Seeing a supernovae within hours of the explosion
For the first time ever, scientists have gathered direct evidence of a rare Wolf-Rayet star being linked to a specific type of stellar explosion known as a Type IIb supernova. Peter Nugent of the Lawrence Berkeley National Laboratory says they caught this star – a whopping 360 million light years away – just a few hours after it exploded.
Stimulating a particular region in the brain via non-invasive delivery of electrical current using magnetic pulses, called Transcranial Magnetic Stimulation, improves memory, reports a new Northwestern Medicine® study.
The discovery opens a new field of possibilities for treating memory impairments caused by conditions such as stroke, early-stage Alzheimer’s disease, traumatic brain injury, cardiac arrest and the memory problems that occur in healthy aging.
“We show for the first time that you can specifically change memory functions of the brain in adults without surgery or drugs, which have not proven effective,” said senior author Joel Voss, assistant professor of medical social sciences at Northwestern University Feinberg School of Medicine. “This noninvasive stimulation improves the ability to learn new things. It has tremendous potential for treating memory disorders.”
The study was published August 29 in Science.
The study also is the first to demonstrate that remembering events requires a collection of many brain regions to work in concert with a key memory structure called the hippocampus – similar to a symphony orchestra. The electrical stimulation is like giving the brain regions a more talented conductor so they play in closer synchrony.
“It’s like we replaced their normal conductor with Muti,” Voss said, referring to Riccardo Muti, the music director of the renowned Chicago Symphony Orchestra. “The brain regions played together better after the stimulation.”
The approach also has potential for treating mental disorders such as schizophrenia in which these brain regions and the hippocampus are out of sync with each other, affecting memory and cognition.
TMS Boosts Memory
The Northwestern study is the first to show TMS improves memory long after treatment. In the past, TMS has been used in a limited way to temporarily change brain function to improve performance during a test, for example, making someone push a button slightly faster while the brain is being stimulated. The study shows that TMS can be used to improve memory for events at least 24 hours after the stimulation is given.
Finding the Sweet Spot
It isn’t possible to directly stimulate the hippocampus with TMS because it’s too deep in the brain for the magnetic fields to penetrate. So, using an MRI scan, Voss and colleagues identified a superficial brain region a mere centimeter from the surface of the skull with high connectivity to the hippocampus. He wanted to see if directing the stimulation to this spot would in turn stimulate the hippocampus. It did.
“I was astonished to see that it worked so specifically,” Voss said.
When TMS was used to stimulate this spot, regions in the brain involved with the hippocampus became more synchronized with each other, as indicated by data taken while subjects were inside an MRI machine, which records the blood flow in the brain as an indirect measure of neuronal activity.
The more those regions worked together due to the stimulation, the better people were able to learn new information.
How the Study Worked
Scientists recruited 16 healthy adults ages 21 to 40. Each had a detailed anatomical image taken of his or her brain as well as 10 minutes of recording brain activity while lying quietly inside an MRI scanner. Doing this allowed the researchers to identify each person’s network of brain structures that are involved in memory and well connected to the hippocampus. The structures are slightly different in each person and may vary in location by as much as a few centimeters.
“To properly target the stimulation, we had to identify the structures in each person’s brain space because everyone’s brain is different,” Voss said.
Each participant then underwent a memory test, consisting of a set of arbitrary associations between faces and words that they were asked to learn and remember. After establishing their baseline ability to perform on this memory task, participants received brain stimulation 20 minutes a day for five consecutive days.
During the week they also received additional MRI scans and tests of their ability to remember new sets of arbitrary word and face parings to see how their memory changed as a result of the stimulation. Then, at least 24 hours after the final stimulation, they were tested again.
At least one week later, the same experiment was repeated but with a fake placebo stimulation. The order of real stimulation and placebo portions of the study was reversed for half of the participants, and they weren’t told which was which.
Both groups performed better on memory tests as a result of the brain stimulation. It took three days of stimulation before they improved.
“They remembered more face-word pairings after the stimulation than before, which means their learning ability improved,” Voss said. “That didn’t happen for the placebo condition or in another control experiment with additional subjects.”
In addition, the MRI showed the stimulation caused the brain regions to become more synchronized with each other and the hippocampus. The greater the improvement in the synchronicity or connectivity between specific parts of the network, the better the performance on the memory test. “The more certain brain regions worked together because of the stimulation, the more people were able to learn face-word pairings, “ Voss said.
