the short duration.Although some studies have shown that concatenating task fMRI data from different fragments of the same condition to calculate FC can obtain similar results of continuous data,these studies still have some limitations.Therefore,this paper demonstrates the feasibility of FC measurement in task fMRI through systematic study and comparison within the block design.In particular,the following two studies are included in this paper:Study 1: The Feasibility and reason of measuring task functional connectivity in short block design.The comparisons of FC results between concatenated and continuous data under the eyes open(EO),eyes closed(EC)and EO/EC differences were studied respectively.The results showed that there was significant difference in FC results between concatenated and continuous data both in EC state and EO/EC differences,although the FC results between concatenated and continuous data showed very similar in EO state.Through analyzing the slow stability of FC under EO and EC conditions respectively,we found that the slow stability of FC between networks in EC state showed slower than EO state,which was probably the main reason for the different FC results of concatenated and continuous data.Study 2: The Feasibility of measuring functional connectivity in long block design.On the basis of study 1,we extend the block length of single condition to 100 seconds.The results showed that the FC results between concatenated and continuous data were similar both in EO and EC state,and there was also no significant difference between concatenated and continuous data in EO/EC differences.According to these results,we concluded that the feasibility of measuring functional connectivity in block design is closely related to the block length,but independent of the design type(block design or continuous design).Block length of a single condition should be no less than 100 seconds for FC studies in task fMRI block design.This conclusion can provide a reference for the related studies on functional connectivity analysis within the block design data.