Functional correlates of callosal atrophy in relapsing-remitting multiple sclerosis patients. A preliminary MRI study

Corpus callosum damage to account for cognitive, affective, and social-cognitive dysfunctions in multiple sclerosis: A model of callosal disconnection syndrome?

The corpus callosum (CC) is the major commissure interconnecting the two hemispheres and is particularly affected in multiple sclerosis (MS). In the present review, we aimed to investigate the role played by callosal damages in the pathogenesis of MS-related dysfunctions and examine whether a model of callosal disconnection syndrome is a valid model for MS. For this purpose, we will first review structural and functional evidence of callosal pathology in MS. Second, we will account for the potential role of CC abnormalities in MS-related dysfunctions. Finally, we will report data concurring with a "multiple disconnection hypothesis" that has been proposed to explain those dysfunctions, and we will examine evidence pointing toward MS as a "callosal disconnection syndrome." We will end by discussing the contribution of this interpretation to the understanding of MS and MS-related deficits.

Corpus callosum atrophy as a marker of clinically meaningful cognitive decline in secondary progressive multiple sclerosis. Impact on employment status

Cognitive impairment in Multiple Sclerosis (MS) is more frequent and pronounced in secondary progressive MS (SPMS). Cognitive decline is an important predictor of employment status in patients with MS. Magnetic Resonance Imaging (MRI) markers have been used to associate tissue damage with cognitive dysfunction. The aim of the study was to designate the MRI marker that predicts cognitive decline in SPMS and explore its effect on employment status. 30 SPMS patients and 30 healthy participants underwent neuropsychological assessment using the Trail Making Test (TMT) parts A and B, semantic and phonological verbal fluency task and a computerized cognitive screening battery (Central Nervous System Vital Signs). Employment status was obtained as a quality of life measure. Brain MRI was performed in all participants. We measured total lesion volume, third ventricle width, thalamic and corpus callosum atrophy. The frequency of cognitive decline for our SPMS patients was 80%. SPMS patients differed significantly from controls in all neuropsychological measures. Corpus callosum area was correlated with cognitive flexibility, processing speed, composite memory, executive functions, psychomotor speed, reaction time and phonological verbal fluency task. Processing speed and composite memory were the most sensitive markers for predicting employment status. Corpus callosum area was the most sensitive MRI marker for memory and processing speed. Corpus callosum atrophy predicts a clinically meaningful cognitive decline, affecting employment status in our SPMS patients.

The association between retinal nerve fibre layer thickness and corpus callosum index in different clinical subtypes of multiple sclerosis

The objective of this paper is to evaluate the association between physical disability in multiple sclerosis (MS) patients, the thickness of the retinal nerve fibre layer (RNFL) and corpus callosum volumes, as expressed by the corpus callosum index (CCI). This study was based on a cohort of 212 MS patients and 52 healthy control subjects, who were age and gender matched. The MS patients included 144 women and 177 relapsing-remitting MS (RRMS) patients. Peripapillary and volumetric optical coherence tomography (OCT) scans of the macula were performed using spectral-domain OCT technology. All magnetic resonance imaging (MRI) scans were performed using 1.5-T systems. CCI and RNFL were lower in MS than healthy control subjects (0.341 versus 0.386, p < 0.01 and 92.1 versus 105.0, p < 0.01). In addition, CCI correlated with RNFL (r = 0.464, p < 0.01). This was also true for the subgroup of patients with no history of optic neuritis (ON). There is a correlation between the thickness of the RNFL and CCI values in MS patients with no history of ON, which suggests that OCT might be a suitable marker for neurodegeneration in MS clinical trials.

MRI/MRS of corpus callosum in patients with clinically isolated syndrome suggestive of multiple sclerosis

A trophy of corpus callosum (C C) related to axonal loss has previously been observed in patients at the early stage of clinically definite multiple sclerosis (CDMS). Atrophy increases with the progression of the disease. Nevertheless, no data concerning the onset of atrophy of C C are currently available. The purpose of this study is to determine if damage in callosal tissue was present at the earliest stage of MS, in a subgroup of patients presenting with a clinically isolated syndrome suggestive of MS (C ISSMS), fulfilling the dissemination in space criteria according to McDonald. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) techniques were applied to measure C C volume, magnetization transfer ratio (MTR), mean diffusivity (MD), N-acetyl aspartate/choline-containing compounds (NAA/C ho) ratio, N-acetyl aspartate/total creatine (NA A/C r) ratio and C ho/C r ratio inside the C C of 46 C ISSMS patients and 24 sexand age-matched controls. No atrophy of C C was observed in the C ISSMS group. C C of patients was character ized by decreased MTR and increased MD. No change in the NA A/C r ratio was observed while the NA A/C ho ratio decreased and C ho/C r ratio increased in the splenium and the central anterio r part of C C. These abnormalities were present in patients with, but also without, macroscopic lesions inside the C C. O ur results indicate that diffuse structural and metabolic changes, which may be interpreted as representing predominantly myelin patho logy, occur in the C C at the earliest stage of MS before any atrophy is detected.

