THE NOTION AND THE NAME (LATIN “ID”= ENGLISH “It” = German “Es”) are most closely associated with the name of Sigmund Freud. Freud, however, quite explicitly and with due acknowledgement, took the term from Georg Groddeck’s Das Buch vom Es. Even before Groddeck, Nietzsche had used the term to refer to the most basic level of human nature along the lines of Schopenhauer’s notion of the will. By the time Freud appropriated and popularized the term, he had abandoned his quest for a scientific (i.e., neurologically-based) psychology, and hence did not speculate deeply about neurology of the id. Recently, however, we have acquired a fairly detailed understanding of the neural location of something very like the Nietzschean id, one without the quirky psychoanalytic baggage.
What I am suggesting as a neurological id has its center deep within the temporal lobes of the brain. Its nucleus is a small structure called the amygdala and includes a number of associated brain structures (such as the basal nucleus of Meynert, the bed nucleus of the stria terminalis, and the anterior cingulate cortex). We might think of these structures, collectively, as constituting the core of an “id brain.” We are also gaining an understanding of the nature and function of this neurological id. Interestingly, this modern version of the id turns out to be, metaphorically speaking, at least as terrified as it is terrifying and more threatened than threatening. This is likely a reflection of the fact that our early ancestors were as likely to have been prey as predators—and, as predators, their own favorite prey.
Neuroimaging studies have shown that the amygdala is particularly responsive to fearful faces, even those presented extremely briefly and without strong evidence of people being conscious of having seen the faces. Thus, signs of danger are processed by the unconscious id well before they enter consciousness. This is possible because the amygdala receives sensory inputs independent of, and more directly than, “higher” cortical centers. Moreover, the amygdala is a well-connected structure that sends out information to a staggering number of centers throughout the brain and, in return, receives information from many cortical sensory systems (vision, hearing, bodily sensations, etc.). Thus, it is not surprising that the amygdala is implicated in many emotional disorders, including depression, phobias, and posttraumatic stress disorder. For example, brain-imaging studies have reported that the amygdalae of PTSD patients are more responsive to fearful faces than are control subjects.