Although your brain isn’t heavy – about three pounds of soft, gooshy tissue like tapioca pudding – it has about 1.1 trillion cells altogether. One hundred billion of those are in the “gray matter,” a kind of “skin” of nerve tissue wrapping around the “white matter” that comprises most of the bulk of the brain. The gray matter is where most of the action for conscious experience takes place.
When a neuron fires, sending neurotransmitters across the synapse – the tiny space between it and another neuron it is connected with – that either excites or inhibits the receiving neuron. To simplify a little, the sum of all the excitatory and inhibitory signals a neuron receives from its “upstream” neurons determines whether it will fire itself – sort of like the dominant message from a crowd of people all shouting “go!”or “stop!”
The receiving side of a synapse – the sensitive tip of the spike called a dendrite – is the most molecularly complex structure in the body, built from 1100 different proteins. This tip has increased in complexity dramatically throughout evolution, indicating that the development of this fundamental crossroads has been vital in what has made us human.
On average, each of the 100 billion neurons in your head has about 1000 connections with other neurons, creating a huge network of about 100 trillion synapses. Like a computer network built from one hundred trillion transistors, each representing a “bit” of information depending on whether it is “on” or “off.”
Adding up all possible combinations of 100 billion neurons firing or not, the number of potential states of that neuronal network is approximately 10 to the millionth power: one followed by a million zeros.
With all that connectivity, circular loops are routine in which – to simplify – the A neuron triggers B which lights up C which signals D which triggers A. This circularity allows and fosters:
- The recursive processes needed for self-regulation – and which, after many layers and lots of evolution — allow you to think about your own thinking
- The dynamic and “chaotic” behavior of complex systems: it’s not random in your brain, but it is inherently unpredictable.
- Wandering stream of consciousness – Again to simplify: the C neuron in the circuit just mentioned could easily be part of another circuit having nothing to do with the first one. Nonetheless, because of that connection, when the first circuit fires the second is more likely to fire as well. That’s why thinking about something like a dripping faucet can bring to mind something seemingly random like your grandmother’s great oatmeal cookies.