Health and Medical News and Resources

General interest items edited by Janice Flahiff

Brain Structure Adapts To Environmental Change

From the 14 June 2011 Medical News Today article

Scientists have known for years that neurogenesis takes place throughout adulthood in the hippocampus of the mammalian brain. Now Columbia researchers have found that under stressful conditions, neural stem cells in the adult hippocampus can produce not only neurons, but also new stem cells. The brain stockpiles the neural stem cells, which later may produce neurons when conditions become favorable. This response to environmental conditions represents a novel form of brain plasticity. The findings were published online in Neuron on June 9, 2011….

June 14, 2011 Posted by | Medical and Health Research News | , , , , | Leave a comment

Masked fears: Are fears that are seemingly overcome only hidden?

Masked fears: Are fears that are seemingly overcome only hidden?

One group of nerve cells in the brain controls the fear behaviour (right). This can be suppressed by a second group of nerve cells (left) — but the fear is only masked, and has not disappeared completely. (Credit: Carlos Toledo/Bernstein Center Freiburg)

From the March 18 2011 Science Daily News Item

ScienceDaily (Mar. 20, 2011) — Fear is a natural part of our emotional life and acts as a necessary protection mechanism. However, fears sometimes grow beyond proportions and become difficult to shed. Scientists from Freiburg, Basel and Bordeaux have used computer simulations to understand the processes within the brain during the formation and extinction of fears.

In the current issue of the scientific journal PLoS Computational Biology [full text of article], Ioannis Vlachos from the Bernstein Center Freiburg and colleagues propose for the first time an explanation for how fears that were seemingly overcome are in reality only hidden

The reason for the persistency of fears is that, literally, their roots run deep: Far below the cerebral cortex lies the “amygdala,” which plays a crucial role in fear processes. Fear is commonly investigated in mice by exposing them simultaneously to a neutral stimulus — a certain sound, for example — and an unpleasant one. This leads to the animals being frightened of the sound as well. Context plays an important role in this case: If the scaring sound is played repeatedly in a new context without anything bad happening, the mice shed their fear again. It returns immediately, however, if the sound is presented in the original, or even a completely novel context. Had the mice not unlearned to be frightened after all?

 

March 22, 2011 Posted by | Medical and Health Research News | , , , , | Leave a comment

Rewrite the textbooks (on what neurons can do)

Rewrite the textbooks

From the February 17 2011 Eureka news alert

Complete neuron cell diagram. Neurons (also kn...

Image via Wikipedia (Click on Image to Enlarge)

 

Neurons are complicated, but the basic functional concept is that synapses transmit electrical signals to the dendrites and cell body (input), and axons carry signals away (output). In one of many surprise findings, Northwestern University scientists have discovered that axons can operate in reverse: they can send signals to the cell body, too.

It also turns out axons can talk to each other. Before sending signals in reverse, axons can perform their own neural computations without any involvement from the cell body or dendrites. This is contrary to typical neuronal communication where an axon of one neuron is in contact with another neuron’s dendrite or cell body, not its axon. And, unlike the computations performed in dendrites, the computations occurring in axons are thousands of times slower, potentially creating a means for neurons to compute fast things in dendrites and slow things in axons.

A deeper understanding of how a normal neuron works is critical to scientists who study neurological diseases, such as epilepsy, autism, Alzheimer’s disease and schizophrenia.

The findings are published in the February issue of the journal Nature Neuroscience.***

“We have discovered a number of things fundamental to how neurons work that are contrary to the information you find in neuroscience textbooks,” said Nelson Spruston, senior author of the paper and professor of neurobiology and physiology in the Weinberg College of Arts and Sciences. “Signals can travel from the end of the axon toward the cell body, when it typically is the other way around. We were amazed to see this.”

