The Experts below are selected from a list of 2166 Experts worldwide ranked by ideXlab platform
Michael C Crair - One of the best experts on this subject based on the ideXlab platform.
-
spatial pattern of spontaneous retinal waves instructs Retinotopic Map refinement more than activity frequency
Developmental Neurobiology, 2015Co-Authors: Timothy J Burbridge, Minggang Chen, Yueyi Zhang, Zhimin Jimmy Zhou, Michael C CrairAbstract:Spontaneous activity during early development is necessary for the formation of precise neural connections, but it remains uncertain whether activity plays an instructive or permissive role in brain wiring. In the visual system, retinal ganglion cell (RGC) projections to the brain form two prominent sensory Maps, one reflecting eye of origin and the other Retinotopic location. Recent studies provide compelling evidence supporting an instructive role for spontaneous retinal activity in the development of eye-specific projections, but evidence for a similarly instructive role in the development of retinotopy is more equivocal. Here, we report on experiments in which we knocked down the expression of β2-containing nicotinic acetylcholine receptors (β2-nAChRs) specifically in the retina through a Cre-loxP recombination strategy. Overall levels of spontaneous retinal activity in retina-specific β2-nAChR mutant mice (Rx-β2cKO), examined in vitro and in vivo, were reduced to a degree comparable to that observed in whole animal β2-nAChR mouse mutants (β2KO). However, many residual spontaneous waves in Rx-β2cKO mice displayed local propagating features with strong correlations between nearby but not distant RGCs typical of waves observed in wild-type (WT) but not β2KO mice. We further observed that eye-specific segregation was disrupted in Rx-β2cKO mice, but retinotopy was spared in a competition-dependent manner. These results suggest that propagating patterns of spontaneous retinal waves are essential for normal development of the Retinotopic Map, even while overall activity levels are significantly reduced, and support an instructive role for spontaneous retinal activity in both eye-specific segregation and Retinotopic refinement.
-
Spatial pattern of spontaneous retinal waves instructs Retinotopic Map refinement more than activity frequency.
Developmental neurobiology, 2015Co-Authors: Timothy J Burbridge, Minggang Chen, Yueyi Zhang, Zhimin Jimmy Zhou, Michael C CrairAbstract:Spontaneous activity during early development is necessary for the formation of precise neural connections, but it remains uncertain whether activity plays an instructive or permissive role in brain wiring. In the visual system, retinal ganglion cell (RGC) projections to the brain form two prominent sensory Maps, one reflecting eye of origin and the other Retinotopic location. Recent studies provide compelling evidence supporting an instructive role for spontaneous retinal activity in the development of eye-specific projections, but evidence for a similarly instructive role in the development of retinotopy is more equivocal. Here, we report on experiments in which we knocked down the expression of β2-containing nicotinic acetylcholine receptors (β2-nAChRs) specifically in the retina through a Cre-loxP recombination strategy. Overall levels of spontaneous retinal activity in retina-specific β2-nAChR mutant mice (Rx-β2cKO), examined in vitro and in vivo, were reduced to a degree comparable to that observed in whole animal β2-nAChR mouse mutants (β2KO). However, many residual spontaneous waves in Rx-β2cKO mice displayed local propagating features with strong correlations between nearby but not distant RGCs typical of waves observed in wild-type (WT) but not β2KO mice. We further observed that eye-specific segregation was disrupted in Rx-β2cKO mice, but retinotopy was spared in a competition-dependent manner. These results suggest that propagating patterns of spontaneous retinal waves are essential for normal development of the Retinotopic Map, even while overall activity levels are significantly reduced, and support an instructive role for spontaneous retinal activity in both eye-specific segregation and Retinotopic refinement. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 75: 621–640, 2015
-
Bone Morphogenetic Proteins, Eye Patterning, and Retinocollicular Map Formation in the Mouse
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2008Co-Authors: Daniel T Plas, Onkar S. Dhande, Joshua E. Lopez, Deepa Murali, Christina Thaller, Mark Henkemeyer, Yasuhide Furuta, Paul A. Overbeek, Michael C CrairAbstract:Patterning events during early eye formation determine retinal cell fate and can dictate the behavior of retinal ganglion cell (RGC) axons as they navigate toward central brain targets. The temporally and spatially regulated expression of bone morphogenetic proteins (BMPs) and their receptors in the retina are thought to play a key role in this process, initiating gene expression cascades that distinguish different regions of the retina, particularly along the dorsoventral axis. Here, we examine the role of BMP and a potential downstream effector, EphB, in Retinotopic Map formation in the lateral geniculate nucleus (LGN) and superior colliculus (SC). RGC axon behaviors during Retinotopic Map formation in wild-type mice are compared with those in several strains of mice with engineered defects of BMP and EphB signaling. Normal RGC axon sorting produces axon order in the optic tract that reflects the dorsoventral position of the parent RGCs in the eye. A dramatic consequence of disrupting BMP signaling is a missorting of RGC axons as they exit the optic chiasm. This sorting is not dependent on EphB. When BMP signaling in the developing eye is genetically modified, RGC order in the optic tract and targeting in the LGN and SC are correspondingly disrupted. These experiments show that BMP signaling regulates dorsoventral RGC cell fate, RGC axon behavior in the ascending optic tract, and Retinotopic Map formation in the LGN and SC through mechanisms that are in part distinct from EphB signaling in the LGN and SC.
