Biomedical subjects

R Callieco

Publications and source records attributed to R Callieco.

At least 19 recordsLinked to original sources

PubMed2000

Periodic alternating nystagmus and vestibulo-spinal system facilitating activity.

OBJECTIVE: Periodic alternating nystagmus has been associated with the instability of the velocity storage mechanism, which is known to play an important role in both the vestibulo-oculomotor and the optokinetic systems. In the present study we looked for a possible spinal equivalent to PAN. METHODS AND RESULTS: In 3 PAN patients, the H-reflex amplitude proved to be slightly but significantly influenced by nystagmus direction, in that it was greater when the nystagmus was beating toward the stimulation side. CONCLUSIONS: This finding suggests that projections from velocity storage may play a role not only in the ocular motor but also in assisting postural stability through the vestibulo-spinal system.

Adolescent↗

PubMed2000

Circadian and hypothermia-induced effects on visual and auditory evoked potentials in multiple sclerosis.

OBJECTIVES: Body cooling has been proposed as a symptomatic treatment for multiple sclerosis. This study aimed to assess the effects of body cooling and of circadian variations on clinical parameters and on visual and auditory evoked potential measures in multiple sclerosis patients. METHODS: Clinical status was assessed and VEPs, BAEPs and MLAEPs (all with two stimulus frequencies) were recorded a total of 4 times on two separate days (two times per day at 08:30 and 15:00 h each day) in 10 multiple sclerosis patients and 10 controls. On one of these days, the subjects were submitted to body cooling before the afternoon session. RESULTS: Tympanic temperature was significantly higher in the afternoon. Cooling lowered the temperature by 1.4 degrees C. No clinical effects were observed. Circadian effects were detected on VEP amplitude, which increased both in controls and in patients at low stimulus frequency (P<0.01), and increased in controls and decreased in patients at high stimulus frequency (interaction: P<0.01). Cooling determined an increase in BAEP I-V peak-to-peak time in controls, and a reduction in patients at high stimulus frequency (interaction: P<0.01). In patients, cooling also determined a great increase in MLAEP amplitude (interaction: P<0.001). We did not find cooling effects on VEP measures. CONCLUSIONS: Visual and auditory evoked potentials showed differences in circadian and cooling effects between controls and multiple sclerosis patients. These differences are consistent with the hypothesis of temperature-dependent conduction blocks in demyelinated fibers. Cooling may have a clinical effect in selected patients only.

Acoustic Stimulation↗

PubMed1999

Amodal completion in texture visual evoked potentials.

Amodal completion refers to the phenomenological finding of perceiving partly occluded objects as continuing uninterrupted behind an occluder. The outlying problem is how the visual system processes such non-local stimuli because the known processes of early vision are spatially restricted operations which segregate local differences in the visual image, and little is known about their interactions in producing the segmentation of the image into functionally coherent, or global, objects. We recorded human visual evoked potentials (VEPs) to texture stimuli and addressed local/non-local relationships in comparing a condition in which local edges were present, due to texture segregation, with a condition in which, in addition to local edges, textures appeared to continue as surfaces behind gray stripes due to non-local amodal completion. Subtraction of offset from onset responses showed: (1) a difference component due to texture segregation characterized by a negativity with onset at about 95 ms and lasting up to about 280 ms; (2) a further negativity, specifically elicited by amodal completion, with onset at about 142 ms, peaking at 175 ms, and lasting up to about 188 ms. Therefore, amodal completion occurs at an early processing stage of image analysis and the difference component in VEPs can be related to figure-ground perception.

Adult↗

PubMed1999

Edge detection and surface 'filling in' as shown by texture visual evoked potentials.

OBJECTIVES: We designed a stimulation paradigm that was designed to ascertain whether specific components of the texture visual evoked potentials were attributable to edge detection or to surface 'filling-in' processes. METHODS: The stimuli were textures of parallel line elements, which were either uniform (all horizontal or vertical lines) or segregated (checkerboards in which texture line elements of neighbor checks were oriented orthogonally). A sequence of 4 stimuli, two uniform followed by two segregated stimuli, was repeated cyclically. Accordingly, segregation could appear from a uniform display; it could also be maintained, with the checkerboard illusory margin location unchanged but with alteration in the orientation of all line elements. Each stimulus was presented for 487 ms and instantly replaced by the following one. RESULTS: Segregation-related components for segregation-appearance (Sa) and for segregation-maintenance (Sm) conditions were obtained separately by subtraction. In both conditions, a negative component was obtained with a peak latency of about 140-150 ms. However, the onset of Sa was earlier than that of Sm, whereas the respective offsets were almost identical. CONCLUSIONS: We hypothesize that the segregation component in VEPs is composed of two subcomponents: an early part, which is related to the segregation of edges, and a final part, which is related to the 'filling-in' of the homogeneous texture surface within the boundary defined by these edges.