Corpus callosum atrophy is strongly associated with cognitive impairment in multiple sclerosis: Results of a 17-year longitudinal study

Background:

Cognitive impairment is common in multiple sclerosis (MS) and may be subtle. The corpus callosum is essential for connectivity-demanding cognitive tasks and is significantly affected in MS, therefore it may serve as a marker for cognitive function.

Objective:

The objective of this paper is to longitudinally study the normalized corpus callosum area (nCCA) as a marker of cognitive function and disability in MS.

Methods:

Thirty-seven MS patients were followed from 1996 with follow-ups in 2004 and 2013. A healthy matched control group was recruited. The Expanded Disability Status Scale (EDSS) and Symbol Digit Modalities Test (SDMT) were assessed. The nCCA was measured on T2-weighted images. Volumetry was performed with FreeSurfer.

Results:

Disease duration spanned five decades (1.6–46 years). Annual corpus callosal atrophy rate decreased with disease duration. nCCA was strongly correlated with SDMT ( r = 0.793, p < 0.001) and moderately correlated with EDSS ( r = −0.545, p < 0.001) after adjusting for disease duration, age and sex. The correlations of brain parenchymal fraction, white matter fraction, gray matter fraction and normalized lesion volume were less strong.

Conclusions:

The nCCA correlates well with physical and cognitive disability in time perspectives close to two decades, outperforming volumetric measurements. The nCCA is fast and could be feasible for clinical implementation where it may help identify patients in need of neuropsychological evaluation.

Corpus Callosum Volume and Interhemispheric Transfer in Multiple Sclerosis

Background:

The corpus callosum (CC) is frequently compromised in patients with multiple sclerosis (MS). Structural and functional measurements of the CC may be useful to monitor the progression of the disease. The aim of this pilot study was to determine if bimanual tactile temporal thresholds correlates with CC volume. A tactile temporal threshold is the longest temporal interval that separates the onsets of two tactile stimuli when they are judged by the observer as simultaneous. Judgments to bimanual stimulations require interhemispheric transfer via the CC.

Methods:

Thresholds were examined in MS patients and matched controls. Magnetic resonance (MR) images were acquired on a 3T MR system within 48 hours of clinical assessment and measurement of thresholds.

Results:

Corpus callosum volume was assessed by using a semiautomatic livewire algorithm. The CC volume was smaller (by 21% on average, p < 0.01) and thresholds were higher (by 49% on average, p < 0.03) in MS patients when compared to controls. A significant correlation (r = -0.66, p = 0.01) between CC volume and thresholds emerged for the MS patients.

Conclusion:

Measuring treatment benefits of neuroprotective and repair therapies is a well recognized challenge in MS research. The overall findings of this study suggest that these measurements, which involve the transfer of information interhemispherically via the CC, may be promising outcome measures that warrant further scientific exploration to develop a model to measure recovery.

Interhemispheric auditory connectivity: structure and function related to auditory verbal hallucinations

Auditory verbal hallucinations (AVH) are one of the most common and most distressing symptoms of schizophrenia. Despite fundamental research, the underlying neurocognitive and neurobiological mechanisms are still a matter of debate. Previous studies suggested that “hearing voices” is associated with a number of factors including local deficits in the left auditory cortex and a disturbed connectivity of frontal and temporoparietal language-related areas. In addition, it is hypothesized that the interhemispheric pathways connecting right and left auditory cortices might be involved in the pathogenesis of AVH. Findings based on Diffusion-Tensor-Imaging (DTI) measurements revealed a remarkable interindividual variability in size and shape of the interhemispheric auditory pathways. Interestingly, schizophrenia patients suffering from AVH exhibited increased fractional anisotropy (FA) in the interhemispheric fibers than non-hallucinating patients. Thus, higher FA-values indicate an increased severity of AVH. Moreover, a dichotic listening (DL) task showed that the interindividual variability in the interhemispheric auditory pathways was reflected in the behavioral outcome: stronger pathways supported a better information transfer and consequently improved speech perception. This detection indicates a specific structure-function relationship, which seems to be interindividually variable. This review focuses on recent findings concerning the structure-function relationship of the interhemispheric pathways in controls, hallucinating and non-hallucinating schizophrenia patients and concludes that changes in the structural and functional connectivity of auditory areas are involved in the pathophysiology of AVH.

The relationship between total and regional corpus callosum atrophy, cognitive impairment and fatigue in multiple sclerosis patients

Objective:

The objective of this paper is to investigate the relationship between total and regional corpus callosum (CC) atrophy, neuropsychological test performance and fatigue in multiple sclerosis (MS) patients.