-
evidence for an instructive role of retinal activity in Retinotopic Map refinement in the superior colliculus of the mouse
The Journal of Neuroscience, 2005Co-Authors: Anand R Chandrasekaran, Daniel T Plas, Ernesto Gonzalez, Michael C CrairAbstract:Although it is widely accepted that molecular mechanisms play an important role in the initial establishment of Retinotopic Maps, it has also long been argued that activity-dependent factors act in concert with molecular mechanisms to refine topographic Maps. Evidence of a role for retinal activity in Retinotopic Map refinement in mammals is limited, and nothing is known about the effect of spontaneous retinal activity on the development of receptive fields in the superior colliculus. Using anatomical and physiological methods with two genetically manipulated mouse models and pharmacological interventions in wild-type mice, we show that spontaneous retinal waves instruct Retinotopic Map refinement in the superior colliculus of the mouse. Activity-dependent mechanisms may play a preferential role in the Mapping of the nasal-temporal axis of the retina onto the colliculus, because refinement is particularly impaired along this axis in mutants without retinal waves. Interfering with both axon guidance cues and activity-dependent cues in the same animal has a dramatic cumulative effect. These experiments demonstrate how axon guidance cues and activity-dependent factors combine to instruct Retinotopic Map development.
Timothy J Burbridge - One of the best experts on this subject based on the ideXlab platform.
-
spatial pattern of spontaneous retinal waves instructs Retinotopic Map refinement more than activity frequency
Developmental Neurobiology, 2015Co-Authors: Timothy J Burbridge, Minggang Chen, Yueyi Zhang, Zhimin Jimmy Zhou, Michael C CrairAbstract:Spontaneous activity during early development is necessary for the formation of precise neural connections, but it remains uncertain whether activity plays an instructive or permissive role in brain wiring. In the visual system, retinal ganglion cell (RGC) projections to the brain form two prominent sensory Maps, one reflecting eye of origin and the other Retinotopic location. Recent studies provide compelling evidence supporting an instructive role for spontaneous retinal activity in the development of eye-specific projections, but evidence for a similarly instructive role in the development of retinotopy is more equivocal. Here, we report on experiments in which we knocked down the expression of β2-containing nicotinic acetylcholine receptors (β2-nAChRs) specifically in the retina through a Cre-loxP recombination strategy. Overall levels of spontaneous retinal activity in retina-specific β2-nAChR mutant mice (Rx-β2cKO), examined in vitro and in vivo, were reduced to a degree comparable to that observed in whole animal β2-nAChR mouse mutants (β2KO). However, many residual spontaneous waves in Rx-β2cKO mice displayed local propagating features with strong correlations between nearby but not distant RGCs typical of waves observed in wild-type (WT) but not β2KO mice. We further observed that eye-specific segregation was disrupted in Rx-β2cKO mice, but retinotopy was spared in a competition-dependent manner. These results suggest that propagating patterns of spontaneous retinal waves are essential for normal development of the Retinotopic Map, even while overall activity levels are significantly reduced, and support an instructive role for spontaneous retinal activity in both eye-specific segregation and Retinotopic refinement.
-
Spatial pattern of spontaneous retinal waves instructs Retinotopic Map refinement more than activity frequency.
