From The Spike by Mark Humphries on two deep misconceptions about spiking:
- Many spikes, probably most, have no cause in the outside world. Collectively this is called spontaneous activity.
- That neurons do not always need inputs from other neurons to make a spike. We find pacemaker neurons throughout the brain.
Perhaps others can add surprising facts here too.
Another one: Assuming a pyramidal neuron in a neighborhood of 10,000 neurons connecting with a probability of 10%. Then it will have about 100 immediate feedback loops. There are about 10,000 feedback loops two neurons long, and about 10,000,000 three neurons long. This is just considering neurons in the same layer, there are loops between layers in the same region, loops between regions, and there are long loops that leave the cortex, run through the thalamus and back to cortex again.