Table II.

Stereotactic coordinates of the local maxima showing differential cerebral activity during motor imagery of writing across groups

Contrast	Functional mask (inclusive)	Anatomical label	Functional label	Cluster size	Hemi‐ sphere	Z‐value	P‐value (corrected for search volume)	x	y	z
(writing2,4,6 > sharpening2,4,6)patients	Biomechanical difficulty and Movement repetitions	Superior frontal gyrus	PMd	59	L	2.89	0.048	−24	−6	66
>
(writing2,4,6 > sharpening2,4,6)controls
(writing0 > sharpening0)patients	Biomechanical difficulty	Superior frontal gyrus	PMd	71	L	3.14	0.047	−28	2	62
>		Inferior frontal gyrus	PMv	6	L	2.13	0.066	−52	8	34
(writing0 > sharpening0)controls

Brain areas with a significant Group × Task interaction, i.e., a larger increase in activity for motor imagery of writing versus motor imagery of sharpening in patients than in controls. The first row describes effects obtained when considering trials involving imagery of 2, 4, or 6 repetitions of either writing or sharpening movements (as indicated by the 2, 4, 6 superscript). The second row describe effects obtained when considering trials involving imagery of grasping movements only (as indicated by the 0 superscript), but occurring in the context of periods involving writing or sharpening movements. In order to isolate cerebral responses sensitive to motor processes, we searched for GROUP × TASK interactions occurring within those region showing increased activity for imagined movements of larger biomechanical difficulty and duration [effects of angle (difficult > easy) and movement repetitions (linear increase as a function of number of movement repetitions), see Methods]. Results are based on the ROI coordinates centered on cerebral areas previously shown to be involved in writing in healthy controls, using spherical volumes (radius: 6 mm) centered at these coordinates: left dorsal premotor cortex, PMd [−28 −1 65] and left ventral premotor cortex, PMv [−53 11 29] (Longcamp 2003) using small volume correction on the selected VOIs (FDR < 0.05). Stereotactic coordinates are reported in Montreal Neurological Institute (MNI) space. Details on the anatomical and functional labelling can be found in the Methods and Results sections. L, left; PMd, dorsal premotor cortex; PMv, ventral premotor cortex; R, right.