Developmental neurobiology, 2015Co-Authors: Timothy J Burbridge, Minggang Chen, Yueyi Zhang, Zhimin Jimmy Zhou, Michael C CrairAbstract:Spontaneous activity during early development is necessary for the formation of precise neural connections, but it remains uncertain whether activity plays an instructive or permissive role in brain wiring. In the visual system, retinal ganglion cell (RGC) projections to the brain form two prominent sensory Maps, one reflecting eye of origin and the other Retinotopic location. Recent studies provide compelling evidence supporting an instructive role for spontaneous retinal activity in the development of eye-specific projections, but evidence for a similarly instructive role in the development of retinotopy is more equivocal. Here, we report on experiments in which we knocked down the expression of β2-containing nicotinic acetylcholine receptors (β2-nAChRs) specifically in the retina through a Cre-loxP recombination strategy. Overall levels of spontaneous retinal activity in retina-specific β2-nAChR mutant mice (Rx-β2cKO), examined in vitro and in vivo, were reduced to a degree comparable to that observed in whole animal β2-nAChR mouse mutants (β2KO). However, many residual spontaneous waves in Rx-β2cKO mice displayed local propagating features with strong correlations between nearby but not distant RGCs typical of waves observed in wild-type (WT) but not β2KO mice. We further observed that eye-specific segregation was disrupted in Rx-β2cKO mice, but retinotopy was spared in a competition-dependent manner. These results suggest that propagating patterns of spontaneous retinal waves are essential for normal development of the Retinotopic Map, even while overall activity levels are significantly reduced, and support an instructive role for spontaneous retinal activity in both eye-specific segregation and Retinotopic refinement. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 75: 621–640, 2015
Dennis D.m. O'leary - One of the best experts on this subject based on the ideXlab platform.
-
Mechanisms of Retinotopic Map development: Ephs, ephrins, and spontaneous correlated retinal activity.
Progress in brain research, 2005Co-Authors: Dennis D.m. O'leary, Todd MclaughlinAbstract:This chapter summarizes mechanisms that control the development of Retinotopic Maps in the brain, focusing on work from our laboratory using as models the projection of retinal ganglion cells (RGCs) to the chick optic tectum (OT) or rodent superior colliculus (SC). The formation of a Retinotopic Map involves the establishment of an initial, very coarse Map that subsequently undergoes large-scale remodeling to generate a refined Map. All arbors are formed by interstitial branches that form in a topographically biased manner along RGC axons that overshoot their correct termination zone (TZ) along the anterior-posterior (A-P) axis of the OT/SC. The interstitial branches exhibit directed growth along the lateral-medial (L-M) axis of the OT/SC to position the branch at the topographically correct location, where it arborizes to form the TZ. EphA receptors and ephrin-A ligands control in part RGC axon Mapping along the A-P axis by inhibiting branching and arborization posterior to the correct TZ. Ephrin-B1 acts bifunctionally through EphB forward signaling to direct branches along the L-M axis of the OT/SC to their topographically correct site. Computational modeling indicates that multiple graded activities are required along each axis to generate a Retinotopic Map, and makes several predictions, including: the progressive addition of ephrin-As within the OT/SC, due to its expression on RGC axon branches and arbors, is required to increase topographic specificity in branching and arborization as well as eliminate the initial axon overshoot, and that interactions amongst RGC axons that resemble correlated neural activity are required to drive Retinotopic refinement. Analyses of mutant mice that lack early spontaneous retinal waves that correlate activity amongst neighboring RGCs, confirm this modeling prediction and show that correlated activity during an early brief critical period is required to drive the large-scale remodeling of the initially topographically coarse projection into a refined one. In summary, multiple graded guidance molecules, retinal waves and correlated spontaneous RGC activity cooperate to generate Retinotopic Maps.