He and his colleagues first discovered individual nerve cells can fire off signals even in the absence of electrical stimulations in the cell body or dendrites. It’s not always stimulus in, immediate action potential out. (Action potentials are the fundamental electrical signaling elements used by neurons; they are very brief changes in the membrane voltage of the neuron.)

Similar to our working memory when we memorize a telephone number for later use, the nerve cell can store and integrate stimuli over a long period of time, from tens of seconds to minutes. (That’s a very long time for neurons.) Then, when the neuron reaches a threshold, it fires off a long series of signals, or action potentials, even in the absence of stimuli. The researchers call this persistent firing, and it all seems to be happening in the axon.

Spruston and his team stimulated a neuron for one to two minutes, providing a stimulus every 10 seconds. The neuron fired during this time but, when the stimulation was stopped, the neuron continued to fire for a minute.

“It’s very unusual to think that a neuron could fire continually without stimuli,” Spruston said. “This is something new — that a neuron can integrate information over a long time period, longer than the typical operational speed of neurons, which is milliseconds to a second.”

This unique neuronal function might be relevant to normal process, such as memory, but it also could be relevant to disease. The persistent firing of these inhibitory neurons might counteract hyperactive states in the brain, such as preventing the runaway excitation that happens during epileptic seizures.

Spruston credits the discovery of the persistent firing in normal individual neurons to the astute observation of Mark Sheffield, a graduate student in his lab. Sheffield is first author of the paper.

The researchers think that others have seen this persistent firing behavior in neurons but dismissed it as something wrong with the signal recording. When Sheffield saw the firing in the neurons he was studying, he waited until it stopped. Then he stimulated the neuron over a period of time, stopped the stimulation and then watched as the neuron fired later.

“This cellular memory is a novelty,” Spruston said. “The neuron is responding to the history of what happened to it in the minute or so before.”

Spruston and Sheffield found that the cellular memory is stored in the axon and the action potential is generated farther down the axon than they would have expected. Instead of being near the cell body it occurs toward the end of the axon.

Their studies of individual neurons (from the hippocampus and neocortex of mice) led to experiments with multiple neurons, which resulted in perhaps the biggest surprise of all. The researchers found that one axon can talk to another. They stimulated one neuron, and detected the persistent firing in the other unstimulated neuron. No dendrites or cell bodies were involved in this communication.

“The axons are talking to each other, but it’s a complete mystery as to how it works,” Spruston said. “The next big question is: how widespread is this behavior? Is this an oddity or does in happen in lots of neurons? We don’t think it’s rare, so it’s important for us to understand under what conditions it occurs and how this happens.”

###

The title of the paper is “Slow Integration Leads to Persistent Action Potential Firing in Distal Axons of Coupled Interneurons***.” In addition to Spruston and Sheffield, other authors of the paper are Tyler K. Best and William L. Kath, from Northwestern, and Brett D. Mensh, from Harvard Medical School.

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February 18, 2011 Posted by | Uncategorized | , , , , , , | Leave a comment

Neurobiologists find that weak electrical fields in the brain help neurons fire together

Neurobiologists find that weak electrical fields in the brain help neurons fire together
Coordinated behavior occurs whether or not neurons are actually connected via synapses

From a February 2, 2011 Eureka News Alert

Ephaptic coupling leads to coordinated spiking of nearby neurons, as measured using a 12-pipette electrophysiology setup developed in the laboratory of coauthor Henry Markram.

 

Pasadena, Calif.—The brain—awake and sleeping—is awash in electrical activity, and not just from the individual pings of single neurons communicating with each other. In fact, the brain is enveloped in countless overlapping electric fields, generated by the neural circuits of scores of communicating neurons. The fields were once thought to be an “epiphenomenon, a ‘bug’ of sorts, occurring during neural communication,” says neuroscientist Costas Anastassiou, a postdoctoral scholar in biology at the California Institute of Technology (Caltech).

New work by Anastassiou and his colleagues, however, suggests that the fields do much more—and that they may, in fact, represent an additional form of neural communication.

