capable of part of receives synaptic input in region sends synaptic output to region receives synaptic input from neuron T4a neuron T5a neuron lobula plate layer 1 lobula plate giant neuron horizontal system neuron HS HS cell VFB:FBbt_00003917 Giant neuron with wide-field dendritic arborization in lobula plate layer 1 (Shinomiya et al., 2022). This arborization is flattened in the anterior-posterior axis (Scott et al., 2002). Most of its input is from T4a and T5a neurons (Shinomiya et al., 2022). Its axon extends medially and ventrally to innervate the adult protocerebrum (Scott et al., 2002). It is involved in the optomotor response (Heisenberg et al., 1978; Schnell et al., 2010) and responds to horizontal motion with graded membrane potential changes in a directional-selective way (Schnell et al., 2010). giant horizontal cell fly_anatomy.ontology Due to their morphology and functional similarity, these cells are judged to be homologous to the three horizontal system cells in larger flies (Heisenberg et al., 1978; Rajashekhar and Shamprasad, 2004; Scott et al., 2002). The presynaptic terminals in the protocerebral region were identified by the presence of a subunit of the GABA receptor (Rdl) in horizontal system cells labelled with the P{GAL4}3A driver (FBti0131277). The postsynaptic terminals in the protocerebral region were labelled with P{UAS-n-syb.mRed} (FBtp0055749] driven by the P{GAL4}3A driver [FBti0131277) (Raghu et al., 2007). FBbt:00003917 HS FlyBrain_NDB:10043 adult protocerebrum adult visual projection neuron optomotor response