"casual reading" like a bathroom read...most of those textbooks are(they are not standard biology text which are boring)...I mean you'll have to look into the books to weed out the chapters you don't need to read...but as fo rlight reading as in physics I doubt there is much if your looking to study the brain indepth.
the question becomes what is your purpose to understanding the brain?
[1]are you looking to study cognitive aspects of the brain...behaviours without actually studying the brain components
[2]are you looking to study processes and how brain components handle them
[3]are you looking to study brain components and the brain as a whole.
if its [1] then there are plenty of books.
if its 2 or 3 it gets harder to find them because you need to go indepth to really study the brain. I have two books that might interest you
Rita Carter "Mapping the Mind" its decent and will probably suit your purpose and it has pretty pictures. I would also suggest to pick up pinel's book or the like to have ea indepth book handy.
Ian Glynn "Anatomy of THought" decent though I'm not done reading it.
...
I think you first need to start off with understanding the Neuron/Synapse
and if you already have move onto how the brain is comprised before
starting to look at "isolated" processes ie memory, taste, vision, imagery etc
(the brain is a very cyclic graph). The Neuron/Synapse you should be able to find in any book. But the brain as a whole is sometimes very hard to find...Pinel Ch3-4 is very good and the Carter book as a simple explanation.
You may want to understand different cell types and firing patterns but you'll come across them when you study the processes...I also suggest picking up a child development book because its not only important to see how the brain handle s a processes but how the processes may be grown.