Andrew Brown in “Depression is not a ‘brain disorder‘” in The Guardian

The mind is not just some decorative pattern read off the brain and mistaken for the real thing. Consciousness is not just the whistle on the steam train, as William James put it. Treating unhappiness as a problem in the brain is good for the profits of drug companies, but doesn’t actually make us all happier in the long run.

To say that the mind depends on the brain is easy enough – and true, so far as we know. But that doesn’t mean that they are the same thing, or that understanding the one will supply a sufficient understanding of the other. Talking about depression as a brain disease is a warning sign that someone has their ideas all wrong – and that’s not a problem with their brain.

John M. Grohol in “Mental Illness is Not Simply a Brain Disease” in PsychCentral

Mental disorders remain complex disorders that involve all aspect of a person’s functioning and life — their brain and biology, their psychological makeup and personality, and their social interactions and relationships with others. The cause isn’t just one of these things in the vast majority of people who have a mental illness — the cause is all of these things, in differing proportions.

I’ve written about this in the past and in fact, I tag it as one of the top 10 myths of mental illness — because it still is. Even well-meaning family physicians and psychiatrists still refer to the false chemical imbalance theory as though it were fact. A theory, by the way, that has never enjoyed strong research support.

Depression, like all mental disorders, is caused by a complex and still poorly-understood confluence of a combination of factors.

Liah Greenfeld in the Introduction to Mind, Modernity, Madness:

[The] psychophysical, or mind/body, assumption has been at the root of the central philosophical problem in the Western tradition since the time of Plato, because no satisfactory solution could be found to the connection between the two heterogeneous expressions: both are a part of every human’s experience and clearly influence each other in it, but it is impossible to account for this coexistence and influence either logically without contradicting this experience or, for that reason, empirically by showing how precisely one translates into the other. Depending on the intellectual fashions of the time, one or another monistic position would be accepted without debate, which would pose that only one of these expressions of reality was real in the sense of being causally active, the other being merely apparent or epiphenomenal, secondary expression of the first one. The causally active factor was for a very long time believed to be the spiritual one–creative divine intelligence. But for the last three centuries or so matter has held the position of the causal factor, and the spiritual element–human consciousness, mind, culture–was gradually reduced to the status of only apparent reality, an epiphenomenon.

Within this philosophical framework my argument that culture (an ideational, symbolic, non-material phenomenon) causes a biologically real (material) disease appears quite incredible. This lack of credibility is, in the first place, a function of the credit given today to the materialist interpretation of the psychophysical relationship. But the real problem lies not in one or another interpretation, but in the assumption of this relationship itself. In most areas of life and of science this philosophical assumption is of no importance–it may exist in the back of our minds but is very rarely, if ever, brought to the surface, and does not in any way interfere with our daily activities. In psychiatry and human neuroscience, however, it forms an impassable obstacle to the understanding of the very phenomena those engaged in these fields aim to understand, for there is no more logical possibility, in the framework of the dual, mind/body view of reality of translating material events occurring in the brain into the symbolic events of human consciousness, than in translating a symbolic cause into a material effect. So long as there remains the unresolved philosophical mind/body problem, no significant advance in human neuroscience and, therefore, psychiatry would be possible. Any claim on a subject involving human consciousness, whether from a materialistic or idealistic perspective, and whether appearing credible or incredible, will remain purely speculative and of little relevance to real-life empirical problems. The first order of the business is, therefore, to escape the mind/body quagmire.

A number of preliminary logically consecutive steps will help the reader to approach my central argument prepared to consider it on its own terms, without the fear that one is committing a scientific heresy. The first chapter, “The Premises,“ demonstrates that it is neither logically nor empirically necessary to imagine reality as expressed in two fundamentally heterogeneous, mutually inconsistent ways. The recognition that this long influential image was a product of a particular historical time and place, thus arbitrary from the point of view of science, makes it easier to give up. Instead, I propose we regard reality, for heuristic purposes, as consisting of three autonomous but logically consistent layers, the physical layer of matter, the organic layer of life superadded to it, and the symbolic layer of culture and the mind superadded to the organic layer. This view is implied in Darwin’s evolutionary theory and is to a no small extent responsible for the spectacular development of biology in the past century and a half. Because the advancement of biology before then was only marginally impeded by the psychophysical assumption, the layer view was never considered as a solution (in fact, elimination) of the mind/body problem. But Darwin did, in fact, transcend the old ontological view and made possible the one suggested here. The presuppositions of logical consistency with the underlying layer(s) and of autonomy make both upper layers of reality in the layer view what philosophers would call emergent phenomena, irreducible to but by definition existing within the boundary conditions of the elements of the underlying reality out of which they have emerged.

Both the organic and the symbolic emergent phenomena are essentially processes which occur in time rather than substances taking place in space (though to different events in the process may correspond specific constructions in space); therefore, they cannot be simply defined as material. No one would judge unreasonable the claim that organic processes are empirical phenomena which are a proper subject of science. Thus, there is nothing unreasonable in treating similarly symbolic processes such as human consciousness, or the mind, and culture.