Using TMS to stimulate memory has multiple advantages, noted first author Jane Wang, a postdoctoral fellow in Voss’s lab at Feinberg. “No medication could be as specific as TMS for these memory networks,” Wang said. “There are a lot of different targets and it’s not easy to come up with any one receptor that’s involved in memory.”
“This opens up a whole new area for treatment studies where we will try to see if we can improve function in people who really need it,“ Voss said.
His current study was with people who had normal memory, in whom he wouldn’t expect to see a big improvement because their brains are already working effectively.
“But for a person with brain damage or a memory disorder, those networks are disrupted so even a small change could translate into gains in their function,” Voss said.
In an upcoming trial, Voss will study the electrical stimulation’s effect on people with early-stage memory loss.
Voss cautioned that years of research are needed to determine whether this approach is safe or effective for patients with Alzheimer’s disease or similar disorders of memory.
The descent into Alzheimer’s disease.
A doctor chronicles the signatures of his patient as the disease took hold of her. Our love goes out to anyone who’s dealt with this awful disease in some way.
When we learn, we associate a sensory experience either with other stimuli or with a certain type of behaviour. The neurons in the cerebral cortex that transmit the information modify the synaptic connections that they have with the other neurons. According to a generally-accepted model of synaptic plasticity, a neuron that communicates with others of the same kind emits an electrical impulse as well as activating its synapses transiently. This electrical pulse, combined with the signal received from other neurons, acts to stimulate the synapses. How is it that some neurons are caught up in the communication interplay even when they are barely connected? This is the crucial chicken-or-egg puzzle of synaptic plasticity that a team led by Anthony Holtmaat, professor in the Department of Basic Neurosciences in the Faculty of Medicine at UNIGE, is aiming to solve. The results of their research into memory in silent neurons can be found in the latest edition of Nature.
Learning and memory are governed by a mechanism of sustainable synaptic strengthening. When we embark on a learning experience, our brain associates a sensory experience either with other stimuli or with a certain form of behaviour. The neurons in the cerebral cortex responsible for ensuring the transmission of the relevant information, then modify the synaptic connections that they have with other neurons. This is the very arrangement that subsequently enables the brain to optimise the way information is processed when it is met again, as well as predicting its consequences.
Neuroscientists typically induce electrical pulses in the neurons artificially in order to perform research on synaptic mechanisms.
The neuroscientists from UNIGE, however, chose a different approach in their attempt to discover what happens naturally in the neurons when they receive sensory stimuli. They observed the cerebral cortices of mice whose whiskers were repeatedly stimulated mechanically without an artificially-induced electrical pulse. The rodents use their whiskers as a sensor for navigating and interacting; they are, therefore, a key element for perception in mice.
An extremely low signal is enough
By observing these natural stimuli, professor Holtmaat’s team was able to demonstrate that sensory stimulus alone can generate long-term synaptic strengthening without the neuron discharging either an induced or natural electrical pulse. As a result – and contrary to what was previously believed – the synapses will be strengthened even when the neurons involved in a stimulus remain silent.In addition, if the sensory stimulation lasts over time, the synapses become so strong that the neuron in turn is activated and becomes fully engaged in the neural network. Once activated, the neuron can then further strengthen the synapses in a forwards and backwards movement. These findings could solve the brain’s “What came first?” mystery, as they make it possible to examine all the synaptic pathways that contribute to memory, rather than focusing on whether it is the synapsis or the neuron that activates the other.
The entire brain is mobilised
A second discovery lay in store for the researchers. During the same experiment, they were also able to establish that the stimuli that were most effective in strengthening the synapses came from secondary, non-cortical brain regions rather than major cortical pathways (which convey actual sensory information). Accordingly, storing information would simply require the co-activation of several synaptic pathways in the neuron, even if the latter remains silent. These findings may also have important implications both for the way we understand learning mechanisms and for therapeutic possibilities, in particular for rehabilitation following a stroke or in neurodegenerative disorders. As professor Holtmaat explains: “It is possible that sensory stimulation, when combined with another activity (motor activity, for example), works better for strengthening synaptic connections”. The professor concludes: “In the context of therapy, you could combine two different stimuli as a way of enhancing the effectiveness.”
