Can you remember when you heard about 9/11? Chances are you’ll be flooded instantly with memories — not only where you were, but what you were doing, who you were with, what you could smell and see at the time as well as how you felt.
How does that happen? In the first half of this fascinating book, Dr Veronica O’Keane explains the neurological pathways and processes involved in memory. We are constantly receiving stimuli from our environment via the five senses of sight, sound, smell, taste and touch. These sensations travel via cells called neurons which are electrically activated and release various transmitters into the spaces between them and other neurons, which are then taken up and cause that neuron in turn to become stimulated. We are also continually receiving internal stimuli from our bodies — organs such as the gut, heart and lungs. Sensations from our senses enter through sensory neurons in the eye, ear, nose, tongue, skin and mucus membranes, and travel to the relevant part of the cerebral hemispheres in our brain. The sensations from our body converge on a part of the brain called the insula.
All of these eventually end up being processed in the hippocampus, and from there selective memories are integrated during REM sleep into the prefrontal cortex just above our eyes. As the hippocampal neurons bombard the prefrontal ones during REM sleep, shards of old memories are activated, leading to dreams. Perhaps the function of dreams is to remind and warn us of the past.
Biographical memories remain consolidated in the pre-frontal cortex, although they are also subject to reprocessing when we recall them and re-store them in a slightly different way. Drawing on them and on sensory memories elsewhere in the cortex leads to learning, insight and wisdom.
Sensate memories being processed in the hippocampus are augmented by emotions, which arise from the amygdala, hypothalamus and insula, after they have received input from the sensory cortices. These seats of emotions also trigger bodily responses to those emotions: sweating, flushing, heart-racing. This is done through the autonomic nervous system, which is unconsciously controlled, and through the endocrine glands which secrete hormones.
Billions of nerves are constantly firing and interacting with each other. When the memory is laid down, it’s likely that vivid emotions will be associated with it. When, in the future, some of those neurons are re-stimulated, they will fire off the other neurons with which they have become associated. So if someone says ‘9/11’, chances are the neurons that enable you to hear that will fire off and stimulate the neurons with which they formed circuits long ago, bringing back to you the sights, sounds, smells, tastes and emotions of what you felt then.
But O’Keane does not only know her neuroscience: she is also a consultant psychiatrist. So throughout this process, she relates how these sensations, both from the external world and from within the body, can go wrong, resulting in psychiatric illness. The contrast between normal physiology and pathology is compelling.
In the second part of the book, O’Keane explores how consciousness develops in the baby, how the infant learns to recognise itself, and how pruning occurs in the connections in the brain so that the developing child is not overwhelmed by the multitude of incoming sensory signals. A baby’s wide, darting eyes and alert expression convey how much sensory information is flooding its brain. Gradually, the baby learns that he or she doesn’t have to process all the signals from scratch; that there are patterns: those who walk on two legs are usually humans; large vertical objects rooted in the ground are usually trees, and so on. Mirror neurons enable us to anticipate sensations with which we’re familiar. The adolescent recognises that the emotions they experience also occur in others, and thus empathy is learned. This is mediated through emotional mirror neurons in the insula-cingulate system. These neurons are more active in those who are very empathetic.
Another intriguing finding from rat experiments is that baby rats exposed to affection (grooming/licking) from their mother grow up to have calmer responses and less stress hormone release when exposed to stress as adults, compared with rats deprived of that maternal love. So early events are vitally important in determining the physiological response to stress. This obviously has implications for the justice system as well as psychiatry and neuroscience. And the hippocampus is visibly shrunken if exposed to stress: it is physically more difficult to make memories when stressed or highly aroused. These changes can be alleviated with psychotherapy and antidepressants.
None of this is in waffly LA consciousness-speak; it’s all evidence-based neuroscience. But O’Keane also brings in writers who were aware of memory and longing — Proust and his madeleines; those who felt alienation, such as Sartre and Camus (was Sartre’s nausea in the eponymous book due to heightened sensations in the insula?); and those who explored consciousness — Henry James and his psychologist brother William; John Berger; Beckett; Dostoevsky; Huxley; Yeats; Joyce; Baudelaire; Munro; Eliot, Carrol; Dylan Thomas; even Nick Cave.
This cogent, meticulously researched book deserves to win the Baillie Gifford or Wellcome Prize.