Economization of cerebral activation under training: The inverse U- shaped function revisited

As already observed as early as 1967 by Ingvar and Risberg in their pioneering work, effects of practice of working memory on cerebral functions have been confirmed repeatedly in a number of neuroimaging studies using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). Accordingly, initial performance gains are typically accompanied by increased cerebral activation, while consolidation of such performance gains goes along with a subsequent decrease in activation resembling an inverse U-shaped function. This observed pattern can be interpreted as an economization of cerebral functioning as tasks are being accomplished with relatively lower effort and may also apply to other cognitive domains. However, the economization of cerebral activation under training may depend on task difficulty and training characteristics on the one hand and individual factors, including age, intelligence, cognitive reserve, education, physical and mental health on the other. These findings bear important implications for the design of neuroimaging studies and stimulation protocols, in which similar tasks are routinely repeated.