The most common and most likely answer to this crossword clue is the 5 letter word GYRUS
I've seen this crossword clue in The Times
G
Y
R
U
S
More clues leading to the result GYRUS
Buddy explains!

The straight part
We know that "A convolution of brain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a convolution of brain = gyrus.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GYRUS mean?
GYRUS noun- A ridge or fold on the cerebral cortex.