At Brookhaven, researchers combined light-activated proteins that stimulate specific brain cells, a technique known as optogenetics, with positron emission tomography (PET) to observe the effects of stimulation throughout the entire brain. Their paper in the Journal of Neuroscience describes this method, which will allow researchers to map exactly which neurological pathways are activated or deactivated downstream by stimulation in specific brain areas. Hopefully, following these pathways will enable researchers to correlate the brain activity with observed behaviors or certain symptoms of disease.

Three markers on the head of a mouse enable the AwakeSPECT system to obtain functional images of the brain of a conscious mouse as it moves around. (Credit: Image courtesy of DOE/Thomas Jefferson National Accelerator Facility)

Scientists at Oak Ridge used dynamic imaging in mice to examine changes in brain chemistry caused by disease or application of a drug. They hope this research tool will be used to develop better disease diagnostics as well as better treatments. The newest aspect of this study, however, is that unlike most nuclear imaging studies where laboratory mice are drugged or kept in place so that their brains can be studied, the new technique allows for moving subjects. The researchers from Jefferson Lab, Oak Ridge, Johns Hopkins and Maryland used their new system to obtain functional images of the brains of conscious mice that were free to move. The system, called AwakeSPECT (Awake Single-Photon Emission Computed Tomography),  was then used to examine the effects of anesthesia on the action of a dopamine transporter in the mouse brain for the first time. These types of dopamine transporter imaging compounds are used for Alzheimer’s, dementia and Parkinson’s disease studies. The technique entails injection of a radionuclide, which gathers in targeted areas of the brain. The radionuclide emits gamma rays that are detected in separate scans from many different angles, all of which are combined by an algorithm to produce a three-dimensional image.

Martin Pomper led a group of researchers at Johns Hopkins Medical School to conduct the first mouse imaging studies with the new system. Their study showed that AwakeSPECT can be used to obtain detailed, functional images of the brain in a conscious mouse that was able to move freely around in an enclosed space. “We’ve shown the technology works. Now, you just have to make it a tool that more people will readily use” says Jefferson Lab’s Drew Weisenberger, who led the multi-institutional collaboration that created the novel technique.

One area of active research that would benefit from such imaging techniques is the question of how animals orient themselves in space. Existing experiments have all looked at how animals move around in two-dimensional settings and they have made the important discovery of place cells, neurons located in the hippocampus responsive to spatial orientation. Populations of place cells working together can produce full representations of an animal’s environment, the only problem being that in the real world animals have to navigate in three dimensions unlike the laboratory experiments. That’s why Dr. Nachum Ulanovsky of the Weizmann’s Institute’s Neurobiology Department chose to study the Egyptian fruit bat to look at how three-dimensional space is perceived in mammalian brains for the first time. His research used a miniaturized neural-telemetry system developed especially for this task, which enabled the measurement of single brain cells during flight. The activity of the  hippocampal neurons in the bats’ brains showed that the representation of three-dimensional space is just like in two dimensions: each place cell is responsible for identifying a particular spatial area in space and sends an electrical signal when the bat is located in that area. The population of place cells provides full coverage of the particular area, say a cave, left, right, forward, back, up and down.

These results give new insights into navigation, spatial memory and spatial perception, all basic functions of the mammalian brain. The study’s success is due to the development of the technology that allowed looking into the brain of a flying animal. Single cell measurement is only the first step, looking at neural circuits can reveal much more about how these place cell representations are then used in conjunction with other brain areas resulting in the behavior we see. Development of new brain imaging techniques continues to provide a more complete understanding of basic human and animal behaviors, and hopefully one day will lead to a full understanding of the human brain.

-Leo Shapiro

Sources:

Lights, Chemistry, Action: New Method for Mapping Brain Activity – ScienceDaily

System Provides Clear Brain Scans of Awake, Unrestrained Mice – ScienceDaily

Neural Activity in Bats Measured In-Flight – ScienceDaily

Can you hear me now? For years, it has been popular doctrine that cell phone use is bad for our brains, but we glue our phones to our ears anyway. Cell phones emit radio frequency-modulated electromagnetic fields (RF-EMFs) that are questioned for their potential danger when the brain is exposed to them. The oscillatory frequencies of RF-EMFs correspond to those measured in neural tissue, and thus could interfere with neural activity. The amount of electromagnetic radiation given off by our communication devices is small, but is radiation all the same. Radiation exposure is dangerous for any kind of cell in our body, and can penetrate cells and damage DNA either by crashing into the molecule directly or causing damage indirectly by forming free radicals from water that can have cancer-causing effects.

Now, a study that empirically investigates the effects of cell phones on the brain with acute cell phone exposure with PET imaging from the National Institute on Drug Abuse has been published in the Journal of the American Medical Association (JAMA). The study investigates if acute cell phone exposure affected activity in the brain by measuring glucose metabolism via PET in subjects with two cell phones affixed to their ears. Readings were obtained with one cell phone antenna activated for 50 minutes (the “on” condition) and with both off (the “off” condition) for control and comparison purposes. Subjects were exposed to either condition and imaging of their brains was analyzed, revealing that whole-brain effects were not significant, but there was significant activation in areas of the brain in the immediate vicinity of the cell phone, justifying our concerns with cell phone radiation. Brain mapping (below) shows the strength of the electric field provided by the affixed cell phone mapped against the brain itself. Magnitude was markedly increased near the antenna, increasing significantly closer to the phone and reaching maximum strength near the lower temporal lobe.

PET scans (below) of the control condition (cell phone off) versus the experimental condition (cell phone on) at the level of the orbitofrontal cortex. Clear increase in glucose metabolism was demonstrated in the right orbitofrontal cortex and the lower right superior frontal gyrus. These brain regions are associated with decision-making and sensory-aided self awareness, respectively. Additional statistical analysis showed that glucose metabolism is positively correlated with the strength of the electric field exposed to the brain. The researchers interpret the spikes in activity as increases in neuronal activation, providing scientific evidence that our cell phones are affecting our brains.

Although no justified claims can be made between this study’s observed brain activity increase and brain cancer of other pathology, the results show that cell phones do have an observable effect on our brains. The authors suggest that further study is needed to elucidate the mechanism by which electric fields stimulate increased brain activity, and that the link between electric fields and neuronal excitation must be corroborated. The researchers are not sure of the implications of this observed increase in neural activation, positive or negative, but research must be continued in this area so we can learn how our technology is affecting our brains. The areas affected included those for decision making and sensory awareness, but it is unclear how activation of such areas can effect behavior or thought. Do cell phones make us impulsive? Do they make us hyper-sensitized or unaware of our other surroundings? What can you do? If this study has alarmed you, one of those headsets would work wonders – just be prepared to look like you’re talking to yourself on the street!

Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism – JAMA