Short Term Memories

The brain represents a memory by a set of neurons.
Neurons may participate in multiple memories.
Some neurons are more central to a particular memory than others.
The neurons of a paricular memory have high mutual synaptic strength.
The strength has been learned via Hebbian learning from environmental stimulation, but this is the long term issue, so more on that later.
When an instance of that memory occurs in the environment, a small number of the neurons are stimulated from the sensory system.
These neurons in turn send activation to other neurons, and a great deal of activation to neurons in the CA (because they have high mutual synaptic strength).
This in turn causes a large number of neurons in the CA to fire.
This causes a cascade of neural activation called CA ignition.
The reverberating circuit (the CA) can remain active after environmental stimulus has ceased.