Neuroscientists have a difficult time figuring out which parts of the brain are involved in different functions. Naturally-occurring lesions to the brain are rarely specific to a particular anatomical region, the complications involved with the injury and treatment act as a smokescreen, and finding a patient who's damaged the particular spot you want to learn about is frustrating at best and nigh-impossible at worst.
Fortunately for researchers, inappropriate surgical interventions of the past can shed light on neurological questions.
The strange and horrifying history of psychosurgery is a topic beyond the scope of this site, and certainly beyond this post. Interested readers can easily find a great wealth of relevant discussion on the Net and in libraries, even (in more extensive collections) works written by the physicians involved in such surgeries during the era in which they were popular. Even a casually-curious individual can find lots of non-technical analysis and history to read - for such people, I particularly recommend Great and Desperate Cures by Elliot Valenstein.
Of especial relevance is the prefrontal leukotomy, more commonly (if somewhat imprecisely) known as the lobotomy. There are several features in particular that are of interest to people interested in the nature of effective thought:
To begin, people with frontal lobe damage have problems with impulse control. And by 'problems', I mean they're pretty much incapable of it. It would be more precise to say that lobotomized patients display a remarkable degree of rigid, stereotyped behavior patterns. Give one patient a broom, and she'll begin to sweep the floor; show another a room with a bed, and he'll lie down on it. And do the same thing every time the stimulus is presented. The precise response varies from person to person, but the general reaction is consistent and replicable. Whatever the strongest association with the stimuli is in their mind, that's what they do when they encounter it - and every time they encounter it.
For this reason, it was at one time suggested that only patients with a reputation for rigorously moral behavior be lobotomized, because people who would characteristically break social mores would do so ostentatiously after the surgery. Shoplifters and petty thieves who might have tried to steal particular kinds of things before they were lobotomized would immediately try to do so when they came across those things again - regardless of whether it was a good opportunity or even whether others were clearly watching. Restraining such behavior, or even limiting it, was simply impossible.
Furthermore, such people don't get bored. Present them with a simple task, and they'll carry it out... and keep doing so, even if the consequences become absurd. Set them to building a picket fence and forget to check up on them, and they'll build it past your property line and down the street if given enough time. Set them to washing dishes, and they'll keep washing - to the point of redoing the job several times over. The ability to interrupt the sequence of behavior, to put a "Stop" order in the chain of macros built up, no longer existed once the connections between the frontal lobes and the rest of the brain had been severed.
Motivation becomes almost non-existent. Left to themselves, lobotomized people often do not initiate action, or they do not begin to act in ways other than patterns they incorporated before. They repeat things they did before, but mindlessly and without variation, and cannot adapt if the pattern is disrupted. More alarmingly, the associations between concepts and basic responses are destroyed, to the point where sensations like pain are noted but not perceived as important, and actions to diminish or avoid the pain are not taken. One well-known case ended when, after having been released to her home, a woman was scalded to death because she didn't leave a bath of too-hot water she'd drawn.
Learning in any abstract sense ceases. Teaching the lobotomized new responses is virtually impossible. And even basic conditioning, such as that is used with dogs to train them, becomes problematic due to lack of avoidance of pain and seeking of pleasure.
These points are only part of a general overview - the details are far, far worse.
There's one point which I have yet to discuss, and yet in the context of the information above, is the most shocking. Lobotomization did not disrupt the IQ of patients to any degree. This was actually one of the excuses made for why doctors didn't realize the utterly destructive effects of the surgery earlier. If it didn't impair IQ, surely it couldn't be grossly harmful, it was claimed. Well, it was.
This sets the stage for an important question: If the lobotomy so profoundly levels the house of the mind, why don't IQ tests measure any of the mental aspects destroyed in the process?
That is a subject for the next posts.