title: Detecting number processing and mental calculation in patients with disorders of consciousness using a hybrid brain-computer interface system.
abstract: BACKGROUND
  For patients with disorders of consciousness such as coma, a vegetative state or a minimally conscious state, one challenge is to detect and assess the residual cognitive functions in their brains. Number processing and mental calculation are important brain functions but are difficult to detect in patients with disorders of consciousness using motor response-based clinical assessment scales such as the Coma Recovery Scale-Revised due to the patients' motor impairments and inability to provide sufficient motor responses for number- and calculation-based communication.
  
  
  METHODS
  In this study, we presented a hybrid brain-computer interface that combines P300 and steady state visual evoked potentials to detect number processing and mental calculation in Han Chinese patients with disorders of consciousness. Eleven patients with disorders of consciousness who were in a vegetative state (n = 6) or in a minimally conscious state (n = 3) or who emerged from a minimally conscious state (n = 2) participated in the brain-computer interface-based experiment. During the experiment, the patients with disorders of consciousness were instructed to perform three tasks, i.e., number recognition, number comparison, and mental calculation, including addition and subtraction. In each experimental trial, an arithmetic problem was first presented. Next, two number buttons, only one of which was the correct answer to the problem, flickered at different frequencies to evoke steady state visual evoked potentials, while the frames of the two buttons flashed in a random order to evoke P300 potentials. The patients needed to focus on the target number button (the correct answer). Finally, the brain-computer interface system detected P300 and steady state visual evoked potentials to determine the button to which the patients attended, further presenting the results as feedback.
  
  
  RESULTS
  Two of the six patients who were in a vegetative state, one of the three patients who were in a minimally conscious state, and the two patients that emerged from a minimally conscious state achieved accuracies significantly greater than the chance level. Furthermore, P300 potentials and steady state visual evoked potentials were observed in the electroencephalography signals from the five patients.
  
  
  CONCLUSIONS
  Number processing and arithmetic abilities as well as command following were demonstrated in the five patients. Furthermore, our results suggested that through brain-computer interface systems, many cognitive experiments may be conducted in patients with disorders of consciousness, although they cannot provide sufficient behavioral responses.
authors.affiliation: Center for Brain Computer Interfaces and Brain Information Processing, South China University of Technology, Guangzhou, 510640, China. auyqli@scut.edu.cn.|Guangzhou Key Laboratory of Brain Computer Interaction and Applications, Guangzhou, China. auyqli@scut.edu.cn.
authors.forename: Yuanqing
authors.initials: Y
authors.lastname: Li
authors.affiliation: School of Software, South China Normal University, Guangzhou, 510641, China.
authors.forename: Jiahui
authors.initials: J
authors.lastname: Pan
authors.affiliation: Guangzhou Key Laboratory of Brain Computer Interaction and Applications, Guangzhou, China.|Coma Research Group, Centre for Hyperbaric Oxygen and Neurorehabilitation, General Hospital of Guangzhou Military Command of People's Liberation Army, Guangzhou, 510010, China.
authors.forename: Yanbin
authors.initials: Y
authors.lastname: He
authors.affiliation: Center for Brain Computer Interfaces and Brain Information Processing, South China University of Technology, Guangzhou, 510640, China.|Guangzhou Key Laboratory of Brain Computer Interaction and Applications, Guangzhou, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.affiliation: Coma Science Group, Cyclotron Research Centre and Neurology Department, University and University Hospital of Liège, 4000, Liège, Belgium.
authors.forename: Steven
authors.initials: S
authors.lastname: Laureys
authors.affiliation: Guangzhou Key Laboratory of Brain Computer Interaction and Applications, Guangzhou, China.|Coma Research Group, Centre for Hyperbaric Oxygen and Neurorehabilitation, General Hospital of Guangzhou Military Command of People's Liberation Army, Guangzhou, 510010, China.
authors.forename: Qiuyou
authors.initials: Q
authors.lastname: Xie
authors.affiliation: Guangzhou Key Laboratory of Brain Computer Interaction and Applications, Guangzhou, China. gesund@21cn.com.|Coma Research Group, Centre for Hyperbaric Oxygen and Neurorehabilitation, General Hospital of Guangzhou Military Command of People's Liberation Army, Guangzhou, 510010, China. gesund@21cn.com.
authors.forename: Ronghao
authors.initials: R
authors.lastname: Yu
mesh_terms: D000328:Adult; D062207:Brain-Computer Interfaces; D004569:Electroencephalography; D018913:Event-Related Potentials, P300 / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D055641:Mathematical Concepts; D008875:Middle Aged; D018458:Persistent Vegetative State / Q000503:physiopathology*; D011340:Problem Solving / Q000502:physiology*