Synaptic efficacy is commonly regulated within a nervous system and predicts individual differences in learning

The hypothesis that an individual's capacity for learning might be predicte d or influenced by basal levels of synaptic efficacy has eluded empirical t ests, owing in part to the inability to compare between animals single iden tified synaptic responses in the mammalian brain. To overcome this limitati on, we have focused our analysis on the invertebrate Hermissenda, whose ner vous system is composed of identifiable cells and synaptic interactions. He rmissendo were exposed to paired presentations of light and rotation such t hat the light came to elicit a learned defensive motor response. An animal' s rate of learning was strongly correlated with the amplitude of the synapt ic potential evoked in that animal's visual (light sensitive) receptors in response to stimulation of presynaptic vestibular (rotation sensitive) hair cells. In naive animals, strong correlations between the amplitude of both inhibitory and excitatory synaptic potentials were observed between synaps es distributed throughout an animal's nervous system, and this conservation of synaptic efficacy was largely attributable to a common influence on tra nsmitter release. These observations suggest that basal synaptic efficacy m ay be uniformly regulated throughout a nervous system, and provide direct e vidence that the basal efficacy of synaptic transmission predicts, and poss ibly contributes to, individual differences between animals in their capaci ty to learn. NeuroReport 11:1253-1258 (C) 2000 Lippincott Williams & Wilkin s.