Neural detection of complex sound sequences or of statistical regularities in the absence of consciousness?

Sir,We read with interest the article by Tzovara et al. (2015), recently published in Brain . In this study the authors adapted a paradigm we previously designed (Bekinschtein et al. , 2009) to probe the EEG of comatose patients in response to two types of violations of auditory regularities. Unfortunately, several important problems mitigate the reliability of their conclusions.In the local-global paradigm, local auditory irregularities correspond to a change of sound within a trial, whereas global irregularities correspond to a change of sound sequence across trials.The authors showed with a decoding algorithm a significant difference in EEG responses to global violations in 10 of 24 comatose patients. Observing such a global effect in unconscious subjects challenges our previous conclusion that this global effect can only be observed in conscious and attentive subjects (Bekinschtein et al. , 2009; Wacongne et al. , 2012; El Karoui et al. , 2014) and systematically disappears in inattentive subjects (Bekinschtein et al. , 2009; King et al. , 2013), sleeping subjects (Strauss et al. , 2015), and clinically unconscious patients in vegetative state (Faugeras et al. , 2011, 2012). Converging findings from multiple functional brain imaging tools [high-density EEG, magnetoencephalography (MEG), intracranial stereoelectroencephalography (SEEG), functional MRI] demonstrated that the global effect is characterized by a late (>300 ms after violation onset) and sustained brain response (King et al. , 2014) typical of conscious access (Dehaene and Naccache 2001; Dehaene et al. , 2011). In our data, the only two patients in a vegetative state showing a late global effect recovered clinical signs of minimally conscious state within the next …