Periodically, we highlight one paper that was recently published by a Ph.D. student in the Neuroscience Institute.
Neuroscience Institute Highlighted Paper:
Tim S. Balmer and Sarah L. Pallas
Refinement but Not Maintenance of Visual Receptive Fields Is Independent of Visual Experience.
Cereb. Cortex (2013). doi: 10.1093/cercor/bht281. First published online: October 9, 2013
Tim Balmer, a PhD student in the laboratory of Professor Sarah Pallas, is interested in the development and plasticity of sensory systems. His dissertation asks a seemingly simple question: is visual experience necessary for the development of vision? A widely held view in neuroscience and medicine is that the act of seeing contributes to the development of visual ability, and that without visual experience vision cannot develop properly.
Since the first experiments by Hubel and Wiesel in the early 1960s, this question has been approached in many different ways. Various methods of visual deprivation (dark rearing, blind folding, eyelid closing) have been employed using different durations and different species, resulting in conflicting interpretations. In addition, different visual properties (selectivity of neurons for stimulus orientation, direction of motion, or eye dominance) and different levels of analysis (electrophysiological, anatomical, or behavioral) have complicated our understanding of this seemingly simple question.
Building off of earlier work in the Pallas lab by Magdalena Carrasco and Khaleel Razak showing that maturation of visual properties of neurons in the superior colliculus (which is essential for object localization) does not depend on visual experience, Tim explored whether this was also the case for visual cortex (which is involved primarily in analysis of spatial detail). Extracellular electrophysiological recordings were made from hamster visual cortex or superior colliculus while presenting light within the visual field. As a neurophysiological measure of visual acuity Tim measures the amount of the visual field that each neuron is responsible for- their receptive fields. Large receptive fields result in poor visual acuity and small receptive fields facilitate high visual acuity.
In his recent paper in Cerebral Cortex, Tim shows that receptive fields refine in both the visual cortex and superior colliculus without visual experience, but become enlarged during continued dark rearing in adulthood. Visual experience during a brief but critical period during late juvenile development prevents this receptive field enlargement. This study suggests that more importance may have been placed on the role of visual experience on receptive field refinement than is warranted. A focus on blocking enlargement of receptive fields or other maladaptive plasticity may be a safer route than enhancing plasticity for recovery from disorders of sensory deprivation such as macular degeneration or cataract.