Is the mother board the mastermind of a computer?

No, the CPU is the brains of the computer and interprets instructions received, equivaqlent to your brain responding to stimuli and selecting a course of action to follow. An equivalent analogy for the motherboard would be your neurological system. The motherboard, like neurotransmitters, receives and transmits messages to and from input/output sources (keyboard, mouse, etc.) to the CPU.