Abstract
The mean amplitude of the EEG alpha (8–12 Hz) power de-synchronization (ERD) is a robust electrophysiological correlate of task anticipation. Furthermore, in paradigms using a fixed period between warning and target stimuli, such alpha de-synchronization tends to increase and to peak just before target presentation. Previous studies from our group showed that the anticipatory alpha ERD can be modulated when magnetic stimulation is delivered over specific cortical regions during a variety of cognitive tasks. In this study we investigate the temporal dynamics of the anticipatory alpha ERD and test whether the magnetic stimulation produces either a general attenuation or an interruption of the typical development of alpha ERD. We report that, during a semantic decision task, rTMS over left AG, a region previously associated to semantic memory retrieval, shortened the peak latency and decreased the peak amplitude of the anticipatory alpha de-synchronization as compared to both active (left IPS) and non-active (Sham) TMS conditions. These results, while supporting the causal role of the left AG in the anticipation of a semantic decision task, suggest that magnetic interference not simply reduces the mean amplitude of anticipatory alpha ERD but also interrupts its typical temporal evolution in paradigms employing fixed cue-target intervals.
Highlights
Temporal expectations are constantly updated in the human brain as we prepare to process forthcoming information[1]
To investigate the effect of magnetic stimulation on the temporal evolution of alpha ERD preceding the target, inhibitory online rTMS was delivered simultaneously with cue onset over the regions of interest using the following parameters: 150 ms duration, 20-Hz frequency, and intensity set at 100% of the individual motor threshold
The present study aimed at shedding light on the mechanisms of transcranial magnetic stimulation (TMS) interference over the left AG in the anticipation of a semantic decision task, by examining the temporal dynamics of pre-stimulus EEG alpha rhythms
Summary
Temporal expectations are constantly updated in the human brain as we prepare to process forthcoming information[1]. Through a time–frequency analysis of a perceptual discrimination task, a recent study has demonstrated that the amplitude of alpha ERD followed the time course of fixed temporal expectations, increasing rhythmically, and peaking just before the expected appearance of the target[15] This result is consistent with the idea that attention www.nature.com/scientificreports/. In the “stop” hypothesis the typical progressive increase of the alpha ERD before target onset would be interrupted by rTMS over left AG, affecting both the amplitude and the latency of the ERD peak This pattern of results would better fit with a specific interference effect on the temporal expectation about the onset the semantic decision task. To test these two hypotheses, we performed a time-frequency analysis of the same dataset from our previous work[14] and tracked the temporal evolution of the preparatory alpha ERD during stimulation of the left AG and two control conditions, one for the main effect of stimulation (SHAM), the other for spatial specificity (stimulation of the left intraparietal sulcus, IPS) (see Fig. 1a for the coordinates of the two cortical regions of interest)
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