Biomedical subjects

J L Relova

Publications and source records attributed to J L Relova.

7 recordsLinked to original sources

PubMed1996

Receptive field asymmetries and sensitivity to random dot stereograms.

The differences between the two monocular receptive fields of cortical cells were measured and compared to their disparity tuning in the awake behaving monkey. Several receptive field properties (direction selectivity, orientation preference, eye preference and response modulation) were determined for each eye using sweeping bright bars. The disparity sensitivity of these cells was also assessed by plotting their response profile, determined for each cell under strictly binocular cyclopean stimulation (dynamic random dot stereograms, RDS). We have found that large differences between the two monocular receptive fields were infrequent and, apparently, not related with the disparity sensitivity profile. We conclude that the monocular asymmetries tested in this study and the sensitivity to positional binocular disparities present in RDS, might be linked to different mechanisms involved in depth perception in the visual system.

Animals↗

PubMed1993

Cell responses to vertical and horizontal retinal disparities in the monkey visual cortex.

Because of the horizontal separation of both ocular globes, the projection angles are slightly different. These differences are commonly termed retinal disparities. Vertical and horizontal retinal disparities occur constantly in normal life. We have investigated the responses of single cells in cortical areas V1 and V2 of behaving Macaca mulatta monkeys to retinal disparities by using dynamic random dot stereograms. Our findings show that cortical visual cells are sensitive to both vertical and horizontal disparities. To calculate the distance between two objects in a three-dimensional space from horizontal disparities, it is necessary to know the fixation distance. It has been suggested that the horizontal gradient of vertical disparity contains information to estimate the fixation distance and therefore to scale horizontal disparities. We suggest that these cells sensitive to horizontal and vertical disparities represent a neural mechanism that provides information to the visual system in order to achieve a correct eye alignment and depth perception.

Animals↗

PubMed1992

Fos expression in the trigeminal sensory nuclei after a chemical lesion of the lower lip mucosa.

C-fos containing neurons were investigated in the trigeminal sensory nuclear complex and in the dorsal horns of the cervical spinal cord (C1-C2) of the rat after a chemical noxious stimulus was applied to the lower lip mucosa. Numerous labelled neuronal nuclei were detected in the dorsolateral area of the caudal half of the trigeminal nucleus interpolaris, and in Rexed's laminae I-IIo of the dorsomedial area of the trigeminal nucleus caudalis and rostral C1. A few c-fos-labelled neurons were observed in laminae IIi and V. No Fos expression was detected in the trigeminal oral and principal nuclei.

Acetates↗

PubMed1991

Somatosensory responses in the cat motor cortex. I. Identification and course of an afferent pathway.

1. The main aim of the present series of experiments was to demonstrate with electrophysiological methods that the spinothalamocortical system may send somesthetic information to the pyramidal and corticospinal tract cells in the motor cortex of the cat. 2. Experiments were carried out on acutely prepared cats anesthetized with alpha-chloralose. Extra- and intracellular recordings were made from the cells located in the pericruciate motor cortex (the lateral portion of area 4 gamma). They were identified by their antidromic responses to pyramidal stimulation and/or stimulation of the dorsolateral funiculus of the spinal cord. The animals were subjected to a set of nervous tissue lesions to prevent any transit of extereoceptive information to the motor cortex via the cerebellum and the somatosensory cortex. A lesion of the dorsal part of the spinal cord was also made, leaving intact only the afferent inflow ascending in the spinal ventral half, i.e., the spinothalamic system. 3. In this cat preparation it was observed that both electrical and natural stimulation of the limbs still efficiently activated the motor cortical efferent cells. 4. The pathway was mapped by applying microstimulation along its whole course in the spinal cord and brain stem. Stimulation of the primary afferent fibers running in the dorsal columns caudally to the spinal cord lesion produced activation and/or inhibition of the cortical cells. The existence of these responses may be attributable to the existence of collaterals from primary afferent fibers located in the dorsal columns, which activate the spinothalamic tract cells either mono- or polysynaptically. In the brain stem the fibers join the medial lemniscus. 5. In view of the short latency of the responses (mean latency 10.5 ms from the spinal cord) it is suggested that this component of the spinothalamic system may play an important role in the sensory regulation of ongoing movements.

Afferent Pathways↗

PubMed1989

Short latency somaesthetic responses in motor cortex, transmitted through the spino-thalamic system, in the cat.

Evidence is presented that in the cat, the spinothalamic system contributes to short latency somaesthetic responses in motor cortex efferent cells. Intracellular recordings performed on identified pyramidal tract cells and corticospinal cells show that these cells are still activated and/or inhibited from the periphery after a set of central nervous lesions leaving intact only the ventral half of the spinal cord. The responses were attributed to the spinothalamic system. The ascending system is activated through collaterals of afferent fibres running in the dorsal columns of the spinal cord. This peripheral link to the motor cortex might participate in updating the motor command on the basis of information feedback from the periphery.

Action Potentials↗

PubMedDate not supplied

A common somaesthetic pathway to red nucleus and motor cortex.

Comparable short latency somaesthetic responses have been observed in the red nucleus and the motor cortex. Since previous experiments showed that a ventral spinal ascending pathway could account for red nucleus responses, the present experiments were designed to establish whether the same pathway could also transmit the short latency peripheral inputs to motor cortex. Two experimental data argue in favour of a such organization: (1) Using the collision technique, it was demonstrated that somaesthetic responses recorded in red nucleus cells are transmitted by collaterals of ascending fibres ending in the ventrobasal thalamus. (2) Intracellular recordings from identified corticospinal cells were performed on cats acutely prepared on section of the brachium conjunctivum and the dorsal columns of the spinal cord. Cortico-cortical connections to motor cortex were also eliminated by lesions of the ipsilateral sensory cortex and contralateral motor cortex. With this preparation it is still possible to record postsynaptic potentials after stimulation of primary afferent fibres in the dorsal columns, caudally to their section. The existence of these somaesthetic parallel inputs to rubro- and corticospinal cells suggest that the ongoing movement might be corrected on-line by these two pathways.

Afferent Pathways↗

PubMedDate not supplied

Electroretinographic changes during childhood and adolescence.

Electroretinogram (ERG) changes with age have been studied widely, but there is no general agreement about the age at which ERG parameters reach adult values. We studied 296 eyes from 148 healthy subjects, divided into 14 age groups, ranging from 1 week to 21 years. Although most of the maturational changes or ERG take place during the first six months, the a wave completes development at three years of age and the b component shows a smooth increase in latency between 3 and 18-21 years. The latter component also shows an increase in amplitude from 7-8 to 12-14 years. During the first period of maturation the b wave parameters follow a multiplicative model. These data are discussed in relation to previously reported findings on ERG maturation and to morphological and functional eye changes with age.

Adolescent↗