Abstract
Pavlovian trace conditioning depends on the temporal gap between the conditioned and unconditioned stimuli. It requires, in mammals, functional medial temporal lobe structures and, in humans, explicit knowledge of the temporal contingency. It is therefore considered to be a plausible objective test to assess awareness without relying on explicit reports. We found that individuals with disorders of consciousness (DOCs), despite being unable to report awareness explicitly, were able to learn this procedure. Learning was specific and showed an anticipatory electromyographic response to the aversive conditioning stimulus, which was substantially stronger than to the control stimulus and was augmented as the aversive stimulus approached. The amount of learning correlated with the degree of cortical atrophy and was a good indicator of recovery. None of these effects were observed in control subjects under the effect of anesthesia (propofol). Our results suggest that individuals with DOCs might have partially preserved conscious processing, which cannot be mediated by explicit reports and is not detected by behavioral assessment.
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Acknowledgements
We thank the care homes and rehabilitation centers in the UK and Argentina, the Cambridge Impaired Consciousness Research Group, the staff of the Wellcome Trust Research Facility for their contribution, and all the study's participants. We especially thank F. Klein and the Anesthesia Favaloro Team. We also thank L. Naccache and C. Koch for comments on an early version of the manuscript. This study was funded by an Antorchas Foundation grant (T.A.B.), a Marie Curie IIF grant (T.A.B.), a StartUp grant (F.F.M.), the Human Frontiers Science Program (M.S.) and a Medical Research Council Acute Brain Injury Collaborative grant (G0600986).
Author information
Author notes
- Tristan A Bekinschtein
Present address: The Medical Research Council, Cognition and Brain Sciences Unit, Cambridge, UK.
- Tristan A Bekinschtein
- & Diego E Shalom
These authors contributed equally to this work.
Affiliations
Institute of Cognitive Neurology, Buenos Aires, Argentina.
- Tristan A Bekinschtein
- , Diego E Shalom
- & Facundo F Manes
Impaired Consciousness Research Group, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
- Tristan A Bekinschtein
- & Martin R Coleman
Raul Carrea Institute, Buenos Aires, Argentina.
- Tristan A Bekinschtein
- , Cecilia Forcato
- & Facundo F Manes
Institute of Neuroscience, Favaloro Foundation, Buenos Aires, Argentina.
- Diego E Shalom
- & Facundo F Manes
Laboratory of Integrative Neuroscience, Physics Department, University of Buenos Aires, Argentina.
- Diego E Shalom
- , Maria Herrera
- & Mariano Sigman
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Contributions
T.A.B. and C.F. designed the study. T.A.B. and F.F.M. conducted the behavioral and neurological assessments. T.A.B., C.F., M.R.C., M.H. and D.E.S. conducted the eye-blink conditioning task in the normal volunteers group and T.A.B., M.R.C. and C.F. conducted the task in the patient group. T.A.B., D.E.S., C.F., M.H., M.R.C., F.F.M. and M.S. analyzed and interpreted the data. T.A.B., D.E.S. and M.S. performed the statistical analysis. T.A.B., D.E.S. and M.S. drafted the manuscript. All of the authors revised the manuscript for important intellectual content.
Corresponding author
Correspondence to Tristan A Bekinschtein.
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