Topology

• While FLIF and compartmental models account for particular neurons, connections between neurons also need to be modelled.
• There are roughly 100,000,000,000 neurons in the brain and each neuron connects to up to 10,000 other neurons.
• This is a graph issue with nodes being neurons and synapses connections.
• A lot of models get this topology wrong. E.g. the Hopfield model uses IF neurons but has a bidirectional well-connected topology.
• Some gross topological features are the brain is a thin roughly metre square sheet crammed into a 3D ball.
• In this sheet, there are 6 layers known as the laminar architecture.
• There are also brain areas for specific function, though developmentally traumatized brains move function about.
• A particular human's topology is pretty stable with relatively little neural or synaptic death or growth.
• Neurons tend to be connected to nearby neurons. Pyramidal neurons, which make up 80% of cortical neurons, have one long distance axon with many synapses at the other end.