I enjoyed the ambiance of this audiobook. Siegel’s pace was measured and calm, his tone disarmingly personal. It turns out that he literally founded the field of interpersonal neurobiology, which purports to synthesize vast swathes of scientific disciplines into a coherent whole. Large claims by an influential man.

The author was careful to precede his discussion by asserting that the mind and the brain are distinct, that he would like to move away from the aphorism that “the brain is the seat of the mind”. Instead, Siegel advocates a philosophical stance of emergentism, that the brain-mind connection is causally bidirectional. In my view, this point was rather underdeveloped & the book as a whole does not hinge on the point.

One interesting chapter relates to attachment theory. Children-caregiver relationships tend to group into four distinctive categories. These can be divined from the Strange Situation test, which places the child in a foreign environment, and then removes the caregiver for a few minutes. Attachment style is linked to child response: secure-attachment children reach out to the parent, and then resume play; avoidant-attachment children ignore the parent; anxious-attachment cling to the parent and are slow to be comforted; disorganized-attachment exhibit confused, contradictory responses.

What Siegel demonstrates is how later in life, a particular interview called the Adult Attachment Interview can predict, with 85% accuracy, the attachment style learned by the adult, earlier in life. When asked to explore feelings about early childhood relationships: the secure adult will be able to fluently conjure feelings; the anxious adult will be derailed by more present anxieties (“just last week, my mom did something nice for my brother, but not for me”; the avoidant adult will not be able to fully access emotional data (“my mom was organized, beautiful”); the disorganized adult will answer relatively normally until faced with questions of loss or abuse.

The demographic ratios between these styles in US society tends to be 55% secure, 20% anxious, 20% avoidant, 5% disorganized.

Another interesting point of the book relates to trauma, or PTSD. Siegel summarizes an impressive swath of research that suggests that PTSD is the result of memory-encoding inconsistency. Memory is not a monolithic system, but rather divides into myriad subsystems. Siegel argues that trauma occurs when the threatening event is encoded into implicit memory, but stress hormone prevents the hippocampus from encoding it into episodic memory. Without access to the conscious “metadata” for the event in episodic memory, flashbacks trigger confusion between the memory, and the event itself.

Finally, Siegel presented a way of thinking about the brain that I found more helpful than Latin names. If one curls up the thumb into the palm, and curls the fingers around the thumb, it is a half-decent model of the brain. The palm represents the brain stem, the wrist the spinal column, the thumb the limbic system, the fingers the cortex. Within the “fingers”, the back section between second and third knuckles represent perceptual systems, the tips, the prefrontal cortex.

I’ll now list two criticisms I have, one specific and one general. The first is a matter of definition; Siegel likes to define the mind as a “process that organizes matter and energy flowing through the brain”. This is largely fine, and reflects the consilience between thermodynamics and information theory. But, he tends to conflate the use of “energy” between thermodynamics and emotional/psychic energy, which is unfortunate. My second criticism is one that I have so far felt against the fields of positive psychology as a whole: I just didn’t learn very much from this book. The brain sciences don’t seem to be sophisticated enough yet to give Siegel the mileage he needs to establish his conclusions. With so little attention given to mechanism, books such as this one will always feel empirically inadequate.

That said, this book does represent a fairly compelling “beginner’s guide” to interpersonal neurobiology, and I look forward to learning more (especially how interpersonal neurobiology relates to mindfulness meditation).