An alternate to #3:
PRIMEAPE is capable of sending extra blood to its muscles in times of need. However, this action results in less oxyegen being supplied to its brain, causing an inablity to make rational desicions.
OR
PRIMEAPE is capable of sending extra blood to its muscles in times of need. This action also results in less oxyegen being supplied to its brain, causing PRIMEAPE to make irrational desicions.