Extroverts were clearly better mobilizing more brain resources for the memory tasks in this report by Gray and colleagues at Kings College. This kind of makes introverts look bad, but maybe it depends how you look at it. Maybe it is just harder to get some of the introverts 'into' the task?
Introversion-Extroversion differences can be source of big personality clashes for some gifted kids in school. Supposedly 77% of the general population is extroverted, whereas 67% of high IQ students are introverted. Maybe introverts are more reluctant to 'perform'?
Also there might be a difference depending on whether the task was intrinsically- motivated or extrinsically-motivated (prior motivation post)? All the same, it is interesting. Maybe the picture also gives us insight into what happens to well-compensated introverts when they need to 'switch on' in performance mode (classroom discussion, networking, lecture circuit) as the needs require.
For those who want to brood more on introversion-extroversion differences, we've listed more links below.
Personality and Cognitive Demand
Introversion: The gifted
Brains on Fire for Parents pdf file