This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. Plural form of cortex.

"The study, funded by Tetris 'makers and authored by investigators at the Mind Research Network in New Mexico, shows that playing the classic puzzle game had two distinct effects on the brains of research subjects: some areas in the brain showed greater efficiency (the blue areas in the diagram above), and different areas showed thicker cortexes, which is a sign of more grey matter (red)."