(Image caption: Astrocyte activity is shown in green in this slice of tissue from the brain region that controls movement in mice. Internal, structural elements of the astrocytes are shown in magenta; cell bodies are in red. Credit: Amit Agarwal and Dwight Bergles, courtesy of Cell Press)

Fight-Or-Flight Chemical Prepares Cells to Shift the Brain From Subdued to Alert State

A new study from The Johns Hopkins University shows that the brain cells surrounding a mouse’s neurons do much more than fill space. According to the researchers, the cells, called astrocytes because of their star-shaped appearance, can monitor and respond to nearby neural activity, but only after being activated by the fight-or-flight chemical norepinephrine. Because astrocytes can alter the activity of neurons, the findings suggest that astrocytes may help control the brain’s ability to focus.

The study involved observing the cells in the brains of living, active mice over long periods of time. A combination of genetically engineered mice and advanced microscopy allowed the researchers to visualize the activity of astrocyte networks in different regions of the brain to learn how these abundant supporting cells are controlled.

The scientists monitored astrocytes in the area of the brain responsible for controlling movement and saw that the cells often increased their activity as the mice walked on treadmills — but not always, and sometimes astrocytes became active when the animals were not moving. This lack of consistency suggested to the researchers that the astrocytes were not responding to nearby neurons, as had been thought.

Similarly, astrocytes in the vision processing area of the brain did not necessarily become active when the mice were stimulated with light, but they were sometimes active, even in the dark. The team solved both mysteries when they tested the idea that the astrocytes needed a signal to “wake them up” before they could respond to nearby neurons. That is how they found that norepinephrine, the brain’s broadly distributed fight-or-flight signal, primes the astrocytes in both locations to “listen in” on nearby neuronal activity.

“Astrocytes are among the most abundant cells in the brain, but we know very little about how they are controlled and how they contribute to brain function,” says Dwight Bergles, Ph.D., professor of neuroscience, who led the study. “Since memory formation and other important functions of the brain require a state of attention, we’re interested in learning more about how astrocytes help create that state.”

For example, Bergles says, “We know that astrocytes can regulate local blood flow, provide energy to neurons and release signaling molecules that alter neuronal activity. They could be doing any or all of those things in response to being activated. It is also possible that they act as a sort of megaphone to broadcast local norepinephrine signals to every neuron in the brain.” Whatever the case may be, researchers now know that astrocytes are not idle loiterers. This ability to study astrocyte network activity in animals as they do different things will help to reveal how these cells contribute to brain function.

This research was published in the journal Neuron on June 18.

Training brain patterns of empathy using functional brain imaging

An unprecedented research conducted by a group of neuroscientists has demonstrated for the first time that it is possible to train brain patterns associated with empathic feelings – more specifically, tenderness. The research showed that volunteers who received neurofeedback about their own brain activity patterns whilst being scanned inside a functional magnetic resonance (fMRI) machine were able to change brain network function of areas related to tenderness and affection felt toward loved ones. These significant findings could open new possibilities for treatment of clinical situations, such as antisocial personality disorder and postpartum depression.

In Ridley Scott’s film “Blade Runner”, based on the science fiction book ‘Do androids dream of electric sheep?’ by Philip K. Dick, empathy-detection devices are employed to measure tenderness or affection emotions felt toward others (called “affiliative” emotions). Despite recent advances in neurobiology and neurotechnology, it is unknown whether brain signatures of affiliative emotions can be decoded and voluntarily modulated.

The article entitled “Voluntary enhancement of neural signatures of affiliative emotion using fMRI neurofeedback” published in PLOS ONE is the first study to demonstrate through a neurotechnology tool, real-time neurofeedback using functional Magnetic Resonance Imaging (fMRI), the possibility to help the induction of empathic brain states.

The authors conducted this research at the D’Or Institute for Research and Education where a sophisticated computational tool was designed and used to allow the participants to modulate their own brain activity related to affiliative emotions and enhance this activity. This method employed pattern-detection algorithms, called “support vector machines” to classify complex activity patterns arising simultaneously from tenths of thousands of voxels (the 3-D equivalent of pixels) inside the participants’ brains.

