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Why We've Failed to Solve the Hard Problem of Consciousness

Our traditional model example, cortical vision, isn't intrinsically conscious.

The philosopher David Chalmers claimed in the 1990s that we neuroscientists have tackled only what he calls the ‘easy’ part of the problem of consciousness, namely “where in the brain does it arise?” That is, we have asked only which brain processes correlate with consciousness, not how they cause it. The hard part of the problem is this: “how (and why) do these physiological processes produce a conscious state of mind?” I believe there are two reasons why we have failed to solve the hard part of the problem. The first is philosophical and the second is scientific.

Physiological processes do not produce consciousness in the sense that the liver produces bile. Consciousness is not a thing but rather a point of view. What we perceive objectively as physiological processes in the brain we perceive subjectively as conscious states. These are two different observational perspectives upon the very same processes: consciousness arises from the being of a brain. This leads to a fundamentally different question: Why is it something to be a brain but not to be a liver, or, for that matter, a rock?

Not all bodily processes possess something-it-is-like-ness, and nor do all brain processes. This takes us to the scientific reason why we have failed to solve the problem: we have been focusing on the wrong brain function as our model example, namely visual perception. Visual perceptual processes are not intrinsically conscious. We know from tachistoscopic experiments, for example, that it is possible to read with comprehension and to recognize familiar faces (both of which are cortical processes) and to respond to these stimuli accordingly, without awareness of having seen anything. That is why Chalmers can assert that complete knowledge of how the brain processes visual information fails to explain why we have visual experience; it is perfectly possible to see without having the experience of seeing.

However, this does not apply to another, more promising brain function, namely affect—or at least to the aspect of affect that we call ‘feeling’. How can you generate a feeling without feeling it? This is not a linguistic issue. Whether you feel something or not makes a difference to what you do. Unlike reading and face recognition, which can occur unconsciously, feeling something has different causal consequences from not feeling it. If you do not feel hungry, energy metabolism proceeds autonomically. However, when you do feel it you are motivated to look for food and to eat. The same applies to all other felt affects. If you are objectively in danger, for example, you do not run and hide unless you become aware of the danger, and you feel scared.

Affects are generated not in the cortex but in the brainstem. Accordingly, children who are born without a cortex, in hydranencephaly, are conscious and emotionally responsive. The same applies to decorticate animals, where the cortex is removed surgically after birth. That is why deep brain stimulation of some brainstem structures – especially the periaqueductal grey (PAG) and reticular activating system (RAS) – produce intense affects within seconds, and that is why most psychiatric medications act on the neuromodulatory systems that are sourced in the reticular activating system. That is also why neuroimaging of affective states shows activation not in the cortex but in the brainstem and the limbic circuits that arise from the RAS and terminate in the PAG.

Most important is that tiny lesions in the brainstem (as small as 2mm3) obliterate all consciousness, including visual consciousness. This stands in sharp contrast to the fact that consciousness is preserved with prenatal or neonatal destruction of the entire cortex. These facts suggest that the fundamental type of consciousness is affect, and that it is generated not in the cortex but the brainstem. The sentient subject is literally constituted by affect, and we only become conscious of our visual (and other) cortical processing when it is ‘palpated’ by these brainstem neuromodulatory systems. In other words, we sentient subjects feel our way into our intrinsically unconscious cortical processes to become aware of them.

Once we have come to these conclusions, the hard problem of consciousness assumes a new form, namely: “How and why do feelings arise?” This is the fundamental question that I try to answer in my new book, The Hidden Spring.


Solms, M. (2021) The Hidden Spring: A Journey to the Source of Consciousness. New York: WW Norton, London: Profile Books.

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