By Stephen Beech

Why the brain feels "foggy" after a poor night's sleep has finally been explained.

Attention lapses due to sleep deprivation coincide with a flushing of fluid from the brain - a process that normally occurs while asleep, say American scientists.

Researchers at Massachusetts Institute of Technology (MIT) found that during such lapses, a wave of cerebrospinal fluid (CSF) flows out of the brain.

They say that the process normally occurs during sleep and helps to wash away waste products that have built up during the day.

The "flushing" is believed to be necessary for maintaining a healthy, normally functioning brain.

When a person is sleep-deprived , it appears that their body attempts to catch up on the cleansing process by initiating pulses of CSF flow.

But tha

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