Callosal contributions to simultaneous bimanual finger movements

Abstract

Corpus callosum (CC) is involved in the performance of bimanual motor tasks. We asked whether its functional role could be investigated by combining a motor behavioral study on bimanual movements in multiple sclerosis (MS) patients with a quantitative magnetic resonance diffusion tensor imaging (DTI) analysis of CC, which is shown to be damaged in this disease. MS patients and normal subjects were asked to perform sequences of bimanual finger opposition movements at different metronome rates; then we explored the structural integrity of CC by means of DTI. Significant differences in motor performance, mainly referred to timing accuracy, were observed between MS patients and control subjects. Bimanual motor coordination was impaired in MS patients as shown by the larger values of the interhand interval observed at all the tested metronome rates with respect to controls. Furthermore, DTI revealed a significant reduction of fractional anisotropy (FA), indicative of microstructural tissue damage, in the CC of MS patients. By correlating the mean FA values with the different motor behavior parameters, we found that the degree of damage in the anterior callosal portions mainly influences the bimanual coordination and, in particular, the movement phase preceding the finger touch. Finally, the described approach, which correlates quantitative measures of tissue damage obtained by advanced magnetic resonance imaging tools with appropriate behavioral measurements, may help the exploration of different aspects of motor performance impairment attributable to the disease.

Figure 1.

Representative fractional anisotropy map of a control subject with the subdivision of corpus callosum in five regions of interest (CC1–CC5) (A) and paths connecting callosal regions with cortical areas obtained by probabilistic tractography and displayed in axial, coronal, and sagittal plane (B).

Figure 2.

Control subjects and MS patients performing bimanual finger opposition movements at 1, 1.5, and 2 Hz: mean interhand interval onset (A) and offset (B) evaluated for the different metronome rates.

Figure 3.

Mean fractional anisotropy in the single regions of interest in the corpus callosum for control subjects and MS patients.

Figure 4.

IHI_onset averaged on the three metronome rates as function of mean FA in CC1 (A), CC2 (B), CC3 (C), CC4 (D), and CC5 (E), with the corresponding linear fitting (solid line). Pearson's correlation coefficient r and p value are reported; as shown, IHI_onset correlated with FA only in CC1 and CC2.