Visuo-motor adaptation in smokeless tobacco users

Neural substrates of graphomotor sequence learning: a combined FMRI and kinematic study

The goal of this study was to characterize the dynamics and functional connectivity of brain networks associated with fast (short-term) learning of handwriting using functional magnetic resonance imaging. Participants (n = 12) performed a graphomotor sequence learning task (naïve subjects learning to draw simple, 3-stroke Chinese word characters), which focused the learning process on the kinematic aspects of sequence learning instead of on the production of the line segments. Learning of the graphomotor sequence was demonstrated by a progressive improvement in movement smoothness as assessed by normalized jerk scores. Examination of the patterns of regional neural activity and functional connectivity during sequence learning demonstrated that cortical regions, which may support visuomotor mapping components of the task, were active prior to subcortical areas that may play a role in encoding and refining the novel sequences. Importantly, differences in the time course of recruitment of basal ganglia and cerebellar networks suggest distinct but integrated roles in the encoding and refining of the handwritten sequences. This implies multiple kinematic representations of graphomotor trajectories may be encoded at various spatiotemporal scales.

Reliability and sensitivity of jerk-cost measurement for evaluating irregularity of chewing jaw movements

Rate of change in movement acceleration (jerk) is a universally accepted quantity to evaluate irregularities of human limb and eye movements. This study was aimed to attest reliability of the jerk measurement of masticatory jaw movements and to identify its sensitivity to discriminate between movements performed with the presence of varied occlusal interference. Jaw movements during gum chewing were recorded with a 3D tracking device. Twelve adult subjects participated in the experiments. For five subjects, normalized jerk-costs (NJC) during jaw closing were compared between those measured on two separate occasions. For seven subjects, the NJCs during closing were compared with those measured with/without introduction of four different types of occlusal interference. The NJCs did not differ significantly between the two recording occasions. The interference at the canine tooth induced greater increase in the NJCs than that at the molar tooth. The comparison between repeated measures revealed reproducibility of the NJCs. In addition, the NJC was shown to be capable of discriminating between irregularities of the movements induced by occlusal interference at the canine and molar tooth sites. These findings suggest that the NJC is a valid indicator of masticatory jaw movement irregularity induced by disturbances of full intercuspation between upper and lower teeth.