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Past recordings of foveal output signals in the living eye

The team from the Howard Hughes Medical Center research team recently made one of the first direct comparisons.

Past recordings of foveal output signals in the living eye had demonstrated that the perceptual specialisations of foveal vision originated largely in the retina itself, rather than in subsequent brain circuits.

Nonetheless, Sinha says, little was known about the cellular and circuitry basis of these functional specialisations due to a lack of intracellular recordings from foveal neurons.

The team from the Howard Hughes Medical Center research team recently made one of the first direct comparisons of the physiological properties of foveal and peripheral retinal neurons and among the first correlations between structure and function in the fovea.

Publishing their work in the journal CELL, their experiments revealed how differences in the cellular and circuit mechanisms of foveal and peripheral retina can account for the well-established differences in their perceptual sensitivities.

The latest study provides one of the first glimpses into how the fovea works at a cellular and circuit level. It turns out to be very different from how other regions of the retina operate.

Returning to the issue of sensitivity to rapidly changing inputs, Sinha and colleagues compared the responses of the cone photoreceptors -- the neurons that are the frontline of the visual system. They found that the responses of cone photoreceptors in the fovea are about two-fold slower than those in the periphery.

This is nearly identical to the differences between central and peripheral vision in the sensitivity to rapidly changing inputs.

The finding suggests that the perceptual differences originate in the cone photoreceptors themselves.

"The novelty of this study is bolstered by a comprehensive structure-function analyses, lacking in previous work on the fovea, using techniques such as particle-mediated gene transfer to study protein expression in a diverse array of ganglion cells," says Hoon, an acting instructor in biological structure at the UW School of Medicine who contributed to the recent research.

These approaches open the door to a wide-range of transient genetic manipulations that will allow scientists to explore properties of other cell types in the fovea.

"Determining the cellular origin of human perception is an important, but rarely realised, goal in neuroscience and biology," Sinha says.

"Our results provide a simple explanation for a salient perceptual observation."

Sinha says the results are important since there is a huge amount of effort underway globally to restore central vision in humans in diseases but our understanding of how the fovea functions is largely missing.

"This is a big step forward in not only our fundamental understanding of foveal function but also for devising therapeutic strategies including designing visual prosthetics to restore deficits in central vision in diseases such as macular degeneration and others."

( Source : PTI )
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