Search PubMed⌕ Search

Biomedical subjects

L Tong

Publications and source records attributed to L Tong.

157 records · Page 9Linked to original sources
PubMed1984

Critical period for the marked loss of retinal X-cells following visual cortex damage in cats.

Visual cortex damage in newborn kittens produces a 78% loss of retinal X-cells whereas damage in adult cats produces only a 22% loss. Retinal Y- and W-cells are unaffected. The present experiment showed that the critical period for the severe loss of retinal X-cells ends between birth and 2 weeks of age. These results have implications for understanding the neural mechanisms of recovery from early visual cortex damage.

Age Factors↗
PubMed1984

Critical periods for functional and anatomical compensation in lateral suprasylvian visual area following removal of visual cortex in cats.

Previous experiments have found that neurons in the cat's lateral suprasylvian (LS) visual area of cortex show functional compensation following removal of visual cortical areas 17, 18, and 19 on the day of birth. Correspondingly, an enhanced retino-thalamic pathway to LS cortex develops in these cats. The present experiments investigated the critical periods for these changes. Unilateral lesions of areas 17, 18, and 19 were made in cats ranging in age from 1 day postnatal to 26 wk. When the cats were adult, single-cell recordings were made from LS cortex ipsilateral to the lesion. In addition, transneuronal autoradiographic methods were used to trace the retino-thalamic projections to LS cortex in many of the same animals. Following lesions in 18- and 26-wk-old cats, there is a marked reduction in direction-selective LS cortex cells and an increase in cells that respond best to stationary flashing stimuli. These results are similar to those following visual cortex lesions in adult cats. In contrast, the percentages of cells with these properties are normal following lesions made from 1 day to 12 wk of age. Thus the critical period for development of direction selectivity and greater responses to moving than to stationary flashing stimuli in LS cortex following a visual cortex lesion ends between 12 and 18 wk of age. Following lesions in 26-wk-old cats, there is a decrease in the percentage of cells that respond to the ipsilateral eye, which is similar to results following visual cortex lesions in adult cats. However, ocular dominance is normal following lesions made from 1 day to 18 wk of age. Thus the critical period for development of responses to the ipsilateral eye following a lesion ends between 18 and 26 wk of age. Following visual cortex lesions in 2-, 4-, or 8-wk-old cats, about 30% of the LS cortex cells display orientation selectivity to elongated slits of light. In contrast, few or no cells display this property in normal adult cats, cats with lesions made on the day of birth, or cats with lesions made at 12 wk of age or later. Thus an anomalous property develops for many LS cells, and the critical period for this property begins later (between 1 day and 2 wk) and ends earlier (between 8 and 12 wk) than those for other properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1984

Critical periods for effects of monocular deprivation: differences between striate and extrastriate cortex.

The critical period of susceptibility to effects of monocular deprivation was compared in striate cortex and the lateral suprasylvian (LS) visual area of cortex. Twenty-three cats received monocular lid suture for a period of 4 weeks beginning at 4, 12, 18, 26, or 35 weeks of age or as adults. Immediately following the deprivation, single cell recordings were carried out in both cortical areas of each cat. Recordings also were made from five normally reared control cats. For both striate and LS cortex, early monocular deprivation had marked effects on neuronal ocular dominance, including an increased percentage of cells dominated by the nondeprived eye, a decreased percentage of cells dominated by the deprived eye, and a decreased percentage of binocularly driven cells. In both cortical areas, these effects were maximal in animals deprived at 4 weeks of age. Both areas then showed similar monotonic declines in effects of the deprivation following onsets from 4 to 18 weeks of age. However, in older animals there were clear differences in the effects of monocular deprivation on LS and striate cortex. In LS cortex, the monotonic decline in effects continued until 26 weeks of age, and no significant abnormalities were present in animals deprived at 26 weeks of age or older. In striate cortex, however, the effects of monocular deprivation remained relatively constant following onsets from 18 to 35 weeks of age, and significant abnormalities in all measures of ocular dominance were present when deprivation was begun as late as 35 weeks of age. Within-animal comparisons indicated that the greater effects of monocular deprivation on striate cortex than on LS cortex were present in every cat deprived at 26 or 35 weeks of age. Neither cortical area showed significant abnormalities following monocular deprivation in adult cats. These results indicate that the critical period for effects of the same regime of monocular deprivation is over sooner in LS cortex (between 18 and 26 weeks of age) than in striate cortex (after 35 weeks of age). This observation has important implications for an understanding of the sites and mechanisms of effects of visual deprivation and the mechanisms that control critical periods of development.

