Objective: This study aimed to investigate the cortical activity in focal right upper limb dystonia patients using functional near infrared spectroscopy (fNIRS) during writing.

Background: Techniques such as fMRI and PET impose important physical constraints. Latter advances in functional near infrared spectroscopy offer a new possibility for investigating cortical areas and the neural correlates of complex motor behaviors non‐invasively under naturalistic experimentation.

Methods: Twenty‐one patients with right upper limb idiopathic dystonia (6 with task‐specific dystonia) and twenty‐one healthy volunteers matched for age and years of education were submitted to a simple right‐hand writing task paradigm that consisted of 4 epochs of alternating writing/resting blocks. To test a priori hypotheses that brain activation to simple handwriting in cortical sensorimotor and supplementary motor regions would be less specific in patients than in controls, we defined right and left primary motor (M1) and somatosensory (S1) and supplementary motor area (SMA) ROIs. Differences between groups on changes in both deoxy and oxy‐Hemoglobin (HbO2) and for each ROI were then compared using Mann Whitney tests.

Results: Channels exhibiting increased HbO2 for the writing task compared to the resting condition in the patient and control groups are described in Fig. 1. In controls, a lateralization predominantly to the left side was observed in most of the central channels covering the primary motor and somatosensory cortices. A more bilateral pattern of activation was observed in patients. However, in a direct channel‐wise comparison between groups, no significant differences were observed in any channel. In the ROI‐based group analysis, between‐group differences were observed in two of the five ROIs: left M1 (p = 0.022) and S1 (p = 0.022) exhibited increased HbO2 in patients in relation to controls.

Conclusions: Overactivity findings on M1 as S1 are in agreement with previous studies of the writing task in non‐ecological conditions1,2,3, reinforcing the role of these areas in dystonia. As symptoms in dystonia are very specific to the task, we believe the pattern of brain activation is as much as specific, therefore the importance of an experimental set that mimics real life conditions. To our knowledge, this is the first study to measure cortical activity during ecological writing (subjects sited in anatomical position, in less noisy environment, using traditional paper and pen) in focal upper limb dystonia patients, outlining the potential of fNIRS for the study of the movement disorders in unconstrained environments.