Spike-timing-dependent plasticity alters electrosensory neuron synaptic strength in vitro , but does not consistently predict changes in sensory tuning in vivo .

How do sensory systems optimize detection of behaviorally relevant stimuli when the sensory environment is constantly changing? We addressed the role of spike-timing-dependent plasticity (STDP) in driving changes in synaptic strength in a sensory pathway, and whether those changes in synaptic strength could alter sensory tuning. It is challenging to precisely control temporal patterns of synaptic activity and replicate those patterns in behaviorally relevant ways. This makes it difficult to make connections between STDP-induced changes in synaptic physiology and plasticity in sensory systems. Using the mormyrid species , which produce electric organ discharges for electrolocation and communication, we can precisely control the timing of synaptic input and replicate these same temporal patterns of synaptic input In central electrosensory neurons in the electric communication pathway, using whole-cell intracellular recordings , we paired presynaptic input with postsynaptic spiking at different delays. Using whole-cell intracellular recordings in awake, behaving fish, we paired sensory stimulation with postsynaptic spiking using the same delays. We found that Hebbian STDP predictably alters sensory tuning and is mediated by NMDA receptors. However, the change in synaptic responses induced by sensory stimulation did not adhere to the direction predicted by the STDP observed . Further analysis suggests that this difference is influenced by polysynaptic activity, including inhibitory interneurons. Our findings suggest that STDP rules operating at identified synapses may not drive predictable changes in sensory responses at the circuit level.