Biomedical subjects

T Pinto-Hamuy

Publications and source records attributed to T Pinto-Hamuy.

16 recordsLinked to original sources

PubMed1999

Deficit in the water-maze after lesions in the anteromedial extrastriate cortex in rats.

The Morris water-maze task was used to evaluate the role of the anteromedial extrastriate visual cortex in the processing of visuospatial information in rats. Six gray male rats received bilateral ibotenic acid injections targeted stereotactically to the rostral part of the anteromedial extrastriate visual cortex. These operated subjects and six other unoperated control rats were tested in the maze. Histological analysis confirmed the localization, symmetry, and depth of lesions in the rostral part of anteromedial area (AMa) in the operated subjects. In these animals, a significantly greater latency to reach the submerged platform was found (U = 0, p = 0.004). The Morris water-maze may be considered as a reference memory task. It presents a stronger demand on the use of allocentric spatial visual cues than on the use of egocentric cues for navigation. Therefore, the present data lend support to the participation of area AMa in the integration of allocentric visuospatial cues or as a link in the memory system involved in the acquisition of this task.

Animals↗

PubMed1999

Persistent neuronal density changes related to the establishment of a motor memory.

Rats were trained in a lateralized reaching motor task during either an 'early' (22-31 days old) or a 'late' (62-71 days old) postnatal period. The 'late' group showed significant neuronal density reduction in cortical layers II-III of the contralateral motor forelimb representation. The 'early' group evidenced a similar localized contralateral effect that persisted after a subsequent period without training. Furthermore, in this group, a bilateral overall decrease in neuronal density was found throughout the motor cortex. This bilateral experience and age-dependent effect is conceivably related to a critical period of motor cortical development. The localized reduction of neuronal density strongly indicates a morphological expression of the motor engram. Our present study supports the concept that the acquisition and retention of motor learning involves the persistence of structural changes in the brain.

Animals↗

PubMed1997

Visuospatial discrimination deficit in rats after ibotenate lesions in anteromedial visual cortex.

To assess the role of the rat anteromedial extrastriate cortex (AM) in a visuospatial discrimination task, restricted bilateral ibotenic acid lesions were placed stereotaxically in this region. Gray rats with lesions in AM were trained in a task requiring them to discriminate the location of a light stimulus placed vertically at different elevations. Correct responses required pressing right or left levers to obtain rewards. In contrast to unoperated controls, lesioned rats failed in learning the visuospatial discrimination task. A correlation was found between the bilateral extent of the lesion in area AM and the behavioral deficit. Another group of lesioned rats was trained to discriminate brightness differences of the light stimulus but requiring the same egocentric right/left motor response. The performance of these rats was similar to that of controls. From these results we conclude that extrastriate area AM in the rat is necessary for visuospatial discrimination, but not for correct egocentric motor responses. The visuospatial functions of area AM in the rat are reminiscent of visuospatial functions ascribed to the parietal streams of extrastriate visual areas in the monkey.

Animals↗

PubMed1996

[Persistence of the cognitive effects of early stimulation assessed with an animal model].

Human and animal studies have clearly demonstrated the advantageous effects of sensorially enriched rearing environments. Nevertheless, little work has been done concerning the long-lasting persistence of all these behavioral modifications. To undertake this question, a very early enrichment animal model was used. From days 10 to 24 after birth, 28 male albino rats were exposed to a multisensory stimulated environment, while other 28 littermates constituted the control group. At 3 and 6 months old two cognitive abilities were analyzed; the spatial working memory (short term memory) and the latent learning capacity (long term memory). The results evidenced an improved working memory in both 3 and 6 months old rats exposed to the early enriched environment. Moreover, the adult early stimulated group performed as well as younger subjects both on error scores and speed to solve this test. Only in the adult group of rats a superior latent learning capacity of stimulated subjects was evidenced. To conclude, the early enriched environment induced: a) persistent cognitive benefits in the adult rat and b) a more relevant influence on the subsequent behavior of older rather than younger subjects.

Age Factors↗

PubMed1994

Interhemispheric structural asymmetry induced by a lateralized reaching task in the rat motor cortex.

The effects of a lateralized reaching task on the morphological structure of the rat motor cortex were studied during the early postweaning period. Our results show that the consistent use of one forelimb accounts for a significant decrease in the numerical density of cells and an increase in cortical thickness of the contralateral 'forelimb' motor cortex. As a consequence of the early motor training the cell distribution, which is lower rostrally than caudally in nontrained hemispheres, is reversed in the trained hemispheres. This may be interpreted as the specific motor training triggering a higher neuronal branching in the corresponding cortical region. The present findings may further the understanding of the mechanisms involved in the generation of morphological brain asymmetries.

