Cowan argues that the true short-term memory (STM) capacity limit is about
4 items. Functional neuroimaging data converge with this conclusion, indica
ting distinct neural activity patterns depending on whether or not memory t
ask-demands exceed this limit. STM for verbal information within that capac
ity invokes focal prefrontal cortical activation that increases with memory
load. STM for verbal information exceeding that capacity invokes widesprea
d prefrontal activation in regions associated with executive and attentiona
l processes that may mediate chunking processes to accommodate STM capacity
limits.