Adolescent↗

PubMed1998

Eye movement abnormalities in myotonic dystrophy.

We studied saccade and smooth pursuit eye movements in 31 patients suffering from myotonic dystrophy (MD). On the basis of mean value comparisons, saccades were slower and hypometric and smooth pursuit eye movements performed worse in MD patients than in controls. On an individual basis, saccade duration was prolonged in 67.7%, saccades were hypometric in 19.4%, saccade latency was delayed in 9.7%, and the smooth pursuit performance index was decreased in 9.7% of patients. Eye movement abnormalities did not correlate with those detectable by visual, brain-stem auditory and somatosensory evoked potentials. We attempted to classify eye movement abnormalities as myogenic or neurogenic on the basis of differences in combination of eye movement abnormalities and the occurrence of D5/D35 dissociation; the latter consists of a prolonged duration for large (35 degrees) but not for small (5 degrees) saccades. Since D5/D35 dissociation occurred in 26/33 multiple sclerosis patients with increased saccade duration, we considered it to be a neurogenic pattern attributable to a central nervous system (CNS) dysfunction. A prolonged duration without dissociation especially in combination with saccade hypometria, is interpreted as a myogenic pattern, although the lack of dissociation may also occur with CNS impairment in case of a marked increase in saccade duration. Accordingly we classified the oculomotor abnormalities detected as neurogenic in 11 MD patients and as myogenic in another 10, but in some subjects belonging to the second group concomitant CNS impairment is not to be excluded.

Adolescent↗

PubMed1996

Estimating reliability of evoked potential measures from residual scores: an example using tibial SSEPs.

A normative study of tibial SSEPs was performed in 74 healthy subjects, and the effects of the variables sex, age and height on SSEP parameters were assessed. In a subgroup of 20 subjects a test-retest study was also performed, which allowed us to estimate the reliability of the different parameters by means of the intraclass correlation coefficient. We demonstrated that the intraclass correlation coefficient may be biased by predictable effects of subject-related variables (such as age, height and sex), if it is computed from raw original values. This bias can be eliminated by estimating reliability indices on residual scores calculated as the differences between observed values and those predicted by subject's age, height and sex.

Adolescent↗

PubMed1995

Recovery functions of early cortical median nerve SSEP components: normative data.

The recovery functions of parietal P14-N20, N20-P27 and frontal P22-N30 amplitudes were assessed in 17 healthy controls aged 20-50 years by means of the paired stimulus technique. One unpaired and 4 paired stimuli with interstimulus intervals (ISIs) of 25, 50, 75 and 100 msec were cyclically presented in a single run. Responses to the unpaired stimulus were subtracted off-line from paired stimulus responses. The highest suppression was reached at shorter ISIs for components with shorter latencies. The mean suppression of P22-N30 was influenced by the subject's age, being greater in younger subjects. Normative data are reported.

Adult↗

PubMed1994

Usefulness of trigeminal somatosensory evoked potentials to detect subclinical trigeminal impairment in multiple sclerosis patients.

Trigeminal somatosensory evoked potentials (TSEPs) by surface electric pulse stimulation were recorded in 30 normal subjects and in 70 multiple sclerosis (MS) patients, 13 of whom presenting clinical trigeminal impairment. We observed significant prolongation of all TSEPs parameters in MS group. TSEPs were abnormal in 45 patients (64.3%). Clinical and neurophysiological data agreed in 36 patients (51%) on 84 sides (60%). TSEPs were able to detect clinically silent lesions 54 times. TSEPs recording proves to be an additional useful test in MS multimodal evoked potential protocols.

Adolescent↗

PubMed1994

Eye movement quantitative evaluation before and after high-dose 6-methylprednisolone in multiple sclerosis.

