PubMed Health⌕ Search

Biomedical subjects

M D Caramia

Publications and source records attributed to M D Caramia.

31 records · Page 2Linked to original sources
PubMed1991

Brain excitability and electroencephalographic activation: non-invasive evaluation in healthy humans via transcranial magnetic stimulation.

Excitability changes of the central motor tracts as a function of the electroencephalographic (EEG) characteristics has been investigated in 10 healthy volunteers. Transcranial magnetic stimulation (TCS) was administered to the right motor cortex with an intensity 5-10% above threshold for the elicitation of motor evoked potentials (MEPs) in the left forearm muscles. Simultaneously, the right median nerve was stimulated to provoke an H-reflex in the forearm flexors and EEG activity was recorded from the left hemiscalp. Subjects were completely relaxed and were asked at random either to keep the eyes closed while maintaining mental inactivity (A) or to open their eyes and perform mental arithmetics (B). Latencies and amplitudes of MEPs and H-reflexes were statistically matched with the spectral content of the EEG. In condition A, MEPs of 119 +/- 61 microV, with up to 36% of missing responses and background EEG activity dominated by rhythms in the alpha range were found. In condition B, MEPs of 219 +/- 66 microV (P less than 0.001), with less than 16% of missing responses, 'blocking' of the background alpha rhythms, and a potentiation of the faster ones' relative power were observed. Changes of the H-reflex characteristics were neither statistically significant nor related to MEP amplitude and EEG spectral profile fluctuations.

Brain↗
PubMed1991

Brain excitability and long latency muscular arm responses: non-invasive evaluation in healthy and parkinsonian subjects.

Thirty healthy and 35 volunteers affected by Parkinson's disease (PD) were examined. Long latency responses (LLRs) and short latency somatosensory evoked potentials (SEPs) after median nerve stimulation were respectively recorded from forearm flexor muscles, and from 19 scalp electrodes, during relaxation (condition 1), light and maximal muscle contraction (conditions 2 and 3). Linear interpolation of SEPs was performed to produce isopotential colour maps. Latencies and amplitudes of the V1-V2 component in LLR, as well as of parietal, central and frontal scalp SEPs were analysed in the 3 experimental conditions. Highly significant inverse correlation matched the frontal SEP to the LLR V2 component amplitudes, both in healthy and in PD subjects. However, the V2 component--which in the former group was reliably identifiable only in condition 3--was presented in conditions 1 and 2 in a high percentage of PD subjects who also showed an abnormally reduced frontal SEP during complete relaxation. Excitability changes of brain motor areas induced by a sensory input were tested as follows: the motor cortex was transcranially stimulated (TCS) by magnetic pulses with an intensity 10% below (A) or above (B) the threshold for twitch elicitation during complete relaxation of forearm muscles; TCS was randomly preceded (range 14-32 msec) by a shock to the median or ulnar nerve at the elbow with identical characteristics as for LLR elicitation. An initial epoch of 'inhibition' followed by a peak of 'facilitation' of the amplitude of motor responses to TCS was observed when conditioning stimuli to the median nerve preceded TCS by 14-20 and by 24-32 msec, respectively. Contrary to normals, conditioning stimulation of the median nerve did not significantly influence the excitability threshold to TCS in those parkinsonians with depressed frontal N30.

Adult↗
PubMed1991

Non-invasive evaluation of central motor tract excitability changes following peripheral nerve stimulation in healthy humans.

The interval between muscle stretch and the onset of the long latency electromyographic responses (LLRs) has been theoretically fragmented into an afferent time (AT), taken at the peak of wave N20 of somatosensory evoked potentials and an efferent time (ET), calculated by means of magnetic transcranial stimulation (TCS), the two being separated by a cortical interval (CI). If this were the case, the afferent input should progressively 'energize' the sensorimotor cortex during the CI and change the excitability of cortico-spinal tracts. To investigate this, motor evoked potentials (MEPs) from thumb flexor muscles were recorded, whilst a conditioning stimulation of median or ulnar nerve randomly preceded (10-48 msec intervals) magnetic brain TCS. Nerve stimulation was adjusted to motor threshold and amplitudes of conditioned and test MEPs at different nerve-TCS interstimulus intervals were evaluated. Conditioned MEPs were significantly attenuated with nerve-TCS intervals between 16 and 20 msec for elbow and 20 and 22 msec for wrist stimulation. This was followed by MEP potentiation with nerve-TCS intervals corresponding to the sum of AT + CI (mean 23.2 msec, range 21.7-24.8). The onset latency of facilitated conditioned MEPs was about 1 msec briefer than that of test MEPs, but invariably longer than the latency of MEPs facilitated by a voluntary contraction. This protocol did not demonstrate amplitude facilitation of the segmental H reflex, corroborating the idea that the facilitated part of the conditioning nerve-TCS curve receives a transcortical loop contribution.

