Evidence for widespread movement-associated functional MRI changes in patients with PPMS

BACKGROUND

Previous work has suggested that functional reorganization of cortical motor areas might have a role in limiting the motor deficits in patients with MS.

OBJECTIVE

To test whether movement-associated cortical changes in MS might extend beyond the "classic" motor areas and involve sites for multimodal integration.

METHODS

fMRI was used to assess patterns of brain activations associated with 3 different motor tasks in 30 right-handed patients with primary progressive MS (PPMS) and variable degrees of motor impairment, which were compared with those from 15 right-handed, sex- and age-matched control subjects.

RESULTS

Compared with control subjects, patients with MS showed increased activation of brain regions within both traditional motor planning and execution regions (including the supplementary motor area and the cingulate motor area), the insula (a region implicated in sensory processing), and several multimodal cortical regions in the temporal, parietal, and occipital lobes. In patients, the extent of the fMRI activations was strongly correlated with MR lesion burden (r ranging from 0.70 to 0.86, p < 0.001).

CONCLUSIONS

This study shows that movement-associated cortical activation in patients with PPMS is widely distributed and also involves multimodal "nonmotor" cortical networks. It also suggests that adaptive cortical reorganization might be one of the mechanisms limiting the clinical impact of MS in the progressive phases of the disease.

Functional reorganization of motor cortex increases with greater axonal injury from CADASIL

BACKGROUND AND PURPOSE

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited small-artery disease that clinically involves only the brain. Particularly early in the disease, patients can show substantial or complete recovery after individual strokes. Cortical functional reorganization may contribute to limiting disability with such ischemic injury. We sought to test whether the extent of any functional changes in the motor cortex increases with greater brain axonal injury from CADASIL.

METHODS

Functional MRI (fMRI) was used to characterize cortical activation during a simple hand-tapping task. Disease-associated pathology in subcortical white matter was assessed with the use of conventional fluid-attenuated inversion recovery (FLAIR) MRI and MR spectroscopic imaging for measurement of N-acetyl aspartate decreases, a relatively specific measure of axonal injury.

RESULTS

There was evidence for variable but substantial hyperintense white matter signal in all of the patients with FLAIR imaging. With the use of fMRI, the brain regions activated during motor tasks were similar for the 9 CADASIL patients and 7 controls, except that most (6 of 9) patients showed primary motor cortex activation both ipsilateral and contralateral to the hand moved, a finding in only 1 of 7 healthy controls. Ipsilateral motor cortex activation increased (r=-0.77, P<0.05) and motor cortex activation lateralization index decreased (r=0.68, P<0.02) with greater white matter injury (as assessed from decreases in the relative N-acetyl aspartate concentration) in a region of interest including descending motor fibers of the corticospinal pathway.

CONCLUSIONS

The extent of functional reorganization of motor cortex increases with increasing axonal injury, consistent with an adaptive role for these changes. Increased functional recruitment of cortex ipsilateral to the limb moved therefore may contribute to limiting motor impairment from the subcortical injury of CADASIL.

An expanded cortical representation for hand movement after peripheral motor denervation

OBJECTIVES

Functional reorganisation of the motor or sensory cortex has been demonstrated in animals after section of mixed peripheral nerves. Here functional changes in the motor cortex specifically after peripheral motor denervation in humans are investigated.

METHODS

Functional MRI (fMRI) was used to study brain activation during a finger flexion-extension task in patients with a late onset, acquired pure motor neuropathy (n=6), contrasting results with those from patients with pure sensory neuropathies (n=4) or healthy controls (n=7).

RESULTS

Increases in the extent of activation in the motor cortex both ipsilateral and contralateral to the hand moved were found in the patients with motor neuropathy. The neuroanatomical localisation of the mixed contralateral sensorimotor cortex activation volume was more posterior for the patients with motor neuropathy than for the healthy controls (mean difference, 12 mm, p<0.05). The pure sensory neuropathy group by contrast showed no change in the extent of activation relative to healthy controls and a trend for more anterior primary sensorimotor cortex activation (p<0.06). To test whether the increased activation volumes found in patients with motor neuropathy were a result simply of factors such as increased effort with movement rather than the motor denervation, patients with hand weakness from inclusion body myositis (n=4) were studied while making similar hand movements. No differences in either the numbers of significantly activated voxels or in their localisation were found relative to healthy controls (n=10).

