PubMed Health⌕ Search

Biomedical subjects

S Meneses

Publications and source records attributed to S Meneses.

11 recordsLinked to original sources
PubMed1995

Effects of GABAB receptor antagonists on two models of focal epileptogenesis.

The acute effects of two GABAB receptor antagonists (phaclofen and CGP-35348) were studied in two types of epileptogenic activity: that produced by intracortical injections of baclofen and that appearing after withdrawal of chronic intracerebral GABA infusion (the GABA-withdrawal syndrome, GWS). Intracortical baclofen induced two types of electrographic paroxysmal discharges: one consisting of single spike-and-wave (pattern I) and another of polyspike-and-wave patterns (pattern II). Both patterns showed similar latencies and temporal evolution of spike frequency discharges. Phaclofen, applied directly into the baclofen-induced epileptogenic focus, suppressed pattern II but was ineffective in modifying both pattern I and the GWS. CGP-35348, administered systemically, inhibited both patterns I and II. Intracortical microinjection of baclofen or phaclofen in rats showing a GWS had no effect, nor the systematically given CGP 35348. These results indicate a differential participation of GABAB receptors in GABA-related epileptic syndromes of cortical origin.

Animals↗
PubMed1993

Chronic infusions of GABA into the medial prefrontal cortex induce spatial alternation deficits in aged rats.

It has been proposed that functions associated with the prefrontal cortex could change as a consequence of aging. Previous experiments in young rats have demonstrated that anatomical lesions or chronic GABA infusions into this area produce deficits in spatial delayed alternation tasks. The present study examines the effect of chronic (7 days) GABA or saline infusion into the prefrontal cortex on the performance of delayed alternation task in old rats (24 months). The results suggested that aged rats needed more sessions to acquire the delayed alternation task. GABA infusions into the prefrontal cortex produced deficits in spatial alternation tasks similar to those previously observed in young rats. Performance rapidly recovered after the infusion period. Histological analysis showed similar lesion size in both groups. The results suggest that aged prefrontal cortex and/or related areas participating in the acquisition of the delayed alternation task are more sensitive to aging processes. Furthermore, the prefrontal cortex is important for the retention of a previously learned spatial delayed alternation task. The structures involved in functional recovery from these deficits appear to be fully functional in aged rats.

Aging↗
PubMed1991

Event related potentials recorded in normal and dyslexic subjects when reading in and out of context.

Clinical evidence has shown that expectancy or anticipatory reactions influence the ability to read. It is possible that the reading problems shown by dyslexic children could be due to the absence of anticipatory hypotheses when they decode verbal material. Research was therefore carried out into these clinical observations to see if they could be detected on an electrophysiological level using a technique for recording Event Related Potentials (ERPs). In this study, our intention was to observe if there were any differences between a sample population of normal children and one of dyslexic children in the ERPs recorded on the presentation of words both in and out of context. The words recorded during the reading in context were: the word "la" (the feminine article "the" in Spanish), an "intermediate" word and a "final" word in a series of sentences. The first two have a greater anticipatory load than the reading of the final word since this is the word that closes the meaning of the sentence. Furthermore, as a control, the ERPs that were produced when reading isolated words were recorded, a situation that does not require the presence of anticipatory processes. The control group was made up of subjects with adequate school performance and no pathological background, and the experimental group was composed of subjects whose performance on a psychoeducational battery, previously administered to 120 Mexican children, had been found to be two standard deviations below the established norms. Following the 10-20 international system, electrodes were placed in zones F3, Cz, P3, O1 and O2 and referred to both earlobes. Statistical analysis revealed significant differences between groups in the amplitude of the ERP recording in the left occipital zone for all conditions when reading in sentences ("la," "intermediate" and "final"). It is suggested that this cortical zone participates in decoding verbal material and that it is deficient in subjects with reading problems.

Adolescent↗
PubMed1990

Chronic infusions of GABA into the medial frontal cortex of the rat induce a reversible delayed spatial alternation deficit.

The effects of bilateral infusions of GABA into the medial frontal cortex of the rat were studied in a delayed spatial alternation task. It was found that GABA (500 mM, 1 microliter/h during 7 days) impaired the performance of the rats in the previously learned task. Upon interruption of the treatment, the animals rapidly recovered normal performance scores. The results show that GABA infusions produce functional deficits similar to those produced by lesions of the frontal cortex. Moreover, the deficits are reversible upon interruption of the treatment. This technique may therefore be a useful tool for studying frontal lobe functions and the involvement of GABAergic mechanisms in cognitive processes.

Animals↗
PubMed1990

The late event related potentials CNV and PINV in normal and dyslexic subjects.

The most prominent ERP to occur during intervals of preparation and anticipation is the contingent negative variation (CNV) or expectancy wave. The resolution of this wave is called the postimperative negative variation (PINV). The purpose of this study was to distinguish the characteristics of the CNV and the PINV in a group of children with reading disabilities or dyslexia and to compare them from a group of normal readers. Nine righthanded boys aged between 10-13 years with reading disabilities were studied. The children were matched with a group of nine normal readers. Four derivations were used: frontal, central, parietal and occipital zones, with reference to linked ears. Data were analyzed using multivariate procedures. Significant differences between groups in CNV amplitude and in PINV amplitude and latency at the left parietal site were observed. We discuss the participation of this zone and we consider processes like expectancy, attention and brain activity signal processing in the differences mentioned.

Adolescent↗
PubMed1989

Effect of normal sleep and sleep deprivation on interhemispheric correlation during subsequent wakefulness in man.

