electrically_synapsed_to horizontal system neuron dorsal giant horizontal cell HSN equatorial giant horizontal cell HSE Horizontal system neuron whose dendritic arbor extends over the central lobula plate (Scott et al., 2002). It has both synaptic input and output in the axon terminal in the protocerebral region (Raghu et al., 2007). The area covered by its dendrite corresponds to the center of the large equatorial field of vision. It is electrically coupled to HSN and HSS (Schnell et al., 2010). There is one of these cells on each side (Shinomiya et al., 2022). HSE horizontal system equatorial cell FBbt:00003919 HS equatorial LPT02 VFB:FBbt_00003919 Electrical coupling was shown indirectly by neurobiotin dye coupling in HSN and HSE cells labelled using the P{GawB}CG1090[NP0282] (FBti0033586) driver (Schnell et al., 2010). The postsynaptic terminals in the protocerebral region were identified by the presence of a subunit of the GABA receptor (Rdl) in horizontal system cells labelled with P{UAS-Rdl.HA} (FBtp0021350] driven by the P{GAL4}3A driver [FBti0131277) (Raghu et al., 2007). Due to their morphology and functional similarity, this cell is judged to be homologous to the equatorial horizontal system cell in larger flies (Heisenberg et al., 1978; Rajashekhar and Shamprasad, 2004; Scott et al., 2002). HSE fly_anatomy.ontology ventral giant horizontal cell HSS