Study: fMRI can shed light on brain activity, led to psychiatric treatments
According to Lead Author Karl Deisseroth, MD, PhD, associate professor of bioengineering and of psychiatry and behavioral sciences at Stanford University in Stanford, Calif. and colleagues, functional MRI can be used to study impact of changes in blood flow and neural circuitry, such as ones that may underlie many neurological and psychiatric diseases in the brain.
In a recent study published online in the May 16 issue of Nature, the researchers combined optogenetics (a technology developed at Stanford that employs genes from microbes to allow neurons to be controlled with pulses of light), and blood-flow fMRI to create a non-invasive technology that could display brain activity taking place when people respond to different stimuli, as well as potentially shedding light on human cognition and emotion.
The authors believed that fMRI signals based on elevated levels of oxygenated blood in specific parts of the brain are caused by an increase in the excitation of specific kinds of brain cells and this increase can be measured by the blood oxygenation level-dependent (BOLD) technique.
"It was often assumed that a positive fMRI BOLD signal can represent increased activity of excitatory neurons, but this was never really known and, in fact, became much more controversial over the years," said Deisseroth.
The researchers utilized an experimental group of rats, under blue light delivered by a fiber optic cable. In one cohort of rats, genetically engineered excitatory neurons were stimulated and in the control group, there was no genetic alteration. After that, all the rats were anesthetized and their brains were observed with fMRI.
Exciting these defined neurons with the optogenetic light produced the same kind of signals that researchers see in traditional fMRI BOLD experiments, displaying the same complex patterns and timing. In the control group of rats, no such signals occurred, the authors said, explaining that this finding proves that true neural excitation can produce positive fMRI BOLD signals.
In extension of the results of this optogenetically-enhanced fMRI BOLD study, the research team conducted a second series of experiments. The authors explained that optogenetics could be used to produce activity in specific kinds of cells in neural circuits. Specifically, they observed how activity they stimulated in the thalamus could affect circuits stretching into the somatosensory cortex, a region of the brain important in processing sensation.
“A key to scientific inquiry is developing tools that allow us to intervene and experiment with brain circuits — engineering a reversible gain or loss of function — rather than simple observation of correlations,” concluded Deisseroth and colleagues, who wrote that these findings may point to new approaches for treatment.
In a recent study published online in the May 16 issue of Nature, the researchers combined optogenetics (a technology developed at Stanford that employs genes from microbes to allow neurons to be controlled with pulses of light), and blood-flow fMRI to create a non-invasive technology that could display brain activity taking place when people respond to different stimuli, as well as potentially shedding light on human cognition and emotion.
The authors believed that fMRI signals based on elevated levels of oxygenated blood in specific parts of the brain are caused by an increase in the excitation of specific kinds of brain cells and this increase can be measured by the blood oxygenation level-dependent (BOLD) technique.
"It was often assumed that a positive fMRI BOLD signal can represent increased activity of excitatory neurons, but this was never really known and, in fact, became much more controversial over the years," said Deisseroth.
The researchers utilized an experimental group of rats, under blue light delivered by a fiber optic cable. In one cohort of rats, genetically engineered excitatory neurons were stimulated and in the control group, there was no genetic alteration. After that, all the rats were anesthetized and their brains were observed with fMRI.
Exciting these defined neurons with the optogenetic light produced the same kind of signals that researchers see in traditional fMRI BOLD experiments, displaying the same complex patterns and timing. In the control group of rats, no such signals occurred, the authors said, explaining that this finding proves that true neural excitation can produce positive fMRI BOLD signals.
In extension of the results of this optogenetically-enhanced fMRI BOLD study, the research team conducted a second series of experiments. The authors explained that optogenetics could be used to produce activity in specific kinds of cells in neural circuits. Specifically, they observed how activity they stimulated in the thalamus could affect circuits stretching into the somatosensory cortex, a region of the brain important in processing sensation.
“A key to scientific inquiry is developing tools that allow us to intervene and experiment with brain circuits — engineering a reversible gain or loss of function — rather than simple observation of correlations,” concluded Deisseroth and colleagues, who wrote that these findings may point to new approaches for treatment.