Oh boy, I get to talk about my area of research! If you don't mind, I'm going to lump the end of the 19th century in with the first half of the 20th because they're a bit hard to separate and the really fascinating stuff moved past theoretical in the second half of that century-long period. I'm also going to answer this in chunks because I have a lot of holiday things to do.
The end of the 19th century brought about a new concept in care for the mentally ill - treatment. Prior to the early 1800's, lunatic asylums were just warehouses for the mentally ill. If you relatives could not afford the time/energy/money to manage you and your symptoms at home, you were sent to an asylum, essentially for storage. There was no evaluation, no treatment plan, no plans to eventually send you home, nothing. There were procedures you might undergo (various types of hydrotherapy, straight-jacket style options, isolation) but that was really all geared towards control during your confinement. Even the expensive, private asylums for the upper classes were basically storage facilities. They were significantly nicer to live in, but there was no treatment as we know it today.
Around the early- to mid-1800's, as medical care overall progressed, people began to consider that, like "physical" health problems, maybe the secrets of mental health problems could be unlocked and solved. The change in attitude started with the private institutions for the elite but trickled down. Mental hospitals were dangerously overcrowded, a better option was needed.
Coming up - the explosion of somatic treatments for mental illness, including some really radical ideas.
Answer Part 4:
Psychosurgery, or Let's talk lobotomies!
By the late 19th century, psychiatrists, anatomists, and researchers had figured out that cognition was the product of the brain. Once they had that figured out - which was a big step, it was long thought to be seated in the heart - it wasn't a big leap to connect lunacy (mental illness) with the brain. And with unintentional brain injuries like those sustained by Phineas Gage, neurologists and psychiatrists had clear evidence that 1) brain function was divided up into multiple areas and 2) the brain could still function overall despite injury to and/or destruction of some of those parts. Most importantly (for psychiatrists) was the revelation that changes to the brain could result in changes in behavior.
Doctors and researchers started to zone in on the frontal lobe as having a significant degree of control over emotions and behavior. A scientist at Yale, John Fulton, started exploring this with chimpanzees by performing frontal lobectomies - completely removing their frontal lobes. This idea was picked up by a Portuguese neurologist by the name of Egas Moniz. Moniz had more or less captive human test subjects from a local mental hospital and he started refining surgery on the frontal lobes as a way to control mental illness. Seeing the drastic changes that occurred in frontal lobectomies, he experimented until he came up with his final product, the prefrontal leucotomy. In this procedure, a number of cores of frontal-parietal brain tissue were removed by a device called a leucotome with the end goal being the easing or complete absence of a patients psychological symptoms/disorder. It is this procedure, for which Moniz would later win the Nobel Prize in Medicine. (His use of non-consenting mental patients as test subjects was swept under the rug).
The ingredient that made psychosurgery widespread and even a household name was actually an American psychiatrist named Walter Freeman. Despite not even inventing the procedure, or even being able to perform it (he was a psychiatrist, not a neurosurgeon), Freeman is considered the father of psychosurgery. He teamed up with a neurosurgeon named James Watts and started offering this procedure to his patients, and colleague's patients, and to local mental hospitals. He was quite the self-promoter, so much so that patients' families started reaching out to him. One of these families, the Kennedys - yes those Kennedys - paid him to try this procedure on a member of their family with what we would now call intellectual and developmental disabilities. Rosemary Kennedy underwent a prefrontal leucotomy and it was a disaster. With brain imaging decades away, sometimes surgeons cut too much, and that is precisely what happened to Ms. Kennedy. She became completely debilitated and never recovered. This was an adverse consequence that doctors just accepted as a risk.
Freeman was not satisfied with the leucotomy procedure. It was brain surgery. You needed anesthesia and a hospital's surgical room, the leucotomes frequently broke apart in the patient's head, it was expensive and time-consuming and most importantly, he couldn't do it. You needed a neurosurgeon. All of these were barriers to widespread use and Freeman truly believed that this could revolutionize the treatment of patients warehoused in mental asylums. He wanted something faster, easier, and cheaper, something that could be available to all of the overcrowded mental hospitals across the country.
