Definition of reptilian brain in English:

reptilian brain

noun

(also reptile brain)
  • 1(in some models of human brain evolution and function) the part of the human brain that corresponds to the brain of vertebrates before the evolution of mammals, and which is associated with behaviors concerned mainly with self-preservation.

    1. 1.1(in nontechnical use) the part of the brain to which primitive, nonrational, or self-interested behavior is attributed.
      • ‘bestsellers succeed by appealing to the reptilian brain’

Origin

1960s compare with lizard brain.