Disentangling Neural Synchronization and Sustained Neural Activity in the Processing of Auditory Temporal Patterns

First paragraph: Temporal regularity within sensory input, can be defined as a uniformly structured and recurring stimulation. Perceiving temporal regularity is integral to effectively perceiving the world around us, such as in speech and music perception. Indeed, natural environments constantly present our perceptual systems with different forms of temporal regularities and rhythms. Efficient sensitivity to temporal changes not only allows us to maintain a coherent perception of our experiences, but importantly, also allows us to build expectations and predict future events (Gutschalk et al., 2002; Nobre and van Ede, 2017). Previous work investigating the underlying neural mechanisms of temporal pattern perception have focused on neural synchronization (NS). This is defined as the ability of neural oscillations to synchronize with temporal regularity in external stimuli (Lakatos et al., 2008; Henry and Obleser, 2012), further suggesting that temporal regularity boosts neural activity at the same frequency as that of the external stimulus. This externally-synchronized neural activity can then be used to predict future auditory activity (Nobre and van Ede, 2017). More recently, the role of sustained activity (SA) has also been investigated in temporal regularity perception, using electroencephalography (EEG) and magnetoencephalography (Barascud et al., 2016; Southwell and Chait, 2018). For instance, detection of regularity in short auditory sequences is demarcated by increased sustained low-frequency evoked magnetoencephalographic activity, which occurs irrespective of the temporal structure (Barascud et al., 2016). The precise relationship between NS and SA is not fully understood. One suggestion is that NS allows the recognition of auditory patterns, while SA subsequently allows the processing of this information in the higher order brain regions. A recently published study by Herrmann and Johnsrude (2018) examined the relationship between NS and SA in the processing of auditory temporal patterns using EEG