Brain correlates of fast and slow handwriting in humans: a PET-performancecorrelation analysis

The present study examined the cerebral control of velocity during handwrit ing. We employed (H2O)-O-15 positron emission tomography (PET) to measure t he regional cerebral blood flow (rCBF) in 10 healthy subjects. Participants were required to write the German verb 'bellen' ('to bark') either at thei r normal speed (i.e. fast open-loop handwriting) or to write at approximate ly half of their normal speed without visual feedback. The second task requ ired a continuous modification of the motor output according to the kinaest hetic feedback from the hand (i.e. slow closed-loop handwriting). Pencil mo vements were recorded during PET scanning and analysed off-line using a str oke-based analysing program. The mean number of inversions in velocity (NIV ) per stroke was used to quantify the mode of motor control during each PET scan. A NIV of 1 indicates fast open-loop processing, whereas an increase in NIV reflects a shift towards slow closed-loop processing of handwriting. Foci in the left primary sensorimotor cortex, the right lateral premotor c ortex, the left anterior parietal cortex, the left anterior putamen, the le ft rostral supplementary motor area and the right precuneus showed a graded increase in functional activation with the mean NIV per stroke, suggesting that this set of brain regions is particularly involved in the processing of slow closed-loop writing movements. No area showed a negative relationsh ip between rCBF and the mean NIV per stroke, suggesting that fast open-loop handwriting is achieved by an optimized cooperation of the manual sensorim otor network rather than by a selective activation of a distinct network co mponent.