Cortical Dynamics of Semantic Priming and Interference during Word Production: An Intracerebral Study.

Abstract

Language production requires that semantic representations are mapped to lexical representations on the basis of the ongoing context to select the appropriate words. This mapping is thought to generate two opposing phenomena, "semantic priming," where multiple word candidates are activated, and "interference," where these word activities are differentiated to make a goal-relevant selection. In previous neuroimaging and neurophysiological research, priming and interference have been associated to activity in regions of a left frontotemporal network. Most of such studies relied on recordings that either have high temporal or high spatial resolution, but not both. Here, we employed intracerebral EEG techniques to explore with both high resolutions, the neural activity associated with these phenomena. The data came from nine epileptic patients who were stereotactically implanted for presurgical diagnostics. They performed a cyclic picture-naming task contrasting semantically homogeneous and heterogeneous contexts. Of the 84 brain regions sampled, 39 showed task-evoked activity that was significant and consistent across two patients or more. In nine of these regions, activity was significantly modulated by the semantic manipulation. It was reduced for semantically homogeneous contexts (i.e., priming) in eight of these regions, located in the temporal ventral pathway as well as frontal areas. Conversely, it was increased only in the pre-SMA, notably at an early poststimulus temporal window (200-300 msec) and a preresponse temporal window (700-800 msec). These temporal effects respectively suggest the pre-SMA's role in initial conflict detection (e.g., increased response caution) and in preresponse control. Such roles of the pre-SMA are traditional from a history of neural evidence in simple perceptual tasks, yet are also consistent with recent cognitive lexicosemantic theories that highlight top-down processes in language production. Finally, although no significant semantic modulation was found in the ACC, future intracerebral EEG work should continue to inspect ACC with the pre-SMA.