Structural integrity of callosal midbody influences intermanual transfer in a motor reaction‐time task

Abstract

Training one hand on a motor task results in performance improvements in the other hand, also when stimuli are randomly presented (nonspecific transfer). Corpus callosum (CC) is the main structure involved in interhemispheric information transfer; CC pathology occurs in patients with multiple sclerosis (PwMS) and is related to altered performance of tasks requiring interhemispheric transfer of sensorimotor information. To investigate the role of CC in nonspecific transfer during a pure motor reaction-time task, we combined motor behavior with diffusion tensor imaging analysis in PwMS. Twenty-two PwMS and 10 controls, all right-handed, were asked to respond to random stimuli with appropriate finger opposition movements with the right (learning) and then the left (transfer) hand. PwMS were able to improve motor performance reducing response times with practice with a trend similar to controls and preserved the ability to transfer the acquired motor information from the learning to the transfer hand. A higher variability in the transfer process, indicated by a significantly larger standard deviation of mean nonspecific transfer, was found in the PwMS group with respect to the control group, suggesting the presence of subtle impairments in interhemispheric communication in some patients. Then, we correlated the amount of nonspecific transfer with mean fractional anisotropy (FA) values, indicative of microstructural damage, obtained in five CC subregions identified on PwMS's FA maps. A significant correlation was found only in the subregion including posterior midbody (Pearson's r = 0.74, P = 0.003), which thus seems to be essential for the interhemispheric transfer of information related to pure sensorimotor tasks.

Impairment in explicit visuomotor sequence learning is related to loss of microstructural integrity of the corpus callosum in multiple sclerosis patients with minimal disability

“…Then, sequence-specific learning (SL) was calculated as the difference in RT between the first and the last block S, subtracting the component due to nonspecific learning (SL = (S1 − S10) − (R2− R4)) (Bonzano et al, 2011). We also calculated the amount of "early" sequence-specific learning at S5 as SL-5=(S1 −S5) −(R2 −R3).…”

“…Further, to investigate the changes in motor performance we defined "nonspecific learning" (NL), indicating right-hand improvement across the random blocks, as the difference in RT between the blocks R2 and R4 (Bonzano et al, 2011;Perez et al, 2007b).…”

“…Further, to investigate a possible functional specificity of callosal subregions, five ROIs were delineated along the CC on the midsagittal FA map for each patient (Bonzano et al, 2008(Bonzano et al, , 2011 following the geometrical scheme proposed by de Lacoste (de Lacoste et al, 1985). Particularly, one ROI (CC1) included the genu and the rostrum, another ROI (CC5) covered the splenium, and three ROIs (CC2, CC3, and CC4) were identified in the remaining portion of the CC, mainly represented by the CC body, subdividing the anterior-toposterior distance into three parts.…”

“…Moreover, a study combining bifocal transcranial magnetic stimulation and DTI tractography in healthy subjects has demonstrated that different fiber bundles of the left SLF connect parietal areas to motor areas involved in the planning of grasping actions . Furthermore, following an experimental approach based on the combination of DTI data with quantitative analyses of finger opposition movements in PwMS, it was previously found that anterior callosal portions are essential for bimanual coordination (Bonzano et al, 2008), while the inter-manual transfer of motor-skill learning during a pure motor reaction-time task (nonspecific transfer) was correlated with the reduced white matter integrity in a specific callosal subregion, including midbody (Bonzano et al, 2011).…”

“…In the present work, we investigated the functional role of intraand inter-hemispheric white matter pathways in explicit sequence learning by correlating FA values in the left and right SLFs and in the CC with the analysis of visuomotor sequence learning in a group of PwMS with minimal disability, which constitutes a homogenous population of patients showing only subtle motor impairments at both neurological examination and behavioral measures of fine finger movements (Bonzano et al, 2011). A modified version of the SRT task based on finger opposition movements was adopted: a group of PwMS and a group of control subjects wore a sensor-engineered glove on their right hand (Bove et al, 2007) and were asked to respond as fast and accurately as possible to a series of visual cues presented on the fingertips of a pictured right hand, by tapping the appropriate finger with the thumb.…”