Methods:

We conducted a cross-sectional study in 113 MS patients: mean age 48±11 years, 75/113 women, 84/113 relapsing–remitting MS, mean disease duration 21±9 years, mean Expanded Disability Status Scale (EDSS) score 3.2±1.7. All patients underwent brain magnetic resonance imaging, standardised neurological assessment and comprehensive cognitive testing including assessments for fatigue and depression. Total and regional CC atrophy was assessed using the corpus callosum index (CCI).

Results:

CCI correlated more strongly with T2- and T1-lesion volume and whole brain volume than with disease duration or EDSS score. CCI correlated strongly with the verbal fluency test (VFT), Symbol Digit Modalities Test (SDMT) and Paced Auditory Serial Addition Test (PASAT). Multivariate regression analysis revealed that atrophy of the posterior CC segment was significantly associated with poor outcome in the PASAT, VFT and SDMT. In contrast, atrophy of the anterior CC segment was significantly associated with fatigue severity and poor outcome in the long-term memory test.

Conclusions:

Atrophy of the CC is associated with cognitive impairment and fatigue. Regional CCI results indicate that these associations are partially spatially segregated.

Callosal atrophy in multiple sclerosis is related to cognitive speed

BACKGROUND

Long-term changes regarding corpus callosum area (CCA) and information processing speed in cognitive and sensory-motor tasks have rarely been studied in multiple sclerosis (MS).

OBJECTIVE AND METHODS

Information processing speed in cognitive (Symbol Digit Modalities Test, SDMT), sensory (visual and auditory reaction time) and motor (finger-tapping speed, FT; right and left hand) tasks as well as auditory inter-hemispheric transfer (verbal dichotic listening, VDL) was related to CCA, measured by MRI at baseline and at follow-up after nine years in 22 patients with MS. Possible confounding by demographic (age, gender and education), clinical (symptom onset, duration, severity of disease) and relative brain volume (RBV) as well as T2 lesion load was taken into account.

RESULTS

The smaller the CCA at baseline, the slower was SDMT performance at baseline. In a similar way, CCA at follow-up was associated with poor SDMT result at follow-up. Furthermore, the higher the annual rate of change in CCA, the poorer was performance in VDL on the left ear and the more pronounced was the right ear advantage. A positive relationship between performance in VDL right ear and annual rate of change in RBV was also seen. Sensory-motor tests were not significantly associated with CCA. T2 lesion load at baseline was associated with FT performance at baseline. Demographic, clinical and radiological (RBV and T2 lesion load) characteristics did not confound the significant relation between CCA and SDMT.

CONCLUSIONS

CCA unlike RBV and T2 lesion load was associated with SDMT, which indicated a marked cognitive rather than perceptual-motor component.

Voxelwise analysis of conventional magnetic resonance imaging to predict future disability in early relapsing–remitting multiple sclerosis

Background:

The ability of conventional magnetic resonance imaging (MRI) to predict subsequent physical disability and cognitive deterioration after a clinically isolated syndrome (CIS) is weak.

Objectives:

We aimed to investigate whether conventional MRI changes over 1 year could predict cognitive and physical disability 5 years later in CIS. We performed analyses using a global approach (T2 lesion load, number of T2 lesions), but also a topographic approach.

Methods:

This study included 38 patients with a CIS. At inclusion, 10 out of 38 patients fulfilled the 2010 revised McDonald’s criteria for the diagnosis of multiple sclerosis. Expanded Disability Status Scale (EDSS) evaluation was performed at baseline, year 1 and year 5, and cognitive evaluation at baseline and year 5. T2-weighted MRI was performed at baseline and year 1. We used voxelwise analysis to analyse the predictive value of lesions location for subsequent disability.

Results:

Using the global approach, no correlation was found between MRI and clinical data. The occurrence or growth of new lesions in the brainstem was correlated with EDSS changes over the 5 years of follow-up. The occurrence or growth of new lesions in cerebellum, thalami, corpus callosum and frontal lobes over 1 year was correlated with cognitive impairment at 5 years.

Conclusion:

The assessment of lesion location at the first stage of multiple sclerosis may be of value to predict future clinical disability.

Corpus callosum microstructural changes correlate with cognitive dysfunction in early stages of relapsing-remitting multiple sclerosis: axial and radial diffusivities approach

The corpus callosum is the largest fiber bundle in the central nervous system and it takes part in several cognitive pathways. It can be affected by multiple sclerosis (MS) early in the disease. DTI is capable of infering the microstructural organization of the white matter. The vectorial analysis of the DTI offers the more specific indices of axial diffusivity (AD) and radial diffusivity (RD), which have shown to be useful to discriminate myelin damage from axon loss, respectively. This study presents DTI results (mean diffusivity (MD), fractional anisotropy (FA), RD, and AD) of 23 relapsing-remitting MS patients and its correlation with cognitive performance. There were 47.8% of cognitive impaired patients (MS CI). We found signs of demyelination, reflected by increased RD, and incipient axon loss, reflected by AD increase, which was slightly higher in the MS CI. The cognitive changes correlated with the DTI parameters, suggesting that loss of complexity in CC connections can impair neural conduction. Thus, cognitive impairment can be related to callosal disconnection, and DTI can be a promising tool to evaluate those changes.

