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Biomedical subjects

M Pirchio

Publications and source records attributed to M Pirchio.

7 recordsLinked to original sources
PubMed1979

Foveal versus peripheral retinal responses: a new analysis for early diagnosis of multiple sclerosis.

Visual potentials evoked by brief flashes (VEPs) were recorded in 85 patients with MS, 30 healthy controls and 25 neurological patients without demyelinating diseases. In a group of 44 patients, diffuse field stimulation was used, resutling in 15 altered responses (34%). In a second group of 41 patients with superimposable characteristics including age, sex, diagnosis of MS (definite, probable and possible) and score on the Rose's scale, the separate responses of central and peripheral retina were analysed. A total of 30 abnormal VEPs were recognized (73%) with the following distribution: 16 foveal VEPs (78%), 4 peripheral responses (13%) and 26 centreperiphery latency differences (CPLD, 60%). Twenty subjects of Group A with normal or slightly altered full field VEPs were retested with both stimulating methods with the following result: 3 altered full field VEPs (15%) and 15 abnormal CPLD (75%). With diffuse field stimulation, the correlation between the VEP scores and the results of other examinations (visual, pyramidal, etc.) were insignficant; on the contrary, the CPLD was clearly correlated with the involvement of the visual and other systems in the fluctuating clinical course of MS.

Adolescent↗
PubMed1979

A perceptual phenomenon and its neurophysiological correlate.

A square-wave grating from which the fundamental harmonic has been subtracted (missing fundamental grating) when viewed from a suitable distance appears similar to another grating of periodicity three times higher. The neurons of the visual cortex of the cat, in a given range of spatial frequencies characteristic of each cell, give similar responses to the two gratings.

Animals↗
PubMed1979

Responses of visual cortical cells to periodic and non-periodic stimuli.

1. The activity of neurones of the visual cortex (area 17) has been recorded in anaesthetized cats in response to gratings of different profile and to single light and dark bars. 2. At very low spatial frequencies, outside the frequency response range to sinusoidal gratings, the response to square-wave drifting gratings is obtainable from a combination of the response to the single bars of the grating presented in isolation. At higher spatial frequencies this is no longer true. 3. At very low spatial frequencies the responses to square-wave gratings and to missing-fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental harmonic) are very similar. 4. At spatial frequencies near the peak of the spatial frequency tuning curve of the cell, the responses to square-wave grating and to sinusoidal gratings are very similar. At these spatial frequencies the response to the missing-fundamental grating is practically zero. 5. At spatial frequencies lower than that of best sensitivity for the cell, the response to square-wave gratings is correlated with the 1st and 3rd harmonic of the stimulus. 6. We conclude that at very low spatial frequencies of the grating the response of cortical cells is correlated with the light or dark edges (or light or dark bars) of the stimulus, because the edges contain high frequencies within the range of sensitivity of the cells. At higher spatial frequencies the results are interpreted best by assuming that cortical cells respond to the harmonics of the visual periodic stimulus. 7. When a background of dynamic visual noise is added to increase the spontaneous discharge of simple cells, their response to visual stimuli becomes linear or quasi-linear. The stimuli could be either single bars or gratings.

Action Potentials↗
PubMed1978

Binocular vision tested with visual evoked potentials in children and infants.

Evoked potentials (EP's) in response to phase-alternating gratings were recorded from normal and stereoblind or stereodefective subjects (adults and children) under monocular and binocular viewing conditions. The amplitude of the binocular EP was found to exceed the larger monocular EP in normal but not in stereodefective subjects, no matter whether the amplitudes of the two monocular EP's were the same or not. This finding provides an objective method for screening out defects of binocular vision. EP's recorded from a group of infants 2 to 18 months old suggest that a larger amplitude of the binocular EP, as compared with the monocular EP's, is the norm even in the earliest period of life.

Adult↗