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Query: UMLS:C0038379 (strabismus)
 9,317 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Orienting behavior was measured in two monocular spatial localization tasks in normal cats and in cats with artificially induced monocular divergent strabismus. Immediately, and for several weeks after the operation, cats made large "past-pointing errors" with the deviated eye in a direction opposite to the misalignment. These errors were replaced later by "over compensation errors" in the same direction as the strabismus deviation, which persisted for many months after the operation. Over-compensation did not occur when the non-deviated eye was sutured in early life. Electrophysiological measures like grating VEP and A17 single unit responses demonstrated the dominance of the non-deviated eye in the strabismic cats. It is suggested that long-term binocular exposure may lead to a reorganization of visual direction for the deviated eye in divergent strabismus.
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PMID:Long-term changes of orienting behavior in cats with artificial divergent strabismus. 648 4

Commissural connections between primary visual cortical maps of the two hemispheres are essential to unify the split representation of the visual field. In normal adult cats, callosal connections are essentially restricted to the border between areas A17 and A18, where the central vertical meridian is projected. In contrast, early convergent strabismus leads to an expanded callosal-receiving zone, as repeatedly indicated by anatomical experiments. We investigated here the functional correlates of this widespread distribution of callosal terminals by analysing transcallosal visual responses in five anaesthetized and paralysed 4-10-month-old cats whose right eye had been surgically deviated on postnatal day 6. After acute section of the optic chiasm, single-unit activity was recorded from A17 and A18 of the right hemisphere while the left eye was visually stimulated. A total of 108/406 units were transcallosally activated. While they were more frequent at the 17/18 border (46% of the units recorded within this region), numerous transcallosally activated units were located throughout A17 (16%), A18 (27%) or within the white matter (17%). In all regions, transcallosally driven units displayed functional deficits usually associated with strabismus, such as decreased binocularity and ability to respond to fast-moving stimuli, and increased receptive field size. Many units also displayed reduced orientation selectivity and increased position disparity. In addition, transcallosal receptive fields were manifestly located within the hemifield ipsilateral to the explored cortex, with almost no contact with the central vertical meridian. Comparison with data from normal adults revealed that strabismus induced a considerable expansion of the callosal receiving zone, both in terms of the cortical region and of the extent of the visual field involved in interhemispheric transfer, with implications in the integration of visual information across the hemispheres.
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PMID:Visual interhemispheric transfer to areas 17 and 18 in cats with convergent strabismus. 1113 12

Neurones activated through the corpus callosum (CC) in the cat visual cortex are known to be almost entirely located at the 17/18 border. They are orientation selective and display receptive fields (RFs) distributed along the central vertical meridian of the visual field ("visual midline"). Most of these cells are binocular, and many of them are activated both from the contralateral eye through the CC, and from the ipsilateral eye via the direct retino-geniculo-cortical (GC) pathway. These two pathways do not carry exactly the same information, leading to interocular disparity between pairs of RFs along the visual midline. Recently, we have demonstrated that a few weeks of unilateral paralytic strabismus surgically induced at adulthood does not alter the cortical distribution of these units but leads to a loss of their orientation selectivity and an increase of their RF size, mainly toward the ipsilateral hemifield when transcallosally activated (Watroba et al., 2001). To investigate interocular disparity, here we compared these RF changes to those occurring in the same neurones when activated through the ipsilateral direct GC route. The 17/18 transition zone and the bordering medial region within A17 were distinguished, as they display different interhemispheric connectivity. In these strabismics, some changes were noticed, but were basically identical in both recording zones. Ocular dominance was not altered, nor was the spatial distribution of the RFs with respect to the visual midline, nor the amplitude of position disparity between pairs of RFs. On the other hand, strabismus induced a loss of orientation selectivity regardless of whether neurones were activated directly or through the CC. Both types of RFs also widened, but in opposite directions with respect to the visual midline. This led to changes in incidences of the different types of position disparity. The overlap between pairs of RFs also increased. Based on these differences, we suggest that the contribution of the CC to binocular vision along the midline in the adult might be modulated through several intrinsic cortical mechanisms.
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PMID:Unilateral paralytic strabismus in the adult cat induces plastic changes in interocular disparity along the visual midline: contribution of the corpus callosum. 1607 8