Adult↗
PubMed1991

'Excitability changes of muscular responses to magnetic brain stimulation in patients with central motor disorders.

The 'excitability' and 'conductivity' of motor pathways during transcranial stimulation (TCS) have been investigated in 49 patients affected by multiple sclerosis (34), amyotrophic lateral sclerosis (7), spino-cerebellar ataxia (3), primary lateral sclerosis (4) and brain metastasis (1). Hyper-reflexia, spasticity and weakness were correlated with the central motor conduction time (CCT) and with the threshold intensity of TCS required to produce a motor evoked potential (MEP). MEPs to magnetic TCS were recorded from hand and foot muscles during relaxation, contraction and after tendon vibration. Thresholds and CCTs of the patients were compared with those of 30 healthy controls. Increased threshold was found in 37 out of 49 patients (75.5%). Prolongation of the CCT was found in 38 out of 63 clinically affected upper limbs (60.3%) and in 56 out of 77 clinically affected lower limbs (72.7%). Absent motor responses to maximal TCS were found in 20 out of 98 lower limbs (20.4%). Excluding ALS patients (in whom there was a lower threshold for MEP elicitation), a significant linear correlation was found between prolonged CCT and increased threshold. While MEPs with prolonged CCTs have elevated TCS threshold, it is important to note that an elevated threshold was found in 14 out of 49 patients (28.5%) despite unchanged CCT. Spasticity and/or hyper-reflexia were more frequently associated with increased threshold than with prolonged CCT, while weakness was correlated equally well with both these parameters. In this respect magnetic TCS proves to represent a new tool for the detection of abnormal 'excitability' of the central motor tracts.

Adolescent↗
PubMed1991

Prime mover muscle in finger lift or finger flexion reaction times: identification with transcranial magnetic stimulation.

When recording the onset of the electromyographic (EMG) voluntary response in reaction time (RT) studies, the electrodes should be placed on the muscle which is first and foremost involved in executing the response. It is thus necessary to identify which is the prime mover muscle among active synergic muscles. This has been investigated for index finger lift or flexion RTs by delivering a magnetic stimulus to motor cortical areas prior to the subject's voluntary response. The EMG responses to the magnetic stimulus were selectively facilitated either in the extensor indicis proprius muscle (in index lift RTs) or in the first dorsal interosseous muscle (in index flexion RTs). These effects are robust and provide a method for identifying the prime mover muscle in voluntary movements.

Adult↗
PubMed1989

Single fibre motor evoked potentials to brain, spinal roots and nerve stimulation. Comparisons of the 'central' and 'peripheral' response jitter to magnetic and electric stimuli.

Single fibre motor evoked potentials to magnetic and electric non-invasive stimulation of brain, spinal cord and peripheral nerve were recorded in 8 healthy volunteers. The 'central motor jitter' and the 'peripheral motor jitter' were respectively calculated and a comparison between the magnetic and electric modalities was made. The highest degree of latency variability was observed for both magnetic and electric central motor jitter, whilst the peripheral motor jitter to nerve stimulation was as low as the neuromuscular one (range 16-60 microsecond). The magnetic 'central motor jitter' (range 94-1024 microsecond) was much larger than the electric one (range 55-280 microsecond), which was in the order of jitter calculated on H-reflex studies; moreover, the former was organized in a bi- or trimodal distribution. On the contrary, no significant differences were observed between the two modalities when the jitter to nerve stimulation was taken into account. Possible contributions of corticocortical circuitries containing several synaptic interruptions during magnetic as opposed to electric transcranial stimulation, is discussed.

