The most common and most likely answer to this crossword clue is the 8 letter word THALAMUS
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Buddy explains!

The straight part
We know that "Part of brain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of brain = thalamus.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 THALAMUS mean?
THALAMUS noun- Either of two large, ovoid structures of grey matter within the forebrain that relay sensory impulses to the cerebral cortex.
- The receptacle of a flower; a torus.
- A thallus.
- An inner room or nuptial chamber.