EM studies have shown that C2 and C3 are presynaptic on several cell types in the lamina (Meinertzhagen and O’Neil, 1991 and Rivera-Alba et al., 2011). By contrast, no synaptic targets are currently known for T1 neurons. Four other lamina-associated neuron classes are multicolumnar: there is less than one neuron per lamina column, and the arbors of each neuron span multiple columns (Figure 1D). With the exception of the lamina intrinsic amacrine neurons (Lai), which are confined to the lamina, the anatomy of these multicolumnar neurons suggests that they function as feedback neurons. Wide-field feedback from the medulla to the lamina

is provided by two types of lamina wide-field neurons (Lawf1 and Lawf2). Lawf2, which was identified in the course of the present study and was also recently reported elsewhere (Hasegawa et al., 2011), can be clearly distinguished from Lawf1 by its layer specificity DNA Damage inhibitor in the medulla (Figure 1D). Finally, lamina tangential LY294002 neurons (Lat), approximately four cells per optic lobe, project from the ipsilateral central brain to the distal surface of the lamina. These neurons do not innervate the medulla proper but have arborizations in the accessory medulla, a small medulla-associated

neuropil thought to function in the control of circadian rhythms (Helfrich-Förster et al., 2007). Several studies have investigated the functional roles of the large monopolar cells, L1 and L2. L1 and L2 are together required for motion detection. Simultaneously silencing both neuron types eliminates behavioral (Clark et al., 2011 and Rister et al., 2007) and electrophysiological (Joesch et al., 2010) responses to motion, while silencing each cell type individually has been reported to cause differential

responses to progressive and regressive motion at low contrasts imiloxan (Rister et al., 2007), contrast-inverting edges (Clark et al., 2011), and motion stimuli defined by brightness increments and decrements (Joesch et al., 2010). Electrophysiological recordings (Laughlin and Hardie, 1978 and Zheng et al., 2006) and calcium imaging studies (Clark et al., 2011) have found that the physiological responses of L1 and L2 are largely similar. Both are nonspiking neurons that respond to luminance increases with a transient hyperpolarization and luminance decreases with a transient depolarization. Neither L1 nor L2 is selective for moving stimuli. Overall, these data suggest that L1 and L2 provide input to motion circuits but are not directly involved in elementary motion computation. In comparison to L1 and L2, little is known about the contributions of the other ten lamina-associated neuron types. This is primarily because the small size of these neurons has, except for a few examples in larger flies (Douglass and Strausfeld, 1995), prevented electrophysiological recording.