ART4 and psychotic disorder: Recent neuroimaging studies have provided in vivo evidence for synaptic density decreases in psychosis patients, using [11C]UBC-J to image synaptic glycoprotein SV2A,31,32 a putative marker of synaptic density.29,30 It is known from previous research that synaptic deficits are present in Erbb4 mutants: excitatory synapses on the fast-spiking inhibitory neurons and presynaptic boutons in chandelier cells,44 which are highly expressed in the hippocampus,95 are reduced.