Researchers have found that the sense of smell could be a reliable tool in determining the rate of recovery and the survival of patients with severe brain injury.

A study, published on April 29 in the journal Nature, exposes how a conventional and cheap 'sniff test' could help doctors diagnose and treat patients with ailments regarding consciousness.

In the study, all of the patients who initially had little to no awareness of the outside world regained consciousness after reacting to the sniff test. Ninety-one percent of these patients have been found to survive their brain injuries even after three and a half years later.

Anat Arzi, the lead researcher from the University of Cambridge's Department of Psychology and the Weizmann Institute of Science Israel, said that the accuracy of the sniff test is exceptional. Arzi and the rest of the team hope that it would help in the treatment of patients with brain injuries all around the world.

In the study, Arzi worked together with Professor Noam Sobel from the Weizmann Institute of Science Israel and Dr. Yaron Sacher from the Loewenstein Rehabilitation Hospital Israel.

The research was funded by the Royal Society, the Blavatnik Family Foundation, the Rob and Cheryl McEwen Fund for Brain Research, and the European Molecular Biology Organisation.

Brain Injury and Level of Consciousness

According to Brainline, a traumatic brain injury can lead to five abnormal states regarding a person's level of consciousness. These are stupor, coma, persistent vegetative state, locked-in syndrome, and brain death.

After a severe brain injury, doctors often find it hard to determine a person's level of consciousness exactly. Errors in diagnosis are made in up to 40% of cases. A precise diagnosis is crucial because it guides physicians in arranging their treatment plans such as pain management and can control decisions regarding the patient's long term survival.

According to Noam Sobel, if you approach an unconscious patient and present them with a particular scent to sniff, they will resume consciousness at some stage and probably live for at least three years.

Scientists say that the sense of smell is a fundamental mechanism that relies on structures deep within the brain. The brain automatically changes the way we sniff in response to different scents. In healthy people, the sniff-response occurs in both waking and sleeping states of consciousness.

Scents of Shampoo and Rotten Fish

The research was done on 43 severely brain-injured patients. They were presented with different jars containing different items with various scents and would be smelling them through a nasal cannula. The facilitator explained the procedure and the contents of each jar, without any indication of comprehension coming from the patients.

The researchers found that slightly conscious patients naturally inhaled less in response to smells. However, they did not show prejudice between pleasant and awful smells. These patients also adjusted their nasal airflow in response to the jar with no scent. This behavior indicates an awareness of the jar or learned expectancy of a smell.

In vegetative state patients, some patients changed their breathing in response to either of the smells, while others did. Arzi said that they found that if patients in this state had a sniff response, they, later on, transitioned to at least slightly conscious state. He added that in some cases, it was the only sign that hinted that the patient's brain was going to recover.

Dr. Tristan Bekinschtein from the University of Cambridge's Department of Psychology said that when the sniff response is functioning normally, it may indicate that the patient could still be conscious at some point, even when other signs are not apparent.