Subjects viewed a
random sequence of images of faces and houses and were asked
to look for an
inverted house like the one at bottom left. "That was a distractor,"
Jeff Ojemann said.
"We were interested in what the brain was doing at the other times."
Illustration by
Kai Miller and Brian Donohue
(January 28, 2016) Electrodes in patients’ temporal lobes
carry information that, when analyzed, enables scientists to predict what
object patients are seeing
Using electrodes implanted in the temporal lobes of awake
patients, scientists have decoded brain signals at nearly the speed of
perception. Further, analysis of
patients’ neural responses to two categories of visual stimuli – images of
faces and houses – enabled the scientists to subsequently predict which images
the patients were viewing, and when, with better than 95 percent accuracy.
The research is published today in PLOS Computational
Biology.
University of Washington computational neuroscientist Rajesh
Rao and UW Medicine neurosurgeon Jeff Ojemann, working their student Kai Miller
and with colleagues in Southern California and New York, conducted the study.
“We were trying to understand, first, how the human brain
perceives objects in the temporal lobe, and second, how one could use a
computer to extract and predict what someone is seeing in real time?” explained
Rao. He is a UW professor of computer
science and engineering, and he directs the National Science Foundation’s
Center for Sensorimotor Engineering, headquartered at UW.
The numbers 1-4
denote electrode placement in temporal lobe,
and neural
responses of two signal types being measured.
“Clinically, you could think of our result as a proof of
concept toward building a communication mechanism for patients who are
paralyzed or have had a stroke and are completely locked-in,” he said.
The study involved seven epilepsy patients receiving care at
Harborview Medical Center in Seattle. Each was experiencing epileptic seizures
not relieved by medication, Ojemann said, so each had undergone surgery in
which their brains’ temporal lobes were implanted – temporarily, for about a
week – with electrodes to try to locate the seizures’ focal points.
Neuroscientist
Rajesh Rao and neurosurgeon Jeff Ojemann
are faculty at the
University of Washington.
“They were going to get the electrodes no matter what; we
were just giving them additional tasks to do during their hospital stay while
they are otherwise just waiting around,” Ojemann said.
Temporal lobes process sensory input and are a common site
of epileptic seizures. Situated behind mammals’ eyes and ears, the lobes are
also involved in Alzheimer’s and dementias and appear somewhat more vulnerable
than other brain structures to head traumas, he said.
In the experiment, the electrodes from multiple
temporal-lobe locations were connected to powerful computational software that
extracted two characteristic properties of the brain signal: “event-related
potentials” and “broadband spectral changes.”