Brain variable is the same as the HP and MP, except you can define it dynamically with arbitrary name of it. Such as, you can define a variable called "morale" just use the output channel. After defining it, its value is 0 initially and it can be changed by output channel values.
Channels
bv:<var name> (the XXX is the name of the variable) for example bv:morale
In value mode (default)
The value of morale will be: decision node active * output value
The brain variable define
In the brain viewer, the morale is 4.46 = 0.89 * 5
In change rate mode (need specify in default decision)
Firstly we need specify the channel to the "change rate" mode. And specify the change speed in "default else", that 0 means "not change" when there is no triggered.
Setup change rate for variable morale
Then we just need specify the change value in the output channel
The morale will Increase 5 each frame
The input channel bv:XXX will get the variable value of it
Return the value of morale