The part of the brain which is responsible for the switch between wakefulness and sleep is what we call the the ventrolateral preoptic nucleus (VLPO or VLPN. This is found in the hypothalamus. This small area’s neurons are present to help in promoting sleep by inhibiting activity in areas of the brainstem that maintain wakefulness. Just like what is happening in the process of mutual inhibition, which happens during waking hours, those areas of the brain that are active in maintaining wakefulness by stimulating the cerebral cortex also work to inhibit the neurons of the VLPO. This is the reason why the VLPO is also called the sleep switch. There are actually several different simultaneous and interactive processes that are involved during the cycle. Though this is the statement, there is as yet not even one unifying theory that will describe all the interactions. It seems like the more humans study about this cycle and the complex physiological and neurological mechanisms of sleep and wakefulness, the more we discover more complications and the more questions arise from this topic.
