I think (this is not official definition, but just my idea) there are 3 different networks in the brain differentiable based on the mechanisms:

1. Synaptic network

2. Epigenetic network (ARC gene mediated)

3. Ephaptic network

These networks interact with each other, regulate each other and work interdependently together.

Synaptic Network

Synaptic network can be seen as a collection of neurons that are bound together with synapses. Synapse is a gap between 2 neurons and it may have different structures: chemical synapses are filled with neurotransmitters while gap junctions or electrical synapses traverse action potential of the presynaptic axon, or the electrical current to the postsynaptic neuron directly. Through synapses, 1 neuron can receive signals from thousands of neurons and transmit signals to thousands of neurons.

Epigenetic Network

Epigenetic network is also a collection of neurons which interact with each other through capsids formed by ARC gene, a retroviral gene that can transfect neighbouring neurons and carry mRNAs of different genes. These ARC gene capsids are important in the organization and optimization of synapses, changing synapse structures which is called synaptic plasticity. Synaptic plasticity is important in the process of learning and memory formation and ARC gene mediated epigenetic regulation is an essential part of different forms of synaptic plasticity. ARC gene capsids are released with the activation of the neuron and it affects tens of thousands of neighbouring neurons that may have synaptic connection with the activated neuron or may not. So, if we only look into the ARC gene capsids’ routes among neurons, we can see another network, affecting many neurons, regulating their synaptic efficiency while driving neural networks’ optimization.

Ephaptic Network

Ephaptic network is, in my opinion, another network that is based on another non-synaptic communication called ephaptic coupling. Ephaptic coupling is a process that is similar to the induction current. When a neuron fires, or generates action potential, which is electrical current essentially, this event produces an electrical field around the firing neuron. This electrical field is not very strong, it is hard to detect and measure, but it is strong enough to modulate neighbouring neurons. These neighbouring neurons, even though they didn’t stimulated through synapses, can generate action potential due to this weak electrical field. So, we can say that firing neurons generate electrical fields and electric fields can cause firing of neighbouring neurons. And these firing neighbouring neurons also generate electrical fields around themselves and that leads to the firing of their neighbouring neurons which can be considered as a network. Ephaptic coupling is important in the synaptic plasticity, sensitivity to the stimulation of postsynaptic neurons, meaning regulation excitability via modulating firing threshold. It also provides some kind of feedback mechanism in the smallest scale.

Let’s Combine Them Together

Now if we combine these together, a firing neuron can stimulate post-synaptic neuron via synaptic connection and neurotransmitters. It also releases ARC gene capsids to the neighbouring neurons, not causing them to fire, but regulating their synapse structures. In addition to that, its firing generates weak electrical field which can make neighbouring neurons, that are within the range of this electrical field, fire as well. And firing neighbouring neurons do the same things. Also, I think we can picture electrical fields as venn diagrams that have intersections, and together, they form pretty consistent and stable electrical field around thousands to millions of neurons.

We already know these mechanisms, but as far as I know, there are no definitions of networks based on these mechanisms except synapses. The only neural networks that are studied are based on their synaptic connections: DMN, Salience, etc. Epigenetic and ephaptic networks (as I named these, not officially recognized) require more attention and beg for more research.

When the chemical structure of the brain, ions, and the physical structure that can be recognized as a plasma environment are added to this formulation of 3 networks, we may be able to solve the puzzle of consciousness, which can be seen as an emergent property of the complexity of the system.