Figure 2.

Principles of resonance and short-term plasticity of synapses. (A) Resonance in neurons. (Top panel) The capacitive properties of the neuronal membrane act as a low pass filter, efficiently dampening high frequency inputs. (Middle panel) The presence of ionic channels, like I_h or I_M, provide high pass properties. Bottom panel. The combination of low and high pass filters makes a pass band filter, with a resonant frequency, i.e., the frequency favored by the cell. (B) Resonance at the synapse. (Top panel) Some synapses, when activated at a given frequency, display short-term depression (i.e., the amplitude of the postsynaptic response decreases), thus making a low pass filter. (Middle panel) Other synapses facilitate (i.e., the amplitude increases), making a high pass filter. The combination of both types of synapses also makes a pass band filter, with an optimal resonance frequency. (C) Examples of frequency-dependent short term plasticity. Different connections are tested: dentate granule cell to CA3 pyramidal cell (top), dentate granule cell to CA3 interneuron (middle), CA3 interneuron to pyramidal cell (bottom). Note the switch from facilitation to depression at excitatory synapses between 10 and 40 Hz, and strong depression at 40 Hz at inhibitory connections. Adapted from Izhikevich et al. (2003) and Mori et al. (2004).