Hormones and dichotic listening: evidence from the study of menstrual cycle effects

This report presents evidence for changes in dichotic listening asymmetries across the menstrual cycle, which replicate studies from our laboratory and others. Increases in the right ear advantage (REA) were present in women at phases of the menstrual cycle associated with higher levels of ovarian hormones. The data also revealed correlations between hormone levels and behavioural measures of asymmetry. For example, the pre-ovulatory surge in luteinising hormone (LH) was related to a decrease in left ear scores, which comprised a key part of the cycle related shift in asymmetry. Further analysis revealed a subgroup of women who had not reached postovulatory status by days 18-25 of the cycle, as verified by low progesterone levels. These women showed laterality profiles at days 18-25 that looked more like the other women when measured at the periovulatory phase (i.e., days 8-11). Data were combined with those from a previous study to highlight the stability of effects. Results showed a distinct menstrual cycle related increase in asymmetry in the combined sample. This final comparison confirmed the nature of sex differences in dichotic listening as being dependent on hormone status in women.

Diffusion tensor tractography reveals disrupted topological efficiency in white matter structural networks in multiple sclerosis

Little is currently known about the alterations in the topological organization of the white matter (WM) structural networks in patients with multiple sclerosis (MS). In the present study, we used diffusion tensor imaging and deterministic tractography to map the WM structural networks in 39 MS patients and 39 age- and gender-matched healthy controls. Graph theoretical methods were applied to investigate alterations in the network efficiency in these patients. The MS patients and the controls exhibited efficient small-world properties in their WM structural networks. However, the global and local network efficiencies were significantly decreased in the MS patients compared with the controls, with the most pronounced changes observed in the sensorimotor, visual, default-mode, and language areas. Furthermore, the decreased network efficiencies were significantly correlated with the expanded disability status scale scores, the disease durations, and the total WM lesion loads. Together, the results suggest a disrupted integrity in the large-scale brain systems in MS, thus providing new insights into the understanding of MS connectome. Our data also suggest that a topology-based brain network analysis can provide potential biomarkers for disease diagnosis and for monitoring the progression and treatment effects for patients with MS.

Impaired small-world efficiency in structural cortical networks in multiple sclerosis associated with white matter lesion load

White matter tracts, which play a crucial role in the coordination of information flow between different regions of grey matter, are particularly vulnerable to multiple sclerosis. Many studies have shown that the white matter lesions in multiple sclerosis are associated with focal abnormalities of grey matter, but little is known about the alterations in the coordinated patterns of cortical morphology among regions in the disease. Here, we used cortical thickness measurements from structural magnetic resonance imaging to investigate the relationship between the white matter lesion load and the topological efficiency of structural cortical networks in multiple sclerosis. Network efficiency was defined using a 'small-world' network model that quantifies the effectiveness of information transfer within brain networks. In this study, we first classified patients (n = 330) into six subgroups according to their total white matter lesion loads, and identified structural brain networks for each multiple sclerosis group by thresholding the corresponding inter-regional cortical thickness correlation matrix, followed by a network efficiency analysis with graph theoretical approaches. The structural cortical networks in multiple sclerosis demonstrated efficient small-world architecture regardless of the lesion load, an organization that maximizes the information processing at a relatively low wiring cost. However, we found that the overall small-world network efficiency in multiple sclerosis was significantly disrupted in a manner proportional to the extent of total white matter lesions. Moreover, regional efficiency was also significantly decreased in specific brain regions, including the insula and precentral gyrus as well as regions of prefrontal and temporal association cortices. Finally, we showed that the lesions also altered many cortical thickness correlations in the frontal, temporal and parietal lobes. Our results suggest that the white matter lesions in multiple sclerosis might be associated with aberrant neuronal connectivity among widely distributed brain regions, and provide structural (morphological) evidence for the notion of multiple sclerosis as a disconnection syndrome.

[Corpus callosum. Landmark of the origin of cerebral diseases]

Diseases of the corpus callosum include developmental disorders, immunomodulated CNS diseases, vascular malformations, disturbances of metabolism including the electrolyte homeostasis, secondary degenerations and mechanical injuries. This report provides information on the differential diagnosis of reversible and irreversible pathological changes of the corpus callosum with special focus on the localization, which often allows conclusions on the pathogenesis to be drawn.

