Brain Circuit for Filtering Out Irrelevant Light

When Zebrafish hunt for food, large objects are irrelevant but small objects are potentially edible (like paramecia). A new paper “Filtering of Visual Information in the Tectum by an Identified Neural Circuit” published October 29, 2010 in Science uses sophisticated techniques such as genetic manipulation, calcium imaging, confocal microscopy, and the elimination of specific brain cells using lasers to identify a brain circuit that helps the Zebrafish to ignore irrelevant visual information and to focus on small objects.

The processes that carry signals (action potentials) from the eye, the retinal axons, to the Zebrafish tectum respond vigorously to both large and small visual stimuli. In contrast, output brain cells (neurons) in the tectum that receive input from the retinal axons only respond vigorously to small visual stimuli. How does this signal transformation take place?

The authors demonstrate that a superficial interneuron in the tectum responds vigorously to large but not to small visual stimuli. These interneurons inhibit the responses of the output neurons in the tectum to large visual stimuli. The superior colliculus in mammals is similar to the tectum. Circuits similar to the one described in the Zebrafish may exist in the superior colliculus of mammals.

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