“In other words,” says Anastassiou, the lead author of a paper about the work appearing in the journal Nature Neuroscience,** “while active neurons give rise to extracellular fields, the same fields feed back to the neurons and alter their behavior,” even though the neurons are not physically connected—a phenomenon known as ephaptic coupling. “So far, neural communication has been thought to occur at localized machines, termed synapses. Our work suggests an additional means of neural communication through the extracellular space independent of synapses.”

Extracellular electric fields exist throughout the living brain, though they are particularly strong and robustly repetitive in specific brain regions such as the hippocampus, which is involved in memory formation, and the neocortex, the area where long-term memories are held. “The perpetual fluctuations of these extracellular fields are the hallmark of the living and behaving brain in all organisms, and their absence is a strong indicator of a deeply comatose, or even dead, brain,” Anastassiou explains……

…..

What does that mean for brain computation? “Neuroscientists have long speculated about this,” Anastassiou says. “Increased spike-field coherency may substantially enhance the amount of information transmitted between neurons as well as increase its reliability. Moreover, it has been long known that brain activity patterns related to memory and navigation give rise to a robust LFP and enhanced spike-field coherency. We believe ephaptic coupling does not have one major effect, but instead contributes on many levels during intense brain processing.”

Can external electric fields have similar effects on the brain? “This is an interesting question,” Anastassiou says. “Indeed, physics dictates that any external field will impact the neural membrane. Importantly, though, the effect of externally imposed fields will also depend on the brain state. One could think of the brain as a distributed computer—not all brain areas show the same level of activation at all times……

 

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February 3, 2011 Posted by | Medical and Health Research News | , , , , , | Leave a comment

Learn more quickly by transcranial magnetic brain stimulation

Learn more quickly by transcranial magnetic brain stimulation
Researchers in Bochum examine the effect of TMS

Top: Brain slice preparation through the frontal cortex of a rat showing nerve cells containing Parvalbumin (colored red) and surrounded by a perineural network (colored green) in untreated animals.
Bottom: After treating the animals with the iTBS protocol, the Parvalbumin has disappeared to a great extent. The perineural network labeled by green dye that the cells still exist, but have not been destroyed by the stimulation.

From the January 28, 2011 Eureka news alert

What sounds like science fiction is actually possible: thanks to magnetic stimulation, the activity of certain brain nerve cells can be deliberately influenced. What happens in the brain in this context has been unclear up to now. Medical experts from Bochum under the leadership of Prof. Dr. Klaus Funke (Department of Neurophysiology) have now shown that various stimulus patterns changed the activity of distinct neuronal cell types. In addition, certain stimulus patterns led to rats learning more easily. The knowledge obtained could contribute to cerebral stimulation being used more purposefully in future to treat functional disorders of the brain. The researchers have published their studies in the Journal of Neuroscience ***and in the European Journal of Neuroscience.***

Magnetic pulses stimulate the brain

Transcranial magnetic stimulation (TMS) is a relatively new method of pain-free stimulation of cerebral nerve cells. The method, which was presented by Anthony Barker for the first time in 1985, is based on the fact that the cortex, the rind of the brain located directly underneath the skull bone, can be stimulated by means of a magnetic field. TMS is applied in diagnostics, in fundamental research and also as a potential therapeutic instrument. Used in diagnostics, one single magnetic pulse serves to test the activability of nerve cells in an area of the cortex, in order to assess changes in diseases or after consumption of medications or also following a prior artificial stimulation of the brain. One single magnetic pulse can also serve to test the involvement of a certain area of the cortex in a sensorial, motoric or cognitive task, as it disturbs its natural activity for a short period, i.e. “switches off” the area on a temporary basis.

