Hello readers! Happy New Year and all that. I took a couple of weeks off for the holidays and went to visit family and friends back in Toronto. It was a time of heart-warming reconnection with people I’ve known for much of my life. But it was also a time of emotional pain: loss, disappointment, regret — stuff like that. Hence the topic of this post…
The limbic system is a widely distributed assembly of very different structures, most notably the amygdala (responsible for emotional associations) and the hippocampus (necessary for encoding episodic memory so that events stay in mind for more than a few seconds). Some people include the ventral striatum (the foundation of anticipation and desire) and its source of dopamine, the VTA, all under the rubric of the limbic system. All these structures are “sub-cortical” — they are more primitive than the cortex. They are its underlying machinery, the stuff in the basement (though they are more advanced than other systems — the ancient engines still at work in the subbasement of the brain stem). And then there are higher structures, sometimes called limbic cortex — parts of the cortex bordering the limbic system. These include the orbitofrontal cortex, which appraises the value, likability or aversiveness of incoming stimuli, and the famous ACC (anterior cingulate cortex) which does response-monitoring, selective attention, and effortful engagement. (All these parts and their functions are described in detail in my book.)
Limbic structures are the basis of learning. They grow synapses that connect with all parts of the cortex. That’s how the sophisticated perceptions of the cortex remain anchored to an emotional self — a core self. The cortex houses the most advanced software, but its programs are grounded in meaning through the limbic system.
A man named Roger had just about all of his limbic system destroyed by a very nasty (and rare) herpes infection. Yes, herpes can be a lot worse than you think. To quote from Neuroskeptic: “…his is the worst case of herpes encephalitis damage among patients currently alive.” And he has been alive since the damage occurred 28 years ago. So what was the result? What happens when you lose your limbic system?
Roger lost his capacity to remember things from then on — called anterograde amnesia — but his mood improved! You’d think losing half your brain would make you a tad grumpy. But in the words of Feinstein et al: ”He readily displays signs of positive emotion including happiness, amusement, interest, and excitement…”
The limbic system evolved with the advent of mammals. The limbic system allows us to play, to be social, to form attachments, to love, to feel our connection with others and with our own goals. And it allows us to suffer. Thanks to the limbic system, we struggle to be the best we can be so that we can partner with other mammals (mates, children, parents). And we expect the same from others. Unlike frogs, whose goals are hard-wired, mammals must learn to achieve what they want, and avoid what they fear, through emotional striving.
So the lesson I take from Roger is that the psychological qualities of creatures like ourselves come with a huge price tag: emotional pain. Roger lost the neural foundation of meaning — of what it feels like to be a human mammal — but he no longer experienced suffering. He became a happy camper in a shallow world.
To my mind, and to other students of addiction, like Gabor Mate, we drink or take drugs to reduce the fundamental pain of life — the emotional suffering that constitutes the background music of the mammalian nervous system. Like other evolutionary achievements, the limbic brain is a double-edged sword. And we use drugs and alcohol in order to protect ourselves from its savage blade. That’s why addiction is an inevitable byproduct of human evolution.