Temporally and Spatially Constrained ICA of fMRI Data Analysis

<div><p>Constrained independent component analysis (CICA) is capable of eliminating the order ambiguity that is found in the standard ICA and extracting the desired independent components by incorporating prior information into the ICA contrast function. However, the current CICA method produces constraints that are based on only one type of prior information (temporal/spatial), which may increase the dependency of CICA on the accuracy of the prior information. To improve the robustness of CICA and to reduce the impact of the accuracy of prior information on CICA, we proposed a temporally and spatially constrained ICA (TSCICA) method that incorporated two types of prior information, both temporal and spatial, as constraints in the ICA. The proposed approach was tested using simulated fMRI data and was applied to a real fMRI experiment using 13 subjects who performed a movement task. Additionally, the performance of TSCICA was compared with the ICA method, the temporally CICA (TCICA) method and the spatially CICA (SCICA) method. The results from the simulation and from the real fMRI data demonstrated that TSCICA outperformed TCICA, SCICA and ICA in terms of robustness to noise. Moreover, the TSCICA method displayed better robustness to prior temporal/spatial information than the TCICA/SCICA method.</p></div

Results of the nonparametric Wilcoxon tests for paired samples in errorrate condition.

<p>Note:asterisk represents P<0.01.</p

Results of the nonparametric Wilcoxon tests for paired samples in CNR condition.

<p>Note:asterisk represents P<0.01.</p

The spatial activation that was estimated by all of the methods.

<p>(A) The activated regions that were detected by GLM. (B) The activated regions of the target component that were estimated by TSCICA using the first spatial reference. (C) The activated regions of the target component that were estimated by SCICA using the first spatial reference. (D) The activated regions of the target component that were estimated by TCICA. (E) The activated regions of the target component that were estimated by TSCICA using the second spatial reference. (F) The activated regions of the target component that were estimated by SCICA using the second spatial reference. (G) The activated regions of the target component that were estimated by FastICA.</p

A comparison of TSCICA, TCICA, SCICA and FastICA.

<p>(A) The spatial correlation coefficient of TSCICA1, TCICA, SCICA1 and FastICA for an individual subject. (B) The spatial correlation coefficient of TSCICA2, TCICA, SCICA2 and FastICA for an individual subject. (C) The mean spatial correlation coefficients of TSCICA1, TCICA, SCICA1 and FastICA. (D) The mean spatial correlation coefficients of TSCICA2, TCICA, SCICA2 and FastICA. The error bar represents the standard deviation. TSCICA1/SCICA1 represents TSCICA/SCICA using the first spatial reference. TSCICA2/SCICA2 represents TSCICA/SCICA using the second spatial reference. The error bar represents the standard deviation. Note: asterisk represents P<0.01.</p

ROI localizer and analysis.

<p>A. Group activation map of the ROI localizer run (<i>p</i><0.001, cluster > 20). The cross refers to the maximum activation in the ROI of the left DLPFC (BA9) in MNI coordinate (-45, 29, 34). The left is on the reader’s right. B. The percent signal change of the ROI in the experimental group and the control group during eight feedback runs (Run 1st_A to 2nd_D respectively represent the feedback run A to D in the first and second rtfMRI training session). Error bar means the standard error. *: significant difference in the comparison of run 2nd_D with run 1st_A (<i>p</i><0.05).</p

Outline of the whole experimental procedure.

<p>Each rtfMRI training session comprised six runs. T1 run was a 10-minute T1-weighted scan. The ROI localizer run comprised four digital 0-back blocks alternated with three digital 3-back blocks; each n-back block lasted for 34.0 s, with 4.0 s for the cue and 30.0 s for the tasks. The feedback run lasted for 6.5 minutes and included four up-regulation blocks (60.0 s each) separated by five baseline blocks (30.0 s each), with the beginning of a baseline block.</p

The log and penalty terms versus candidate order k and the bound BD versus the temporal data size.

<p>A) The variation of the negative log-likelihood with k at different noise levels. B) The penalty terms of AIC, KIC and MDL versus k. C) The variation of the negative log-likelihood with candidate order k at different temporal data size with SD = 1. D) The variation of the bound <i>BD</i> versus the temporal data size.</p

Pre-defined regions and the simulated fMRI response.

<p>(A) The predefined ROI for the simulated datasets including one task-related component. (B) One spatial reference with a 10% overlap rate applied to the simulated datasets including one task-related component. (C) The predefined ROI1 and ROI2 of the simulated datasets including two task-related components. (D) The simulated fMRI response added to the two ROIs. Solid line corresponds to the time course added to ROI1 and dotted line corresponds to the time course that was added to ROI2. (E) The spatial reference that was applied to the simulated datasets, including two task-related components. (F) The temporal reference that was applied to the simulated datasets, including two task-related components.</p

Results of the robustness to spatial overlap rate, temporal accuracy and spatial error rate.

<p>(A) The variation of the mean ROC area with overlap rates for TSCICA, TCICA and SCICA. (B) The variation of the mean ROC area with temporal reference for TSCICA, TCICA and SCICA. CC represents the correlation coefficient between the temporal reference and the true time course. (C) The variation of the mean ROC area with error rate in the case of a high temporal accuracy (CC = 0.8) for TSCICA, TCICA and SCICA. (D) The variation of the mean ROC area with error rate in the case of a low temporal correlation(CC = 0.6) for TSCICA, TCICA and SCICA. CC represents the correlation coefficient between the temporal reference and the true time course.</p