Joe Herbert starts well in his article on Aeon Why we can't treat mental illness by fixing the brain?. He explains that although we have some understanding of how a brain neurone is activated and how this activation is passed on to another neurone, we do not know the answer to the wider question of "how a collection of neurons makes a thought, a memory, a decision, an emotion". As he says, "The problem of relating events at the level of neurons with the known functions of the brain is a critical one." There is a "mysterious and seemingly unfathomable gap" between psychology and neuroscience, which "bedevils not only psychiatry, but all attempts to understand the meaning of humanity".
Herbert recognises within psychiatry that there is "no evidence at all that the levels of serotonin or noradrenaline in the brains of depressed people are any different from normal". As he says, "a pathologist looking at the brain of a depressed person could not distinguish it from the brain of someone who was mentally well".
This is all well and good. But then he goes on to spoil the article by speculating that "one day, someone, somewhere will make the critical step, or steps, and we will enter a new world of psychiatry". The advance would be one "that can relate what psychiatrists see in their patients to what can be seen in the brain".
I suppose such wishful thinking can be used to justify the research of his Cambridge Centre for Brain Repair. However, there's no need to wait, and I think we'll be waiting forever, for some new breakthrough at a cellular, chemical or 'systems' level. The problem is conceptual and philosophical, not scientific in that sense. Mental health problems can be treated psychosocially now. It's misleading to suggest that the way forward is by moving psychiatry to neurology (see eg. previous post).