Electrophysiological studies of brain plasticity of the motor system

Neurological Sciences - Brain plasticity, intended as the pattern of functional and structural changes in responses to environmental physiological or pathological events, is underlined by several...     

A multiparametric MRI study of frontal lobe dementia in multiple sclerosis

Previous studies achieved conflicting results when correlating magnetic resonance imaging (MRI) abnormalities and cognitive impairment in multiple sclerosis (MS) patients. Recently, the estimation of MS lesion load on T1-weighted images and the analysis of magnetization transfer ratio (MTR) histograms, increased the degree of the correlation between physical disability and MRI findings in MS. We assessed the relationship of conventional and non-conventional MRI-derived measures with frontal lobe dementia in MS. Dual echo, T1-weighted and MT MRI scans of the brain were obtained in 11 MS patients with and in 11 without frontal lobe dementia, matched for age, sex, education and disability. Total (TLL) and frontal (FLL) lesion loads were assessed from T2- and T1-weighted scans. MTR histogram analysis was performed for the whole brain, the frontal lobe and the cerebellum. Median TLL and FLL were significantly higher in cognitively impaired patients on both T2- and T1-weighted scans. The MRI measure that better discriminated the two groups of patients was T1-weighted TLL (median values were 19.1 ml for demented and 1.9 ml for non-demented patients, P=0.006). Average MTR, peak height and location of overall brain and frontal lobe histograms were significantly lower for cognitively impaired than for cognitively intact patients (P values ranged from 0.0001 to 0.001). Cerebellar MTR histogram metrics did not significantly differ in patients with and without cognitive decline. The presence of cognitive decline in MS is associated with the extent and pathological severity of brain MRI abnormalities.     

Electroencephalographic coherence analysis in multiple sclerosis: correlation with clinical, neuropsychological, and MRI findings

OBJECTIVE: To explore functional corticocortical connections in multiple sclerosis by means of coherence of the EEG, and to evaluate their correlations with the degree of cognitive impairment and with brain lesion load assessed by MRI. METHODS: EEG coherence was studied from 28 patients with clinically definite multiple sclerosis. Ten minutes of resting EEG were recorded with 20 scalp electrodes, with binaural reference. FFT power and coherence were calculated in artifact free epochs of 1 second and compared with values from 22 control subjects of comparable age and sex distribution. Patients also underwent MRI (n=27) and neuropsychological examination (n=21). RESULTS: Compared with controls, patients with multiple sclerosis showed increased theta power in the frontotemporal-central regions (p<0.005). theta Band coherence was decreased between homologous areas (p<0.02). alpha Band coherence was decreased both in the local and long distance connections (p<0.0005). These findings were most striking both in patients with high MRI subcortical lesion load and in patients with cognitive involvement. A significant correlation was found between interhemispheric theta (p=0.02) and alpha (p=0. 017) and anteroposterior alpha (p=0.013) coherence and subcortical MRI lesion load, but not with exclusively periventricular lesion load. CONCLUSIONS: These findings support the hypothesis that cognitive impairment in multiple sclerosis is mostly dependent on involvement of corticocortical connections related to demyelination and/or axonal loss within the white matter immediately underlying the cortex.     

Neurophysiological investigations in multiple sclerosis

The advent of magnetic resonance imaging techniques has greatly reduced the diagnostic value of neurophysiological tests, particularly evoked potentials, in multiple sclerosis patients, because of the higher sensitivity in revealing subclinical involvement of the central nervous system. Technical progress and new methods of investigating afferent and efferent nervous pathways would seem to increase the sensitivity in detecting neural dysfunction, but the 'clinical gain' is modest at best. More promising is the utilization of neurophysiological tests to quantify the severity of white matter involvement. Transversal and longitudinal studies have demonstrated good correlations between neurophysiological parameters and disability measures, indicating that a battery of neurophysiological tests could be useful in monitoring the disease evolution in single patients and as surrogate endpoints in clinical trials. Further studies are needed for a better definition of the applications of evoked potentials and other neurophysiological techniques. Finally, event-related potentials and advanced electroencephalogram techniques, such as coherence analysis, could provide useful information on the pathophysiology of cognitive dysfunction, so common in multiple sclerosis patients, and with a strong impact on the quality of life.     

