These connections are implemented by the synapses, the interface between two neurons: a presynaptic neuron that is sending a signal out and a postsynaptic neuron that is receiving the signal. The inputs to any given neuron come from its presynaptic partners, each providing bioelectrical whispers. Excitatory synapses encourage the postsynaptic neuron to “fire”—that is, generate an output by sending an electrical signal to all its downstream neurons (its own postsynaptic partners). In contrast, inhibitory synapses attempt to persuade the postsynaptic neuron to keep quiet. With so many neurons
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