The use of pupil dilation to communicate with locked-in syndrome patients
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1
University of Melbourne, Psychological Sciences, Australia
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2
Philips-University, Neurophysics, Germany
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3
University and University Hospital of Liege, Coma Science Group, Belgium
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4
Allen Institute for Brain Science, United States
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5
Bielefeld University, Center for Interdisciplinary Research (ZiF), Germany
Background: For patients with severe motor disabilities, a robust means of communication is a crucial factor for their well-being. Typically this involves the use of brain computer interfaces that require sophisticated machinery that are unsuitable for home use due to cost and physical size or require continued expert technical support to adjust and maintain equipment over sustained use. Despite recent progress in BCI research, developing a system that provides the patient maximal autonomy remains challenging.
Methods: Here we exploit pupil size as an alternative simple and robust measure for communication. Based on the data of six young, healthy controls, we established a protocol that enables them to control their own pupil size by increasing or decreasing cognitive load (i.e., performing mental arithmetic or not) and to use this signal to answer yes/no questions. The system was then tested in eleven patients suffering from locked-in-syndrome (LIS), seven of whom were in a typical LIS due to a brainstem stroke (i.e., without supratentorial brain lesions and with normal cognitive function), and four atypical LIS (i.e., with supratentorial lesions and resulting cognitive dysfunction) as result of a severe brain injury. Finally, we tested command-following responses with the same system in a single patient in a non-communicative minimally conscious state (MCS).
Results: As reported recently (Stoll et al 2013, Current Biology R647-8) we found that all healthy controls could use the system for communication, with an average decoding performance of over 90% and significant decoding in each individual. The responses of six out of seven typical LIS patients could be decoded above chance level, with three reaching significance individually. In contrast, none of the atypical LIS patients reached a performance significantly different from chance. Finally, in the MCS patient, who was explicitly instructed to react either to the "yes" or the "no" alternative in each question, the response could again be decoded significantly above chance.
Discussion: Our data provides proof-of-principle that pupil size can be used as a means of communication with at least a subset of LIS patients. In addition, the MCS data renders the use of this system as a diagnostic tool conceivable, permitting the identification of motor-independent (i.e., pupil-dependent) signs of command-following in a population whose state of consciousness is in question.
References
Stoll, J., Chatelle, C., Carter, O., Koch, C., Laureys, S. & Einhauser, W. (2013). Pupil responses allow communication in locked-in syndrome patients. Current Biology. 23, R647-8
Keywords:
pupil dilation,
Coma,
locked-in syndrome,
Brain Computer Interface,
human
Conference:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013.
Presentation Type:
Oral
Topic:
Other
Citation:
Carter
O,
Stoll
J,
Chatelle
C,
Koch
C,
Laureys
S and
Einhauser
W
(2013). The use of pupil dilation to communicate with locked-in syndrome patients.
Conference Abstract:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference.
doi: 10.3389/conf.fnhum.2013.212.00126
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Received:
15 Oct 2013;
Published Online:
25 Nov 2013.
*
Correspondence:
Dr. Olivia Carter, University of Melbourne, Psychological Sciences, Melbourne, Australia, ocarter@unimelb.edu.au