-
Computational Modeling of Retinotopic Map Development to Define Contributions of EphA-EphrinA Gradients, Axon-Axon Interactions, and Patterned Activity
Journal of neurobiology, 2004Co-Authors: Paul A. Yates, Todd Mclaughlin, Alex D. Holub, Terrence J. Sejnowski, Dennis D.m. O'learyAbstract:The topographic projection of retinal ganglion cell (RGC) axons to mouse superior colliculus (SC) or chick optic tectum (OT) is formed in three phases: RGC axons overshoot their termination zone (TZ); they exhibit interstitial branching along the axon that is topographically biased for the correct location of their future TZ; and branches arborize preferentially at the TZ and the initial exuberant projection refines through axon and branch elimination to generate a precise Retinotopic Map. We present a computational model of Map development that demonstrates that the countergradients of EphAs and ephrinAs in retina and the OT/SC and bidirectional repellent signaling between RGC axons and OT/SC cells are sufficient to direct an initial topographic bias in RGC axon branching. Our model also suggests that a proposed repellent action of EphAs/ephrinAs present on RGC branches and arbors added to that of EphAs/ephrinAs expressed by OT/SC cells is required to progressively restrict branching and arborization to topographically correct locations and eliminate axon overshoot. Simulations show that this molecular framework alone can develop considerable topographic order and refinement, including axon elimination, a feature not programmed into the model. Generating a refined Map with a condensed TZ as in vivo requires an additional parameter that enhances branch formation along an RGC axon near sites that it has a higher branch density, and resembles an assumed role for patterned neural activity. The same computational model generates the phenotypes reported in ephrinA deficient mice and Isl2-EphA3 knockin mice. This modeling suggests that gradients of counter-repellents can establish a substantial degree of topographic order in the OT/SC, and that repellents present on RGC axon branches and arbors make a substantial contribution to Map refinement. However, competitive interactions between RGC axons that enhance the probability of continued local branching are required to generate precise retinotopy.
-
Retinotopic Map refinement requires spontaneous retinal waves during a brief critical period of development.
Neuron, 2003Co-Authors: Todd Mclaughlin, Christine L. Torborg, Marla B. Feller, Dennis D.m. O'learyAbstract:Abstract During retinocollicular Map development, spontaneous waves of action potentials spread across the retina, correlating activity among neighboring retinal ganglion cells (RGCs). To address the role of retinal waves in topographic Map development, we examined wave dynamics and retinocollicular projections in mice lacking the β2 subunit of the nicotinic acetylcholine receptor. β2 −/− mice lack waves during the first postnatal week, but RGCs have high levels of uncorrelated firing. By P8, the wild-type retinocollicular projection remodels into a refined Map characterized by axons of neighboring RGCs forming focal termination zones (TZs) of overlapping arbors. In contrast, in P8 β2 −/− mice, neighboring RGC axons form large TZs characterized by broadly distributed arbors. At P8, glutamatergic retinal waves appear in β2 −/− mice, and later, visually patterned activity appears, but the diffuse TZs fail to remodel. Thus, spontaneous retinal waves that correlate RGC activity are required for Retinotopic Map remodeling during a brief early critical period.
-
Retroviral Misexpression of engrailed Genes in the Chick Optic Tectum Perturbs the Topographic Targeting of Retinal Axons
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1996Co-Authors: Glenn C. Friedman, Dennis D.m. O'learyAbstract:We have investigated the role of the homeodomain transcription factor genes En-1 and En-2, homologs of the Drosophila segment polarity gene engrailed, in regulating the development of the Retinotopic Map in the chick optic tectum. The En proteins are distributed in a gradient along the rostral-caudal axis of the developing tectum, with highest amounts found caudally. Previous evidence suggests that En-1 and En-2 may regulate the polarity of the rostral-caudal axis of the tectum and the subsequent topographic Mapping of retinal axons. We have tested this hypothesis by using a recombinant replication-competent retrovirus to overexpress the En-1 or En-2 genes in the developing tectum. Anterograde labeling with the axon tracer Dil was used to analyze the topographic Mapping of retinal axons after the time that the retinotectal projection is normally topographically organized. Overexpression of either En-1 or En-2 perturbed the topographic targeting of retinal axons. In En-infected tecta, nasal retinal axons form an abnormally diffuse projection with numerous aberrant axons, branches, and arbors found at topographically incorrect locations, colocalized with domains of viral infection. In contrast, temporal axons did not form a diffuse projection or discrete aberrant arbors; however, many temporal axons were stunted and ended aberrantly rostral to their appropriate TZ, or in other cases either did not enter the tectum or formed a dense termination at its extreme rostral edge. These findings indicate that En-1 and En-2 are involved in regulating the development of the Retinotopic Map in the tectum. Furthermore, they support the hypothesis that En genes regulate the polarity of the rostral-caudal axis of the tectum, most likely by controlling the expression of retinal axon guidance molecules.