Striatal hand in Parkinson’s disease: the re-evaluation of an old clinical sign

Among postural abnormalities in Parkinson’s disease (PD), striatal hand (SH) is a particularly underexplored phenomenon. It leads to extreme abnormalities of hand posture, causing altered dexterity, pain and disfigurement. In our study, three blinded investigators examined several pictures of the hands of individuals with PD (N = 40) and controls (N = 15). The investigators quantified postural alterations using the Striatal Hand Score. Demographic and clinical data were also collected. As no differences were detected among investigators agreement, a final Hand Score (HS, range 0–4) was obtained for each hand. The Striatal Hand Score in both the left and right hand was significantly different in PD compared to controls (p < 0.001 for both left and right hand). Striatal hand was significantly worse on the side of PD onset, and on the side with greater PD symptomatology. The finding of a striatal hand was 100 % specific for a diagnosis of PD. Nine PD subjects were evaluated both on and off medication, and dopaminergic treatment did not significantly change the Striatal Hand Score. Our findings suggest that in patients without any explanation for hand deformities other than PD, striatal hand occurs very often, and is highly specific for the side of worst PD involvement. We recommend including an evaluation for SH as part of routine practice. This study emphasizes the importance of a careful observation of the patient in order to improve diagnostic accuracy.     

Visual evoked potentials may be recorded simultaneously with fMRI scanning: A validation study

Integrating electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data may help to optimize anatomical and temporal resolution in the investigation of cortical function. Successful removal of fMRI scanning artifacts from continuous EEG in simultaneous recordings has been reported. We assessed the feasibility of recording reliable visual evoked potentials (VEPs) during fMRI scanning using available artifact removing procedures. EEG during administration of visual stimuli was recorded using MRI-compatible 32-channel equipment in nine normal subjects (mean age, 23.9 +/- 2.5 years), with and without fMRI acquisition. fMRI scanning and cardioballistographic artifacts were removed after subtraction of averaged artifact waveforms. Consistency between VEPs waveforms and of P1 and N1 peak latencies and amplitudes in the two conditions was assessed. Good correlation was found between VEP waveforms (Pearson's correlation coefficient: r(P) between 0.76-0.94 across subjects; P < 0.0001) and between latency or amplitude of P1 and N1 peaks (latencies: r = 0.7, P < 0.035; amplitudes: r > 0.65, P < 0.05; Spearman rank correlation coefficient) in the two recording conditions. No significant differences were found between P1 and N1 parameters in the two conditions (Wilcoxon signed rank test). Consistent VEP waveforms, latencies, and amplitudes with and without fMRI scanning indicate that reliable VEPs may be obtained simultaneously with fMRI recording. This possibility might be helpful by shortening recording times and reducing variability from learning, habituation, and fatigue phenomena from separate recordings for the integration of event-related EEG and fMRI data.     

Physiopathology and treatment of fatigue in multiple sclerosis

Fatigue is a common symptom of patients with multiple sclerosis (MS). It is reported by about one-third of patients, and for many fatigue is the most disabling symptom. Fatigue may be associated with motor disturbances and/or mood disorders, which makes it very difficult to determine whether the fatigue is an aspect of these features or a result per se of the disease. Although peripheral mechanisms have some role in the pathogenesis of fatigue, in MS there are clear indications that the more important role is played by “central” abnormalities. Neurophysiological studies have shown that fatigue does not depend on involvement of the pyramidal tracts and implicate impairment of volitional drive of the descending motor pathways as a physiopathological mechanism. Metabolic abnormalities of the frontal cortex and basal ganglia revealed by positronemission tomography and correlations between fatigue and magnetic resonance imaging lesion burden support this hypothesis. Some recent studies also suggest that pro-inflammatory cytokines contribute to the sense of tiredness. No specific treatments are available. Management strategies include medications, exercise, and behavioural therapy; in most cases a combined approach is appropritate. Received: 26 September 2000, Accepted: 28 September 2000