Volunteers who received real time information of their ongoing neural activity could change brain network function among connected areas related to tenderness and affection felt toward loved ones, while the control group who performed the same fMRI task without neurofeedback did not show such improvement.

Thus, it was demonstrated that those who received a “real” feedback were able to “train” specific brain areas related to the experience of affiliative emotions that are key for empathy. These findings can lead the way to new opportunities to investigate the use of neurofeedback in conditions associated with reduced empathy and affiliative feelings, such as antisocial personality disorders and post-partum depression.

The authors point out that this study may represent a step towards the construction of the ‘empathy box’, an empathy-enhancing machine described by Philip K. Dick’s novel.

Neuroscience’s grand question

When your car needs a new spark plug, you take it to a shop where it sits, out of commission, until the repair is finished. But what if your car could replace its own spark plug while speeding down the Mass Pike? 

Of course, cars can’t do that, but our nervous system does the equivalent, rebuilding itself continually while maintaining full function. 

Neurons live for many years but their components, the proteins and molecules that make up the cell, are continually being replaced. How this continuous rebuilding takes place without affecting our ability to think, remember, learn or otherwise experience the world is one of neuroscience’s biggest questions.

And it’s one that has long intrigued Eve Marder, the Victor and Gwendolyn Beinfield Professor of Neuroscience. As reported in Neuron on May 21, Marder’s lab has built a new theoretical model to understand how cells monitor and self-regulate their properties in the face of continual turnover of cellular components.

Ion channels, the molecular gates on the surface of cells, determine neuronal properties needed to regulate everything from the size and speed of limb movement to how sensory information is processed. Different combinations of types of ion channels are found in each kind of neuron. Receptors are the molecular ‘microphones’ that enable neurons to communicate with each other.

Receptors and ion channels are constantly turning over, so cells need to regulate the rate at which they are replaced in a way that avoids disrupting normal nervous system function. Scientists have considered the idea of a ‘factory’ or ‘default’ setting for the numbers of ion channels and receptors in each neuron. But this idea seems implausible because there is so much change in a neuron’s environment over the course of its life. 

If there is no factory setting, then neurons need an internal gauge to monitor electrical activity and adjust ion channel expression accordingly, the team asserts. Because a single neuron is always part of a larger circuit, it also needs to do this while maintaining homeostasis across the nervous system.

The Marder lab built a new theoretical model of ion channel regulation based on the concept of an internal monitoring system. The team, comprised of postdoctoral fellow Timothy O’Leary, lab technician Alex Williams, Alessio Franci, of the University of Liege in Belgium, and Marder, discovered that cells don’t need to measure every detail of activity to keep the system functioning. In fact, too much detail can derail the process. 

“Certain target properties can contradict each other,” O’Leary says. “You would not set your air conditioning to 64 degrees and your heat to 77 degrees. One might win over the other but they would be continually fighting each other and you would end up paying a big energy bill.”

The team also learned that cells can have similar properties but different ion channel expression rates — like cellular homophones, they sound alike but look very different. 

The model showed that the very internal monitoring system designed to control runaway electrical activity can actually lead to neuronal hyperexcitability, the basis of seizures. Even if set points are maintained in single neurons, overall homeostasis in the system can be lost. 

The study represents an important advance in understanding the most complex machinery ever built — the human brain. And it may lead to entirely different therapeutic strategies for treating diseases, O’Leary says. “To understand and cure some diseases, we need to pick apart and understand how biological systems control their internal properties when they are in a normal healthy state, and this model could help researchers do that.”

