The brain's task is to match blood-flow "demand" and 'supply". Demand varies all day.
After meals the digestive system requires more blood to flow , -i.e., "demand" increases and the brain does three things : (1) it increases the amount of blood ejected by each stroke
of the heartbeat
(2) it increases the number of heart beats per minute, and
(3) it dilates the blood vessels (particularly those associated with digestion) to help flow, - that is, blood is diverted from other organs to the digestive organs.
So, .... you get a stronger pulse, a faster pulse, and most people would feel sleepy after a heavy meal, because some of the cardiac output is diverted FROM other organs (including the brain) TO the digestive tract. It, (blood) flows better through the dilated blood vessels (arteries, arterioles, and capillaries) of the stomach etc.