This means that if a person abstains abruptly from caffeine use, then in effect they have an over-supply of adenosine receptors and this accounts for the unpleasant effects, the disphoric effects, the tiredness, the lethargy, the irritability and the headaches. The low feeling is addiction and the hit only feels like a hit. Caffeine is actually just bringing you back up to normal speed. Of course, what everyone wants to know is whether caffeine really gets you on the ball. Psychologist Dr Paula Mitchell at the Alfred Hospital in Melbourne, put volunteers through a series of brain-teasers to find out.
Caffeine increases alertness.
Therefore you would expect caffeine to be particularly beneficial at times of the day when alertness is low. The body has a natural 24 hour rhythm of alertness which decreases overnight. Therefore caffeine seems to be particularly beneficial at those times, when it brings arousal back up to an optimal level. In tests that draw on short term memory, and cool-headed reasoning, caffeine's influence is far more subtle. Providing a mental task is relatively easy, you can actually get a better score.