Classical conditioning in the vegetative and minimally conscious state

• Published in: Nature neuroscience Vol. 12; no. 10; pp. 1343 - 1349
• Main Authors: Herrera, Maria, Bekinschtein, Tristan A, Shalom, Diego E, Forcato, Cecilia, Manes, Facundo F, Sigman, Mariano, Coleman, Martin R
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.10.2009; Nature Publishing Group
• Subjects: Acoustic Stimulation - methods; Adult; Analysis of Variance; Animal Genetics and Genomics; Attention - physiology; Avoidance Learning - physiology; Awareness - physiology; Behavioral assessment; Behavioral Sciences; Biological Techniques; Biomedical and Life Sciences; Biomedicine; Blinking - physiology; Conditioning, Classical - physiology; Consciousness Disorders - diagnosis; Consciousness Disorders - physiopathology; Consciousness Disorders - rehabilitation; Contingent Negative Variation - physiology; Electromyography - methods; Evoked Potentials - physiology; Female; Humans; Male; Methods; Middle Aged; Neurobiology; Neurosciences; Persistent vegetative state; Physiological aspects; Psychoacoustics; Reaction Time - physiology; Risk factors; Structure; Temporal lobes; Young Adult; United Kingdom
• ISSN: 1097-6256; 1546-1726
• DOI: 10.1038/nn.2391

Trace conditioning in humans is thought to require explicit knowledge of the temporal contingency between the conditioned and unconditioned stimuli. Bekinschtein et al . demonstrate that such conditioning can occur in individuals with disorders of consciousness, suggesting the possibility that these individuals may have partially preserved conscious processing that cannot be measured by behavioral assessment. 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.