At UCLA the research team recorded responses of single brain cells in the auditory cortex of two pre-surgical patients wired with intracranial electrodes as they watched a nine minute clip of the 1967 Clint Eastwood movie, "The Good, the Bad and the Ugly." They then used the data to accurately predict the configuration of fMRI signals measured in 11 healthy subjects as they watched the same clip while lying in a MRI scanner several thousands miles away near Tel Aviv, Israel.
"Although functional magnetic resonance imaging is widely accepted as an important research tool, the relationship between fMRI signals in the human brain and the underlying neuronal activity has been unclear until now," said study co-investigator and corresponding author Dr. Itzhak Fried, professor-in-residence of neurosurgery and psychiatry and biobehavioral sciences at UCLA's David Geffen School of Medicine and the Semel Institute for Neuroscience and Human Behavior.
"Our findings help validate the use of fMRI in a wide array of leading-edge neuroscience research in humans. However, additional research will be needed to see whether this striking correlation between fMRI signals and single neuronal activity also exists in brain regions other than the auditory cortex," Fried cautioned.
Most neurobiological research involves animals, post-mortem tissue or one of a range of imaging techniques. The magnetic properties of blood allow fMRI to show changes in neural activity as a measure of brain blood flow. The technique is popular because it is safer and less invasive than some other imaging options, such as Positron Emission Tomography (PET).
In contrast to imaging techniques, Fried and his UCLA team measure electrical activity directly from the brains of consenting clinical patients with epilepsy at UCLA Medical Center who have been wired with intracranial electrodes to identify the seizure origin for potential surgical treatment.
The study is the latest of several landmark observations made in recent years by the UCLA team, which is probing the underpinnings of the human mind at the single-neuron level in humans. Two years ago, they identified single cells in the human hippocampus specific to places during human navigation. Earlier this year, they found single cells can translate varied visual images of the same item into a single instantly and consistently recognizable concept.
The study was conducted in collaboration with Rafael Malach at the Weizmann Institute; lead author Roy Mukamel, as well as Hagar Gelbard and Amos Arieli of the department of neurobiology at the Weizmann Institute of Science; and Uri Hasson of the Center for Neural Science at New York University.
Primary funding was provided by the National Institute of Neurological Disorders and Stroke at the National Institutes of Health, and the Binational U.S.-Israeli Science Foundation.