Structurally-Constrained Relationships between Cognitive States in the Human Brain

The anatomical connectivity of the human brain supports diverse patterns of correlated neural activity that are thought to underlie cognitive function. In a manner sensitive to underlying structural brain architecture, we examine the extent to which such patterns of correlated activity systematically vary across cognitive states. Anatomical white matter connectivity is compared with functional correlations in neural activity measured via blood oxygen level dependent (BOLD) signals. Functional connectivity is separately measured at rest, during an attention task, and during a memory task. We assess these structural and functional measures within previously-identified resting-state functional networks, denoted task-positive and task-negative networks, that have been independently shown to be strongly anticorrelated at rest but also involve regions of the brain that routinely increase and decrease in activity during task-driven processes. We find that the density of anatomical connections within and between task-positive and task-negative networks is differentially related to strong, task-dependent correlations in neural activity. The space mapped out by the observed structure-function relationships is used to define a quantitative measure of separation between resting, attention, and memory states. We find that the degree of separation between states is related to both general measures of behavioral performance and relative differences in task-specific measures of attention versus memory performance. These findings suggest that the observed separation between cognitive states reflects underlying organizational principles of human brain structure and function.

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Illuminating neuron activity in 3-D

Researchers at MIT and the University of Vienna have created an imaging system that reveals neural activity throughout the brains of living animals. This technique, the first that can generate 3-D movies of entire brains at the millisecond timescale, could help scientists discover how neuronal networks process sensory information and generate behavior.

The team used the new system to simultaneously image the activity of every neuron in the worm Caenorhabditis elegans, as well as the entire brain of a zebrafish larva, offering a more complete picture of nervous system activity than has been previously possible.

“Looking at the activity of just one neuron in the brain doesn’t tell you how that information is being computed; for that, you need to know what upstream neurons are doing. And to understand what the activity of a given neuron means, you have to be able to see what downstream neurons are doing,” says Ed Boyden, an associate professor of biological engineering and brain and cognitive sciences at MIT and one of the leaders of the research team. “In short, if you want to understand how information is being integrated from sensation all the way to action, you have to see the entire brain.”

The new approach, described May 18 in Nature Methods, could also help neuroscientists learn more about the biological basis of brain disorders. “We don’t really know, for any brain disorder, the exact set of cells involved,” Boyden says. “The ability to survey activity throughout a nervous system may help pinpoint the cells or networks that are involved with a brain disorder, leading to new ideas for therapies.”

Boyden’s team developed the brain-mapping method with researchers in the lab of Alipasha Vaziri of the University of Vienna and the Research Institute of Molecular Pathology in Vienna. The paper’s lead authors are Young-Gyu Yoon, a graduate student at MIT, and Robert Prevedel, a postdoc at the University of Vienna.

High-speed 3-D imaging

Neurons encode information — sensory data, motor plans, emotional states, and thoughts — using electrical impulses called action potentials, which provoke calcium ions to stream into each cell as it fires. By engineering fluorescent proteins to glow when they bind calcium, scientists can visualize this electrical firing of neurons. However, until now there has been no way to image this neural activity over a large volume, in three dimensions, and at high speed.

Scanning the brain with a laser beam can produce 3-D images of neural activity, but it takes a long time to capture an image because each point must be scanned individually. The MIT team wanted to achieve similar 3-D imaging but accelerate the process so they could see neuronal firing, which takes only milliseconds, as it occurs.

The new method is based on a widely used technology known as light-field imaging, which creates 3-D images by measuring the angles of incoming rays of light. Ramesh Raskar, an associate professor of media arts and sciences at MIT and an author of this paper, has worked extensively on developing this type of 3-D imaging. Microscopes that perform light-field imaging have been developed previously by multiple groups. In the new paper, the MIT and Austrian researchers optimized the light-field microscope, and applied it, for the first time, to imaging neural activity.

With this kind of microscope, the light emitted by the sample being imaged is sent through an array of lenses that refracts the light in different directions. Each point of the sample generates about 400 different points of light, which can then be recombined using a computer algorithm to recreate the 3-D structure.

“If you have one light-emitting molecule in your sample, rather than just refocusing it into a single point on the camera the way regular microscopes do, these tiny lenses will project its light onto many points. From that, you can infer the three-dimensional position of where the molecule was,” says Boyden, who is a member of MIT’s Media Lab and McGovern Institute for Brain Research.

Prevedel built the microscope, and Yoon devised the computational strategies that reconstruct the 3-D images.

