Some coma patients who appear to be completely unresponsive to the outside world are still capable of the most basic kind of learning, according to a small new study. Researchers found that both vegetative and “minimally conscious” patients were capable of a Pavlovian response, learning to associate a noise with a slightly unpleasant stimulus.
The researchers built on the work of 19th-century Russian psychologist Ivan Pavlov, who famously conditioned his dogs to salivate at the ring of a bell by associating the sound with the presentation of food. In this case, they sounded a tone, which was followed about 500 milliseconds later with a light puff of air to the eye [Scientific American]. At first the patients only responded after the puff of air by blinking or twitching or flinching. But after repeated trials, 15 of the 22 patients began to blink or flinch immediately after the tone sounded, before the puff of air. Electrodes by their eyes picked up the subtle muscle movements.
A control experiment doing the same tests on people under general anaesthesia did not produce the same responses, suggesting that the learning does not happen when truly unconscious [BBC News]. The study also suggests that even patients in persistent vegetative states may have some very rudimentary level of consciousness that isn’t detected in other tests.
The fascinating (but preliminary) findings, presented in Nature Neuroscience, may eventually help doctors evaluate coma patients’ potential for recovery. The authors found a strong correlation between cognitively damaged patients who seemed to exhibit such learning and those who showed some level of improvement months after their injury, as measured by a standard coma recovery scale [The Scientist]. Because the experimental setup is so simple, doctors who don’t have access to sophisticated brain imaging techniques could use this system to inform their diagnoses.
These study also suggests possible new forms of therapy to lead researcher Tristan Bekinschtein. Next his team hopes to explore whether learning this type of task might actually help recovery. “If you train networks in the brain, you can transform the network itself,” he says [New Scientist].
Image: flickr / el7bara