Visual evoked potentials in response to pattern reversal in the cat cortex.

A model of the visually evoked potential (VEP) in the cerebral cortex of the cat after binocular stimulation by means of pattern reversal is presented. The VEP is defined by four components: P1, N1, P2 and N2, which appear during the 100 ms following the stimulus. This model is repeated for the majority of recording points although N1 and P2 do not appear to be homogeneous over the entire cortex. The variability of the VEPs recorded at the same point in different cats is lower than the one observed by means of stimulation with flashes. The possible origin of the four components in the primary visual area is presented as a hypothesis and a discussion is made of the differences which exist between the models proposed for flash and pattern reversal.

Visual evoked potentials in response to flashes in the cat cortex.

A model is presented of visually evoked potentials (VEPs) in the cerebral cortex of cats after binocular stimulation by means of flashes. The VEPs consist of four components: P1, N1, P2 and N2 which appear during the first 100 ms after the stimulation is produced. This model has been found in all the animals used in the experiments and is repeated with small variations at almost all the recording points. After studying the data obtained, a hypothesis is put forward for the possible origin of the four components in the primary visual area.

Effect of stimulus intensity on visually-evoked electrical brain activity maps in rabbit.

Stimulation by means of flashes is a commonly-used method in basic research into evoked potentials. Nevertheless, the different responses obtained at different luminous intensities, to which the inter-individual and intra-individual differences are added, determine the need to control this stimulus parameter for each experimental model. Maps of visually-evoked activity in the rabbit brain, obtained after monocular stimulation with flashes at different intensities of luminosity, are presented. Variation in the intensity of the luminous stimulus does not substantially affect the distribution of the electrical potential on the surface of rabbit brain described in previous articles.

[Optic atrophy, sensorineural deafness and sensory neuropathy]. / Atrofia óptica, sordera neurosensorial y neuropatía sensitiva.

We present a patient with slowly progressing optic atrophy, sensorineural deafness and sensory neuropathy. Clinical examination and testing revealed the exclusively sensorineural nature of this syndrome. Nerve biopsy pointed to primary degeneration. Our review of the literature indicates that this syndrome is categorized as heredo-degenerative.

[Maps of visually evoked brain electrical activity in rabbits]. / Mapas de la actividad eléctrica cerebral evocada visualmente en conejos.

A basic model of topographic distribution of the electric response visually evoked in rabbits by means of flashes (0.69 joules/flash) has been obtained. The model is composed of four main parts--N0, P1, N1 y P2--linked to the VI visual area and displayed on a dipole shaped. The dipole turnaround time oscillates between 20 and 25 ms. The use of electrical activity brain maps on the study of the PE makes it possible to notice the phenomenon simultaneousness, thus facilitating its interpretation. A multinomial interpolation method of continuous function has been used to perform the maps.

[Brain potential mapping by a new method of polynomial interpolation]. / Mapas de potenciales cerebrales por un nuevo método de interpolación polinomial.

The mapping of evoked cerebral activity is largely determined by the choice of the interpolation system used. When the number of electrodes is very large, practically any interpolation system is valid, but the geometrical and anatomical limitations imposed by the animals normally chosen for these experiments impede the use of a large number of electrodes; hence the overriding importance of a workable interpolation system. The polynomic interpolation method on the monomial structure is presented as valid, and compared with the pseudolineal interpolation method, which is more commonly used.

[Visual evoked potentials produced by monocular flash stimuli in the cerebral cortex of the rabbit. I. Typology]. / Potenciales evocados visuales producidos por estímulos monoculares de flash, en la corteza cerebral del conejo. I. Tipología.

Visually evoked potentials obtained from the cerebral cortex of pigmented rabbits in response to monocularly applied flashes were studied. In agreement with their morphology, the VEP of the cerebral cortex of the rabbit were classified in three fundamental types: the first one is characterized by the presence of a large positive wave, (P1), followed by a negative wave, (N1), and finally, another positive wave, (P2); these last two being of quite variable amplitudes. The second one is characterized by an initial large negative wave, (N1), followed by a usually large positive wave, (P2). Should a positive, (P1), appear previous to N1 there would be little amplitude. The third one is characterized by the presentation of an early negative wave, (N0), of variable amplitude. This is usually followed by a large wave, (P1). N1 and P2 are present but their amplitude is variable.

[Visual evoked potentials produced by monocular flash stimuli in the cerebral cortex of the rabbit. I. Typography]. / Potenciales evocados visuales producidos por estímulos monoculares de flash, en la corteza cerebral del conejo. II. Topografía.

The visually evoked potentials in the hemisphere contralateral to the stimulated eye in rabbit, can be described topographically as follows. While a positive wave (P1) begins forming in the anterior zones and in the V I binocular zone, the N0 wave, at times very large, is produced in a more occipital zone, which corresponds to the visual streak. Immediately afterwards, the positivity, P1, practically invades the whole of the hemisphere. After this, the N1 wave which is produced in the most posterior parts of the V I, begins forming. The whole phenomenon comes to an end when the P2 wave is generated in the most occipital zones.