In fact, his more primitive brain is so much in charge (his rational brain is very much still in process), that he is the victim of his emotions and impulses. (themotherco.com)
This increases brain activity during a time when labor progress relies on a woman's primitive brain instincts. (birthquestservices.com)
The neuroscientist Jaak Panksepp, for example, has noted that the neural machinery for attachment and bonding is actually cobbled together out of more primitive brain areas used for temperature regulation. (scientificamerican.com)