Electrophysiological and clinical correlates of corpus callosum atrophy in patients with multiple sclerosis

Multiple sclerosis (MS) is an idiopathic inflammatory demyelinating disorder of the central nervous system (CNS) characterized by demyelination and axonal degeneration. Corpus callosum (CC) is commonly involved during the disease process leading to atrophy (93%). Currently, there are no established markers of disease progression and the interplay of processes leading to brain atrophy in MS remains unknown. The primary aim of this study was to assess the frequency of CC atrophy in MS patients. Furthermore, the relationship between expanded disability status scale (EDSS) and transcranial magnetic stimulation (TMS) evoked motor potentials (MEP) were assessed to capture disease effects by independent parameters. Seventy-nine MS patients and 50 controls were included and their CC volumes were assessed. Out of 79 patients, 31 patients (39·2%) had CC atrophy. The distribution of EDSS scores among the group with CC atrophy [13 (32%) patients with EDSS 0-2; 11 (58%) patients with EDSS 2-4; 19 (24%) patients with EDSS ≥4] was not statistically significant (p>0·05). MEP latency was abnormal in 34 (43%) patients, 67 (85%) patients had abnormal MEP amplitude and CMCT was abnormal in 32 (41%) patients. The relation between EDSS and MEP was statistically significant among the patient population including the subgroup of patients with CC atrophy (p<0.05). Our results lacked to provide an association between disability and CC atrophy, but there was a correlation between CC atrophy and TMS evoked motor potentials. Early evolution of axonal degeneration and brain atrophy should be considered in terms of follow-up measures to provide long-term efficiency impacting disability, progression and brain atrophy.

Corpus callosum damage and cognitive dysfunction in benign MS

Corpus callosum (CC), the largest compact white matter fiber bundle of the human brain involved in interhemispheric transfer, is frequently damaged in the course of multiple sclerosis (MS). Cognitive impairment is one of the factors affecting quality of life of patients with benign MS (BMS). The aim of this study was to investigate the relationship between the cognitive profile of BMS patients and the extent of tissue damage in the CC. Brain conventional and DT MRI scans were acquired from 54 BMS patients and 21 healthy controls. Neuropsychological tests (NPT) exploring memory, attention, and frontal lobe cognitive domains were administered to the patients. DT tractography was used to calculate the mean diffusivity (MD) and fractional anisotropy (FA) of the CC normal appearing white matter (NAWM). An index of CC atrophy was also estimated. Nine (17%) BMS patients fulfilled criteria for cognitive impairment. Compared with controls, BMS had significantly different CC diffusivity and volumetry (P < 0.001). Compared with cognitively preserved patients, those with CI had significantly higher CC lesion volume (LV) (P = 0.02) and NAWM MD (P = 0.02). The scores obtained at PASAT were significantly correlated with CC T2 LV, and NAWM FA and MD (r values ranging from -0.31 to 0.66, P values ranging from 0.04 to <0.001). Cognitive impairment in BMS is associated with the extent of CC damage in terms of both focal lesions and diffuse fiber bundle injury. MRI assessment of topographical distribution of tissue damage may represent a rewarding strategy for understanding the subtle clinical deficits of patients with BMS.

Cognitive impairments in relapsing-remitting multiple sclerosis: a meta-analysis

There is debate in the literature regarding the magnitude, nature, and influence of cognitive impairment in individuals with relapsing-remitting multiple sclerosis (RRMS). Therefore, we conducted a meta-analysis that quantified the overall magnitude of cognitive impairment in individuals with RRMS and identified the domains of cognition and clinical/demographic variables that were moderators of the overall effect. We included 57 studies with 3891 participants that yielded a total of 755 effect sizes. Overall, there was a moderate decline in cognitive functioning in individuals with RRMS compared with healthy controls. Larger effects were observed in cognitive domains of motor functioning, mood status and memory and learning. Regarding demographic and clinical variables, age and gender were moderators of cognitive impairment in all cognitive domains, whereas neurological disability and disease duration primarily moderated performance on tasks assessing memory and learning.

Progression of non-age-related callosal brain atrophy in multiple sclerosis: a 9-year longitudinal MRI study representing four decades of disease development

BACKGROUND

In multiple sclerosis (MS), multiple periventricular lesions are commonly the first findings on MRI. However, most of these MS lesions are clinically silent. The brain atrophy rate has shown better correlation to physical disability, but it is not clear how atrophy develops over decades. Corpus callosum forms the roof of the third and lateral ventricles. The corpus callosum area (CCA) in a midsagittal image is age independent in a normal adult population up to the seventh decade; therefore it can be used as a marker for non-age-related, pathological brain atrophy.

OBJECTIVES

To investigate whether and how CCA decreases in size over time in patients with MS.

METHODS

In a clinical observational study, 37 patients with MS with a wide range of disease duration at baseline (1-33 years) were followed. Three different MS courses were represented. The mean of individual MRI follow-up was 9 years. Multiple sclerosis severity score (MSSS) was also applied to evaluate disability at baseline and after 9 years of follow-up.

RESULTS

A significant decrease in CCA over 9 years (p<0.001) and a persisting association between CCA and the disability status were found. The atrophy rate was similar ever four decades of MS for all MS courses. The mean annual CCA decrease was 9.25 mm2 (1.8%). Surprisingly, atrophy rate did not correlate with sex, disease duration, age at MS onset or MS course.