Aravinthan Samuel, a professor of physics at Harvard University, says this approach seems to be an “extremely promising” way to speed up 3-D imaging of living, moving animals, and to correlate their neuronal activity with their behavior. “What’s very impressive about it is that it is such an elegantly simple implementation,” says Samuel, who was not part of the research team. “I could imagine many labs adopting this.”

Neurons in action

The researchers used this technique to image neural activity in the worm C. elegans, the only organism for which the entire neural wiring diagram is known. This 1-millimeter worm has 302 neurons, each of which the researchers imaged as the worm performed natural behaviors, such as crawling. They also observed the neuronal response to sensory stimuli, such as smells.

The downside to light field microscopy, Boyden says, is that the resolution is not as good as that of techniques that slowly scan a sample. The current resolution is high enough to see activity of individual neurons, but the researchers are now working on improving it so the microscope could also be used to image parts of neurons, such as the long dendrites that branch out from neurons’ main bodies. They also hope to speed up the computing process, which currently takes a few minutes to analyze one second of imaging data.

The researchers also plan to combine this technique with optogenetics, which enables neuronal firing to be controlled by shining light on cells engineered to express light-sensitive proteins. By stimulating a neuron with light and observing the results elsewhere in the brain, scientists could determine which neurons are participating in particular tasks.

Regulate brain boosting devices so everyone can have a go

Gamers around the world are snapping up a new device that promises to give them an edge on competitors by boosting their gaming focus. It is certainly easy to see the appeal of being able to improve your levels of attention at the push of a colourful, glowing button.

The foc.us device works by electrically stimulating the brain to increase the activity of neurons. More neuron activity, more focus, more winning – or so the manufacturers claim. It is just one product in a growing market of cognitive enhancement devices. All these devices affect the brain in some way, be it by improving your memory, attention, learning speed or another mental process.

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Fast contractions and depolarizations in mitochondria revealed with multiparametric imaging

When something bad happens to otherwise healthy neurons it’s easy to blame the usual suspects—the mitochondria. In some cases the nucleus might be the one at fault, as in a de novo mutation in a critical gene or in some other runaway error process in the instruction pipeline. Other times there could be leakage into the brain of toxins, bacteria, or even overzealous patriot cells of the host. But by and large, it’s the mitochondria who bear responsibility for nearly everything the brain does and so it is they who must accept it when it fails. To better understand how these organelles function, researchers have turned to special imaging methods that let them observe multiple aspects of their behavior all at once.

In one of the most revealing studies of its kind to date, researchers in Germany were able to observe the tiny contractions that mitochondria undergo during their complex shifts through different redox states and levels of depolarization. Publishing in a recent issue of Nature Medicine they relate these effects to pH and calcium concentration in the both the mitochondria and surrounding axon, and also to the larger spiking activity of the neuron.

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Researchers reveal new cause of epilepsy

A team of researchers from Sanford-Burnham and SUNY Downstate Medical Center has found that deficiencies in hyaluronan, also known as hyaluronic acid or HA, can lead to spontaneous epileptic seizures. HA is a polysaccharide molecule widely distributed throughout connective, epithelial, and neural tissues, including the brain’s extracellular space (ECS). Their findings, published on April 30 in The Journal of Neuroscience, equip scientists with key information that may lead to new therapeutic approaches to epilepsy.

The multicenter study used mice to provide the first evidence of a physiological role for HA in the maintenance of brain ECS volume. It also suggests a potential role in human epilepsy for HA and genes that are involved in hyaluraonan synthesis and degradation.

While epilepsy is one of the most common neurological disorders—affecting approximately 1 percent of the population worldwide—it is one of the least understood. It is characterized by recurrent spontaneous seizures caused by the abnormal firing of neurons. Although epilepsy treatment is available and effective for about 70 percent of cases, a substantial number of patients could benefit from a new therapeutic approach.

“Hyaluronan is widely known as a key structural component of cartilage and important for maintaining healthy cartilage. Curiously, it has been recognized that the adult brain also contains a lot of hyaluronan, but little is known about what hyaluronan does in the brain,” said Yu Yamaguchi, M.D., Ph.D., professor in our Human Genetics Program.