Animals↗

PubMed1992

Development of a computerized system for simultaneous visual discrimination in rats.

In order to automate a simultaneous visual discrimination system, a Sutherland jumping-stand box was modified by adding two lateral alleys which connect the feeder compartment with the starting box. By means of a digital interface, this modified box was connected to an Apple IIe PC. A group of rats (n = 8) was trained. All subjects learned. Advantages relevant to the apparatus design, as well as the benefits derived from the automated procedure are discussed.

Animals↗

PubMed1989

Effects of preweaning environmental enrichment on basilar dendrites of pyramidal neurons in occipital cortex: a Golgi study.

The effects of postnatal environmental stimulation on the branching patterns of cortical dendrites were measured in rats. Pups were exposed to 4 daily multisensory enrichment sessions from days 10-24, while littermates were maintained in standard conditions. At 25 days of age, the brains were stained using the Golgi-Cox-Sholl method. Camera lucida drawings were made of the basilar dendritic trees from a total of 528 layer-III occipital cortex pyramidal neurons. A highly significant increase was found in number and length of segments from order 1-5 in the neurons from the enriched subjects.

Animals↗

PubMed1988

Greater efficacy of preweaning than postweaning environmental enrichment on maze learning in adult rats.

In order to assess the behavioural effects of environmental stimulation at different stages of development, two groups of rats were exposed to multisensory enrichment on days 10-24 (preweaning) or 25-39 (postweaning). Both groups had four 25-min sessions per day in a large cage with a variety of stimuli, in addition to 3 min of handling before each session. The mother of the preweaning group remained in the home cage during the stimulation sessions. A third group was maintained in a social condition. Testing in a Hebb-Williams maze started when the rats of the 3 groups were 100 days old. Error, latency and running time scores were lowest in the preweaning group.

Aging↗

PubMed1987

Rats with lesions in anteromedial extrastriate cortex fail to learn a visuosomatic conditional response.

The involvement of rat anteromedial extrastriate cortex (area AM, in the anterior portion of area 18b) in the integration of visual and somatic cues was assessed behaviorally. Following restricted bilateral lesions of selected cortical regions, rats were tested on their ability to retain or relearn a conditional visuosomatic discrimination task learned prior to surgery. Two compound, visuosomatic stimuli were used: white or black associated with either one of two degrees of roughness. The use of a guided-response procedure was essential for rats to learn this difficult conditional bimodal task. None of the 6 rats with lesions aimed at area AM retained the habit postoperatively. Four of these rats were incapable of relearning the task after 3 postoperative training series, and they had either extensive lesions of area AM or relatively small, symmetric damage of anterior portions of AM. The remaining two rats with lesions in area AM were able to relearn the task in the second postoperative training series, and their lesions either were restricted to posteromedial aspects of area AM or they involved asymmetric loci in anterior area AM. In contrast to rats with lesions of area AM, rats with lesions in visual cortex in areas 17 and 18a, or in auditory cortex in area 41, were able either to retain the task or to relearn in the first postoperative training series. These results indicate that the integrity of area AM appears necessary for rats to discriminate between pairs of compound stimuli that differ in brightness and roughness. The behavioural data point to the notion that this area might be involved in the integration of these types of visual and somatic stimuli. In addition, our finding that performance was largely unimpaired following extensive lesions of lateral extrastriate area supports previous reports indicating that medial and lateral extrastriate visual areas differ in function.

Animals↗

PubMed1987

Analysis of a guided-response procedure in visual discriminations by rats.

A guided-response procedure was used to train a visual pattern discrimination by rats in a modified Sutherland box. The method consisted of guiding the animal to the correct choice by means of a retractable bridge that led to reinforcers, followed by gradually removing this prompt. This method was compared to a stimulus-fading procedure, in which the initial differences between discriminative stimuli were gradually faded until they differed only with respect to the critical dimension for discrimination, and to a trial-and-error procedure. Both gradual procedures resulted in fewer errors compared to the trial-and-error procedure. The higher efficiency of the fading procedures was attributed to less aversiveness derived from performance with few errors and to the use of step-by-step requirements relative to the criterion performance.

Animals↗

PubMed1981

[Monocular enucleation causes a deficit in visual learning in rats].

Behavioral effects of monocularity were assessed in rats, by means of visual discrimination training in a jumping box. The results showed that the experimental subjects did not differ from controls in brightness discrimination, however, were significantly inferior on a conditional discrimination task. This particular test involves the association of present cues with previously learned ones. Since previous work proposes the consideration of the rat's brain as a functional split-brain, and in our condition the visual information was highly lateralized only to the contralateral hemisphere, we suggest that our results may be due to an impairment produced by the reduction of the brain mass available for the discrimination.

Animals↗

PubMed1976