I'm very new to Inkscape and I'm trying to edit the SVG schematic of a brain which I've attached below. The outlines consist of separate brushstrokes. I would like to fill some of the gyri with red, so I would like to fill an area with red that is partially delimited by the outlines, but not everywhere. I've also attached a low quality example of what I want to achieve.
I think I probably have to convert some brushstrokes to paths and then connect nodes at the end of the paths to create the borders that aren't defined by brushstrokes? But I haven't managed to figure out how.
original image: https://svgur.com/s/T9S
coloured in: https://i.stack.imgur.com/JrJm4.jpg