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Biomedical subjects

A Fiaschi

Publications and source records attributed to A Fiaschi.

At least 55 records · Page 3Linked to original sources
PubMed1997

Selective gating of lower limb cortical somatosensory evoked potentials (SEPs) during passive and active foot movements.

We evaluated subcortical and cortical somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation in 4 experimental conditions of foot movement and compared them with the baseline condition of full relaxation. The experimental conditions were: (a) active flexion-extension of the stimulated foot; (b) active flexion-extension of the non-stimulated foot; (c) passive flexion-extension of the stimulated foot in complete relaxation; (d) tonic active flexion of the stimulated foot. We analyzed latencies and amplitudes of the subcortical P30 potential, of the contralateral pre-rolandic N37 and P50 responses and of the P37, N50 and P60 potentials recorded over the vertex. Latencies did not vary in any of the paradigms. The amplitude of subcortical P30 potential did not change during any of the paradigms. Among the cortical waves, P37, N50 and P60 amplitudes were significantly attenuated in all conditions except active movement of the non-stimulated foot (b). This attenuation was less during passive (c) than during active movements of the stimulated foot (a and d). The contralateral pre-rolandic waves N37 and P50 showed no significant decrease during any of the paradigms. These results suggest that gating occurs rostrally to the cervico-medullary junction, probably at cortical level. The different behavior of N37, P50 and P37, N50 cortical responses during movement of the stimulated foot provides evidence suggestive of a highly localized gating process occurring at cortical level. These potentials could reflect activation of separate, functionally distinct generators.

Adult↗
PubMed1997

Crossed and direct effects of digital nerves stimulation on motor evoked potential: a study with magnetic brain stimulation.

We studied the influence of contralateral and ipsilateral cutaneous digital nerve stimulation on motor evoked potentials (MEPs) elicited in hand muscles by transcranial magnetic stimulation (TMS). We tested the effect of different magnetic stimulus intensities on MEPs recorded from the thenar eminence (TE) muscles of the right hand while an electrical conditioning stimulus was delivered to the second finger of the same hand with an intensity four times above the sensory threshold. Amplitude decrement of conditioned MEPs as a function of magnetic stimulus intensity was observed. The lowest TMS stimulus intensity produced the largest decrease in conditioned MEPs. Moreover, we investigated the effects of ipsilateral and contralateral electrical digital stimulation on MEPs elicited in the right TE and biceps muscle using an intensity 10% above the threshold. Marked MEP inhibition in TE muscles following both ipsilateral and contralateral digital stimulation is the main finding of this study. The decrease in conditioned MEP amplitude to ipsilateral stimulation reached a level of 50% of unconditioned MEP amplitude with the circular coil and 30% with the focal coil. The amplitude of conditioned MEPs to contralateral digital stimulation showed a decrease of 60% with the circular coil and more than 50% with the focal coil. The onset of the inhibitory effect of contralateral stimulation using the focal coil occurred at a mean of 15 ms later than that of ipsilateral stimulation. No MEP inhibition was observed when recording from proximal muscles. Ipsilateral and contralateral digital stimulation had no effect on F wave at appropriate interstimulus intervals, where the main MEP suppression was noted. We stress the importance of selecting an appropriate test stimulus intensity to evaluate MEP inhibition by digital nerves stimulation. Spinal and cortical sites of sensorimotor integration are adduced to explain the direct and crossed MEP inhibition following digital nerves stimulation.

Adult↗
PubMed1997

Reversible changes of motor cortical outputs following immobilization of the upper limb.

