Alterations in resting functional connectivity due to recent motor task

Abstract

The impact of recent experiences of task performance on resting functional connectivity MRI (fcMRI) has important implications for the design of many neuroimaging studies, because, if an effect is present, the fcMRI scan then must be performed before any evoked fMRI or after a time gap to allow it to dissipate. The present study aims to determine the effect of simple button presses, which are used in many cognitive fMRI tasks as a response recording method, on later acquired fcMRI data. Human volunteers were subject to a 23-minute button press motor task. Their resting-state brain activity before and after the task was assessed with fcMRI. It was found that, compared to the pre-task resting period, the post-task resting fcMRI revealed a significantly higher (p=0.002, N=24) cross correlation coefficient (CC) between left and right motor cortices. These changes were not present in sham control studies that matched the paradigm timing but had no actual task. The amplitude of fcMRI signal fluctuation (AF) also demonstrated an increase in the post-task period compared to pre-task. These changes were observed using both the right-hand-only task and the two-hand task. Study of the recovery time course of these effects revealed that the CC changes lasted for about 5 min while the AF change lasted for at least 15 min. Finally, voxelwise analysis revealed that the pre/post-task differences were also observed in several other brain regions, including the auditory cortex, visual areas, and the thalamus. Our data suggest that the recent performance of the simple button press task can result in elevated fcMRI CC and AF in relevant brain networks and that fcMRI scan should be performed either before evoked fMRI or after a sufficient time gap following fMRI.

Figure 1

Experimental design. (A) The experiment started with a pre-task fcMRI, followed by a motor task in which the subject attended to a white crosshair and pressed a button when the color of the crosshair changed to grey for 1000ms. The session concluded with a post-task fcMRI. (B) In the one-hand motor experiment (N=24), the post-task fcMRI was five minutes in duration. (C) In the two-hand motor experiment (N=24), the post-task fcMRI was 15 minutes in duration.

Figure 2

Correlation coefficient (CC) between left and right motor cortex before and after the one-hand motor task (N=24). (A) CC values calculated using fcMRI time series that were bandpass-filtered to 0.01–0.1 Hz. (B) CC values calculated using time series further filtered to 0.01–0.05 Hz and 0.05–0.1 Hz, respectively. Error bar = standard error of mean across subjects.

Figure 3

FcMRI amplitude of fluctuation (AF) in the bilateral motor cortices before and after the one-hand motor task (N=24). (A) Left Motor Cortex (LMC). (B) Right Motor Cortex (RMC). Error bar = standard error of mean across subjects.

Figure 4

Results of two-hand motor experiment (N=24) in motor cortex (top panels) and parietal cortex (bottom panels). (A) CC between LMC and RMC during the pre-task period and during three segments of the post-task periods. (B) AF in LMC during the pre-task period and during three segments of the post-task periods. (C) AF in RMC during the pre-task period and during three segments of the post-task periods. (D) CC between LPC and RPC during the pre-task period and during three segments of the post-task periods. (E) AF in LPC during the pre-task period and during three segments of the post-task periods. (F) AF in RPC during the pre-task period and during three segments of the post-task periods. CC values were based on 0.05–0.1 Hz data. p values of less than 0.05 are marked in the plots. Error bar = standard error of mean across subjects.

Figure 5

Voxel based map illustrating regions with significant increases in post-task resting CC with respect to the averaged motor time course. Statistical threshold: p<0.05 FDR corrected, minimum cluster size 1350 mm³. Only voxels delineated in both one-hand and two-hand experiments are shown. The label below each slice denotes its location relative to anterior commissure-posterior commissure (AC-PC) line.

Figure 6

Voxel based map illustrating regions with significant increases in post-task resting AF. Statistical threshold: p<0.05 FDR corrected, minimum cluster size 1350 mm³. Only voxels delineated in both one-hand and two-hand experiments are shown. The label below each slice denotes its location relative to anterior commissure-posterior commissure (AC-PC) line.