If you stick a smelly jar under the nose of people laying in a vegetative state, some of them will start to spontaneously sniff. As bizarre as it might sound, a new study shows that this technique could prove to be an effective way of accurately diagnosing patients with disorders of consciousness and gauging their chances of recovery.
Reported in the journal Nature, researchers from the University of Cambridge in the UK and the Weizmann Institute of Science Israel used this “sniff test” on 43 patients with severe brain injuries who were showing minimal or no signs of awareness of the external world. Researchers placed a jar containing either a pleasant smell of shampoo, an unpleasant smell of rotten fish, or no smell near the patient’s nose for five seconds, while a specialized tube kept tabs on the breathing through their nose.
In 100 percent of the cases where the patient reacted to the test by increasing their strength of sniffing, they went on to regain consciousness. In a follow-up 3.5 years later, over 91 percent of these patients were still alive, while 63 percent of those who had shown no response to the smells had died. This suggests the “sniff test” could be used to predict a patient's outcomes after suffering from a severe brain injury.
"The accuracy of the sniff test is remarkable,” Anat Arzi, lead author and psychologists at the University of Cambridge and the Weizmann Institute of Science Israel, said in a statement.
"We found that if patients in a vegetative state had a sniff response, they later transitioned to at least a minimally conscious state. In some cases, this was the only sign that their brain was going to recover – and we saw it days, weeks and even months before any other signs," explained Arzi.
Around 35.5 percent of patients in a minimally conscious state had no sniff response, "indicating that a lack of sniff responses does not necessarily indicate unconsciousness," write the authors. The researchers also found that some of the patients that did not have a sniff response had damage to olfaction-related brain structures that process smells, which perhaps explains some of their results.
However, the study suggests sniffing can predict the patient’s long-term outcomes as those who can process smells still have some degree of consciousness, despite not showing any meaningful responses or signs of awareness. None of the patients discriminated between the nice and nasty smells, although some of the patients also started sniffing in response to the jar with no smell, suggesting some wider awareness of the jar or some kind of learned anticipation of a smell. Alternatively, it could highlight that sniffing is one of the basic and fundamental mechanisms of arousal in the brain.
“When the sniff response is functioning normally it shows that the patient might still have some level of consciousness even when all other signs are absent," continued Dr Tristan Bekinschtein, who was also involved in the study. "This new and simple method to assess the likelihood of recovery should be immediately incorporated in the diagnostic tools for patients with disorders of consciousness."