CONCLUSIONS

These results provide a novel demonstration that peripheral denervation (as distinguished from factors related to weakness) leads to functional reorganisation of the sensorimotor cortex in the adult brain. This suggests that adaptive responses to motor denervation involve the central as well as the peripheral nervous system.

Attention to movement modulates activity in sensori-motor areas, including primary motor cortex

Attention to sensory stimulation modulates behavioural responses and cortical activity. Attention to movement can also modulate motor responses. For example, directing attention away from cued movements can increase reaction times. This study used fMRI to determine where in the motor cortex attention to movement modulates activity. Attention to movement was reduced by asking subjects to perform a concurrent distractor task (counting backwards). Sensori-motor areas showing a negative interaction between counting and movement (i.e. reduced activation in the dual task condition relative to the sum of the single task conditions) included the supplementary motor area (SMA), cingulate cortex, insula and post-central gyrus. A separate volumes-of-interest analysis revealed significant reductions in mean percent signal change in the dual task compared to the single task in a portion of the pre-central gyrus, deep in the central sulcus (thought to correspond to area 4p) and SMA. We conclude that the brain network for motor control is modulated by attention at multiple sites, including the primary motor cortex. These results are also discussed with reference to theories concerning the neural correlates of dual task performance and mental calculation and have implications for the interpretation of functional imaging studies of normal and impaired motor performance.

Altered hemodynamic responses in patients after subcortical stroke measured by functional MRI

BACKGROUND AND PURPOSE

Blood oxygenation level-dependent (BOLD) functional MRI (fMRI) is a promising method for defining brain recovery after stroke quantitatively. Applications thus far have assumed that the BOLD hemodynamic response in patients after stroke is identical to that in healthy controls. However, because of local vascular compromise or more diffuse vascular disease predisposing to infarction, this assumption may not be justified after stroke. We sought to test whether patients who have suffered a lacunar stroke show BOLD fMRI response characteristics identical to those of healthy controls.

METHODS

We measured the BOLD fMRI signal time course in the sensorimotor cortex contralateral to the affected hand with finger- or hand-tapping tasks for minimally or mildly impaired right-handed patients (n=12) after lacunar strokes causing limb weakness and for healthy controls (n=20).

RESULTS

With a right-handed sequential finger-tapping task, the rate of rise and maximum increase of the BOLD signal in the contralateral sensorimotor cortex were > 30% lower (P< or =0.01) in the stroke patients. Similar relative decreases were found for the same task performed with the left hand. These changes were found in patients both in the hemisphere affected by stroke and in the unaffected hemisphere, suggesting that the BOLD fMRI time course differences observed arise from a diffuse functional pathology. The difference between patients and controls is not a result of age alone, since differences were not found between the younger (n=10; aged 22 to 38 years) and the older (n=10; aged 56 to 83 years) healthy controls. The effect also does not seem to be dependent on the specific hand movement task used.

CONCLUSIONS

The magnitude of the BOLD fMRI response can be reduced in stroke patients even if infarcts do not involve the cortex. This may be a consequence of the stroke, but the observation that the BOLD signal time course is similar in the affected and unaffected hemispheres suggests that it also could result from preexisting pathophysiological changes in the cerebral microvasculature.

Exacerbation of pain by anxiety is associated with activity in a hippocampal network

It is common clinical experience that anxiety about pain can exacerbate the pain sensation. Using event-related functional magnetic resonance imaging (FMRI), we compared activation responses to noxious thermal stimulation while perceived pain intensity was manipulated by changes in either physical intensity or induced anxiety. One visual signal, which reliably predicted noxious stimulation of moderate intensity, came to evoke low anxiety about the impending pain. Another visual signal was followed by the same, moderate-intensity stimulation on most of the trials, but occasionally by discriminably stronger noxious stimuli, and came to evoke higher anxiety. We found that the entorhinal cortex of the hippocampal formation responded differentially to identical noxious stimuli, dependent on whether the perceived pain intensity was enhanced by pain-relevant anxiety. During this emotional pain modulation, entorhinal responses predicted activity in closely connected, affective (perigenual cingulate), and intensity coding (mid-insula) areas. Our finding suggests that accurate preparatory information during medical and dental procedures alleviates pain by disengaging the hippocampus. It supports the proposal that during anxiety, the hippocampal formation amplifies aversive events to prime behavioral responses that are adaptive to the worst possible outcome.

