How Low-Frequency Neural Activity Structures Language in Time.

The integration of sensory information in humans may be confined to a time window of 2-3 s. In language, this time window constrains the grouping of words into multi-word chunks, required for comprehension. Chunk boundaries are known to elicit a characteristic event-related brain potential, the Closure Positive Shift (CPS). The likelihood of a CPS increases with the duration of the chunk. In the frequency-domain, boundaries have been associated with neural oscillations in the delta band (<4 Hz). Here, we assessed whether the pace for chunking might be imposed by electrophysiological processing cycles of the brain with phase-locking of such activity underlying the CPS. We recorded participants' magnetoencephalogram while they listened to globally ambiguous sentences allowing for two alternative ways of chunking. Chunking was not externally imposed, but the temporal limits of integration windows influenced chunk termination. Phase-locking of narrow-band low-frequency neural activity (i.e., <4 Hz) at the boundaries of multi-word chunks increased with sentence duration, and covaried with event-related fields. Behavioral data further indicate subtle interindividual differences in the duration of the integration time window. Source localization revealed neural generators in bilateral posterior temporal and right anterior regions. The brain appears to project duration-limited integration windows onto the incoming auditory speech signal, thus structuring language comprehension in time.