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L Leocani

Publications and source records attributed to L Leocani.

At least 37 records · Page 2Linked to original sources
PubMed1999

Neurophysiological imaging techniques in dementia.

Neurophysiological methods, such as electroencephalography (EEG) and event-related potentials, are useful tools in the investigation of brain cognitive function in normal and pathological conditions, with an excellent time resolution when compared to that of other functional imaging techniques. Advanced techniques using a high number of EEG channels also enable a good spatial resolution to be achieved. This, together with the possibility of integration with other anatomical and functional images, may increase the ability to localize brain functions. Spectral analysis of the resting EEG, which gives information on the integrity of the cortical and subcortical networks involved in the generation of cortical rhythms, has the limitation of low sensitivity and specificity for the type of cognitive impairment. In almost all types of dementia, decreased power of the high frequencies is indeed observed in mild stages, accompanied by increased power of the slow rhythms in the more advanced phases. The sensitivity for the detection of spectral abnormalities is improved by studying centroid modifications. More specific information on the type of dementia can be provided by coherence analysis of the resting EEG, a measure of functional cortico-cortical connections, which has different abnormal patterns in Alzheimer's disease, cerebrovascular dementia and dementia associated with multiple sclerosis. Another tool for improving the assessment of demented patients is the study of EEG activity related to particular tasks, such as event-related potentials and event-related desynchronization/synchronization of the EEG, which allow the study of brain activation during cognitive and motor tasks.

Brain↗
PubMed1999

Review neuroimaging in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a chronic degenerative disorder of unknown etiology affecting the motor system. Conventional and non-conventional neuroimaging techniques can provide essential help both to increase the confidence in ALS diagnosis and to assess the disease evolution. Signal abnormalities at the level of the motor cortex and the corticospinal tract on conventional T2-weighted magnetic resonance (MR) images are a potentially useful marker of ALS pathology. However, the prognostic value of these conventional MR abnormalities is still hampered by their low pathological specificity. Non-conventional MR techniques with a higher pathological specificity, such as MR spectroscopy, magnetization transfer imaging and diffusion-weighted imaging, seem to have some potential not only for ALS diagnosis, but also for monitoring disease evolution either naturally or when modified by experimental treatments.

Amyotrophic Lateral Sclerosis↗
PubMed1999

EEG coherence in pathological conditions.

Coherence analysis of the electroencephalogram is considered an indicator of functional cortico-cortical connections, which makes it suitable for the neurophysiologic investigation of brain connectivity in normal and pathological conditions. In the clinical environment, coherence analysis has been applied in the study of brain development and in the assessment of diseases potentially involving brain connectivity, such as cortical and subcortical dementia, schizophrenia, and corpus callosum lesions. Whereas coherence decrease, at least for the high-frequency bands, is considered the expression of decreased functional cortico-cortical connections, more work needs to be performed in interpreting coherence increases. A special consideration is also required by technical aspects, such as the recording conditions and the reference used, which may greatly influence the results and need to be accounted for when drawing physiopathological interpretations. At present, whereas coherence analysis resulted successful in differentiating patients groups from the normal population, the specificity of coherence changes in various pathological conditions is questionable at the best. The same limits apply to the diagnostic value of the technique in individual patients.

Age Factors↗
PubMed1999

Measuring evoked responses in multiple sclerosis.

Evoked potentials (EPs) have been widely utilised in Multiple Sclerosis (MS) patients to demonstrate the involvement of sensory and motor pathways. Their diagnostic value is based on the ability to reveal clinically silent lesions and to objectivate the central nervous system damage in patients who complain frequently of vague and indefinite disturbances which frequently occurs in the early phases of the disease. The advent of magnetic resonance imaging (MRI) techniques has greatly reduced the clinical utilisation of EPs, which is not fully justifiable, as the information provided by EPs are quite different from those provided by MRI. The abnormalities of evoked responses reflect the global damage of the evoked nervous pathway and are significantly correlated with the clinical findings, while the vast majority of MRI lesions are not associated to symptoms and signs. Transversal and longitudinal studies have demonstrated that EP changes in MS are more strictly related to disability than MRI lesion burden. On the contrary, MRI is more sensitive than EPs in revealing the disease activity. Evoked responses modifications observed in MS are not disease-specific; moreover longitudinal studies showed latency and morphology changes of evoked responses not always related to clinical changes. Such a dissociation can be explained both by technical factors and by subclinical disease activity. To reduce the negative impact of technical aspects, only reproducible parameters of the evoked responses should be used to monitor disease evolution and therapeutic interventions.

Brain↗
PubMed1998

Event-related desynchronization to contingent negative variation and self-paced movement paradigms in Parkinson's disease.