[Cerebral vasoreactivity and functional response in stroke: a study with functional MR]

INTRODUCTION

Lacunar infarcts are usually associated with anatomical and possibly functional changes in the walls of small blood vessels (penetrating arteries). The functional effect varies and is accompanied by cerebral adaptive/reorganizational changes. BOLD contrast, originated in the microvasculature (especially with ultra high magnetic fields) depends, in the end, on haemodynamic changes and is useful for exploring patterns of cerebral activation using fMR.

OBJECTIVES

To compare the temporal behaviour of the BOLD signal and the distribution of activation between a group of patients with no functional sequelae following a stroke and a control group, by using fMR at 3T.

RESULTS

The stroke group showed a smaller number of voxels activated, but this was not statistically significant. The patterns of activation, size of the sensor motor area (SM or ASM) and index of laterality were similar in both groups. In SM the BOLD response was 85% slower (p< 0.01) and 25% less (not statistically significant).

CONCLUSIONS

We found no differences in the patterns of activation of the two groups. This may be explained by the minimal lesions of the stroke group, which were insufficient to produce reorganizational/adaptive changes or by the great variety of responses. The temporal response of the BOLD response was different in the stroke group, probably as a result of the alteration in the haemodynamic response in relation to the underlying processes which damage the functional properties of the vascular wall. This difference in the BOLD response should be interpreted with caution, and borne in mind when interpreting activation in persons with vascular pathology. Further studies are necessary for better understanding of its significance.

Size-selective neuronal changes in the anterior optic pathways suggest a differential susceptibility to injury in multiple sclerosis

Axonal damage is found in both acute and chronic lesions of multiple sclerosis. Direct axon counting in post-mortem tissue has suggested that smaller axons might have a greater susceptibility to damage, but methodological limitations have precluded unequivocal interpretation. However, as neuronal and axonal sizes are linked and neuronal changes would be expected with retrograde or transsynaptic degeneration following axon injury, we hypothesized that an alternative strategy for studying this phenomenon would be to define multiple sclerosis-associated changes in neurones. To test this hypothesis, we measured both axonal loss and neuronal size changes in the anterior optic pathway [including the optic nerve (ON), optic tract (OT) and lateral geniculate nucleus] of the brains of eight patients who died with multiple sclerosis and in eight control brains. The ONs and OTs in brains from the multiple sclerosis patients showed a trend to smaller mean cross-sectional areas (ON, multiple sclerosis = 6.84 mm(2), controls = 9.25 mm(2); and OT, multiple sclerosis = 6.45 mm(2), controls = 7.94 mm(2), P = 0.08) and had reduced axonal densities (ON, multiple sclerosis = 1.1 x 10(5)/mm(2), controls = 1.7 x 10(5)/mm(2); and OT, multiple sclerosis = 1.4 x 10(5)/mm(2), controls = 1.8 x 10(5)/mm(2), P = 0.006). Estimated total axonal counts were reduced by 32 (OT)-45% (ON) in the patients relative to controls (ON, multiple sclerosis = 8.1 x 10(5) axons, controls = 14.8 x10(5), P = 0.05; and OT, multiple sclerosis = 9.1 x 10(5), controls = 13.3 x 10(5), P = 0.02). The size distributions of the magnocellular cells in the lateral geniculate nucleus were similar for the two groups, but in multiple sclerosis brains the parvocellular cells were significantly smaller (mean sizes: multiple sclerosis = 226 microm(2), controls = 230 microm(2), P < 0.001) and had a larger variation in size, suggesting a greater proportion of atrophic neurones. Axon loss in the optic nerves of multiple sclerosis patients correlated strongly with measures of increased dispersion of cell sizes in the parvocellular layer (r = 0.8, P < 0.04). These data demonstrate that both atrophy and decreased density contribute to the substantial axonal loss in the anterior visual pathway of these patients. This appears related to a relatively selective atrophy of the smaller neurones of the parvocellular layer in the lateral geniculate nucleus, supporting the hypothesis that smaller axons may be preferentially susceptible to injury in multiple sclerosis.

