I do not remember exactly the first time that I heard about pioneering neuroscientist Paul MacLean’s concept of the triune brain. The idea of a neocortex sitting atop a primordial cortex sitting atop the brain stem. The brain of a human sitting atop the brain of a horse sitting atop the brain of a reptile, all three brains located inside each of our heads. I do remember being electrified by the idea. Instantly struck by what a gorgeous, evocative, instructive, illuminating insight this was.

But like so many other gorgeous, evocative, instructive, illuminating discoveries, the idea of the triune brain has not always stood the test of further, better scientific inquiry all that well. The problem mainly is that the roles of the trio of brains are not nearly as independent as Dr. MacLean had thought. What is going on in the general neighborhood of one of Paul MacLean’s trio of brains is often having an outsized influence over what is going on in other brain areas.

But the idea that the brain has separate “processing” areas that don’t cooperate well—that’s a MacLean idea that has stood the test of time.

For example, the region where MacLean located his middle (primordial) brain contains a little almond-shaped organ called the amygdala. It turns out that the amygdala has a mind of its own. That is, it can learn—reason?— independent of the (higher) cortex. Moreover, the means that the amygdala and the cortex have for communicating what each “is thinking” are imperfect at this point in our evolving capabilities, and that creates endless trouble for us.

For non-brain-scientists (me, for one), no one whom I know about has offered better, clearer explanations of all this than Joseph LeDoux at New York University’s Center for Neural Science. In Synaptic Self: How Our Brains Become Who We Are, Dr. LeDoux suggests that the reason why the all-important amygdala can’t “talk” well with its higher-up synapses is because the wires leading there aren’t well enough developed. And the reason for that is because the development of language by humans required so much space and so many connections to pull off. Consequently, the cognitive systems in our heads have inordinate trouble communicating with the emotional and motivational systems, and vice versa.

Writes Dr. LeDoux, “This is why a brilliant mathematician or artist, or a successful entrepreneur, can like anyone else fall victim to sexual seduction, road rage, or jealousy, or be a child abuser or rapist, or have crippling depression or anxiety….Doing the right thing doesn’t always flow naturally from knowing what the right thing to do is.”

The trilogy of brain functions that LeDoux finds most compelling are indeed those governing thoughts, emotions and motivations. If this triune grouping breaks down, he writes, “the self is likely to begin to disintegrate and mental health to deteriorate. When thoughts are radically dissociated from emotions and motivations, as in schizophrenia, personality can, in fact, change drastically. When emotions run wild, as in anxiety disorders or depression, a person is no longer the person he or she once was. And when motivations are subjugated by drug addiction, the emotional and intellectual aspects of life suffer.”

In short, Dr. LeDoux says that the self is synaptic: “You are your synapses.” Meaning that what happens between key parts of the brain—or doesn’t happen—can be all-important and all-defining. On this point, Dr. MacLean would most likely have been in full agreement.

See here for order info for Dr. LeDoux’s book: “Synaptic Self: How Our Brains Become Who We Are”