A third family of gain control mechanisms acts on the inputs to the neurons. When many nearby inputs on a dendrite are activated, they amplify each other’s effects so that their impact is larger than their algebraic sum.12 Even more selective gain control, acting at single synapses, can be achieved via the short-term plasticity of synaptic strength. The synaptic efficacy of the action potential from a presynaptic neuron is not fixed over time but shows large fluctuations. Some synapses increase (“facilitatory synapses”) whereas others decrease (“depressing synapses”) their response to the
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