Repeated stimuli change cerebral activity

Since the mid-1990’s, repetitive TMS has been used to make purposeful changes to the activability of nerve cells in the human cortex: “In general, the activity of the cells drops as a result of a low-frequency stimulation, i.e. with one magnetic pulse per second. At higher frequencies from five to 50 pulses per second, the activity of the cells increases”, explained Prof. Funke. Above all, the researchers are specifically addressing with the effects of specific stimulus patterns like the so-called theta burst stimulation (TBS), in which 50 Hz bursts are repeated with 5 Hz. “This rhythm is based on the natural theta rhythm of four to seven Hertz which can be observed in an EEG“, says Funke. The effect is above all dependent on whether such stimulus patterns are provided continuously (cTBS, attenuating effect) or with interruptions (intermittent, iTBS, strengthening effect).

Contact points between cells are strengthened or weakened

It is unknown to a great extent how precisely the activity of nerve cells is changed by repeated stimulation. It is assumed that the contact points (synapses) between the cells are strengthened (synaptic potentation) or weakened (synaptic depression) as a result of the repeated stimulation, a process which also plays an important role in learning. Some time ago, it was also shown that the effects of TMS and learning interact in humans.

Inhibitory cortical cells react particularly sensitive to stimulation

The researchers in Bochum have now shown for the first time that an artificial cortex stimulation specifically changes the activity of certain inhibitory nerve cells as a function of the stimulus protocol used. The balanced interaction of excitatory and inhibitory nerve cells is the absolute prerequisite for healthy functioning of the brain. Nerve cells specialised in inhibition of other nerve cells show a much greater variety in terms of cell shape and activity structure than their excitatory counterparts. Amongst other things, they produce various functional proteins in their cell body. In his studies, Prof. Funke has concentrated on the examination of the proteins Parvalbumin (PV), Calbindin-D28k (CB) and Calretinin (CR). They are formed by various inhibitory cells as a function of activity, with the result that their quantity gives information about the activity of the nerve cells in question.

Stimulus patterns act specifically on certain cells

For example, the examinations showed that activating stimulation protocol (iTBS) almost only reduces the PV content of the cells, whereas continuous stimulation attenuating activity (cTBS protocol), or a likewise attenuating 1 Hz stimulation, mainly reduces the CB production. CR formation was not changed by any of the tested stimulus protocols. Registration of the electrical activity of nerve cells confirmed a change in inhibition of the cortical activity.

Learning more quickly after stimulation

In a second study, recently published in the European Journal of Neuroscience, Prof. Funke’s group was able to show that rats also learned more quickly if they were treated with the activating stimulus protocol (iTBS) before each training, but not if the inhibiting cTBS protocol has been used. It was seen that the initially reduced formation of the protein Parvalbumin (PV) was increased again by the learning procedure, but only in the areas of the brain involved in the learning process. For animals not involved in the specific learning task, production of PV remained reduced following iTBS. “The iTBS treatment therefore initially reduces the activity of certain inhibiting nerve cells more generally, with the result that the following learning activities can be stored more easily,” concludes Prof. Funke. “This process is termed “gating”. In a second step, the learning activity restores the normal inhibition and PV production.”

More purposeful treatment in future

Repetitive TMS is already being used in clinical trials with limited success for therapy of functional disorders of the brain, above all in severe depressions. In addition, it was shown that especially disorders of the inhibitory nerve cells play an important role in neuropsychiatric diseases such as schizophrenia. “It is doubtless too early to derive new forms of treatment of functional disorders of the brain from the results of our study, but the knowledge obtained provides an important contribution for a possibly more specific application of TMS in future”, is Prof. Funke’s hope.

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Related article

Learning causes structural changes in affected neurons
When a laboratory rat learns how to reach for and grab a food pellet — a pretty complex and unnatural act for a rodent — the acquired knowledge significantly alters the structure of the specific brain cells involved, which sprout a whopping 22 percent more dendritic spines connecting them to other motor neurons.

January 31, 2011 Posted by | Medical and Health Research News | , , , , , , | Leave a comment

   

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