Novel approaches to imaging brain tumors

Brain imaging techniques are assuming a greater range of roles in neuro-oncology. New techniques promise earlier recognition of the spread of tumors to the brain, which is useful in staging of disseminated disease, as well as better definition of small lesions associated with presentations of epilepsy. There is the promise that entirely noninvasive, specific diagnosis of brain tumors may become possible. Imaging methods are being used increasingly to direct and monitor therapy. Preoperative and intraoperative imaging are being used for guiding tumor surgery. An exciting potential goal for greater use of imaging is in the individualization of medical therapies either by analysis of in vitro responses or by visualization of drug responses on the tumor in situ. An important focus for technical development is in the robust integration of complementary information to allow optimization of the sensitivity and specificity of multimodal examinations.

Magnetic resonance imaging of multiple sclerosis: new insights linking pathology to clinical evolution

Magnetic resonance imaging methods allow observation of pathological changes in vivo. Magnetic resonance-based studies have provided a number of important insights into the spatio-temporal evolution of the pathology of multiple sclerosis in vivo, particularly with respect to the relation between pathology and progression of disability. Magnetic resonance techniques have shown that this pathology is not restricted to the plaques that are evident at autopsy, but also involve the so-called normal-appearing white matter. Nonconventional magnetic resonance imaging strategies such as magnetization transfer imaging and spectroscopic imaging provide measures with higher pathological specificity for myelin and axonal injury. These and other advanced magnetic resonance techniques (such as the measurement of atrophy, lesion relaxation spectra, and lesion dynamics) are affording opportunities to use observations of patients to test biologically specific hypotheses. This should help us to better define new targets for drug therapy and to assess responses to new therapeutic agents.

[Functional magnetic resonance and the motor cortex II: measurement of activity]

INTRODUCTION

Functional magnetic resonance (fMR) with BOLD contrast has been shown to be a useful tool for clinical investigation. It is still uncertain which is the best way to establish the measures of activation for subsequent comparisons and their physiological significance.

OBJECTIVE

To explore the activation expressed as a function of different parameters.

PATIENTS AND METHODS

We did fMR with BOLD contrast at 3T and a motor paradigm in 14 healthy persons. The activation was expressed as the number of voxels activated within each area; their percentage in relation to the total number of voxels activated; z value; laterality index, speed and degree of temporal variation in the signal of these voxels.

RESULTS

Somatomotor area (SM) activated 121% more voxels than supplementary motor area (SMA), but their variation expressed with their standard variation was very large. The percentage of voxels activated was 163.6% greater in SM than in SMA. The laterality index increased at the expense of activation outside SM. The variation of the two relative measurements was less than the total number of voxels. The z value did not correlate with the degree of activity. The time course of the SMA signal was slightly different to SM.

CONCLUSIONS

Very high field fMR is very sensitive to changes in signal. The number of voxels activated varies considerably, so its use as a measurement of activity should be limited. Relative value, such as the index of laterality of the percentage of voxels may show less variability. The centre of mass and z value are stable figures but the physiological significance of the latter is not clear. The study of the temporal variation of the signal seems to be a potentially useful parameter with a certain degree of physiological significance, although better understanding and further analysis is necessary.

[Functional magnetic resonance and the cerebral cortex. 1: Group analysis]

INTRODUCTION

Various strategies are used to increase the sensitivity to activation in functional magnetic resonance (RMf) with bold contrast, including raised magnetic fields and group analysis. Although very important, study of the behaviour of the signal in a group (normal pattern) remains a problem in RMf.

OBJECTIVES

To study the behaviour of the signal in response to the motor paradigm using RMf with bold contrast at 3T in a group, by random effect analysis.