We studied saccadic and smooth pursuit eye movements in 24 patients suffering from multiple sclerosis during disease worsening, before and after high-dose 6-methylprednisolone infusions. Quantitative evaluation of saccades was based on amplitude/duration and amplitude/peak velocity relationships, precision (i.e. the ratio of actual to desired saccade amplitude) and the latency, whereas smooth pursuit eye movements were studied using target velocity/performance index relationship. At basal recordings, 22/24 (91.7%) of the patients showed at lest one abnormality. Eleven of the 24 patients (45.8%) showed modification of one or several parameters: improvement in 6 patients, worsening in 2, coexistence of both trends in 3. Latency improvement was the only significant modification when patients were considered as a group. Neurophysiological modifications did not correspond to clinical changes.

Adult↗

PubMed1993

Somatosensory evoked potentials by median nerve stimulation recorded with cephalic and non-cephalic references. I). Normative study.

Somatosensory evoked potentials by median nerve stimulation were obtained in 50 healthy subjects (aged 15-70 years) with cephalic and non cephalic references. Most parameters were influenced by one or more independent variables (sex, age, arm lengths). The coefficients of the appropriate linear models are reported to compute correct individual normal limits.

Adolescent↗

PubMed1993

Somatosensory evoked potentials by median nerve stimulation recorded with cephalic and non-cephalic references. II). Reliability study.

Reliabilities of parameters of median nerve short-latency somatosensory, evoked potential obtained using both cephalic and non-cephalic references was measured in 20 healthy volunteers (aged 20-50 years) who repeated the recording session after one week. All latency measures and peak-to-peak times were highly reliable; amplitudes were less reliable. Upper normal test-retest variability limits of all the analyzed parameters were also computed.

Adolescent↗

PubMed1993

One-week test-retest reliability of spinal and cortical somatosensory evoked potentials by tibial nerve stimulation.

Spinal (Th12) and cortical somatosensory evoked potentials by right and left posterior tibial nerve stimulation at the ankle were performed in 20 healthy volunteers (10 females and 10 males) aged 23-50 years. The procedure was repeated after one week to assess the reliability of the parameters and to establish upper normal variability limits. Reliability was measured by the intraclass correlation coefficient and was excellent for all absolute latencies and at least good for amplitudes and for the spinal-cortical conduction time. Upper variability limits were calculated using a method based on the within-subject mean square, which can be also applied in the case of more than two repetitions.

Adult↗

PubMed1992

Multimodal evoked potentials in myotonic dystrophy (MyD).

By means of multimodal evoked potentials (EPs), we evaluated the central nervous system (CNS) involvement in 25 subjects suffering from myotonic dystrophy: brainstem auditory evoked potentials (BAEPs), middle-latency auditory evoked potentials (MLAEPs) and somatosensory evoked potentials (SEPs) from the upper limb were performed on all subjects, whereas only the 19 patients, whose clinical ocular abnormalities were slight, underwent pattern-electretinograms (PERGs) and pattern visual-evoked potentials (VEPs) in order to identify the site of lesion among visual pathways (retinal and/or retroretinal). PERGs were abnormal in 8/19 subjects, VEPs in 8/19 subjects (the two techniques were simultaneously abnormal in 8 eyes), BAEPs in 7/25 subjects, MLAEPs in 4/25 subjects (in one subject both BAEps and MLAEPs were abnormal) and SEPs were abnormal in 1/25 subjects. 13/25 of our subjects showed at least one EP that revealed a CNS involvement. The electrophysiological alterations were not correlated either with subject age or with disease duration. Multimodal EPs enabled us to demonstrate that CNS involvement in myotonic dystrophy is important and mainly affects the visual and auditory system.

Adult↗

PubMed1992

Spinal and cortical potentials evoked by tibial nerve stimulation in humans: effects of sex, age and height.

