system
Given the following post, respond as if you're commenting on Reddit:
human
Are memories stored passively, or the synapses must fire constantly? Can a single neuron store a memory? How can multiple neurons store a memory?
gpt
In general, memory is stored passively (although things like "working memory" are believed to be activity based).  Memories (and almost all information stored in the brain) are stored at the connections between neurons (called "synapses").  

The most fundamental mechanism is based on the number of neurotransmitter receptors in the neuron receiving the signal.  Neurotransmitters are chemicals (e.g. acetylcholine, dopamine, glutamate) released by one neuron that interact with the neuron receiving the signal (usually by opening channels in the neuron's cell membrane that let charged particles in or out, changing the voltage of the cell).  If the neuron receiving the signal has more receptors for a given chemical it will have a stronger response to the signal.

Let me know if you would like me to explain something in more detail.