We simulated behavioral training as before by applying pulses of serotonin, but now we could apply them selectively to one or the other set of synaptic connections. A single pulse of serotonin applied to one set of synapses produced short-term facilitation in those synapses only, as expected. Yet five pulses of serotonin applied to one set of synapses produced long-lasting facilitation and growth of new synaptic terminals only at the stimulated synapses.