Somatosensory evoked potentials by posterior tibial nerve stimulation at the ankle were performed in 74 healthy volunteers (36 females and 38 males) aged 14-76 years. Cortical potentials were obtained in all subjects and spinal potentials (N22) in 71 subjects. All parameters were related to subject's age, height and sex. Sex influenced only P40-N50 amplitude, which was greater in females. All latencies of spinal and cortical components increased in a similar manner with subject's height (about 0.16-0.18 ms per cm), whereas the N22-P40 interpeak latency was independent from height, but related to T12-Cz distance. Absolute latencies of the spinal and of most cortical components, but not interpeak latencies, increased with subject's age (about 0.06-0.09 ms per year). The parameters to compute normative data (according to univariate or bivariate regression models) are furnished. Limits of right-left differences are reported.

Adolescent↗

PubMed1992

A one-week test-retest reliability study of Brainstem Auditory Evoked Potentials.

Brainstem Auditory Evoked Potentials (BAEPs) are increasingly used in longitudinal evaluation of brainstem function. The reliability of the neurophysiological parameters and definition of the normal test-retest variability are required for such investigations. In the present study we submitted 20 healthy volunteers (10 males and 10 females; mean age 35.1 years, range 24-49) to BAEPs in two sessions separated by seven days. The reliability of the parameters was estimated by means of intraclass correlation coefficient (R). All BAEP parameters showed excellent R values (above 0.75). In addition, the confidence interval lower limits of all R coefficients had good to excellent values. Finally we computed the upper normal limits of the test-retest variability of each parameter, with alpha = 0.01, using the within-subjects mean square. The confirmed good reliability of the analyzed parameters enables us to employ BAEPs as useful monitoring instruments in longitudinal studies.

Adult↗

PubMed1991

Multimodal evoked potentials in progressive external ophthalmoplegia with mitochondrial myopathy.

Multimodal evoked potentials were studied in 13 patients affected by progressive external ophthalmoplegia with histologically proven mitochondrial myopathy. Progressive external ophthalmoplegia occurred with craniosomatic spreading in all the patients and with a varying degree of nervous and/or other system involvement in most of them. In all but one of the subjects, at least one evoked potential modality was abnormal; 11 of them demonstrated an abnormal visual evoked potential, but this finding might have been influenced by concurrent retinal dysfunction. Abnormalities in brainstem auditory evoked potentials and/or somatosensory evoked potentials, revealing an impairment of central sensory pathways, were detected in 7 subjects, 5 of whom lacked clinical evidence of central nervous system involvement. Thus, evoked potentials represent an useful tool for the detection of subclinical central nervous system involvement in patients affected by progressive external ophthalmoplegia with mitochondrial myopathy.

Adult↗

PubMed1991

Evoked potentials monitoring of a cerebral focal ischemia model.

A model of cerebral ischemia by microsphere embolization in the rabbit was monitored with somatosensory evoked potentials by median nerve stimulation (SEPs) and by flash visual evoked potential (VEPs). The degree of SEP alterations paralleled the type of lesions (focal or multifocal ischemia or diffuse oedema). Alterations present at the first hour after ischemia were generally unchanged during the follow-up, which ended at the 24th hour. The prevalence of VEP alterations was low (only 16% in focal ischemia). These results are compared to EEG modifications performed in the same animals.

Animals↗

PubMed1991

Somatosensory evoked potentials by electrical stimulation of the third trigeminal branch in humans.

Somatosensory Evoked Potentials by stimulation of the trigeminal nerve (TSEPs) were recorded from 30 healthy subjects (15 males, 15 females; mean age: 45.2 years; range: 21-66 years) in order to assess normative data for clinical purposes. To elicit the TSEPs, electrical square pulses (duration: 0.1 msec; frequency: 3.3 Hz; intensity: 4-6 mA) were delivered by bipolar skin electrodes (cathode over the foramen mentale and anode on the middle of the chin, stimulating the trigeminal third branch). TSEPs were obtained from C3-Fpz and C4-Fpz by twice averaging 1000 responses. Time base was 100 msec; bandpass filter setting was 5-1500 Hz. In our normal subjects the TSEPs were composed of several components (N1, P1, N2, P2 and N3); the components, with the exception of N3, were always bilaterally detectable. Statistical analysis (repeated measures analysis of variance) demonstrated a dependence of TSEP latencies on sex; it did not demonstrate an analogous dependence on either side of stimulation or age. Finally, we propose some guidelines for the evaluation of TSEPs: consider N1, P1, N2 and P2 waves, base the judgement of normality on latencies rather on amplitudes, use differing normative data according to sex.

Adult↗