Abstract
Low-frequency oscillations in the electroencephalogram (EEG) are thought to reflect periodic excitability changes of large neural networks. Consistent with this notion, detection probability of near-threshold somatosensory, visual, and auditory targets has been reported to co-vary with the phase of oscillations in the EEG. In audition, entrainment of δ-oscillations to the periodic occurrence of sounds has been suggested to function as a mechanism of attentional selection. Here, we examine in humans whether the detection of brief near-threshold sounds in quiet depends on the phase of EEG oscillations. When stimuli were presented at irregular intervals, we did not find a systematic relationship between detection probability and phase. When stimuli were presented at regular intervals (2-s), reaction times were significantly shorter and we observed phase entrainment of EEG oscillations corresponding to the frequency of stimulus presentation (0.5 Hz), revealing an adjustment of the system to the regular stimulation. The amplitude of the entrained oscillation was higher for hits than for misses, suggesting a link between entrainment and stimulus detection. However, detection was independent of phase at frequencies ≥1 Hz. Furthermore, we show that when the data are analyzed using acausal, though common, algorithms, an apparent “entrainment” of the δ-phase to presented stimuli emerges and detection probability appears to depend on δ-phase, similar to reports in the literature. We show that these effects are artifacts from phase distortion at stimulus onset by contamination with the event-related potential, which differs markedly for hits and misses. This highlights the need to carefully deal with this common problem, since otherwise it might bias and mislead this exciting field of research.
Highlights
Oscillatory ongoing neural activity on macro, meso, and microscopic scales appears to be highly relevant for information processing in various brain structures (Klimesch, 1999; Hutcheon and Yarom, 2000; Engel et al, 2001; Linkenkaer-Hansen et al, 2004; Becker et al, 2011; Cohen, 2011; Scheeringa et al, 2011; Zoefel et al, 2011)
When stimuli were presented at regular intervals (2-s), reaction times were significantly shorter and we observed phase entrainment of EEG oscillations corresponding to the frequency of stimulus presentation (0.5 Hz), revealing an adjustment of the system to the regular stimulation
Detection of nearthreshold auditory targets in noise or of gaps in ongoing sounds has been reported to depend on the phase of EEG δ, θ, or αoscillations presumed to be driven by the background sounds (Henry and Obleser, 2012; Ng et al, 2012) or by oscillating transcranial direct current stimulation (o-tDCS; Neuling et al, 2012)
Summary
Oscillatory ongoing neural activity on macro-, meso-, and microscopic scales appears to be highly relevant for information processing in various brain structures (Klimesch, 1999; Hutcheon and Yarom, 2000; Engel et al, 2001; Linkenkaer-Hansen et al, 2004; Becker et al, 2011; Cohen, 2011; Scheeringa et al, 2011; Zoefel et al, 2011) Both power and phase of neural oscillations in different frequency bands matter (e.g., Fries et al, 2001; Lakatos et al, 2005; Rajkai et al, 2008; Schyns et al, 2011; Sauseng, 2012) and are assumed to reflect the instantaneous state of neural excitability (Arieli et al, 1996; Supèr et al, 2003; Buzsáki and Draguhn, 2004; Fiser et al, 2004; Jensen et al, 2012). These findings, together with the fact that the δ-band covers important temporal scales of human speech (Giraud and Poeppel, 2012; Peelle and Davis, 2012), suggest an important role of the δ-phase, but possibly of θ- and α-phases (see Thorne et al, 2011), for auditory perception
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