RESULTS

The areas of most solid activation were the somatomotor area, the contralateral SMA and ipsilateral cerebellar area. Other areas showed greater variability (the number of persons who activated them and their localization). Analysis of the group showed close correlation between individuals both in the areas mentioned and in the basal ganglia, and to a lesser extent in ipsilateral premotor and somatomotor areas. There was wide variability in prefrontal, frontal, dorsolateral and parietal areas.

CONCLUSIONS

There is some variation in activation (number and position of the activated areas). SM, SMA and cerebellum have a high degree of inter individual anatomofunctional concordance. Activity in the basal ganglia, in spite of high inter individual anatomofunctional correlation, may not be easy to observe. Some areas are activated in certain persons but not on analysis of the group. This shows inter individual functional and/or anatomical variability. Such variation in activation should be remembered in subsequent analysis. Group analysis is useful for showing collective patterns which determine the most consistent areas on which to base subsequent individual analysis.

Normalized accurate measurement of longitudinal brain change

PURPOSE

Quantitative measurement of change in brain size and shape (e.g., to estimate atrophy) is an important current area of research. New methods of change analysis attempt to improve robustness, accuracy, and extent of automation. A fully automated method has been developed that achieves high estimation accuracy.

METHOD

A fully automated method of longitudinal change analysis is presented here, which automatically segments brain from nonbrain in each image, registers the two brain images while using estimated skull images to constrain scaling and skew, and finally estimates brain surface motion by tracking surface points to subvoxel accuracy.

RESULTS AND CONCLUSION

The method described has been shown to be accurate ( approximately 0.2% brain volume change error) and to achieve high robustness (no failures in several hundred analyses over a range of different data sets).

Teaching sexual history taking to health care professionals in primary care

OBJECTIVES

Although it is accepted that history taking is central to correct diagnosis, little work has been undertaken on the development of sexual history taking, particularly in a primary care context where sexual health may not occur to the patient. Embarrassment is recognized as one major problem. This paper reports on a series of teaching interventions designed to help primary health care professionals (doctors and nurses) to identify and deal effectively with sexual health issues in the consultation.

METHODS

141 participants took part in nine different courses, with 114 returning evaluations. All courses involved tutorial teaching on clinical and ethicolegal issues and role play with trained professional role-players; some involved video-based dramatizations to particularize principles in context. During role play sessions, which were followed by detailed, contextualized feedback, clinical issues, attitudinal issues (e.g. articulating a sense of personal embarrassment, and the risk of stereotyping), and ethicolegal issues were all discussed, as were examples of words and phrases which participants were invited to try out.

OUTCOMES

The overall quality of the courses was rated by participants, on average, at 89.95 (maximum 100), and the relevance of the topic at 91.40. Free text comments centred on the power of the training as a consciousness raiser, on the need to alter communication strategies, the need to change existing clinical practice and the value of role play as a methodology. Interactive courses on sexual health are highly acceptable to participants.

Altered cortical activation with finger movement after peripheral denervation: comparison of active and passive tasks

We wished to contrast cortical activation during hand movements in profoundly weak patients with motor neuropathy and in normal controls using a paradigm that is behaviourally matched between the two groups. Previous work has suggested that a passive movement task could be appropriate. Using functional magnetic resonance imaging (fMRI), we first characterised patterns of brain activation during active and passive index finger movements in healthy controls (n=10). Although the relative activation differences were highly variable, there was a trend for the mean number of significantly activated voxels in the primary motor cortex contralateral to the hand moved (CMC) to be lower for the passive than for the active task (40% relative decrease, P=0.09). There was a small posterior shift in the centre of mass of the CMC (mean, 8 mm, P<0.02) and of the ipsilateral sensorimotor cortex (IMC) (mean, 11 mm, P<0.05). No activation with passive movement was found in the patients with severe distal sensory neuropathy (n=2), suggesting that activation with passive movements is dependent on sensory feedback and unlikely to be due to mental imagery alone. In contrast, patients with severe pure motor neuropathies (MN, n=2) showed substantial increases in the volumes of activation compared to controls. The relative increases in numbers of voxels activated above threshold in different regions of interest for both the active (MN/controls: CMC, 2. 1; IMC, 8.1; supplementary motor area [SMA], 5.2) and passive (CMC, 2.6; IMC, 8.0; SMA, 5.1) tasks were similar. These results confirm expansion of cortical representation for finger movement in patients with motor neuropathy and demonstrate central reorganisation as a consequence of the motor nerve loss. An expanded representation for finger movement in the primary motor cortex with peripheral weakness suggests the possibility that the primary motor cortex may encode motor unit activation rather directly.

