Some Subcortical Connections of the Visual System in Tree Shrews and Squirrels

Abplanalp, Paul

doi:10.1159/000125468

Cited by 65 publications

(25 citation statements)

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“…The gradient of development of argyrophyllia of the retinal projections to the SC corresponds closely with the maximal density gradient of ter minal debris resulting from striate cortex lesions [Abplanalp, 1970]. In an electron microscopic study of this region in the rat, Lund [1969] was unable to conclude whether these two afferent pathways end on the same or different cells.…”

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confidence: 88%

Topography of Retinal Efferent Connections in Sciurids; pp. 362–375

Abplanalp¹

1974

Brain Behav Evol

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The sciurid retina projects to the contralateral superior colliculus, pretectal complex, ventral nucleus of the lateral geniculate body and to five distinct zones in the dorsal nucleus of the lateral geniculate. Ipsilateral projections are distributed to the same targets except the superior colliculus. Zones of terminal debris as identified by the Fink-Heimer method do not develop uniformly; instead some structures become argyrophyllic before others do so that an injudicious choice of survival times may produce misleading data.The topography of the retinal mosaic is preserved in all its projections except those to the accessory optic system. In the cases of the superior colliculus, ventral nucleus of the lateral geniculate body and the anterior pretectal nucleus, these retinal projections are in perfect register with other afferent connections which are also retinotopically organized. An enormous proportion of the cells in the dorsal nucleus of the lateral geniculate body are connected with the overlapping portions of the retina; only a very small part of this structure receives input from the much larger nonoverlapping retinal quadrants.

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confidence: 88%

Topography of Retinal Efferent Connections in Sciurids; pp. 362–375

Abplanalp¹

1974

Brain Behav Evol

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“…In both, the superior colliculus, the major visual center of the midbrain, is unusually large and distinctly laminated [Abplanalp, 1970;Lane et al, 1971] compared to the superior colliculus of most mammals, including all primates [Kaas and Huerta, 1988]. The specialization of this structure is especially obvious when compared to the small, poorly differentiated superior colliculus of a nocturnal hedgehog ( fig.…”

Section: Comparing Tree Shrews and Squirrelsmentioning

confidence: 99%

Convergences in the Modular and Areal Organization of the Forebrain of Mammals: Implications for the Reconstruction of Forebrain Evolution

Kaas

2002

Brain Behav Evol

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Early efforts to reconstruct the course of the evolution of the human brain relied on comparing the brains of a few related mammals with brains at successively higher levels of complexity. This Clark or ladder of levels approach is now seen as having limited usefulness in that species are not easily assigned to levels, and extant mammals are now recognized as mosaics of primitive and derived features. In addition, direction of change does not necessarily proceed from simple to complex, small to large, or diffuse to differentiated. A modern cladistic approach reconstructs the brains of ancestors by identifying brain characters within and across phylogenetic groups (clades), and uses parsimony or likelihood to infer direction of change and distinguish ancestral features from independently evolved convergences. Unfortunately, an idealized cladistic approach is often difficult to realize because characters may be hard to identify and validate, key species may be unavailable for study, and broadly based comparative studies can be costly, poorly funded, and labor intensive. Thus, many investigators pursue a truncated approach that is superficially Clark-like but conceptually cladistic. A truncated approach that relies on the extensive study of a few species may compensate for weaknesses by including niche-matched species that offer the opportunity to estimate the likelihood of similar brain features evolving as convergent adaptations. Because inferences about the brains of the primate ancestor are often made from the brains of tree shrews, we compare the brains of squirrel-like tree shrews with the brains of diurnal squirrels, and suggest that many of the primate-like features of the visual system of tree shrews arose independently of those in primates.

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“…This connection has been considered to contribute to the retino-pulvino-cortical pathway and to convey information from the peripheral visual field (Itaya and Van Hoesen 1983). However, previous studies (Ti es 1970; Weber et al 1977;Cusick and Kaas 1982) have either failed to support such a projection in the squirrel or have presented alternative explanations for the findings, although this animal is known to have a well-developed visual system, including large eyes and broad brain region related to vision (Abplanalp 1970;Kicliter and Bruce 1983). This discrepancy raises the question as to whether this failure is related to the method used or to the visual specificity of this species.…”

Section: Discussionmentioning

confidence: 93%