Adult↗
PubMed1989

Electric vs magnetic trans-cranial stimulation of the brain in healthy humans: a comparative study of central motor tracts 'conductivity' and 'excitability'.

Motor evoked potentials (MEPs) were elicited in the thenar muscles of 11 healthy volunteers via individual electric unifocal and magnetic trans-cranial stimuli (TCS). The effects of TCS strength, of the muscular state (relaxed, contracted) as well as of the amplitude-latency characteristics and the duration of the motor tracts central conduction times (CCTs) to hand muscles, were evaluated and compared between the two types of brain excitation. MEPs with the shortest latency (18.91 +/- 1.31 ms) were recorded in the voluntarily contracted muscle during electric TCS, whilst those with maximal latency (23.3 +/- 1.63 ms) were found after magnetic TCS with an intensity at threshold for eliciting an MEP of about 0.1 mV in the relaxed muscle. Mean CCTs for electric and magnetic TCS calculated in the contracted target muscles, were respectively 5.07 +/- 0.51 and 6.34 +/- 0.46 ms. MEPs with larger amplitudes and durations were observed during magnetic TCS, being maximal when suprathreshold stimuli were delivered. A restricted range of liminar values of magnetic TCS was obtained by defining the threshold for raising motor responses in complete muscle relaxation, indicating that magnetic pulses might represent a useful probe for testing the 'excitability' of the motor tracts.

Action Potentials↗
PubMed1989

Sensory (VEP, BAEP, SEP) and motor-evoked potentials, liquoral and magnetic resonance findings in multiple sclerosis.

In order to define the most suitable instrumental protocol for the diagnosis of multiple sclerosis (MS), 41 patients with definite (D = 14), probable (P = 14) and suspected (S = 13) MS were examined with CSF immunology, brain MRI and multimodal evoked potentials. The central motor tracts were also tested. The following alteration rates were found: MRI = 78%, CSF = 63.6%, VEP = 70.0%, median nerve SEP = 50%, peroneal nerve SEP = 68.0%, BAEPs = 35.7%, motor-evoked potentials (MEPs) = 74.0%. Altogether, EPs were abnormal in 90% of cases. Normal MRI with altered EPs were found in 22% of cases, whilst a normal EP battery with defective CSF or MRI findings were found in 7%. Twenty-six out of 27 patients with P or S forms were reclassified into a D one when considering EPs and MRI features.

Adolescent↗
PubMed1988

Neurophysiological evaluation of the central nervous impulse propagation in patients with sensorimotor disturbances.

Motor evoked potentials (MEPs) to transcranial stimulation (TCS) and somatosensory evoked potentials to median nerve stimulation (MN-SEPs) were examined in 74 patients affected by multiple sclerosis (MS = 49 cases), amyotrophic lateral sclerosis (ALS = 9 cases), cervical cord lesions (7 cases), Parkinson's disease (PD = 5 cases), Huntington's chorea (HC = 2 cases), Wilson's disease (WD = 1 case), subacute combined degeneration (SCD = 1 case). MN-SEPs were altered in 38% of arms in MS with a higher incidence in clinically affected than in clinically 'silent' arms (= 77.8% vs. 27.5%). MEP alterations were found in 54% of examined arms, mostly because of a prolongation of the motor CCT. This index was invariably altered in the affected arms, whilst it was involved in 40% of the 'silent' ones. Twelve out of 18 arms displayed abnormal MEPs in ALS. These were mainly due to an absent response, even if moderate motor CCT prolongation and 'giant' MEPs were also encountered. MN-SEPs were altered in 3/18 arms. By recording MEPs from proximal and distal upper limb muscles, cues on the level of abnormal propagation were obtained in patients suffering from 'focal' lesions of the spinal cord. Combining SEP records enhanced the diagnostic yield in this field. Both MEPs and SEPs were normal in patients with PD and HC, whilst abnormally prolonged CCTs were found in the case with WD. MEP and SEP recording revealed central propagation abnormalities coupled to a severe clinical picture of the peripheral nerve involvement (as in the case of SCD).

Central Nervous System↗
PubMed1987

Mechanisms of nervous propagation along central motor pathways: noninvasive evaluation in healthy subjects and in patients with neurological disease.

