  Short-term changes in efficacy have been postulated to enhance the ability of
synapses to transmit information between neurons, and within neuronal networks.
Even at the level of connections between single neurons, direct confirmation of
this simple conjecture has proven elusive. By combining paired-cell recordings,
realistic synaptic modelling and information theory, we provide evidence that
short-term plasticity can not only improve, but also reduce information
transfer between neurons. We focus on a concrete example in rat neocortex, but
our results may generalise to other systems. When information is contained in
the timings of individual spikes, we find that facilitation, depression and
recovery affect information transmission in proportion to their impacts upon
the probability of neurotransmitter release. When information is instead
conveyed by mean spike rate only, the influences of short-term plasticity
critically depend on the range of spike frequencies that the target network can
distinguish (its effective dynamic range). Our results suggest that to
efficiently transmit information, the brain must match synaptic type, coding
strategy and network connectivity during development and behaviour.
