Consciousness is everything people experience, from the taste of chocolate to the pain of a migraine. But the origin and nature of consciousness have puzzled scientists for centuries. A new study published in the May 25, 2018 issue of the journal Nature Communications identifies and measures the neural activity associated with a new conscious experience and takes researchers a step closer to solving the mystery.
“Computers and robots interact with the world without being conscious. But something miraculous happens inside our brains to make us conscious and experience the world from a subjective perspective,” said study lead author Dr. Hagar Gelbard-Sagiv, a researcher with Tel Aviv University, Caltech and the University of California, Los Angeles.
“Our new study brings us one step closer to understanding consciousness and conscious experience at the most concrete level: the electrical activity of individual neurons.”
In the study, Dr. Gelbard-Sagiv and colleagues took advantage of a unique medical opportunity: the surgical implantation of electrodes in the brains of patients with epilepsy to determine the precise areas responsible for their seizures.
Patients were monitored for a week or two, until enough data on their seizures had been collected.
During this time, the implanted electrodes recorded the activity of individual neurons in their vicinity.
The team presented two different images to the patient, one to each eye, to probe the moment in which a new experience arises.
For example, an image of a house was presented to the right eye and an image of a face to the left eye. In this situation, known as ‘binocular rivalry,’ the brain cannot combine the two images. Instead, the subject sees either the house or the face, and this alternates irregularly every few seconds. These alternations happened involuntarily, while the physical stimulus remained constant.
This allowed the scientists to isolate brain activity related to the change in perception and differentiate it from brain activity related to the physical stimulus.
They discovered that the activity in frontal lobe neurons changed almost two seconds before the patient reported an alternation in perception, and that the neuronal activity in the medial temporal lobe changed one second before a report.
“Two seconds is a long time in terms of neural activity. We believe that the activity of these neurons not only correlates with perception, but also may take part in the process that leads to the emergence of a conscious percept,” Dr. Gelbard-Sagiv said.
“Our study captures individual cells in the human brain just before one conscious experience is replaced by another,” added co-author Professor Itzhak Fried, of Tel Aviv University and the University of California, Los Angeles.
“It is a unique privilege to gain such a rare glimpse into human consciousness. At the same time, we can provide clinical care aimed at alleviating severe epilepsy in our patients.”
Hagar Gelbard-Sagiv et al. 2018. Human single neuron activity precedes emergence of conscious perception. Nature Communications 9, article number: 2057; doi: 10.1038/s41467-018-03749-0