EEG activity was recorded from the right and left central, temporal, parietal and occipital derivations in 10 volunteers under the following conditions: at night before going to sleep, at night before sleep deprivation, in the morning after waking, in the morning after sleep deprivation and in the morning 48 h after recovery. Interhemispheric correlation and relative power were calculated for EEG samples of 20.48 sec. In the morning after normal sleep interhemispheric correlations were higher in all derivations in comparison to presleep values, while in the morning after sleep deprivation, interhemispheric correlations were lower or similar to predeprivation values in all derivations except the temporal cortex. The relative power of beta was significantly lower after normal sleep and higher after sleep loss, while the relative power of low frequencies was higher in the morning after sleep and lower in the morning after deprivation.

Adult↗
PubMed1987

Neuroelectric correlates of a neuropsychological model of word decoding and semantic processing in normal children.

The use of event-related potentials (ERPS) as a technique in the study of word decoding and semantic processing in the cerebral cortex was investigated. Ten right-handed boys, aged between nine and eleven, with adequate school performance were studied. Visual ERPS were obtained using four derivations: occipital (O1-O2) and parietal (P3-P4). Four stimuli were presented: a frequently used noun written in capitals; the same noun in handwriting; the pictorial representation of this noun (drawing); and a pattern consisting of a checkerboard (25 squares). The data were analyzed using multivariate procedures. A Principal Component Analysis with varimax rotation of the solution was applied. Concepts about reading contributed by cognitive psychology, neuropsychology and neurophysiological research are reviewed, and a hypothetical model of the neuronal bases underlying the act of reading is presented. This model emphasizes the complex, dynamic interplay of the neural structures involved and points to the differences which probably exist between beginning and fluent readers. The results are discussed in accordance with the proposed model.

Brain↗
PubMed1987

Neuroelectric correlates of a neuropsychological model of word decoding and semantic processing in reading disabled children.

The purpose of this study was to distinguish the characteristics and components of event related potentials (ERPs) correlated with word decoding and semantic processing in a subgroup of children with specific reading disabilities related to visual processing deficiencies. The results were compared with those obtained from a group of normal readers previously studied (Ostrosky et al. in press). Visual ERPs were recorded to four stimuli: three physically different but with the same semantic content: a frequently used noun written in capitals (COCHE), the same noun in handwriting, the pictorial representation of the noun (drawing), and a neutral stimulus consisting of a checkerboard. Four derivations were used: occipital (O1-O2) and parietal (P3-P4) with reference to linked mastoids. Data were analyzed using multivariate procedures. A Principal Component Analysis with Varimax rotation of the solution was applied. In the normal readers, we found some components in the occipital derivations which identified the words presented in different styles of handwriting and others which seemed to identify these words with the pictorial representation (and not with the neutral stimuli). The first "verbal" components were situated around the 156-256 ms latency range and the second "semantic" components were observed at over 380 ms. In the disabled readers, there was no "verbal" or "semantic" recognition grouping of these physically different stimuli. As opposed to the normal readers, interhemispheric responses were symmetrical. At the left parietal leads in the normal readers, the morphology of the verbal stimuli (capitals and handwriting) were very similar throughout the sweep and both were very different from the nonverbal stimuli. At 376 ms the four stimuli elicited a prominent negative peak in which the verbal stimuli elicited significantly higher amplitude than the nonverbal stimuli. In the disabled group, the morphologies of the four stimuli were very similar and no significant differences were observed. The results are discussed in accordance with a hypothetical model of the neural bases underlying reading. The model takes into account the complexity of the reading process and the various cognitive skills required for its adequate performance, and emphasizes a complex, dynamic interplay between occipital, parietal and temporal areas.

Cerebral Cortex↗
PubMed1985

Sociocultural effects in neuropsychological assessment.

The group selected for this evaluation consisted of 109 normal people with an average age of 25, coming from two different sociocultural levels (high and low) of Mexico City. All were completely evaluated by Luria's battery for neuropsychological assessment, adapted by Ardila, Ostrosky, and Canseco, 1981. This group of tests measures nine different areas: Motor Functions, Somatosensory Knowledge, Auditory Knowledge, Visuospatial Knowledge, Cognitive Processes, Language, Reading, Writing and Basic Calculations. For all of these, the higher performance standards were achieved by the subjects from the high sociocultural level. A significant interaction between sociocultural level and sex was observed. The differences between sexes appear only in subjects from the low sociocultural level. Factor analysis of the battery revealed that the most sensitive items to sociocultural level were those related on one hand, to the handling of complex structural and conceptual aspects of language and on the other hand, to the organization of motor sequences and in general motor programming. Research related to the differences found is reviewed and implications for clinical assessment are discussed.

Adult↗
PubMedDate not supplied

[Contingent negative variation in normal and dyslexic children].

The most prominent ERP to occur during intervals of preparation and anticipation is the contingent negative variation (CNV) or expectancy wave. The purpose of the study was to distinguish the characteristics of the CNV in a group of children with reading disabilities or dyslexia, and to compare it with a group of normal readers. Nine right handed boys aged between 9 and 13 years with reading disabilities were studied. The children were matched with a group of nine normal readers. Four derivations were used: F3, Cz, P3, and O1, with reference to linked ears. Data were analyzed using multivariate procedures. Significant differences between groups in the CNV amplitude at the left parietal site were observed. We discuss the participation of this zone and we consider processes like expectancy and attention in the differences observed.

Adolescent↗