, 2003; Eichner et al., 2011). L1 and L2 provide inputs to EMDs and thus their outputs must represent some of these filtering stages (Rister Docetaxel ic50 et al., 2007; Joesch et al., 2010; Clark et al., 2011). We show that L2 outputs

are strongly shaped by the light distribution across a broad region in space and by contrast polarity. Thus, the kinetics and amplitudes of L2 outputs differ for bright and dark objects of different shapes and sizes. Consequently, probing EMDs with minimal motion cues that differ in contrast and spatial extent could produce different results due to differential input filtering rather than differences in motion detection per se (Hassenstein and Reichardt, 1956; Egelhaaf and Borst, 1992; Eichner et al., 2011; Clark et al., 2011). More generally, spatiotemporal coupling observed in L2 can give rise to speed tuning, differentially regulated for bright and dark objects, and thus affect tuning of downstream EMDs to different speeds or to dark or bright Venetoclax solubility dmso motion cues (Fleet et al., 1985; Fleet and Jepson, 1985; Egelhaaf and Borst, 1989; Srinivasan et al., 1990; Juusola and French, 1997; Zanker et al., 1999). Finally, the surround responses of L2 effectively

convert a contrast increment at one spatial location into depolarizing responses at neighboring locations, providing a route by which increment information could enter a dark edge-detecting pathway, even given downstream half-wave rectification (Clark et al., 2011). Anatomical studies describe a dense network of connections in the lamina (Meinertzhagen and O’Neil, 1991; Rivera-Alba et al., 2011). Here we show how GABAergic circuits within this network shape the functional properties of L2 (Figures 6, 7, and 8). Photoreceptors until receive direct GABAergic input that depends on both GABAARs and GABABRs and shapes the RF surround in L2 (and presumably other LMCs). GABAAR-dependent synapses elsewhere in the circuit relay surround inputs into photoreceptors. A possible surround input is the centrifugal cell, C3, the only cell that is both presynaptic

to photoreceptors and GABAergic (Buchner et al., 1988; Kolodziejczyk et al., 2008; Rivera-Alba et al., 2011). Furthermore, since our genetic manipulation of GABARs affected both L2 cells as well as photoreceptors, we cannot exclude the possibility that receptors on both cells are redundantly required. Thus, the GABAergic centrifugal cell C2, which is presynaptic to L2, could provide these inputs. Additional GABAARs have been identified in L4 and another wide-field tangential cell (Enell et al., 2007; Kolodziejczyk et al., 2008) and could mediate the distal effects of manipulating GABAARs. Modulation of GABAergic signaling in L2 expands the RF center and increases spatial pooling. Such a change in RF shape increases signal-to-noise ratios and occurs under low light level conditions (Dubs et al., 1981; Dubs, 1982).