We mapped the cortical representations of the abductor pollicis brevis, flexor carpi radialis, biceps and deltoid muscles in six subjects with unilateral wrist fractures, immediately after the removal of the splint. This was repeated 1 month later in three out of the six subjects. Duration of immobilization was 1 month. Muscle maps were obtained by delivering four focal magnetic pulses for each scalp position (1 cm apart with reference to Cz) over the contralateral hemisphere. Motor evoked potentials (MEPs) were averaged off-line and expressed as a percentage of the motor action potential evoked by supramaximal peripheral nerve stimulation. Volume, area and threshold of the motor maps showed no significant hemispheric differences within each muscle in 10 control subjects. In the first recording session the volume of each immobilized muscle was distinctly higher when compared to that of controls in terms of absolute value and side-to-side ratio. This finding disappeared 1 month later. Moreover, MEP amplitude difference recorded from hand muscle could be reversed during a small tonic voluntary contraction. Immobilization had no significant effect on the threshold for activation of the target muscles and on the area of the motor map. The increase in MEP amplitudes occurred without changes in spinal excitability as tested by the F wave. These findings suggest that immobilization of the upper limb induces a reversible enhancement of the excitability of structures along the corticomotoneuronal pathway. Sustained restriction of volitional movements and reduction in somatic sensory inputs might promote this functional modulation of the motor system.

Adult↗
PubMed1997

Amplitude changes of tibial nerve cortical somatosensory evoked potentials when the ipsilateral or contralateral ear is used as reference.

We performed topographical mapping of somatosensory evoked potentials (SEPs) to the posterior tibial nerve using earlobe references both ipsilateral and contralateral to the stimulation side. The voltage of the frontal contralateral N37 and P50 components was enhanced, while the voltage of the parietal ipsilateral P37 and N50 components was reduced when the contralateral earlobe was substituted by the ipsilateral earlobe reference. Maps of the same data documented concomitant changes in negative and positive potential fields, showing an expansion of the pre-Rolandic N37 toward the centrotemporal contralateral regions, and a tendency of the parietal ipsilateral P37, N50 components to be more focally distributed at the vertex. SEPs recorded at each earlobe (Cv6 reference) provided an explanation of these results: The contralateral earlobe detected a negative potential corresponding to the N37 potential recorded over the scalp, followed by a P50 potential that attenuated the contralateral responses and enhanced the ipsilateral ones. The ipsilateral earlobe had no significant effects on scalp SEPs, since it detected only a large N33 negativity. Current source density (CSD) maps were, of course, not influenced by the ear used as reference. Our results suggest that the ipsilateral ear reference is better than the contralateral one for recording "genuine" cortical SEPs. Therefore, it can be recommended in the clinical domain for mapping studies of lower-limb cortical SEPs.

Adult↗
PubMed1996

'Direct' and 'crossed' modulation of human motor cortex excitability following exercise.

Rapid repetitive movements of the thumb (1 min duration) produce a reversible decrease in the activated primary motor cortex (MI) excitability to transcranial magnetic stimulation (TMS) with recovery within 35-40 min. In the present study we investigated (1) the role of peripheral sensory feedback in inducing such decrease and (2) possible effects of exercise on the non-activated MI. Stimulation of peripheral Ia afferent fibres, induced by 1 min vibration of thenar muscles and 2 Hz electrical stimulation of the median nerve at the wrist, have no effect on motor evoked potential (MEP) amplitude to TMS suggesting no role for sensory feedback to produce MI excitability modulation. Exercise produces a significant (P < 0.01) decrease of MEPs for homologous non-exercised muscles with concomitant contraction of corresponding motor cortical output maps, suggesting that changes in MI excitability also occur in the nonactivated hemisphere. This 'crossed' effect might relate to an interhemispheric transfer of information, via homotopic connections of the corpus callosum.

Adult↗
PubMed1996

Neural generators of tibial nerve P30 somatosensory evoked potential studied in patients with a focal lesion of the cervicomedullary junction.

The tibial nerve P30 potential was studied in 6 patients with focal lesions located in the vicinity of the cervicomedullary junction. P30 potential was unaffected while cortical P39 was abnormal in the patients with a supramedullary lesion affecting the somatosensory pathway just above its decussation. Conversely, P30 was abnormal in the presence of a lesion situated caudally to the cervicomedullary junction affecting the lower limb sensory fibers just below their decussation. Median nerve P14 behaved similarly to the P30 potential in these cases. These clinical observations suggest that P30 potential, as P14 of median nerve somatosensory evoked potentials, is generated in the lower brain stem probably before the decussation of the sensory fibers; nucleus gracilis and medial lemniscus fibers in the lower brain stem are probably the anatomical structures generating P30 potential. This suggests that P30 potential may be used to study intraspinal and intracranial conduction times separately in the afferent somatosensory pathways.