Functional MRI detects posterior shifts in primary sensorimotor cortex activation after stroke: evidence of local adaptive reorganization?

BACKGROUND AND PURPOSE

Further recovery from stroke can occur late, long after the end of the apparent evolution of pathological changes. This observation and evidence obtained from functional imaging for altered patterns of activation after brain injury suggest that cortical reorganization may contribute to recovery. Here, we have tested for potentially adaptive reorganization in the primary sensorimotor cortex.

METHODS

We used functional MRI to study brain activation with dominant hand movement in right-handed healthy control subjects (n=20) and in patients after subcortical ischemic infarcts causing mild to moderate right hemiparesis (n=8). The numbers of pixels activated above threshold and the geometric centers of activation clusters were determined.

RESULTS

Although random-effects analysis identified some differences in activation maxima, similar regions of the brain were activated with sequential finger tapping in the patient and control groups. However, consistent with the heterogeneity in the locations, sizes, and times after the infarcts, patterns and magnitudes of activation showed some heterogeneity between patients. Nonetheless, for the group as a whole, there was a decreased motor cortex lateralization index (-0.1+/-0.7 in patients and 0.7+/-0.3 in control subjects, P=0.05). The geometric center of activation of the primary sensorimotor cortex activation cluster contralateral to the affected hand in patients was also shifted posteriorly (mean 12 mm, P<0.04) relative to that of the control subjects. To confirm the latter observation, the activation response with a simple hand-tapping task was examined in some of the subjects. With this task, there was also a trend (mean 10 mm, P=0.07) toward a more posterior activation in patients.

CONCLUSIONS

These results confirm altered patterns of activation in the contralateral and ipsilateral primary sensorimotor cortices after recovery from strokes causing hemiparesis. These (and other changes) suggest that modulation of widely distributed parts of the cortical network for motor control may contribute to adaptations leading to functional recovery after stroke.

Evidence of axonal damage in the early stages of multiple sclerosis and its relevance to disability

OBJECTIVE

To assess axonal damage and its contribution to disability at different stages of multiple sclerosis (MS).

BACKGROUND

Recent in vivo imaging and in situ pathologic studies have demonstrated that substantial axonal damage accompanies the inflammatory lesions of MS. However, the relation of axonal damage to the duration of MS and its contribution to disability at different stages of the disease remain poorly defined.

DESIGN

We performed proton magnetic resonance spectroscopic imaging in 88 patients with a wide range of clinical disability and disease duration to measure N-acetylaspartate (NAA, an index of axonal integrity) relative to creatine (Cr) in a large central brain volume that included mostly normal-appearing white matter on magnetic resonance imaging.

RESULTS

We observed that the NAA/Cr values were abnormally low in the early stages of MS, even before significant disability (measured using the Expanded Disability Status Scale [EDSS]) was evident clinically, and declined more rapidly with respect to EDSS at lower than at higher EDSS scores (P<.001). The correlation of NAA/Cr values with EDSS score was significantly (P<.03) stronger in patients with mild disability (EDSS score <5, Spearman rank order correlation = -0.54, P<.001) than in patients with more severe disability (EDSS score >/=5, Spearman rank order correlation = -0.1, P<.9). When similar analyses were performed in patients with MS grouped for duration of disease, the subgroup with early disease duration (<5 years) also showed central brain NAA/Cr resonance intensity ratios significantly lower than healthy controls (P<.001).

CONCLUSION

Cerebral axonal damage begins and contributes to disability from the earliest stages of the disease.

[Introduction to functional magnetic resonance]

INTRODUCTION

During recent years we have seen the birth and development of a technique destined to revolutionize the world of the neurosciences, functional magnetic resonance (fMR). This new technique presents many challenges, both from the hardware point of view (little signal, relatively limited spatial and temporal resolution, artefacts, etc.) and of analysis (correction for movement, improved signal/noise ratio, statistical models used, etc.).

