Corpus Callosum Volume and Interhemispheric Transfer in Multiple Sclerosis

[Alexithymia in Multiple Sclerosis - Narrative Review]

Alexithymia is a multidimensional construct of personality implicating difficulties in identifying and describing another's feelings, and externally oriented thinking. It is broadly reported in psychiatric patients but has gained little attention regarding its occurrence and pathophysiology in multiple sclerosis (MS). This narrative review aims to address prevalence, etiology, neurobiological, and clinical findings of alexithymia. The prevalence of alexithymia in MS ranges from 10 to 53%. There seems to be an association with anxiety, depression, fatigue, and some aspects of social cognition, while the relationship with clinical and classical cognitive variables was rarely evaluated. Only a few studies referred to its pathophysiology assuming an aberrant interhemispheric transfer or regional cerebral abnormalities. The prevalence of alexithymia in MS and the potential negative impact on quality of life and interpersonal communication could severely impact clinical MS management and a screnning for these factors should be mandatory. Thus, further evaluation is needed concerning its relationship with clinical, emotional, and cognitive confounders. Large-scale studies employing neuroimaging techniques are needed for a better understanding of the neural underpinnings of this MS feature.

Interactions between brain structure and behavior: the corpus callosum and bimanual coordination

Bimanual coordination skills are required for countless everyday activities, such as typing, preparing food, and driving. The corpus callosum (CC) is the major collection of white matter bundles connecting both hemispheres that enables the coordination between the two sides of the body. Principal evidence for this brain-behavior relationship in humans was first provided by research on callosotomy patients, showing that sectioning (parts of) the CC affected interactions between both hands directly. Later, new noninvasive in vivo imaging techniques, such as diffusion tensor imaging, have energized the study of the link between microstructural properties of the CC and bimanual performance in normal volunteers. Here we discuss the principal factors (such as age, pathology and training) that mediate the relationship between specific bimanual functions and distinct anatomical CC subdivisions. More specifically, the question is whether different bimanual task characteristics can be mapped onto functionally distinct CC subregions. We review the current status of this mapping endeavor, and propose future perspectives to inspire research on this unique link between brain structure and behavior.

Interhemispheric cooperation in global-local visual processing in pediatric multiple sclerosis

Impairments in visuospatial abilities are commonly reported in children and adolescents with multiple sclerosis (MS). Corpus callosum (CC) pathology occurs in patients with MS and may contribute to impairment in visuospatial perception, particularly when interhemispheric information transfer is required. This study used a global-local hierarchical letter paradigm to examine the relationship between interhemispheric information transfer and white matter integrity in the CC assessed using diffusion tensor imaging. Thirteen cognitively preserved pediatric-onset MS patients and 15 age-matched healthy controls were asked to determine whether a target letter E appeared at the attended level of the stimulus. As expected, both groups processed global and local information more slowly under divided than selective attention conditions. The MS group performed similarly to the control group with respect to reaction time and accuracy on selective and divided attention conditions, with one exception. Specifically, the presence of a global target when attending to a local target caused greater response conflict in the MS group than in controls (p = .01). Pooling both the patient and control data, greater response conflict was associated with reduced white matter integrity as indicated by lower fractional anisotropy in the anterior body of the CC (r = -.33, p < .05). Results suggest that reduced white matter integrity in anterior regions of the CC may lead to less efficient inhibition of task-irrelevant global information in the hierarchal processing of visual information.

Functional homotopic changes in multiple sclerosis with resting-state functional MR imaging

BACKGROUND AND PURPOSE

CC is extensively involved in MS with interhemispheric dysfunction. The purpose of this study was to determine whether interhemispheric correlation is altered in MS by use of a recently developed RS-fMRI homotopy technique and whether these homotopic changes correlate with CC pathology.

MATERIALS AND METHODS

Twenty-four patients with relapsing-remitting MS and 24 age-matched healthy volunteers were studied with RS-fMRI and DTI acquired at 3T. The Pearson correlation of each pair of symmetric interhemispheric voxels of RS-fMRI time-series data was performed to compute VMHC, and z-transformed for subsequent group-level analysis. In addition, 5 CC segments in the midsagittal area and DTI-derived FA were measured to quantify interhemispheric microstructural changes and correlate with global and regional VMHC in MS.

RESULTS

Relative to control participants, patients with MS exhibited an abnormal homotopic pattern with decreased VMHC in the primary visual, somatosensory, and motor cortices and increased VMHC in several regions associated with sensory processing and motor control including the insula, thalamus, pallidum, and cerebellum. The global VMHC correlates moderately with the average FA of the entire CC for all participants in both groups (r = 0.3; P = .03).

CONCLUSIONS

Our data provide preliminary evidence of the potential usefulness of VMHC analyses for the detection of abnormalities of interhemispheric coordination in MS. We demonstrated that the whole-brain homotopic RS-fMRI pattern was altered in patients with MS, which was partially associated with the underlying structural degenerative changes of CC measured with FA.