  It is recently demonstrated that cortical activity can track the time courses
of phrases and sentences during speech listening. Here, we propose a plausible
neural processing framework to explain this phenomenon. It is argued that the
brain maintains the neural representation of a linguistic unit, i.e., a word or
a phrase, in a processing buffer until the unit is integrated into a
higher-level structure. After being integrated, the unit is removed from the
buffer and becomes activated long-term memory. In this model, the duration each
unit is maintained in the processing buffer depends on the linguistic structure
of the speech input. It is shown that the number of items retained in the
processing buffer follows the time courses of phrases and sentences, in line
with neurophysiological data, whether the syntactic structure of a sentence is
mentally parsed using a bottom-up or top-down predictive model. This model
generates a range of testable predictions about the link between linguistic
structures, their dynamic psychological representations and their neural
underpinnings.