-
Control of topographic retinal axon branching by inhibitory membrane-bound molecules
Science (New York N.Y.), 1994Co-Authors: Adina L. Roskies, Dennis D.m. O'learyAbstract:Retinotopic Map development in nonmammalian vertebrates appears to be controlled by molecules that guide or restrict retinal axons to correct locations in their targets. However, the Retinotopic Map in the superior colliculus (SC) of the rat is developed instead by a topographic bias in collateral branching and arborization. Temporal retinal axons extending across alternating membranes from the topographically correct rostral SC or the incorrect caudal SC of embryonic rats preferentially branch on rostral membranes. Branching preference is due to an inhibitory phosphatidylinositol-linked molecule in the caudal SC. Thus, position-encoding membrane-bound molecules may establish Retinotopic Maps in mammals by regulating axon branching, not by directing axon growth.
Hollis T. Cline - One of the best experts on this subject based on the ideXlab platform.
-
Optic flow instructs Retinotopic Map formation through a spatial to temporal to spatial transformation of visual information
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Masaki Hiramoto, Hollis T. ClineAbstract:Retinotopic Maps are plastic in response to changes in sensory input; however, the experience-dependent instructive cues that organize retinotopy are unclear. In animals with forward-directed locomotion, the predominant anterior to posterior optic flow activates retinal ganglion cells in a stereotyped temporal to nasal sequence. Here we imaged retinotectal axon arbor location and structural plasticity to assess Map refinement in vivo while exposing Xenopus tadpoles to visual stimuli. We show that the temporal sequence of retinal activity driven by natural optic flow organizes retinotopy by regulating axon arbor branch dynamics, whereas the opposite sequence of retinal activity prevents Map refinement. Our study demonstrates that a spatial to temporal to spatial transformation of visual information controls experience-dependent topographic Map plasticity. This organizational principle is likely to apply to other sensory modalities and projections in the brain.
-
In vivo development of neuronal structure and function.
Cold Spring Harbor symposia on quantitative biology, 1996Co-Authors: Hollis T. Cline, Roberto MalinowAbstract:The formation of the nervous system requires a coordinated development of neuronal morphology and synaptic physiology. We have used the frog retinotectal system to examine the development of brain structure and function. The retinotectal system of frogs is well known for its developmental and experience-dependent synaptic plasticity. As the animal grows, retinotectal axon arbors migrate considerable distances within the contralateral optic tectum in order to maintain a high degree of refinement in the Retinotopic Map. The capacity of the arbors to move within the tectal neuropil indicates that the retinotectal synapses and axon arbor branches are dynamic. The maintenance of retinotopy despite the axonal mobility indicates that there must be a mechanism which controls sites of synapse formation and stabilization. Considerable evidence supports the hypothesis that N-methyl-d-aspartate (NMDA) receptor activity is required to maintain the Retinotopic Map (Cline 1991), but it is still not clear how activity influences the neuronal
-
The Activity-Dependent Mechanism in the Development of the Refined Retinotopic Map
The Visual System from Genesis to Maturity, 1992Co-Authors: Hollis T. ClineAbstract:A central problem in the development of the central nervous system (CNS) concerns the formation of specific or appropriate synaptic connections. The developing visual system of amphibia is an optimal system in which to study this problem. The frog visual system is characterized by a highly refined topographic projection from each retina to the contralateral optic tectum, the central visual processing area in these animals. We know that at least two discreet, but interacting mechanisms operate during the development of the retinotectal projection: (1) an activity-independent mechanism, based on differential distributions of cell surface molecules on retinal axon terminals and the tectal cells, can account for a crude topographic organization of retinal ganglion cell axons within the tectal neuropil; and (2) an activity-dependent mechanism, which is thought to recognize correlated patterns of afferent activity, refines the projection to yield a point-to-point specificity in the position of the retinal axons within the tectal neuropil. The activity-dependent mechanism is the subject of this review.
Sarah L. Pallas - One of the best experts on this subject based on the ideXlab platform.
-
Regulation of ephrin-A expression in compressed retinocollicular Maps.
