Writing and drawing tilts after right hemisphere stroke are signs of a wrong verticality representation

Many signs of spatial dysgraphia and drawing errors after right hemispheric stroke (RHS) have been attributed to spatial neglect or impaired sensory feedback. Counterclockwise (contralesional) tilts of graphomotor productions remained to be explained.

To test whether graphomotor tilts stem from a tilted representation of verticality transposed to the top/bottom axis of the sheet of paper, using data from the DOBRAS cohort.

Handwriting and drawing orientations were measured from the writing of 3 lines and the drawing of the Gainotti Figure (house roof lines). Verticality perception was measured with the visual (VV) and postural (PV) verticals. Severity of extra-body (EBN) and body (BN) neglect were each quantified with composite scores (battery of 8 tests).

We analyzed data from 133 individuals: 64 healthy individuals (median [Q1; Q3] age 63 [59; 71] years) and 69 in the subacute phase after RHS (median age 68 [62; 73] years). With respect to normal cut-offs (writing -5.4°; drawing -8.1°), 26/69 (38 %) individuals with RHS showed at least one graphomotor tilt (median [IQR] writing tilt:6.8° [-9.7; -1.7]; drawing tilt:10.9° [-17.6; -6.4]). Compared to individuals without graphomotor tilts, those with both writing and drawing tilts showed greater contralesional tilts in verticality perception (VV:1.4° [-4; 0.6] vs -7.9° [-11.5; - 7.5]; PV:1° [-2.4; 0.2] vs -8° [-9; -5.4], P-values ≤0.001) and more severe spatial neglect (EBN: 4.2 [1.8; 9.3] vs 16.6 [10.2; 20.4]; BN: 22.7 [17; 28.2] vs 37.8 [35.9; 39.7], P-values ≤0.001). Composite graphomotor z-scores for writing and drawing correlated with verticality estimates (VV+PV, r_s =0.46, P < 10^-4) and spatial neglect scores (EBN+BN, r_s = -0.36, P < 0.01).

Contralesional tilts of writing and drawing after RHS are primarily related to a tilted representation of verticality and secondarily to spatial neglect. They are easy to detect and could be considered a first step to perform early, before conventional tests of verticality perception.

ClinicalTrials.gov: NCT03203109.