Navigation Links
Neurobiologists find that weak electrical fields in the brain help neurons fire together
Date:2/2/2011

Pasadena, Calif.The brainawake and sleepingis 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 moreand 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 connecteda 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.

Previously, neurobiologists assumed that the fields were capable of affectingand even controllingneural activity only during severe pathological conditions such as epileptic seizures, which induce very strong fields. Few studies, however, had actually assessed the impact of far weakerbut very commonnon-epileptic fields. "The reason is simple," Anastassiou says. "It is very hard to conduct an in vivo experiment in the absence of extracellular fields," to observe what changes when the fields are not around.

To tease out those effects, Anastassiou and his colleagues, including Caltech neuroscientist Christof Koch, the Lois and Victor Troendle Professor of Cognitive and Behavioral Biology and professor of computation and neural systems, focused on strong but slowly oscillating fields, called local field potentials (LFP), that arise from neural circuits composed of just a few rat brain cells. Measuring those fields and their effects required positioning a cluster of tiny electrodes within a volume equivalent to that of a single cell bodyand at distances of less than 50 millionths of a meter from one another.

"Because it had been so hard to position that many electrodes within such a small volume of brain tissue, the findings of our research are truly novel," Anastassiou says. Previously, he explains, "nobody had been able to attain this level of spatial and temporal resolution."

An "unexpected and surprising finding was how already very weak extracellular fields can alter neural activity," he says. "For example, we observed that fields as weak as one millivolt per millimeter robustly alter the firing of individual neurons, and increase the so-called "spike-field coherence"the synchronicity with which neurons fire with relationship to the field."In the mammalian brain, we know that extracellular fields may easily exceed two to three millivolts per millimeter. Our findings suggest that under such conditions, this effect becomes significant."

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 computernot all brain areas show the same level of activation at all times.

"Whether an externally imposed field will impact the brain also depends on which brain area is targeted. During epileptic seizures, pathological fields can be as strong as 100 millivolts per millimetersuch fields strongly entrain neural firing and give rise to super-synchronized states." And that, he adds, suggests that electric field activityeven from external fieldsin certain brain areas, during specific brain states, may have strong cognitive and behavioral effects.

Ultimately, Anastassiou, Koch, and their colleagues would like to test whether ephaptic coupling affects human cognitive processing, and under which circumstances. "I firmly believe that understanding the origin and functionality of endogenous brain fields will lead to several revelations regarding information processing at the circuit level, which, in my opinion, is the level at which percepts and concepts arise," Anastassiou says. "This, in turn, will lead us to address how biophysics gives rise to cognition in a mechanistic mannerand that, I think, is the holy grail of neuroscience."


'/>"/>

Contact: Deborah Williams-Hedges
debwms@caltech.edu
626-395-3227
California Institute of Technology
Source:Eurekalert  

Related biology news :

1. UCLA stem cells scientists make electrically active motor neurons from iPS cells
2. Electrical circuit runs entirely off power in trees
3. 24-carat gold snowflakes improve graphenes electrical properties
4. NJIT electrical engineer Yanchao Zhang receives NSF CAREER Award
5. New tissue-hugging implant maps heart electrical activity in unprecedented detail
6. Stanford researchers find electrical current stemming from plants
7. Tyco International To Pursue Spin-Off of Electrical & Metal Products Business
8. Shock tactics: Bioelectrical therapy for cancer and birth defects?
9. DNA sequence variations linked to electrical signal conduction in the heart
10. Bioengineers provide adult stem cells with simultaneous chemical, electrical and mechanical cues
11. Carnegie Mellon to receive $900,000 from EPA for brownfields research
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Neurobiologists find that weak electrical fields in the brain help neurons fire together
(Date:2/13/2017)... 2017  RSA Conference -- RSA, a Dell Technologies ... to enhance fraud detection and investigation across digital ... Fraud & Risk Intelligence Suite. The new platform ... insights from internal and external sources as well ... customers from targeted cybercrime attacks. "Fraudsters ...
(Date:2/10/2017)... Research and Markets has announced the addition ... and Commercial Aspects" to their offering. ... Biomarkers play an ... for selection of treatment as well for monitoring the results. ... in modern medicine. Biochip/microarray technologies and next generation sequencing are ...
(Date:2/8/2017)... NEW YORK , Feb. 8, 2017 /PRNewswire/ ... an individual,s voice to match it against a ... voice such as pitch, cadence, and tone are ... systems require minimal hardware installation, as most PCs ... remotely for different transactions. Voice recognition biometrics are ...
Breaking Biology News(10 mins):
(Date:2/16/2017)... ANGELES , Feb. 16, 2017   ... ), a clinical-stage biotechnology company developing first-in-class biological ... announced that it has elected to terminate its ... natriuretic peptide receptor agonists, including Cenderitide. ... strategic move as we prioritize our efforts to ...
(Date:2/16/2017)... SAN DIEGO , Feb. 16, 2017 /PRNewswire/ ... and innovative products to treat a variety of ... $5 million Series 1a financing and entered into ... Bank (SVB).  Dermata intends to use the capital ... of making major advancements in the treatment of ...
(Date:2/16/2017)... , Feb. 16, 2017  Rhythm, ... rare genetic deficiencies that result in life-threatening ... a $41 million mezzanine round of financing ... OrbiMed, MPM Capital, New Enterprise Associates, Pfizer ... undisclosed public healthcare investment fund. Rhythm will ...
(Date:2/15/2017)... ... 15, 2017 , ... Park Systems , a leader in Atomic Force ... that drastically boosts productivity with single click reliable nanoscale images, is now available on ... up and taking the image once done manually by the operator producing high quality ...
Breaking Biology Technology: