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Sarah Pallas

Associate Professor of Biology

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.

Learn more at Pallas group

Academic Background

  • Postdoc MIT 1988-1992
  • PhD Cornell Univ 1987

  • MS Iowa State Univ magna cum laude 1980

  • BS Univ Minnesota summa cum laude 1977

Dynamic Alterations of Retinal EphA5 Expression in Retinocollicular Map Plasticity. Cheng Q, Graves MD, Pallas SL. Dev Neurobiol. 2019 Mar;79(3):252-267. doi: 10.1002/dneu.22675.
The Impact of Ecological Niche on Adaptive Flexibility of Sensory Circuitry. Pallas SL. Front Neurosci. 2017 Jun 28;11:344. doi: 10.3389/fnins.2017.00344.
Visual experience prevents dysregulation of GABAB receptor-dependent short-term depression in adult superior colliculus. Balmer TS, Pallas SL. J Neurophysiol. 2015 Apr 1;113(7):2049-61. doi: 10.1152/jn.00882.2014.
Cross-modal plasticity results in increased inhibition in primary auditory cortical areas. Mao YT, Pallas SL. Neural Plast. 2013;2013:530651. doi: 10.1155/2013/530651.
Refinement but not maintenance of visual receptive fields is independent of visual experience. Balmer TS, Pallas SL. Cereb Cortex. 2015 Apr;25(4):904-17.
Regulation of ephrin-A expression in compressed retinocollicular maps. Tadesse T, Cheng Q, Xu M, Baro DJ, Young LJ, Pallas SL. Dev Neurobiol. 2013 Apr;73(4):274-96. doi: 10.1002/dneu.22059.
Compromise of auditory cortical tuning and topography after cross-modal invasion by visual inputs. Mao YT, Pallas SL. J Neurosci. 2012 Jul 25;32(30):10338-51. doi: 10.1523/JNEUROSCI.6524-11.2012.
Competition and convergence between auditory and cross-modal visual inputs to primary auditory cortical areas. Mao YT, Hua TM, Pallas SL. J Neurophysiol. 2011 Apr;105(4):1558-73. doi: 10.1152/jn.00407.2010.
Inhibitory plasticity underlies visual deprivation-induced loss of receptive field refinement in the adult superior colliculus. Carrasco MM, Mao YT, Balmer TS, Pallas SL. Eur J Neurosci. 2011 Jan;33(1):58-68. doi: 10.1111/j.1460-9568.2010.07478.x.
Inhibitory plasticity facilitates recovery of stimulus velocity tuning in the superior colliculus after chronic NMDA receptor blockade. Razak KA, Pallas SL. J Neurosci. 2007 Jul 4;27(27):7275-83. doi: 10.1523/JNEUROSCI.1143-07.2007.
Early visual experience prevents but cannot reverse deprivation-induced loss of refinement in adult superior colliculus. Carrasco MM, Pallas SL. Vis Neurosci. 2006 Nov-Dec;23(6):845-52. doi: 10.1017/S0952523806230177.
Dark rearing reveals the mechanism underlying stimulus size tuning of superior colliculus neurons. Razak KA, Pallas SL. Vis Neurosci. 2006 Sep-Oct;23(5):741-8. doi: 10.1017/S0952523806230062.
Neural mechanisms of stimulus velocity tuning in the superior colliculus. Razak KA, Pallas SL. J Neurophysiol. 2005 Nov;94(5):3573-89. doi: 10.1152/jn.00816.2004.
Visual experience is necessary for maintenance but not development of receptive fields in superior colliculus. Carrasco MM, Razak KA, Pallas SL. J Neurophysiol. 2005 Sep;94(3):1962-70. doi: 10.1152/jn.00166.2005.
NMDA receptor blockade in the superior colliculus increases receptive field size without altering velocity and size tuning. Razak KA, Huang L, Pallas SL. J Neurophysiol. 2003 Jul;90(1):110-9. doi: 10.1152/jn.01029.2002.
Contact Info

Department of Biology
418 Morrill II
Amherst, MA 01003-9292

(413) 577-2254