CONCLUSIONS

Serial evaluations of CCA might be a robust method in monitoring a non-age-related decrease in CCA, reflecting progression of irreversible destructive changes in MS.

Ipsilateral silent period: A marker of callosal conduction abnormality in early relapsing–remitting multiple sclerosis?

OBJECTIVE

The corpus callosum (CC) is commonly affected in multiple sclerosis (MS). The ipsilateral silent period (iSP) is a putative electrophysiological marker of callosal demyelination. The purpose of this study was to re-assess, under recently established optimised protocol conditions [Jung P., Ziemann U. Differences of the ipsilateral silent period in small hand muscles. Muscle Nerve in press.], its diagnostic sensitivity in MS, about which conflicting results were reported in previous studies.

METHODS

ISP measurements (onset, duration, and depth) were obtained in the abductor pollicis brevis (APB) muscle of either hand in 49 patients with early relapsing-remitting MS (RRMS) (mean EDSS, 1.3). Standard central motor conduction times to the APB (CMCT(APB)) and tibial anterior muscles (CMCT(TA)), and magnetic resonance images (MRI) were also obtained.

RESULTS

ISP measurements showed a similar diagnostic sensitivity (28.6%) as CMCT(APB) (24.5%), while diagnostic sensitivities of CMCT(TA) (69.4%) and MRI of the CC (78.6%) were much higher. Prolongation of iSP duration was the most sensitive single iSP measure. ISP prolongation occurred more frequently when CMCT(APB) to the same hand was also prolonged (40.0% vs. 8.4%, p<0.0001). The correlation between iSP duration and CMCT(APB) was significant (Pearson's r=0.24, p<0.02), suggesting that iSP duration can be contaminated by demyelination of the contralateral corticospinal tract. ISP duration did not correlate with MRI abnormalities of the CC.

CONCLUSIONS

ISP measures are neither a sensitive nor a specific marker of callosal conduction abnormality in early RRMS.

Differences of the ipsilateral silent period in small hand muscles

The ipsilateral silent period (iSP) is thought to depend on activity transmitted by the corpus callosum but ipsilateral corticospinal pathways may also contribute. Because the presence of ipsilateral corticospinal pathways differs between small hand muscles, we compared the iSP in the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles. The iSP was elicited in 20 healthy subjects by focal transcranial magnetic stimulation of one primary motor cortex during maximal voluntary contraction of the ipsilateral target muscle. The iSP duration was significantly longer in the FDI than APB because of an irregularly occurring second phase of inhibition in the FDI that was absent in the APB. Although the first phase of inhibition is transmitted by the corpus callosum, we provide evidence that the second phase is mediated through ipsilateral corticospinal pathways. Therefore, for specific assessment of callosal conduction, the iSP should be measured in the APB rather than FDI.

Loss of interhemispheric inhibition in patients with multiple sclerosis is related to corpus callosum atrophy

Axonal injury and loss in the corpus callosum (CC) is characteristic of the pathology of multiple sclerosis (MS). Functional magnetic resonance imaging (fMRI) potentially allows neurophysiological consequences of this interhemispheric axonal loss to be defined quantitatively. Here we have used 3T fMRI to study the activation in the contralateral primary sensorimotor cortex and deactivation (mediated by transcallosal tracts) in the homologous ipsilateral region in 14 patients with MS and in 14 matched healthy controls during a simple hand-tapping task. Both healthy controls and MS patients showed similar activation in the motor cortex contralateral to the hand moved, but the patients showed a significantly smaller relative deactivation in the ipsilateral motor cortex (P = 0.002). The difference was accounted for by the sub-group of MS patients who previously had impairment of motor function of the hand tested (MS-phd). The CC of the whole patient group was significantly thinner than for the controls (P = 0.001). Atrophy of the CC was correlated with loss of deactivation for the whole patient group (r = -0.50, P = 0.035), but particularly for MS-phd (r = -0.914, P = 0.004). Interhemispheric physiological inhibition thus is impaired in patients with MS, potentially contributing to impairment of motor control. This work suggests one way in which FMRI monitoring of the transcallosal interactions in motor cortex could become a tool for evaluation of therapies that may enhance function in reversibly impaired pathways.

Corpus callosum size correlates with asymmetric performance on a dichotic listening task in healthy aging but not in Alzheimer's disease

Alzheimer's disease (AD) involves not only gray matter but also white matter pathology, as reflected by atrophy of the corpus callosum (CC). Since decreased CC size may indicate reduced functional interhemispheric connectivity, differences in callosal size may have cognitive consequences that may become specifically apparent in neuropsychological tasks that tap hemispheric laterality. In the present study, we examined callosal functioning with a dichotic listening task in 25 Alzheimer patients, 20 healthy elderly and 20 healthy elderly with subjective memory complaints. We found decreased performance, increased ear asymmetry, and decreased callosal size in the AD group compared to healthy elderly. As expected, in the healthy elderly, we found significant negative correlations between ear asymmetry and callosal size, specifically in the anterior and posterior callosal subareas. While the association with the posterior subareas (isthmus and splenium) points at involvement of temporal areas mediating language processing, the association with the anterior subarea (the rostrum and genu) points at involvement of frontal areas mediating attention and executive functions. Remarkably however, in contrast to the healthy elderly, callosal size was not related to ear asymmetry in the AD group. The absence of an association between callosal atrophy and ear asymmetry implies that other pathological processes, next to reduced callosal functioning, attribute to ear asymmetry in AD. Difficulties to attend specifically to the left ear during dichotic listening in some of the AD patients, points at decreased attention and executive functions and suggests that pathology of specifically the frontal areas is involved.

