Interaction between ICVF and bimanual performance. Clusters with a lower (blue to light blue colour) or higher (red to yellow colour) slope in Parkinson’s disease patients compared with HC in the association of participants’ ICVF values and error rates as revealed by the whole-brain analysis. P-values were corrected for multiple comparisons using a permutation-based approach. Results are displayed as the negative decadic logarithm of the P-value (P = 10^-x).