Motor evoked potentials (MEPs) to scalp stimulation have been obtained in 45 control patients and in 70 patients with neurological diseases. Optimal responses were obtained through a pericranial cathode consisting of 6 to 12 regularly spaced, interconnected pericranial cathodal discs whose resistance was carefully balanced with that of a stimulating anodal disc placed on the appropriate scalp region. The foci of maximal response for proximal and distal upper limb muscles as well as for lower limb muscles were localized. The scalp to cervical cord central conduction time (CCT) along motor tracts governing the hand muscles was 5.21 +/- 0.42 ms. This index was highly correlated with the subject's height and stable in time when repeatedly tested. Collision between orthodromically and antidromically propagated motor impulses was obtained. Response facilitation was achieved by means of prestimulus voluntary contraction of the target muscle, continuous vibration of its tendon, or scalp stimulation with paired shocks. The presence of a premovement facilitation of MEPs was also demonstrated, as was the presumed presence of transcallosal facilitation. An efferent volley secondary to scalp stimulation was recorded from the nerve trunk. Abnormalities in MEP characteristics as well as in CCTs were found in patients with multiple sclerosis, amyotrophic lateral sclerosis, cord compression, and degenerative diseases of the central nervous system.

Adult↗
PubMedDate not supplied

Neurophysiological evaluation of central-peripheral sensory and motor pudendal fibres.

Extensive neurophysiological investigations were carried out in 18 healthy volunteer subjects, and 6 patients with neurological disease. The tests consisted of spinal and scalp somatosensory evoked potentials (SEPs) to stimulation of the dorsal nerve of penis/clitoris, motor evoked potentials (MEPs) from the bulbocavernosus muscle (BC) and anal sphincter (AS) in response to scalp and sacral root stimulation, and measurement of sacral reflex latency (SRL) from BC and AS. In the control subjects, the mean sensory total conduction time (sensory TCT), as measured at the peak of the scalp P40 wave was 40.9 msec (range: 37.8-44.2). The mean sensory central conduction time (sensory CCT = spine-to-scalp conduction time) was 27.0 msec (range: 23.5-30.4). Transcranial brain stimulation was performed by using a magnetic stimulator both at rest and during voluntary contraction of the examined muscle. Sacral root stimulation was performed at rest. Motor total conduction times (motor TCT) to BC and AS muscles were respectively 28.8 and 30.0 msec at rest, and 22.5 and 22.8 msec during contraction. Motor central conduction times (motor CCT) to sacral cord segments controlling BC and AS muscles were respectively 22.4 and 21.2 msec at rest, and 15.1 and 12.4 msec during contraction. The mean latencies of SRL were respectively 31.4 msec in the bulbocavernosus muscle and 35.9 msec in the anal sphincter. Combined or isolated abnormalities of SEPs, MEPs and SRL were found in a small group of patients with neurological disorders primarily or secondarily affecting the genito-urinary tract.

Adult↗
PubMedDate not supplied

Bit-mapped somatosensory evoked potentials and muscular reflex responses in man: comparative analysis in different experimental protocols.

Bit-colour maps of somatosensory evoked potentials (SEPs) and muscular responses from forearm and hand muscles were simultaneously recorded after median nerve stimulation. Subjects were asked either to relax totally (A), or to contract the examined muscle continuously and isometrically at 10-20% (B) and 80-100% (C) of the maximal strength. Isotonic contractions ipsilateral (D) and contralateral to the stimulus (E) were also examined. Both SEPs and EMG responses were elicited by individual near-motor threshold pulses delivered at 0.2/sec to the median nerve at the elbow. SEPs were maximal in amplitude during complete relaxation, whilst all the components following the parietal N20 were depressed by muscle contraction. Such decrements affected predominantly the parietal and frontal peaks of positive polarity during condition B, whilst the frontal negative component (wave N30) dropped remarkably in conditions C and D. Early EMG responses (V1 = spinal circuitry) were usually absent in condition A; they were present together with later components (= V2 possibly long-loop, transcortical circuitry) in C and D, whilst they were alone recordable in B and E. The amplitudes of the frontal wave N30 in SEPs and of V2 in LLRs were inversely correlated. This observation is consistent with the hypothesis that a change in the reactivity of the sensorimotor brain areas to afferent impulses is coupled to LLR elicitation in forearm and hand muscles.

Adult↗