Multiple sclerosis patients show a highly significant decrease in alpha band interhemispheric synchronization measured using MEG

MEG data were acquired from a group of relapsing-remitting multiple sclerosis (MS) patients and a group of healthy controls, using an eyes-closed no-task condition. An interhemispheric coherence measure (IHCM), reflecting the synchronization between the left and right hemispheres, showed a decrease in the patients, particularly in the alpha band. No comparable differences were seen in the alpha band power or its distribution over the head. The observed difference is in agreement with a reduced long-range connectivity in the brains of MS patients. The IHCM was found to be reproducible in controls over a period of more than 15 months. Further studies should investigate whether MEG derived synchronization measures may be useful as markers for MS disease load.

Clinical callosum syndrome in a case of multiple sclerosis

This case report confirms that a clinical callosal disconnection could be observed in multiple sclerosis. Moreover, this case describes a new kind of strange manual behavior related to callosal disconnection. This behavior could neither be considered as a diagonistic dyspraxia nor as an alien hand, but they evoke rather a conflict of intentions.

Principles and clinical applications of auditory evoked potentials in the geriatric population

Age-related changes in auditory evoked potentials are complex and complicated by the confounding effects of gender; concomitant high-frequency hearing sensitivity loss; and, in the case of event-related responses, the nature of the task used to elicit the response. There is a tendency for amplitude to decline and latency to increase, but these trends are not always clear-cut. There is also a tendency for activation patterns to move forward from parietal to frontal areas as age increases. The dichotic listening tool has revealed age-related changes in interaural and interhemispheric asymmetries. These asymmetries seem to be related to loss in the efficiency of interhemispheric transfer via the corpus callosum.

3-D echo planar (1)HMRS imaging in MS: metabolite comparison from supratentorial vs. central brain

To determine if metabolite ratios as measured by 3-dimensional echo planar spectroscopy imaging (3D-EPSI) from central brain regions of interest (ROI) centered at the corpus callosum reflect imaging metrics of large volumes of supratentorial brain (STB) from patients with multiple sclerosis.

METHODS

48 MS patients with relapsing-remitting, secondary progressive, and primary progressive disease underwent a 3D-EPSI sequence covering large volumes of STB. Metabolite ratios were first estimated from all voxels within a STB mask using a linear regression of N-acetylaspartate (NAA) over Creatine (Cr), NAA over choline (Cho) and Cho over Cr. Secondly, spectroscopic voxels from a central brain (CB) ROI centered at the corpus callosum were selected within the STB. Ratios were compared using Bland-Altman regression analysis and Spearman's correlation coefficients between STB versus central brain. Ratios from studied ROIs were correlated with the EDSS and compared to normal controls.

RESULTS

Very strong correlations ranging from 0.884 and 0.938 (p < 0.0001) were found for all metabolite ratios between STB versus central brain. NAA/Cr ratios were similarly and negatively correlated with the EDSS across all ROIs, trends ranging from -0.257 to -0.314 (p < 0.1). NAA/Cr from all MS patients was similarly decreased compared to controls across all ROIs (p < 0.01).

CONCLUSION

Metabolite ratios from a central brain ROI were statistically equivalent and highly correlated with ratios from the STB. The study of NAA/Cr using (1)HMRS from a central brain ROI centered at the corpus callosum seems to be representative of brainwide axonal changes in patients with MS.

The neuropsychology of multiple sclerosis: contributions of neuroimaging research

Multiple sclerosis (MS) is often associated with cognitive and emotional changes that affect daily activities and quality of life. Deficits in memory, executive function, processing speed, and other cognitive domains are frequently reported. In addition, mood disturbances and fatigue are common. In this article, the authors highlight research on individual differences in the neuropsychology of MS, and emphasize neuroimaging studies that help elucidate the basis of the deficits.

Sex differences in corpus callosum size: relationship to age and intracranial size

This quantitative MRI study reports measurement of corpus callosum area taken from midsagittal brain images in 51 healthy men and 41 healthy women, spanning the adult age range (22 to 71 years). Men had larger brains and corpora callosa than women, but callosal size did not correlate with age in either sex. Intracranial (i.c.) volume (ICV) and midsagittal i.c. area (ICA) of brain were used in covariate, regression, and ratio analyses to determine whether sex differences in the corpus callosum endured with statistical adjustment for sex differences in maximally attained brain size. With the exception of one ratio measure, the different statistical adjustments for the contribution of sex differences in brain size to corpus callosum size all indicated that men had larger corpora callosa than women for their brain size. A subsample of men and women selected to be matched on i.c. volume and age confirmed this statistical observation. Sexual dimorphism in the corpus callosum is not a simple artifact of sex differences in brain size and may reflect differences in connectivity necessitated by differences in brain size.

