Functional connectivity of cortical motor areas in the resting state in Parkinson's disease

Abstract

Parkinson's disease (PD) patients have difficulty in initiating movements. Previous studies have suggested that the abnormal brain activity may happen not only during performance of self-initiated movements but also in the before movement (baseline or resting) state. In the current study, we investigated the functional connectivity of brain networks in the resting state in PD. We chose the rostral supplementary motor area (pre-SMA) and bilateral primary motor cortex (M1) as "seed" regions, because the pre-SMA is important in motor preparation, whereas the M1 is critical in motor execution. FMRIs were acquired in 18 patients and 18 matched controls. We found that in the resting state, the pattern of connectivity with both the pre-SMA or the M1 was changed in PD. Connectivity with the pre-SMA in patients with PD compared to normal subjects was increased connectivity to the right M1 and decreased to the left putamen, right insula, right premotor cortex, and left inferior parietal lobule. We only found stronger connectivity in the M1 with its own local region in patients with PD compared to controls. Our findings demonstrate that the interactions of brain networks are abnormal in PD in the resting state. There are more connectivity changes of networks related to motor preparation and initiation than to networks of motor execution in PD. We postulate that these disrupted connections indicate a lack of readiness for movement and may be partly responsible for difficulty in initiating movements in PD.

Figure 1

Brain regions show significant positive (hot color) and negative (cold color) functional connectivity in the rostral supplementary motor area (pre‐SMA) in the resting state in normal control subjects (A), and Parkinson's disease (PD) patients (B). Hot and cold colors indicate significant positive and negative connectivity with the pre‐SMA, respectively. The results are shown across each group (one‐sample t test, P < 0.05, FWE corrected). C: Differences of functional connectivity with the pre‐SMA between patients with PD and normal subjects in the resting state (two‐sample t test; P < 0.05, FWE corrected). Hot and cold colors indicate increases and decreases of connectivity with the pre‐SMA in patients with PD compared to normal subjects, respectively. T score bars are shown on the right. Green spot: the position of the region of interest (ROI). L, left; R, right.

Figure 2

Brain regions show significant positive (hot color) and negative (cold color) connectivity with the left primary motor cortex (M1) in the resting state in normal control subjects (A) and patients with PD (B). The results are shown across each group (one‐sample t test, P < 0.05, FWE corrected). C: The increase of functional connectivity with the left M1 in patients with PD compared to normal subjects (two‐sample t test; P < 0.05, FWE corrected). T score bars are shown on the right. Green spot: the position of the ROI. L, left; R, right.

Figure 3

Brain regions show significant positive (hot color) and negative (cold color) connectivity with the right M1 in the resting state in normal control subjects (A) and patients with PD (B). The results are shown across each group (one‐sample t test, P < 0.05, FWE corrected). T score bars are shown on the right. Green spot: the position of the ROI. L, left; R, right.

Figure 4

The results of correlation analysis between connectivity t score (y‐axis) and Unified Parkinson's Disease Rating Scale (UPDRS) motor score (x‐axis) in the right M1 (triangle), and left putamen (square) in PD patients. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]