External input causes processing which in turn generates more processing because the result of the former is internal input. The processing result must then be prevented from causing additional internal processing or the entity must shut down external input / output and become 'introspective'.
An animal then has three principle brain functions:
Because new data generates more internal input than
old already known data, infants require more
sleep. Context is not yet
established and there is no significant output. The
infant is then primarily taking in information and organizing it internally (and little else)
requiring half time (or more) sleep cycles.