Makes sense why some walk whilst studying
While reading, children and adults alike must avoid confusing mirror-image letters (like b/d or p/q). Why is it difficult to differentiate these letters? When learning to read, our brain must be able to inhibit the mirror-generalization process, a mechanism that facilitates the recognition of…
When you’re expecting something—like the meal you’ve ordered at a restaurant—or when something captures your interest, unique electrical rhythms sweep through your brain.
These waves are called gamma oscillations and they reflect a symphony of cells—both excitatory and inhibitory—playing together in an orchestrated way. Though their role has been debated, gamma waves have been associated with higher-level brain function, and disturbances in the patterns have been tied to schizophrenia, Alzheimer’s disease, autism, epilepsy and other disorders.
Now, new research from the Salk Institute shows that little known supportive cells in the brain known as astrocytes may in fact be major players that control these waves.
In a study published July 28 in the Proceedings of the National Academy of Sciences, Salk researchers report a new, unexpected strategy to turn down gamma oscillations, by disabling not neurons but astrocytes—cells type traditionally thought to provide more of a support role in the brain. In the process, the team showed that astrocytes, and the gamma oscillations they help shape, are critical for some forms of memory.
"This is what could be called a smoking gun," says co-author Terrence Sejnowski, head of the Computational Neurobiology Laboratory at the Salk Institute for Biological Sciences and a Howard Hughes Medical Institute investigator. "There are hundreds of papers linking gamma oscillations with attention and memory, but they are all correlational. This is the first time we have been able to do a causal experiment, where we selectively block gamma oscillations and show that it has a highly specific impact on how the brain interacts with the world."
A collaboration among the labs of Salk professors Sejnowski, Inder Verma and Stephen Heinemann found that activity in the form of calcium signaling in astrocytes immediately preceded gamma oscillations in the brains of mice. This suggested that astrocytes, which use many of the same chemical signals as neurons, could be influencing these oscillations.
To test their theory, the group used a virus carrying tetanus toxin to disable the release of chemicals released selectively from astrocytes, effectively eliminating the cells’ ability to communicate with neighboring cells. Neurons were unaffected by the toxin.
After adding a chemical to trigger gamma waves in the animals’ brains, the researchers found that brain tissue with disabled astrocytes produced shorter gamma waves than in tissue containing healthy cells. And after adding three genes that would allow the researchers to selectively turn on and off the tetanus toxin in astrocytes at will, they found that gamma waves were dampened in mice whose astrocytes were blocked from signaling. Turning off the toxin reversed this effect.
The mice with the modified astrocytes seemed perfectly healthy. But after several cognitive tests, the researchers found that they failed in one major area: novel object recognition. A healthy mouse spent more time with a new item placed in its environment than it did with familiar items, as expected.
In contrast, the group’s new mutant mouse treated all objects the same. “That turned out to be a spectacular result in the sense that novel object recognition memory was not just impaired, it was gone—as if we were deleting this one form of memory, leaving others intact,” Sejnowski says.
The results were surprising, in part because astrocytes operate on a seconds- or longer timescale whereas neurons signal far faster, on the millisecond scale. Because of that slower speed, no one suspected astrocytes were involved in the high-speed brain activity needed to make quick decisions.
"What I thought quite unique was the idea that astrocytes, traditionally considered only guardians and supporters of neurons and other cells, are also involved in the processing of information and in other cognitive behavior," says Verma, a professor in the Laboratory of Genetics and American Cancer Society Professor.
It’s not that astrocytes are quick—they’re still slower than neurons. But the new evidence suggests that astrocytes are actively supplying the right environment for gamma waves to occur, which in turn makes the brain more likely to learn and change the strength of its neuronal connections.
Sejnowski says that the behavioral result is just the tip of the iceberg. “The recognition system is hugely important,” he says, adding that it includes recognizing other people, places, facts and things that happened in the past. With this new discovery, scientists can begin to better understand the role of gamma waves in recognition memory, he adds.
An evolutionarily ancient and tiny part of the brain tracks expectations about nasty events, finds new UCL research.
The study, published in Proceedings of the National Academy of Sciences, demonstrates for the first time that the human habenula, half the size of a pea, tracks predictions…