For thousands of years people have wondered about the mystery of consciousness. How can anything made of physical stuff – a brain, for instance – be identical to, or give rise to, a subjective experience? Despite a revival in the scientific study of consciousness over recent decades, the only real consensus so far is that there is still no consensus.

Into the fray steps Mark Solms with his intriguing new book The Hidden Spring – which, as he puts it, is the culmination of his lifelong quest to understand the nature of consciousness. Solms brings a unique Vitae to the task. His early training in neuropsychology, at South Africa’s University of Witwatersrand, provided him with direct insight into how brain damage can change a person’s experience of the world, and of themselves. Unusually, he then came to London to train in psychoanalysis – a field which had become increasingly marginalized from the mainstream mind and brain sciences. Solms has been a major voice calling for its reintegration, a pioneer of what is now called ‘neuropsychoanalysis’.

Solms’ debt to Freud is explicit throughout his book: he sees himself as continuing Freud’s incomplete project to provide a biological account of mental life. As part of this renewal, Solms decries the traditional emphasis of consciousness research on processes like visual perception, arguing instead that the basis of conscious experience is to be found in how the brain perceives – and regulates – the physiological condition of the body. This perspective, which I have argued for too (though without the Freudian gloss), places feelings and emotions at the core of consciousness science, and Solms is at his best when exploring its implications.

Less easy to swallow is his claim about where consciousness happens in the brain. Most neuroscientists believe that the cortex – the densely folded outer layer of brain that houses many billions of neurons – plays a necessary role. Solms demurs, arguing that the source of consciousness – the ‘hidden spring’ of the book’s title – lies in the deeply recessed core of the brainstem. He provides us with evocative descriptions of ‘hydraencephalic’ children – children born without much or any cortex, but who still show emotional responses – evidence, Solms says, that consciousness cannot depend on cortex. If he is correct, the implications are substantial. But while Solms is right to caution against assuming that such children are not conscious, it remains a leap to assume the opposite, and his conclusions run counter to a large body of work showing that recovery from coma and the vegetative state is best tracked by what happens in cortical networks. (When it comes to the role(s) of the brainstem in consciousness I find myself closer to the view of Josef Parvizi and Antonio Damasio.)

The Hidden Spring is not easy going. There is a wealth of neurobiological detail, not all of which seems necessary, and his lengthy exposition of the mathematically tortuous ‘free energy principle’ (the FEP – the brainchild of the neuroscientist Karl Friston, with whom Solms has collaborated) is distractingly murky – perhaps inevitably so. In Solms’ view, the FEP allows him to claim that consciousness is closely related to so-called ‘precision optimisation’ in the brain, which – put simply – is a kind of on-the-fly adjustment of signal-to-noise ratio. This is an interesting idea, but precision optimisation is typically associated with attention rather than with consciousness, and although the exact relationship between attention and consciousness is still much debated, they are not the same thing.

Even when the way is clear his orientation to the surrounding literature can be uneven, leaving much to quibble with. (Examples: there is not good evidence that we are “unaware of most of what we perceive and learn”, p.78, and there is not anymore a broad consensus that conscious perception is uniquely tied to gamma-band oscillations, p.126). Nevertheless, the book repays a close read. Even if, like me, you remain unconvinced by his vision for neuropsychoanalysis, his analysis of David Chalmers’ famous ‘hard problem of consciousness’, or his claim to have provided a blueprint for building a conscious machine (and what to do about it), there is plenty to provoke and fascinate along the way. And the book’s primary message – that the source of consciousness is deeply bound up with our nature as flesh-and-blood living creatures – stands up by itself. Solms is one of a small number of scientists making this important argument, and for this alone his book is a welcome contribution.

This review was first published in a different form in the Times Higher Education Supplement on Feb 08, 2021. Mark Solms and I will hopefully be debating our positions (and books) in an event to be organised later this year by the Neuropsychoanalysis Association. (Being You – my book – will be published in September 2021).