How do neuropeptides alter cognitive performance?

It is pointed out in this article that efficient cognitive performance depends on two independent parameters, one concerned with the intrinsic capacity of the nervous system, the other with motivational processes such as arousal. It is argued that a substance should be regarded as a true cognition enhancer only if it improves the former. There is evidence suggesting that some neuropeptides--for example vasopressin--act on motivational and arousal processes, and a model which offers a plausible mechanism is discussed. The need for techniques and designs which permit us to separate these different effects is highlighted.