Adult↗
PubMed1996

Effect of stimulus rate on the cortical posterior tibial nerve SEPs: a topographic study.

We performed topographical mapping of somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation delivered at 2, 5 and 7.5 Hz in 15 healthy subjects. P37 was significantly attenuated at 5 and 7.5 Hz and the N50 component attenuated only at 5 Hz, its amplitude remaining stable for further increases in stimulus frequency. Frontal N37 and P50 potentials showed no significant decrease when the stimulus repetition frequency was changed from 2 to 7.5 Hz. P60 showed an attenuation of the amplitude only at 7.5 Hz. Latency and scalp topographies of all cortical components examined remained unchanged for the 3 stimulus rates tested. The optimal stimulus rate for mapping of tibial nerve SEPs was lower than 5 Hz. The distinct recovery function of the contralateral. N37-P50 and ipsilateral P37-N50 responses suggests that these potentials arise from separate generators.

Adult↗
PubMed1995

Long-lasting depression of motor-evoked potentials to transcranial magnetic stimulation following exercise.

We used transcranial magnetic stimulation to study the modulation of motor cortex excitability after rapid repetitive movements. Eleven healthy subjects aged 24-32 years were evaluated. Serial motor-evoked potential (MEP) recordings were performed from the right thenar eminence every 5 min for a period of 20 min at rest and for a period of 35 min after repetitive abduction-adduction of the thumb at maximal frequency for 1 min. All subjects presented distinct changes in MEP amplitude after exercise with an approximately 55% mean maximal decrease compared with basal conditions and complete recovery 35 min after the end of the exercise. The time course of MEP amplitude changes presented the following trend: (1) a rapid decrease phase within the first 5 min; (2) a maximal depression phase of 10 min duration (from the 5th to the 15th min); and (3) a slow recovery phase. No significant modifications in post-exercise MEP amplitude were found in ipsilateral non-exercised muscles. In order to determine the level where these changes take place, we recorded the M and F waves induced by median nerve stimulation at the wrist (all subjects) and MEPs in response to transcranial electrical stimulation (five subjects) at rest and during the decrease and maximal depression phases. None of these tests were significantly affected by exercise, indicating that the motor cortex was the site of change. Evaluation of maps of cortical outputs to the target muscle, performed in four subjects, showed an approximately 40% spatial reduction in stimulation sites evoking a motor response during the maximal depression phase. These data prove that exercise induces a reversible, long-standing depression of cortical excitability, probably related to intracortical presynaptic modulation, which transitorily reduces the motor representation area.

Adult↗
PubMed1995

Subcortical P30 potential following tibial nerve stimulation: detection and normative data.

Stimulation of the tibial nerve evokes a P30 far-field potential over the scalp which, like the median nerve P14, probably originates in the vicinity of the cervico-medullary junction. Unlike the P14 potential, P30 recording has not been systematically performed in clinical practice, probably because of doubts about the generator of the potential and the possibility of consistently recording it on the scalp after the unilateral stimulation of the tibial nerve. In this study, we tested the reliability of the tibial nerve scalp far-field P30 potential in 34 normal subjects using different montages, of which the Fpz-Cv6 derivation gave the highest signal to noise ratio, making it possible to obtain a P30 potential peaking at 29.2 +/- 1.6 msec in all normal subjects. This suggests that this component should to be included in the routine recording of tibial nerve SEPs in order to evaluate the spinal and intracranial conduction of the somatosensory pathway separately.

Adult↗
PubMed1995

Neurophysiological and urodynamic examinations in the functional assessment of the spinal cord below the injury site.