Animals↗
PubMed1982

Thalamic projections to visual areas of the middle suprasylvian sulcus in the cat.

The thalamic afferents to two areas of the lateral suprasylvian visual cortex in the cat were studied by using retrograde transport of horseradish peroxidase (HRP). Injections were localized retinotopically with electrophysiological recording. The posteromedial lateral suprasylvian area (PMLS) of Palmer et al. ('78) receives afferents from the pulvinar (P), the posterior nucleus of Rioch (PN), the C-laminae of the lateral geniculate nucleus (LGNd) and the centrolateral (CL), lateral posterior (LP), medial interlaminar (MIN) nuclei. The anteromedial lateral suprasylvian area (AMLS) receives afferents from CL, P, LP, PN, MIN, and probably from the posterior nuclear group (PO), and the lateral dorsal (LD) and ventral anterior (VA) nuclei. The LP-pulvinar complex has been divided into four zones on the basis of connectivity: geniculate wing, pulvinar, the lateral division of LP, and the interjacent division of LP (Updyke, '77; Graybiel and Berson, '80; Guillery et al., '80). The locations of labeled cells in the present experiments suggest that both AMLS and PMLS receive afferents from each of the four zones, although differences exist in the strength of the projections. While AMLS and PMLS receive afferents from many of the same nuclei (CL, P, LP, PN, and MIN), differences in their afferents also were noted. These differences are of three types. The first is that some nuclei project to only one of the cortical areas. PMLS alone receives input from the C-laminae of the LGNd while AMLS alone receives probable input from PO, LD, and VA. The second difference is in the strength of the projection from some nuclei. AMLS receives a stronger projection from CL and P than does PMLS. The third difference concerns the pattern of distribution of neurons that project to each cortical area. Labeled cells in LP are dispersed after an AMLS injection, but are found in clusters or bands after a PMLS injection. Thus our results indicate that the thalamic afferents to AMLS and PMLS are in general similar: however, differences in input to AMLS and PMLS suggest that inputs to PMLS are predominantly visual while AMLS receives a broader spectrum of afferent information.

Animals↗
PubMed1982

Loss of retinal X-cells in cats with neonatal or adult visual cortex damage.

Recordings were made from single retinal ganglion cell somas in cats whose visual cortical areas 17 and 18 were damaged on the day of birth or in adulthood. Neonatal lesions produced a 78 percent loss of X-cells in the retina, while lesions made in adulthood produced a 22 percent loss. Y-cells and W-cells were unaffected. This retinal abnormality needs to be considered when interpreting studies of behavioral deficits and neural mechanisms of recovery after damage to the visual cortex.

Aging↗
PubMedDate not supplied

Sexual abuse of children: an area with room for professional reforms.

The cases of 46 children who had been abused sexually an average of 2.6 years previously, were reviewed and the non-offending parents were interviewed with emphasis on how they viewed the professional persons who had seen their children, and their opinions of the legal processes that were instituted. The parents found most professional groups helpful, with officers from the Department of Youth and Community Services being seen as the least helpful. Twenty-one of the cases went to court; in 12 cases this resulted in a conviction, and prison sentences were imposed on six of the offenders. Children found the court experience distressing and most parents expressed dissatisfaction with the outcome of the court hearing. Children were more likely to be required to give evidence in court if the offender had legal representation. Persisting behavioural problems and poor school performance were more likely to occur in those cases in which there had been court hearings. A review of Police Department records of children who had attended the hospital for the management of sexual assault, showed that 10 of the 107 children who are now aged over 14 years, have themselves been convicted of violent crimes since their episode of sexual assault. Long-term intervention is required to help many of these children, some legal reforms are necessary to reduce the stress that they experience when there is a court hearing, and all the professional groups that are likely to become involved with the problem of the sexual abuse of children need to be better informed about its seriousness and consequences.

Adult↗