An adder is at a (mental) level that requires more concentration than the ‘volume’ of that space can provide .His inability to focus and concentrate is more the result of an overgrowth than a lack, his mind having retained the overall organization better suited to that of a lower mental level. Perhaps he can be viewed psychologically as neg-narcisistic lacking the ability to coalesce the elements of the mind around the self. Stimulants bring him into a more primitive level with his over developed mind intact, where the greater concentration of that level is balanced with the overall organization of his mind.
The normal, on the other hand, is drawn into that level giving hyper-concentration of a mind adapted to function on the level it naturally occupies, accounting for the temporary increase in intelligence, really processing speed, and hence his frenetic behavior. A possible explanation of this is that concentration, viewed geometrically as a coalescence around the self, grows stronger as the self is approached, countering the neg-narcisistic aspect of the adder. The adder’s mind is overgrown, but retains the more primitive characteristic of the lower space, and hence requires an artificial lowering to its volume, where the concentration is naturally higher owing to the closer proximity to the self.