The event-related desynchronization (ERD) to voluntary movement is an indicator of cortical activation with a high time resolution and a specific spatial representation. We have evaluated 10 patients affected by Parkinson's disease (PD), free from L-dopa treatment for at least 12 hours, and 10 control subjects. Each subject underwent ERD examination during self-paced movement (SPM) and during contingent negative variation (CNV) paradigms. ERD was measured as the percentage decrease of alpha band power and calculated for frequency bands of 1 Hz, ranging between 8 and 12 Hz. For group comparisons, the frequency showing the highest ERD was selected for each subject and for each side. In the control group, ERD in the CNV paradigm began over the contralateral centroparietal electrodes 1475 ms before movement onset of the right hand and 1375 ms for the left. In the SPM paradigm, ERD started over the contralateral central electrodes 2150 ms and 1775 ms before movement onset of the right and left hand, respectively. In the PD group, ERD started over the contralateral central areas 800 ms and 475 ms before movement onset of the right and left hand, respectively, for CNV paradigm and 1200 ms and 750 ms for the right and left hand, respectively, for SPM paradigm. Therefore, contralateral ERD began closer to movement onset in PD compared with the control group in both paradigms. ERD over the sensorimotor areas ipsilateral to the movement was not significantly different in PD compared with the control group. The finding of delayed contralateral ERD in PD is according to the view that functional cortical activation related to movement preparation is impaired in PD. The lack of group differences in the onset of ipsilateral ERD, which appears close to movement execution than contralateral ERD both in normal subjects and in PD, suggests that different mechanisms may be involved in generating ERD over the hemispheres ipsilateral and contralateral to the movement, and that only the latter are impaired in PD.

Adult↗
PubMed1998

Cyclic modulation of the H-reflex in a wrist flexor during rhythmic flexion-extension movements of the ipsilateral foot.

In 12 subjects, each sitting on an armchair with the right forearm prone, the H-reflex elicited in the resting flexor carpi radialis muscle underwent cyclic excitability changes correlated with rhythmic flexion-extension movements of the ipsilateral foot (frequency of oscillations between 1.5 and 2.5 Hz). During foot plantar flexion, the H-reflex underwent a clear-cut increase, the maximum facilitation falling, in most subjects, within the second half of that phase; then, a gradual reduction in size led the reflex amplitude back to the initial value at the end of foot dorsal extension. If present also when the wrist and the ankle are moved together, this facilitation should favour the in-phase (isodirectional) association between movements and, conversely, hinder the anti-phase coupling.

Adult↗
PubMed1998

Task-related coherence and task-related spectral power changes during sequential finger movements.

In order to investigate the activity of cortical regions in the control of complex movements, we studied task-related coherence (TRCoh) and task-related spectral power (TRPow) changes in 8 right-handed subjects during the execution of 4 different finger movement sequences of increasing complexity. All sequences were performed with the right hand and were paced by a metronome at 2 Hz. EEG power spectra and coherence values were computed within alpha (8-12 Hz) and beta (13-20 Hz) frequency bands for 29 scalp EEG positions during the execution of the sequences and were compared with values obtained during a rest (control) condition. Movement sequences were associated with TRPow decreases in the alpha and beta frequency bands over bilateral sensorimotor and parietal areas, with a preponderance over the contralateral hemisphere. Increases of TRCoh occurred over bilateral frontocentral regions. TRCoh decreases were present over the temporal and occipital areas. The spatial extent and the magnitude of TRPow decreases and TRCoh increases in both frequency bands were greater for sequential movements of higher complexity than for simpler ones. These results are consistent with previous findings of bilateral activation of sensorimotor areas during sequential finger movements. Moreover, the present results indicate an active intercommunication between bilateral and mesial central and prefrontal regions which becomes more intense with more complex sequential movements.

Adult↗
PubMed1998

Neurophysiological and cognitive markers of disease evolution in multiple sclerosis.

Both evoked potentials and cognitive tests may provide useful information which cannot be derived from the clinical observation. For this reason, there have been some attempts to use EPs in monitoring the natural history of the disease and in assessing the efficacy of therapeutic trials. However, no conclusion can be derived from the few available data. Although MRI is more sensitive than EPs in revealing new lesions in brain, cerebellum and brainstem, EPs are more sensitive in revealing optic nerve and spinal cord lesions. Moreover, the poor relationship between brain MRI abnormalities and disability has raised the possibility that cognitive evaluation may be an additional sensitive marker of brain involvement over time. Since the gold standard for the assessment of disease activity is uncertain, it is therefore advisable that frequent MRI, EPs and cognitive assessment may integrate clinical outcomes measured by conventional scales, both in the study of the natural disease course and in monitoring clinical trials.

Biomarkers↗
PubMed1998

Clinical, neurophysiological, and magnetic resonance imaging correlations in multiple sclerosis.

