AUTHOR=Wu Wanchun , Xu Chengwei , Liang Qimei , Zheng Xiaochun , Xiao Qiuyi , Zhong Haili , Chen Na , Lan Yue , Huang Xiyan , Xie Qiuyou 

TITLE=Olfactory response is a potential sign of consciousness: electroencephalogram findings

JOURNAL=Frontiers in Neuroscience

VOLUME=17

YEAR=2023

URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1187471

DOI=10.3389/fnins.2023.1187471

ISSN=1662-453X

ABSTRACT=<sec><title>Objective</title><p>This study aimed to explore whether olfactory response can be a sign of consciousness and represent higher cognitive processing in patients with disorders of consciousness (DoC) using clinical and electroencephalogram data.</p></sec><sec><title>Methods</title><p>Twenty-eight patients with DoC [13 vegetative states (<italic>VS</italic>)/unresponsive wakefulness syndrome (UWS) and 15 minimally conscious states (MCS)] were divided into two groups: the presence of olfactory response (ORES) group and the absence of olfactory response (N-ORES) group according to behavioral signs from different odors, i.e., vanillin, decanoic acid, and blank stimuli. We recorded an olfactory task-related electroencephalogram (EEG) and analyzed the relative power and functional connectivity at the whole-brain level in patients with DoC and healthy controls (HCs). After three months, the outcomes of DoC patients were followed up using the coma recovery scale-revised (CRS-R).</p></sec><sec><title>Results</title><p>A significant relationship was found between olfactory responses and the level of consciousness (<italic>χ</italic><sup>2</sup>(1) = 6.892, <italic>p</italic> = 0.020). For olfactory EEG, N-ORES patients showed higher theta functional connectivity than ORES patients after stimulation with vanillin (<italic>p</italic> = 0.029; <italic>p</italic> = 0.027). Patients with N-ORES showed lower alpha and beta relative powers than HCs at the group level (<italic>p</italic> = 0.019; <italic>p</italic> = 0.033). After three months, 62.5% (10/16) of the ORES patients recovered consciousness compared to 16.7% (2/12) in the N-ORES group. The presence of olfactory response was significantly associated with an improvement in consciousness (<italic>χ</italic><sup>2</sup>(1) = 5.882, <italic>p</italic> = 0.023).</p></sec><sec><title>Conclusion</title><p>Olfactory responses should be considered signs of consciousness. The differences in olfactory processing between DoC patients with and without olfactory responses may be a way to explore the neural correlates of olfactory consciousness in these patients. The olfactory response may help in the assessment of consciousness and may contribute to therapeutic orientation.</p></sec>