I just revisited the Crumb documentary that was released in 1995 (most of the footage shot in 1991,92). Yeah, they displayed much of R. Crumb’s art and illustrations. But the angle that was hit hardest was what mental processes were inside the Crumb mind. They found all sorts of mental dysfunction in R. Crumb, some quite disturbing. But he was very capable of taking care of himself.
Not the case for his brother Charles. Charles hit adulthood with a full stop. They showed Charles’ comics as he went through his late teens. The most revealing was his last comic book. The characters were being filled in more and more with concentric circles (wrinkles). White space in the background was being filled in more and more. The text bubbles were getting bigger, to the extent by the end of the comic, it was all text. His head was being taken over by a power that he could not control. My guess is a flavor of schizophrenia.
Below is a video of a cat illustrator who was befallen by late onset schizophrenia. Same general pattern as Charles except with sharp edges instead wrinkles/circles. The latter images look more like fractal patterns, rather than cats. They also look quite abstract and wonderfully artistic.