Synapsin is an evolutionarily conserved presynaptic phosphoprotein. It is 
encoded by only one gene in the Drosophila genome and is expressed throughout 
the nervous system. It regulates the balance between reserve and releasable 
vesicles, is required to maintain transmission upon heavy demand, and is 
essential for proper memory function at the behavioral level. Task-relevant 
sensorimotor functions, however, remain intact in the absence of Synapsin. Using 
an odor-sugar reward associative learning paradigm in larval Drosophila, we show 
that memory scores in mutants lacking Synapsin (syn(97)) are lower than in 
wild-type animals only when more salient, higher concentrations of odor or of 
the sugar reward are used. Furthermore, we show that Synapsin is selectively 
required for larval short-term memory. Thus, without Synapsin Drosophila larvae 
can learn and remember, but Synapsin is required to form memories that match in 
strength to event salience-in particular to a high saliency of odors, of 
rewards, or the salient recency of an event. We further show that the residual 
memory scores upon a lack of Synapsin are not further decreased by an additional 
lack of the Sap47 protein. In combination with mass spectrometry data showing an 
up-regulated phosphorylation of Synapsin in the larval nervous system upon a 
lack of Sap47, this is suggestive of a functional interdependence of Synapsin 
and Sap47.