Which functional area of the brain is responsible for keeping the cortex alert and conscious and enhancing its excitability?

Reticular formation

Explanation:

The reticular formation is the netlike region and consists of interspersed gray and white matter. Reticular activating system (RAS) is a sensory part of the reticular formation and is responsible for consciousness. RAS of reticular formation obtains sensory information from eyes, ears, etc. Its projections into the cerebral cortex regulate sensory signals that reach the cerebrum.

RAS of reticular formation is responsible for keeping the cerebral cortex alert to maintain the attention of the individuals. The projections of the sensory part of reticular formation also regulate the excitability of cerebral cortex by releasing acetylcholine and noradrenaline (the excitatory neurotransmitters).