Continuing my interest in the neuroscience of emotion, I recently finished reading neuroscientist Joseph LeDoux’s book “The Emotional Brain”(*). This is a quick review and synopsis, in particular of those points relevant to psychotherapy.
LeDoux is one of the best known figures in the field, alongside Antonio Damasio, whose work I have also delved into, but found rather indigestible. Although I found Ledoux more readable than Damasio, I have two major gripes with the book. The main one is the title: there is not a lot in the book about emotions in general; Ledoux rapidly zeroes in on the single emotion of fear, which is his area of specialism. On this subject he is relatively enlightening, but it wasn’t what I expected or hoped for. In addition, some of the statements he does make about emotions in general, even if they may apply to fear are not obviously true of all emotions.
Additionally, the blurb suggests a book which is highly readable, but I did not find this to be really the case. It’s fairly readable, but has a tendency, especially in the later chapters, to get lost in detail. I would say it is not ideally pitched to the non-specialist reader (though likely at the same time to be oversimplified for a specialist), and does not belong to the best in science writing. Having been written in 1998, it is of course also somewhat dated by now, though I have not come across anything more recent.
LeDoux argues convincingly – but it is not very surprising – that there is no single “emotional system” in the brain, but we have to look at each emotion separately. As i said, he focuses on fear, which presumably is one of the easier emotions to study because it has a much longer evolutionary history than some of the “higher” emotions like love and joy which seem more particularly to relate to human experience. It is quite hard to read any conclusions across from fear to these other emotions.
LeDoux argues that we typically have little reliable insight into the factors which trigger our emotions, but a great tendency to make up stories about them and to believe in these stories. Indeed, we are unreliable in our reports of our emotional states as such. Emotions, unlike cognition, are intrinsically linked to the body and prompt bodily response; they evolved as “behavioral and physiological specializations” (p.40). The characteristic “feel” of emotions reflect their different physiological signatures.
Emotions operate below the level of consciousness. This is illustrated by the phenomenon of “emotional priming” whereby the response to an explicit stimulus is influenced by a preceding stimulus the duration of which is too short for it to be captured in conscious memory (p.59). Mere exposure is sufficient; there is no need for any logical connection between the two stimuli.
The study of fear has, of course, a particular relevance to psychotherapy and some of LeDoux’s arguments bear consideration in this context, as he himself notes, though does little to develop. LeDoux argues that fear, and comparable emotions, are registered in the amygdala from where they govern programmed physiological reactions; at the same time there is a feedback loop to cognition which passes via the hippocampus. This latter circuit is obviously much more developed in humans than in lower mammals, but in all species it is notably asymmetric: the hippocampus, which is where new memories are created, has the equivalent of a broadband connection to the medial prefrontal cortex, but the available bandwidth is much less in the opposite direction. This, LeDoux argues, makes it difficult to reprogram the association made in the hippocampus between certain remembered events and the fear response. This sounds plausible, and may reflect experimental observations on the persistence of conditioned fear responses in rodents as well as the observed difficulties of therapy, but it is no more than suggestive of the conclusion which LeDoux draws.
Fear conditioning is the process which “turns meaningless stimuli into warning signs” (p.141). Some stimuli are preprogrammed: “laboratory-bred rats who have never seen a cat will freeze if they encounter one” (p.143). But most, of course, are learned. The simultaneous presence of two stimuli of which only one, the “unconditioned stimulus” (US) is intrinsically unpleasant is sufficient to form a link between them, on the basis of which the second or conditioned stimulus (CS) is subsequently sufficient to evoke the fear response, regardless of its intrinsic link to the US. This link is highly persistent and may indeed be impossible to forget completely even if, subsequently, no link between the stimuli is observed for a protracted period. The best that can be done is to extinguish it by presenting the CS repeatedly in the absence of the US, but there is always the risk of recurrence if relevant circumstances, such as re-exposure to the unconditioned stimulus, or simply a high level of ambient unrelated stress, arise. A CS may be almost anything: a place, a gesture, an expression, a tone of voice… Of course, the atomicity of these candidate stimuli is hard to determine : is being in exactly the same place necessary to evoke the conditioned response, or is it sufficient that a place bear some resemblance and, if so, in what respects?
In stressful situations, memory formation by the hippocampus is impaired. This would imply that traumatic events might not leave a memory trace, but still result in fear conditioning. In such cases, there may be no way to “reverse-engineer” the event out of the conditioned reaction. This has the clear implication that going after memories of traumatic events may be a fruitless strategy, and that resolution of trauma might happen without those underlying events ever being recalled, even if they occurred past the stage of childhood amnesia. However, the stress hormone cortisol has the opposite effect on the amygdala. Thus it is “completely possible that one might have poor conscious memory of a traumatic experience, but at the same time form very powerful implicit, unconscious emotional memories” (p.245). At the same time, recreating the emotional state conditioned does facilitate recall of explicit memories (p.212).
LeDoux’s analysis of conditioning and memory therefore sheds some light on problems encountered in therapy and on effective therapeutic strategies. I learnt something from this book, but I suspect that a general book on recent contributions of neuroscience to psychotherapy might have gotten me more rapidly to my goal.
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(*) References are to the 1999 paperback edition published by Orion books.