“This is the first study that demonstrates the important role of this unique molecule for normal functioning of the brain, and that its deficiency may be a cause of epileptic disorders. A better understanding of how hyaluronan regulates brain function could lead to new treatment approaches for epilepsy,” Yamaguchi added.

The extracellular matrix of the brain has a unique molecular composition. Earlier studies focused on the role of matrix molecules in cell adhesion and axon pathfinding during neural development. In recent years, increasing attention has been focused on the roles of these molecules in the regulation of physiological functions in the adult brain.

In this study, the investigators examined the role of HA using mutant mice deficient in each of the three hyaluronan synthase genes (Has1, Has2, Has3).

“We showed that Has-mutant mice develop spontaneous epileptic seizures, indicating that HA is functionally involved in the regulation of neuronal excitability. Our study revealed that deficiency of HA results in a reduction in the volume of the brain’s ECS, leading to spontaneous epileptiform activity in hippocampal CA1 pyramidal neurons,” said Sabina Hrabetova, M.D., Ph.D., associate professor in the Department of Cell Biology at SUNY.

“We believe that this study not only addresses one of the longstanding questions concerning the in-vivo role of matrix molecules in the brain, but also has broad appeal to epilepsy research in general,” said Katherine Perkins, Ph.D., associate professor in the Department of Physiology and Pharmacology at SUNY.

“More specifically, it should stimulate researchers in the epilepsy field because our study reveals a novel, non-synaptic mechanism of epileptogenesis. The fact that our research can lead to new anti-epileptic therapies based on the preservation of hyaluronan adds further significance for the broader biomedical community and the public,” the authors added.

Studies Identify Spinal Cord Neurons that Control Skilled Limb Movement

Researchers have identified two types of neurons that enable the spinal cord to control skilled forelimb movement. The first is a group of excitatory interneurons that are needed to make accurate and precise movements; the second is a group of inhibitory interneurons necessary for achieving smooth movement of the limbs. The findings are important steps toward understanding normal human motor function and potentially treating movement disorders that arise from injury or disease.

“We take for granted many motor behaviors, such as catching a ball or flipping a coin, that in fact require considerable planning and precision,” said Columbia University Medical Center’s (CUMC’s) Thomas M. Jessell, PhD, a senior author of both studies, which were published separately in recent issues of Nature (1, 2). “While such motor acts seem effortless, they depend on intricate and carefully orchestrated communication between neural networks that connect the brain to the spinal cord and muscles.”

To move one’s hand to a desired target, the brain sends the spinal cord signals, which activate the motor neurons that control limb muscles. During subsequent movements, information from the limb is conveyed back to the brain and spinal cord, providing a feedback system that can support the control and adjustment of motor output.

“But feedback from muscles is not quick enough to permit the most rapid real-time adjustments of fine motor control,” said Dr. Jessell, “suggesting that there may be other, faster, systems at play.” Dr. Jessell is the Claire Tow Professor of Motor Neuron Disorders in the Departments of Neuroscience and of Biochemistry and Molecular Biophysics, co-director of the Mortimer B. Zuckerman Mind Brain Behavior Institute, co-director of the Kavli Institute for Brain Science, and a Howard Hughes Medical Institute investigator, all at Columbia.

Researchers had suspected that one rapid form of feedback might derive from a group of interneurons in the cervical spinal cord called propriospinal neurons (PNs). Like many other neurons, PNs send signals to motor neurons that innervate arm muscles and trigger movement. But this subset of neurons also has a distinct output branch that projects away from motor neurons towards the cerebellum. Through this dual-branched anatomy, these neurons have the potential to carry internal copies of motor output signals up to the brain.

However, the nature of this internal feedback pathway and whether it has any impact on movement have not been clear. “If PNs were indeed sending copies of outgoing motor commands to the brain, they could provide a conveniently rapid means of adjusting ongoing movements when things go awry,” said Eiman Azim, PhD, a postdoctoral fellow in Dr. Jessell’s lab and lead author of the first paper. “But without a way to selectively target the copy function of PNs, there was no way to test this theory.”

