Both parietal lobes are involved in drawing: a functional MRI study and implications for constructional apraxia.

In clinical studies, many researchers have reported that drawing can be disturbed by left or right unilateral parietal lobe damage (constructional apraxia). There seem to be two possible predictions about the cerebral laterality for drawing. The first is that drawing requires both parietal lobes, therefore, a lesion to either side can disrupt drawing. The second is that individuals can differ in laterality: some have only right or left activations, and some have bilateral. To test these predictions, we investigated with functional magnetic resonance imaging (fMRI) the cerebral activation whilst 17 right-handed healthy subjects performed a drawing task. The experiment consisted of two conditions: (1). naming an object in a presented picture and drawing it by using right index finger (DRAWING & NAMING); (2). naming an object in a presented picture (NAMING). We considered the brain regions that had greater activity in the DRAWING&NAMING condition than in the NAMING condition were the neural substrates of drawing. Individual analysis revealed that all subjects showed parietal activation bilaterally. We interpret that the results support the first prediction that both parietal lobes are required for drawing. By calculating the laterality indices of the individual parietal activations, it was found that there were more left dominant subjects than right dominant subjects (left, 12; right, 5). The results are inconsistent with previous studies on the incidence of constructional apraxia. In addition, we found activation in regions that were not previously reported in the literature of constructional apraxia: they are the ventral premotor area and posterior part of inferior temporal sulcus.