| Human Brain | Evolution | A Model | Building Blocks | A System | Testing | Instability | Behavior & Self | Evolving Self |

The human brain consists of 10 billion highly interconnected cells or neurons.  Every fraction of a second, each of these neurons is making a decision - whether or not to fire, thereby releasing stored brain chemicals (neurotransmitters) that form the communication link to either Excite or Inhibit the other neurons that are connected in a “neural network”. The critical communication code between individual neurons is the rate of this firing. These rules and the inordinate complexity of individual neurons have constituted the bulk of the information explosion about the brain over past decades. However, there are different rules at different scales of brain function as is the case in other complex dynamical systems in nature (such as the weather).   So despite the inordinate complexity of single neurons or networks, it would appear that relatively simple rules might underlie whole brain function. Some of the overarching rules that plausibly shape the functions of the brain at a system level are listed in the box below.

Some rules and mechanisms of overall brain function Spatio-Temporal Integration: information processing reflects integration among networks that preferentially process different types of information, and exquisite “timing” among these networks.   The brain seems to operate predominantly in two temporal modes (across scale):  neurons either “fire” or they do “not”;  networks operate in "burst” or “tonic” modes;  whole brain modes are either “synchronising” or “desynchronising” and in relatively “Automatic” or “Controlled” processing modes. Whilst the key communication code between individual neurons is the rate of firing, a key mechanism that facilitates reinforcement of connections between neurons in a network – is firing simultaneously: "neurons that fire together wire together", also known as Long Term Potentiation (LTP) or Hebb’s learning rule.   At the network and whole brain level – “synchrony of firing” (rather than the rate alone) – seems to be a key mechanism as to how the brain orchestrates its diverse network activities. Neurons activated at 40 cycles per second (“Gamma”) and in phase, may underlie the way in which the brain coordinates its diverse network activities. The balance between Excitatory – Inhibitory feedforward and feedback activity underpins all of the brain’s functions.   The overall pattern of the brain’s chemistry consists of: Widespread rapid excitatory (glutamate) and inhibitory (GABA) interactions; They are modulated by slower acting noradrenaline (associated with “fight or flight”), dopamine (reward and motor activity), acetylcholine (memory), serotonin (aggression and emotion); Long acting widely distributed neuropeptides (such as endorphin’s and over 50 others) – further modulate this neurochemical cocktail. The business of the brain above all, is HOMEOSTASIS - optimal adaptation to a rapidly changing environment.

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