The CUMC team, in collaboration with Bror Alstermark, PhD, a professor in integrative medical biology at Umeå University in Sweden, overcame this technical barrier by developing a genetic method for accessing and eliminating PNs in mice, abolishing both motor-directed and copy signals sent by the neurons. When the researchers quantified the limb movements of the PN-deprived mice in three dimensions as they reached for food pellets, they found that the mice’s ability to reach for the target accurately was badly compromised. “Basically, their movements were uncoordinated,” said Dr. Azim. “The PN-deprived mice consistently over- or under-reached.”

But with both PN output signals gone, the precise role of the PN copy signal remained unclear. The researchers then turned to optogenetics—the use of light to control neuronal activity. They selectively activated the copy axonal branch alone, decalibrating this copy signal from the version sent to motor neurons. With the copy signal altered, the animals’ ability to reach was severely compromised, indicating that the PN copy pathway is capable of influencing the outcome of goal-directed reaching movements.

The PN copy signal also works blazingly fast. It takes just 4 to 5 milliseconds for motor neuron activity to be altered after transmission of a PN copy signal. “These reaching movements typically take 200 to 300 milliseconds, so the PN copy signal pathway appears well equipped to correct arm movements,” said Dr. Azim. The researchers think that this copy signal represents just one of many similar internal feedback pathways that the spinal cord and brain use to validate and correct movements throughout the body.

Are these findings relevant to human motor performance? Many of the pathways and circuits that influence reach and grasp in monkeys and humans are conserved in mice. “We need to learn more about these pathways before we can evaluate how their dysfunction contributes to deficits seen after spinal cord injury and neurodegenerative disease,” said Dr. Azim.

In the second Nature study, CUMC researchers examined how spinal circuits regulate sensory feedback from muscles to control movement. The simplest form of this feedback system involves a reflex pathway (such as the knee-jerk reflex), in which sensory endings in muscles convey signals to the motor system through direct monosynaptic connections with motor neurons. Signals from motor neurons, in turn, cause muscles to contract, completing the reflex cycle.

Researchers have long wondered how the strength of this sensory signal might be regulated. Studies had shown that spinal interneurons—in particular those that release the neurotransmitter GABA, inhibiting neuronal activity—play a key role in this process. But most GABA-releasing interneurons exert their effects postsynaptically, by blocking the excitation of neurons on the receiving end of a synapse (the gap across which two neurons communicate).

“We knew that such neurons are unlikely to be responsible for fine-tuning the sensory signal,” said lead author Andrew J. P. Fink, PhD, a former graduate student in Dr. Jessell’s lab. “Postsynaptic inhibition affects the entire neuron, and motor neurons receive many different inputs. So a mechanism that shut down the motor neuron to all of its inputs would lack refinement.”

Researchers have long speculated that one subset of GABAergic interneurons might regulate movement by controlling the strength of sensory feedback signals from muscles. “These particular neurons are known to work presynaptically, by forming direct connections with the terminals of sensory neurons and suppressing the release of sensory neurotransmitter,” said Dr. Fink. For technical reasons, the function of these interneurons, if any, in motor behavior has remained elusive.

Dr. Fink and his colleagues identified a way to access this subset of interneurons genetically in mice and then devised approaches to manipulate their function in a selective manner. In one experiment, they activated presynaptic inhibitory interneurons optogenetically, decreasing the strength of sensory-motor transmission. They also ablated these interneurons by making them selectively sensitive to a lethal toxin, abolishing their control over sensory feedback strength. Without sensory feedback regulation, forelimb movements were dominated by severe oscillatory tremors, drastically diminishing motor accuracy.

This finding, along with parallel modeling studies, indicates that presynaptic inhibitory neurons normally adjust the “gain” of sensory feedback at synapses with motor neurons and are therefore crucial for the smooth execution of movement. Understanding how these basic microcircuits regulate sensory input and motor output may, in the long run, provide insight into ways to combat the movement instability and tremor seen in many neurological disorders.

“These two studies shed new light on how discrete classes of spinal interneurons empower the nervous system to direct motor behaviors in ways that match the particular task at hand,” said Dr. Jessell.