Interhemispheric transfer evaluation in multiple sclerosis 1The authors would like to thank Claude-Alain Hauert and Christoph Michel for their assistance in the evaluation of motor tapping and Michel Habib for his suggestions and comments. This work was supported by a grant from the Swiss Society of Multiple Sclerosis

Patients suffering from Multiple Sclerosis (MS) have frequently been found to suffer from damage to callosal fibers. Investigations have shown that this damage is associated with signs of hemisphere disconnections. The aim of our study was to provide evidence for the first signs of interhemispheric dysfunction in a mildly disabled MS population. Therefore, we explored whether the Interhemispheric Transfer (IT) deficit is multi-modal and sought to differentiate two MS evolution forms, on the basis of an interhemispheric disconnection index. Twenty-two patients with relapsing-remitting form of MS (RRMS) and 14 chronic-progressive (CPMS) were compared with matched controls on four tasks: a tachistoscopic verbal and non-verbal decision task, a dichotic listening test, cross tactile finger localization and motor tapping. No overall impairment was seen. The dichotic listening and lexical decision tasks were the most sensitive to MS. In addition, CPMS patients' IT was more impaired and was related to the severity of neurological impairment. The different sizes of the callosal fibers, which determine their vulnerability, may explain the heterogeneity of transfer through the Corpus Callosum. Therefore, evaluation of IT may be of value as an index of evolution in MS.

Brain atrophy in relapsing-remitting multiple sclerosis: relationship with 'black holes', disease duration and clinical disability

Recent MRI studies in multiple sclerosis have highlighted the potential role of brain atrophy evaluation as a putative marker of disease progression. In the present study, we evaluated the supratentorial and infratentorial brain volume in patients with relapsing remitting multiple sclerosis (RR MS) and in healthy subjects. Moreover, we determined whether brain volumes of MS patients are associated with different aspects of brain MRI abnormalities and clinical findings. Two-dimensional acquired MRI was performed on 52 relapsing-remitting multiple sclerosis and 30 healthy subjects. The volume of supratentorial and infratentorial structures was measured in selected representative slices. Gd-enhancement, T2 hyperintense, T1 hypointense (i.e. 'black holes') total lesion load, as well as the area of corpus callosum was calculated in the MS group and related to brain volume measures. Correlations between MRI parameters and clinical features were also considered. MS patients had significantly lower supratentorial, infratentorial brain volume and corpus callosum area than healthy subjects (P<0.01). Supratentorial brain volume was significantly related to corpus callosum area (r=0.58; P<0.01) and T1 hypointense lesion load (r=0.48; P<0.01), but not with T2 hyperintense lesion load. Infratentorial/supratentorial ratio was significantly associated with disease duration and EDSS score (r=-0.34; P=0.02 and r=-0.49; P<0.01, respectively). This study documents that brain atrophy is an early MRI finding in RR MS and it is closely related to 'black holes' burden. The use of relative values (infratentorial/supratentorial ratio) may increase the conspicuity of correlation between clinical and MRI findings.

Volumes of brain atrophy and plaques correlated with neurological disability in secondary progressive multiple sclerosis

The objectives of the present study was to correlate the segmented magnetic resonance imaging (MRI) volumes of intracranial cerebrospinal fluid (CSF) spaces (expressing the extent of brain atrophy) and cerebral plaques with the neurological disability in secondary progressive multiple sclerosis (MS). Earlier studies have mainly correlated MS plaques and neurological disability measured by expanded disability status scale (EDSS). The data on the association between brain atrophy and EDSS or regional functional scoring scale (RFSS) are very limited. We measured the volumes of intracranial CSF spaces in 28 patients with secondary progressive MS using MRI, and semiautomatic segmentation software. The volumes of T1-weighted hypointense and T2-weighted hyperintense MS plaques were also measured. In multiple regression analysis, increasing volumes of total (P=0.006) and relative (P=0.005) intracranial CSF spaces were significantly associated with worsening neurological disability as expressed by EDSS. No associations were found between these intracranial CSF space volumes and total RFSS scores. The mean volume of T2-weighted plaques showed a tendency to associate with total RFSS score (r=0.40, P=0.03), but no correlations were detected between T1- or T2-weighted plaque volumes and EDSS. The application of a new segmentation technique in quantifying intracranial cerebrospinal fluid spaces allowed an exact and sensitive way of assessing brain atrophy. The associations between brain atrophy and neurological disability expressed by EDSS suggests that the effect of MS therapies should be evaluated by measurement of brain atrophy.