The doctor is referring to the cortex of the brain.
Cortex refers to the outer covering of the brain. It is one component of the brain and is accountable for the majority of complex thinking tendencies. The memory, personality, language, spatial ability, intentional motor skills, and visual perception are all monitored by the cortex.
The cortex is differentiated into four distinct lobes, the parietal, frontal, occipital, and temporal that are each accountable for processing distinct kinds of sensory information.