DEVELOPMENT

In this paper we review the most important aspects of fMR regarding artefacts, analysis and origin of the signal, based on the widely used BOLD contrast.

CONCLUSION

Although still at its beginnings, and in spite of aspects which need improvement, fMR appears to be a very useful tool both for clinical applications and investigation, and its use should be encouraged by normal MR imaging teams in everyday clinical practice.

Proton MR spectroscopy in multiple sclerosis

Axonal injury in multiple sclerosis (MS) is focal and diffuse, and is directly responsible for irreversible disability. Acute inflammatory events can be associated with reversible disability that may parallel reversible axonal injury. This in part accounts for the remission following relapses early in the disease. By the time there is clinical disability, substantial axonal injury already has occurred. This provides a strong rationale for the early limitation of inflammation and its consequences.

Evidence for adaptive functional changes in the cerebral cortex with axonal injury from multiple sclerosis

Axonal injury occurs even in the earliest stages of multiple sclerosis. Magnetic resonance spectroscopic imaging (MRSI) measurements of brain N:-acetylaspartate (NAA), a marker of axonal integrity, show that this axonal injury can occur even in the absence of clinically evident functional impairments. To test whether cortical adaptive responses contribute to the maintenance of normal motor function in patients with multiple sclerosis, we performed MRSI and functional MRI (fMRI) examinations of nine multiple sclerosis patients who had unimpaired hand function. We found that activation of the ipsilateral sensorimotor cortex with simple hand movements was increased by a mean of fivefold relative to normal controls (n = 8) and that the extent of this increase was strongly correlated (sigma = -0.93, P = 0.001) with decreases in brain NAA. These results suggest that compensatory cortical adaptive responses may help to account for the limited relationship between conventional MRI measures of lesion burden and clinical measures of disability, and that therapies directed towards promoting cortical reorganization in response to brain injury could enhance recovery from relapses of multiple sclerosis.

Regional axonal loss in the corpus callosum correlates with cerebral white matter lesion volume and distribution in multiple sclerosis

Previous imaging studies have suggested that there is substantial axonal loss in the normal-appearing white matter (NAWM) of brains from multiple sclerosis patients and that this axonal loss may be an important determinant of disability. Recently, substantial axonal loss in the NAWM has been confirmed directly in post-mortem tissue. Whether the NAWM changes occur as a consequence of damage to axons traversing lesions or to a more diffuse injury process is uncertain. Using formalin-fixed brains of eight multiple sclerosis patients and eight age-matched controls, we examined the relationship between demyelinating lesion load in three volumes of the cerebral white matter and the loss of axons in NAWM of the corresponding three projection regions (anterior, middle, posterior) in the corpus callosum (CC). There was a significant loss of calculated total number of axons crossing the CC in each of the three regions relative to the non-multiple sclerosis controls. Strong correlations were found between the regional lesion load and both the axonal density (r = -0.673, P: = 0.001) and the total estimated number of axons crossing the corresponding projection area in the CC (r = -0. 656, P: = 0.001) for the patients. This suggests that Wallerian degeneration of axons transected in the demyelinating lesions makes a major contribution to the substantial, diffuse loss of axons in the NAWM in multiple sclerosis. These findings emphasize the need to consider the consequences of multiple sclerosis lesions in terms of both local and distant effects in functionally connected regions of the brain.

An fMRI study of the lateralization of motor cortex activation in acallosal patients

Transcranial magnetic stimulation (TMS) studies have suggested that callosal afferents may mediate inhibition of the ipsilateral motor cortex (IMC) during unilateral hand movements. To test this concept, we used fMRI to determine whether acallosal patients have increased IMC activation with either complex or simple unilateral finger movements. Neither the localization of motor cortical regions activated, the volumes of activation, or the relative hemispheric lateralization of activations were different between the patients and normal controls. The potential callosal inhibitory pathway identified by TMS therefore does not appear to contribute to the interhemispheric suppression of physiologically relevant activations in the motor cortex as measured by fMRI.