Sarah Pallas
Research areas include: Stability of visual receptive field properties after traumatic brain injury: My studies of the effects of damage to neonatal superior colliculus showed that compression of the retinal projection onto a partially lesioned SC led to a compensatory process that- while increasing convergence at the population level- somehow preserved single cell convergence ratios, maintaining normal receptive field sizes. Furthermore, size and velocity tuning were preserved. This occurred by reductions in retinal axon arbor extent and by both NMDA receptor-dependent plasticity and GABAA receptor- dependent inhibitory plasticity. The compression of the retinotopic map in SC is correlated with alterations in steepness of the graded axon guidance cues (ephrinA, EphA) that are necessary for formation of the normal projection during development. This is a remarkable degree of self-repair by the retino-SC circuit, and a current goal is to determine how retinal axons perform this feat of reorganization.
Current Research
Development and maintenance of refined visual receptive fields: Decades of research on visual cortex have led to the view that visual experience is necessary for normal development of visual pathways. We expected the same finding in superior colliculus (SC), but instead found that refinement of visual projections to SC occurred normally under dark rearing conditions. Surprisingly, although spontaneous activity is sufficient for development of refined retino-SC receptive fields, visual experience is necessary to maintain refinement in adulthood. We find that prolonged visual deprivation leads to a loss of lateral inhibition, leading to enlarged receptive fields. We demonstrated that this is true not only in SC but also in visual cortex. A brief exposure to light during the second postnatal month protects against receptive field enlargement for the life of the animal. No amount of light exposure after this critical period can reverse the detrimental loss of refinement. Plasticity in adulthood, whether adaptive or maladaptive, is increasingly being acknowledged, although the threshold and extent of plasticity is higher in young animals. Because our work was done in hamsters and previous work was done primarily in non-human primates and carnivores, we have forwarded and are testing the hypothesis that dependence on visual stimulation for initial refinement of visual pathways depends on the evolutionary history and ecological niche of the species.
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Academic Background
- Postdoc MIT 1988-1992
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PhD Cornell Univ 1987
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MS Iowa State Univ magna cum laude 1980
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BS Univ Minnesota summa cum laude 1977