And so the frontal lobotomy was born. The story goes that one day Watts walked into the offices he shared with Freeman to find Freeman hovering over an unconscious patient with what appeared to be an ice pick inserted into her brain via the inner orbit of her eye. Watts was horrified and never worked with Freeman again.
Now a free agent, Freeman was able to refine his procedure and sell it to the world. I think most people are familiar with the details of the procedure, but just in case, it can be described as thus: you anesthetize a patient with ECT and insert a surgical instrument called an orbitoclast into the corner of the patient's eye, break through the orbital wall, insert the orbitoclast into the frontal lobes, and swing it to destroy the white matter connections between the frontal lobe and the rest of the brain. How you swing it and how much you swing it depends on the patient and their particular symptoms.
Freeman truly believed that this was the best treatment available to the mentally ill. He thought it could empty the asylums, making patients at least functional enough to go home to their families, if not cure them completely. So he bought himself an RV/camper and traveled from asylum to asylum, performing the procedure and teaching doctors and other staff how to perform the procedure as well. The camper quickly earned the name "The Lobotomobile".
Many hospitals welcomed Freeman and the procedure, being desperate for treatment options. Even if the procedure failed to cure the patient, the patient might be quieted and made more manageable, the hospital would count that as a win. But other hospitals refused to adopt the procedure. They saw it as we see it now - a drastic, barbaric procedure that at best didn't work and at worst, left people brain-damaged for life. In fact, Freeman's home hospital, where he had privileges (St. Elizabeth's in DC), refused to use the procedure and wouldn't allow Freeman to perform the surgery on patients there. Doctors and researchers were similarly divided. Some hailed the procedure as a miracle, some condemned it as barbaric. Over the years, with the accumulation of lobotomy patients whose outcome was clearly not what was promised, more and more doctors condemned the procedure and more hospitals stopped performing it. By the time of the Second World War, the procedure had largely fallen out of use. The advent of psychotropic medications was the final nail in lobotomy's coffin.
Psychosurgery did not die with the lobotomy. With the advent of brain imaging and improved microsurgical techniques, it is now possible to target brain tissue by the millimeter, which, as it turns out, can be an effective if last-resort treatment for certain mental illnesses. It is used by one hospital in the US (Massachusetts General) for treatment of medication-refractory intractable mood, anxiety, and OCD disorders. Outside of the US it's used for all of those and even eating disorders. It is not, however, effective on the disorders it was initially designed for (schizophrenia and other psychotic disorders).
So there you have it. The last, desperate treatment attempts of lunatic asylums was tinkering with the human brain. Of all of the treatments I have listed in this post, only ECT is considered effective and still used today.
Answer Part 3:
Surgical Treatments The idea of operating on a psychologically ill patient to somehow remove what is thought to be causing the illness was not new in the 19th-20th century. Archeological excavations have found a surgery called trepanation. Skulls from multiple civilizations have shown evidence of the removal of pieces of skull - with evidence that the individual survived the procedure. Obviously, it's hard to identify motivation in the absence of written records, but clearly, doctors in the 19th century weren't the first people to consider surgical methods to relieve patients suffering.
Surprisingly, the brain was not the first or only place people looked. Focal infection theory was an early theory that mental illness was caused by focal infections in other places in the body, particularly the teeth and the lower digestive tract, and in women, parts of the reproductive system. This being the era before antibiotics were discovered, the only treatment was to remove the locus of infection. The problem with this is that the theory was, well, completely wrong. So when the locus of infection was removed, and the patient did not get better, they had to find the real locus of infection and remove it. Depending on how zealous your doctor was, you could lose a lot of "infected" tissue. If, for example, your doctor was Henry Cotton of the New Jersey State Hospital at Trenton, well, you'd lose all of your teeth, one by one, followed by large stretches of your colon and intestines, plus your cervix and/or uterus (if you had them available). Not one of psychiatry's shining moments.
Up next: Lobotomy and other psychosurgeries.
Let me know if anyone is still interested in hearing about the last type of treatment, psychosurgery (lobotomies).