Abstract
In many animals, a fast and reliable circuit for discriminating between predator-sized objects and edible (prey-sized) objects is necessary for survival. How are receptive fields (RFs) in visual brain areas organized to extract information about size? Recent studies from the zebrafish optic tectum and the mouse visual cortex suggest de novo shaping of RFs by subtypes of inhibitory neurons. Del Bene et al. (2010) describe a population of GABAergic neurons in the zebrafish optic tectum (superficial interneurons, SINs) that are necessary for size filtering during prey capture. Adesnik et al. (2012) describe a somatostatin-expressing interneuron population (SOMs) that confers surround suppression on layer II/III pyramidal cells in mouse V1. Strikingly both the SINs and the SOMs, display size-dependent response properties. Increasing visual stimulus size increases excitatory input to these neurons. Dampening SIN or SOM activity alters tuning of neighboring circuits such that they lose preference for small objects. Both results provide exciting evidence for mechanisms of size filtering in visual circuits. Here we review the roles of the SINs and the SOMs and speculate on the similarity of such spatial filters across species.
Highlights
THE SINs The pursuit and capture of small prey by the zebrafish larva require that information about the size and motion of the prey object be continually tracked
Dendrites of periventricular neurons (PVNs) stratifying within the deep layers of the tectal neuropil were preferentially tuned to small moving bars, whereas many periventricular interneurons (PVINs) dendrites in the superficial neuropil were responsive to both full-field visual stimuli and small moving bars
pyramidal cells (PCs) size tuning was determined through extracellular recordings of single units, while loose patch recordings were employed to determine size tuning in parvalbumin-expressing neurons (PVs) and somatostatin-expressing neurons (SOMs)
Summary
THE SINs The pursuit and capture of small prey (e.g., paramecia) by the zebrafish larva require that information about the size and motion of the prey object be continually tracked. Del Bene et al (2010) describe a population of GABAergic neurons in the zebrafish optic tectum (superficial interneurons, SINs) that are necessary for size filtering during prey capture. Dampening SIN or SOM activity alters tuning of neighboring circuits such that they lose preference for small objects.
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