Developmental Neurobiology, 2012Co-Authors: Tizeta Tadesse, Deborah J. Baro, Mei Xu, Larry J Young, Qi Cheng, Sarah L. PallasAbstract:Retinotopic Maps can undergo compression and expansion in response to changes in target size, but the mechanism underlying this compensatory process has remained a mystery. The discovery of ephrins as molecular mediators of Sperry's chemoaffinity process allows a mechanistic approach to this important issue. In Syrian hamsters, neonatal, partial (PT) ablation of posterior superior colliculus (SC) leads to compression of the Retinotopic Map, independent of neural activity. Graded, repulsive EphA receptor/ephrin-A ligand interactions direct the formation of the retinocollicular Map, but whether ephrins might also be involved in Map compression is unknown. To examine whether Map compression might be directed by changes in the ephrin expression pattern, we compared ephrin-A2 and ephrin-A5 mRNA expression between normal SC and PT SC using in situ hybridization and quantitative real-time PCR. We found that ephrin-A ligand expression in the compressed Maps was low anteriorly and high posteriorly, as in normal animals. Consistent with our hypothesis, the steepness of the ephrin gradient increased in the lesioned colliculi. Interestingly, overall levels of ephrin-A2 and -A5 expression declined immediately after neonatal target damage, perhaps promoting axon outgrowth. These data establish a correlation between changes in ephrin-A gradients and Map compression, and suggest that ephrin-A expression gradients may be regulated by target size. This in turn could lead to compression of the retinocollicular Map onto the reduced target. These findings have important implications for mechanisms of recovery from traumatic brain injury. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013
-
visual behaviour mediated by retinal projections directed to the auditory pathway
Nature, 2000Co-Authors: Sarah L. Pallas, Laurie Von MelchnerAbstract:An unresolved issue in cortical development concerns the relative contributions of intrinsic and extrinsic factors to the functional specification of different cortical areas1,2,3,4. Ferrets in which retinal projections are redirected neonatally to the auditory thalamus5 have visually responsive cells in auditory thalamus and cortex, form a Retinotopic Map in auditory cortex and have visual receptive field properties in auditory cortex that are typical of cells in visual cortex5,6,7,8. Here we report that this cross-modal projection and its representation in auditory cortex can mediate visual behaviour. When light stimuli are presented in the portion of the visual field that is ‘seen’ only by this projection, ‘rewired’ ferrets respond as though they perceive the stimuli to be visual rather than auditory. Thus the perceptual modality of a neocortical region is instructed to a significant extent by its extrinsic inputs. In addition, gratings of different spatial frequencies can be discriminated by the rewired pathway, although the grating acuity is lower than that of the normal visual pathway.
-
Morphology of retinal axon arbors induced to arborize in a novel target, the medial geniculate nucleus. II. Comparison with axons from the inferior colliculus.
The Journal of comparative neurology, 1994Co-Authors: Sarah L. Pallas, Mriganka SurAbstract:Specific neonatal lesions in ferrets can induce retinal axons to project into the medial geniculate nucleus (MGN). In the accompanying paper (Pallas et al., this issue), we described the morphology of these retinal ganglion cell axons. Those results and others (Roe et al. [1993] J. Comp. Neurol. 334:263) suggest that these axons belong to the W class of retinal axons. In this paper, the retino-MGN axons are compared with the normal inputs to the MGN from the brachium of the inferior colliculus (BIC). We first sought to determine further the extent to which a novel target might influence retinal axon arbor morphology. The second issue concerns retinal topography. Ferrets with retinal projections to the MGN have a two-dimensional Retinotopic Map in the MGN and the primary auditory cortex rather than the one-dimensional tonotopic Map normally present (Roe et al. [1990] Science 250:818). To investigate whether there might be an anatomical substrate for a two-dimensional Retinotopic Map in the MGN, we compared the space-filling characteristics of the retino-MGN axons with the IC-MGN axons. Our results show that the branched retino-MGN axons resemble normal retinal W axons much more closely than they resemble the normal inputs to MGN. In addition, most of the axon arbors from the BIC are elongated along the rostrocaudal (isofrequency) axis, whereas the branched retino-MGN axons are more spatially restricted, suggesting an anatomical substrate for a Retinotopic Map in the MGN of the rewired ferrets. © 1994 Wiley-Liss, Inc.
