Wiktionary
subcortex
n. The part of the brain that lies directly below the cortex.
Usage examples of "subcortex".
If I do not use enough, the subcortex will retain vague residual images, which under the influence of external stimuli might one day fuse to form specific memories.
I liked to compare it to the subcortex, generating your quick but base impulses, and Ground Control instead was like your cortex, filtering and directing those impulses.