We examined the characteristics of specific components of the evoked electrospinogram (EESG) in response to tibial nerve stimulation in 28 patients with traumatic injury of the dorsal and cervical spinal cord. The data were correlated with clinical, urodynamic and additional neurophysiological findings. In the majority of patients (82%), 11 with complete and 12 with partial spinal cord lesions, the lumbar components of the EESG were normal. In 4 of these patients with complete lesion above T2 the dorsal EESG was absent. In 5 cases (18%), the lumbosacral EESG was altered in the presence of an atypical clinical syndrome characterized by persistent urinary retention associated with lower leg atrophy and reduced tendon jerks. In these cases, MRI provided evidence of an unexpected sacral lesion. Unlike the dorsal EESG reflecting the afferent dorsal column volley, the lumbar components of the EESG are usually unaffected by interruption of the cord pathways; these last events thus originate from segmental neuronal activity, the involvement of which bears witness to additional lumbosacral damage.

Adolescent↗
PubMed1994

Cortical output modulation after rapid repetitive movements.

Transcranial magnetic stimulation was used to evaluate changes in motor cortex excitability after rapid repetitive movements in five healthy subjects aged 23-30 years, by considering the amplitude of motor evoked potentials (MEPs) at rest and after one minute of maximal frequency repetitive abduction-adduction movements of the thumb. In addition, M and F waves were evaluated by stimulating the median nerve at the wrist. All of the examined subjects showed a clear modification in post-exercise MEP amplitudes, with a mean maximal reduction of 50-60% in comparison with basal values and complete recovery after a period of about 35 minutes. The time course of this phenomenon showed a triphasic pattern: (I) a rapid decrease phase up to the fifth minute; (II) a maximal depression phase for a period of about ten minutes; (III) a slow return to basal values. No significant changes were observed in post-exercise M and F waves. These results show the existence of a reversible modulation of the excitability of the upper motor neuron after rapid repetitive movements. It is likely that this modulation takes place at the level of the motor cortex and that its anatomo-functional substrate is represented by the activation of inhibitory intracortical circuits.

Adult↗
PubMed1994

Hemiparkinsonism-hemiatrophy syndrome: neuroradiological and neurophysiological findings.

A rare form of secondary parkinsonism has been recently described as 'hemiparkinsonism-hemiatrophy syndrome'. We report a case with such clinical features. A neurophysiological study of the evoked potentials, somatosensory and motor, has been conducted. We stress the neuroradiological findings at nuclear magnetic resonance, which documented the presence of an area of altered signal in the mesencephalon, between the cerebral pedunculus and the red nucleus on the right side. The etiopathogenetic considerations and diagnostic criteria are discussed. Moreover we evaluate the efficacy of levodopa therapy.

Adult↗
PubMed1993

Short term prognosis of stroke in a clinical series of 94 patients.

We conducted a study on the factors predictive of early mortality (within 30 days of onset of symptoms) in a clinical series of 94 patients at their first stroke. Irrespective of the type of stroke, ischemic or hemorrhagic, early mortality proved to correlate with clinical parameters, such as coma at onset, presence of paralysis, changes in ocular motility, and neuroradiological parameters (lesion size on the CT scan) indicative of stroke severity.

Adult↗
PubMed1992

Dementia of Alzheimer type (DAT) in a man chronically exposed to pesticides.

A patient chronically exposed to pesticides with dementia of Alzheimer type (DAT) is presented. We evaluate the pathogenic role of these substances in the disease and suggest the usefulness of an epidemiological attention on the environmental factors in certain neurodegenerative diseases.

Alzheimer Disease↗
PubMed1991

Rigidity and painful muscle spasms in a patient with probable myelitis.

We describe a case of continuous motor unit potential (MUP) activity of central origin (unlike stiff man syndrome and progressive encephalomyelitis) characterized clinically by rigidity, painful muscle spasms, abnormal postures and spinal myoclonus. The topography of the manifestations, the subacute and benign course, the presence of stable sequels 2 years after onset and a searching process of differential diagnosis lead us to attribute the condition to an inflammation of the cord, which makes the case of particular clinical interest.

Adult↗