Magnetic resonance imaging (MRI) has a pivotal role in diagnosis of multiple sclerosis and is being increasingly used as a paraclinical measure to assess treatment efficacy in clinical trials. However, the correlations between clinical and MRI findings in patients with multiple sclerosis are weak and, therefore, newer MR techniques are being developed to increase both MRI sensitivity for detecting disease activity and its pathological specificity for better assessing disease evolution. Evoked potentials (EPs) can be used to confirm the diagnosis of multiple sclerosis and their abnormalities are correlated with symptoms and signs referable to involvement of the corresponding nervous pathways. However, their use is limited when assessing disease progression and monitoring clinical trials in multiple sclerosis. Both magnetic resonance imaging (MRI) and evoked potentials (EPs) provide information which cannot be obtained by clinical evaluation, especially for assessing disease activity. Nevertheless, both these paraclinical techniques cannot substitute for clinical measures of disability when assessing disease progression and monitoring phase III clinical trials in multiple sclerosis.

Blood-Brain Barrier↗
PubMed1997

Event-related desynchronization (ERD) in the alpha frequency during development of implicit and explicit learning.

To understand the role of the motor cortex in implicit and explicit learning, we studied alpha event-related desynchronization (ERD) while 13 right-handed individuals performed a variation of the serial reaction time task (SRTT). EEG signals were recorded simultaneously from 29 scalp locations and the ERD was computed. During data collection, all subjects developed implicit knowledge, demonstrated by shortening of the response time, and explicit knowledge of the test sequence. The average ERD maps of all 13 subjects demonstrated that during the initial learning, there was a decline in alpha band power that was maximal over the contralateral central region. The ERD reached a transient peak amplitude at a point when the subjects attained full explicit knowledge, and diminished subsequently. The transient peak in ERD was highly significant at C3. These electrophysiologic findings support previous studies which have demonstrated that motor activity changes as behavior changes over the course of learning.

Adult↗
PubMed1997

Event-related coherence and event-related desynchronization/synchronization in the 10 Hz and 20 Hz EEG during self-paced movements.

To investigate the activity of cortical regions in the control of movement, we studied event-related desynchronization/synchronization (ERD/ERS), event-related coherence (ERC), and phase coherence in 29-channel EEGs from 9 subjects performing self-paced movements of the right index finger. Movement preparation and execution produced ERD over the sensorimotor areas at 10 Hz and 20 Hz, followed by ERS. ERD corresponded spatiotemporally to an increase in coherence over the frontocentral areas. For both frequency bands, ERD began over the left sensorimotor areas and became bilateral at the time of movement onset. The coherence increase with frontal areas began in the left central areas and became symmetrical after EMG onset. The ERD and coherence increase was longer at 10 Hz than at 20 Hz. Phase coherence at 10 Hz showed a lead of anterior regions to posterior regions throughout the time period, and at 20 Hz showed a tendency toward zero phase delay corresponding with the movement. EEG desynchronization parallels functional coupling over sensorimotor and frontal areas. Event-related coherence and phase coherence findings implicate the frontal lobes in control of movement planning and execution. The involvement of different frequency bands with different timings may represent parallel changes in the cortical network.

Adult↗
PubMed1997

Steady-state movement-related cortical potentials: a new approach to assessing cortical activity associated with fast repetitive finger movements.

Traditionally, studies of movement-related cortical potentials have focused on the preparation of single self-paced movements performed slowly. We studied MRCPs elicited by metronome-paced, fast repetitive finger movements (2/s) with 28-channel (10 normal subjects) and 122-channel (two subjects) EEG. EMG-locked averaging of 500 ms time windows (300 ms before to 200 ms after each EMG onset) produced a distinct pattern of phasic MRCPs (steady-state MRCPs). The main components were a pre-movement peak (pre-MP), 57 ms before EMG onset, and a post-movement peak (post-MP), 93 ms after EMG onset. From timing information and topographic mapping results, we propose that the pre-MP is largely generated by a tangential source in the anterior bank of the central sulcus and reflects precentral motor processing, whereas the post-MP is generated in the posterior bank of the central sulcus and represents post-central feedback processing. Steady-state MRCPs require actual recording times of less than 10 min, and show excellent inter-session reproducibility. These characteristics may make them convenient for studying sensorimotor cortex activity experimentally and clinically.

Adult↗
PubMed1997

Intravenous immunoglobulin treatment in multifocal motor neuropathy and other chronic immune-mediated neuropathies.

This review deals with the use of intravenous IVIg immunoglobulins in the treatment of chronic immune-mediated neuropathies: multifocal motor neuropathy, chronic inflammatory demyelinating polyneuropathy, neuropathies associated with monoclonal gammopathies. A particular attention is given to case series and trials which compare IVIg to other therapies, such as steroid treatment immunosuppressors and plasma exchange. At present clinical and instrumental data seem to indicate the short term efficacy of IVIg in multifocal motor neuropathies, especially as early treatment; further studies are need in order to prove its long term efficacy in this disease. Concerning chronic inflammatory demyelinating polyneuropathies, short term IVIg efficacy is comparable to that of plasma exchange and in the long term most patients need repeated treatments. Most patients respond to the initial therapy and the initial nonresponders usually improve with a second treatment modality.

Autoimmune Diseases↗