Although they only account for a fraction of the synapses in the visual cortex, neurons in the thalamus get their message across loud and clear by coordination -- simultaneously hitting the "send" button—according to a computer simulation developed by researchers at the Salk Institute for Biological Studies.
Their findings may hold important clues to how the brain encodes and processes information, which can be applied to a wide variety of applications, from understanding psychiatric disorders to the development of novel pharmaceuticals and new ways of handling information by computers or communication networks. The results are published in Science.
Historically, neuroscientists have been limited to recording the activity of single brain cells, which led to the widely accepted view that neurons communicate with each other through volleys of electrical spikes and that they increase the average rate of spiking to "speak up."
This is an image of a spiny stellate cell.
(Photo Credit: This image originally appeared in Churchill et al. BMC Neuroscience 2004 5:43.)
But communication between neurons is not limited to one-on-one interactions. Instead, any given cell receives signals from hundreds of cells, which send their messages through thousands of synapses, specialized junctions that allow signals to pass from one neuron to the next.
"Unfortunately, we don't have the technology yet to actually measure what all these neurons are saying to the recipient cell, which would require recording simultaneously from hundreds of cells, " says graduate student and first author Hsi-Ping Wang. "For this reason, nobody could answer a very basic question that's been puzzling neuroscientist for decades, which is: 'How many neurons or synapses does it take to reliably send a signal from point A to point B?'"
This question is particularly pressing for the thalamus, the central switchboard that processes and distributes incoming sensory information to all parts of the cortex. Thalamic input only accounts for five percent of the signals that so-called spiny stellate cells in the cortex receive, even though they drive a good portion of activity throughout the cerebral cortex.
"That is a paradox," says Howard Hughes Medical Institute investigator Terrence J. Sejnowski, Ph.D., professor and head of the Computational Neurobiology Laboratory. "How can so few synapses have such a big impact? If the average spiking rate were the determining factor, thalamic input would be drowned out by the other 95 percent of the inputs from other cortical cells."
Based on the assumption that the brain cares about the reliability and precision of spikes, Sejnowki's team developed a realistic computer model of a spiny stellate cell and the signals it receives through its roughly 6,000 synapses. "We found that it is not the number of spikes that's relevant but rather how many spikes arrive at the same time," says Sejnowski.
"Surprisingly, our model predicts that it only takes about 30 synapses out of 6,000 firing simultaneously to create extremely reliable signaling," explains Wang, "and our prediction lines up with currently available in vivo measurements and understanding. You could have all 6,000 synapses firing at the same time, but it would be a waste of resources."
The researchers hope that their findings will give them new insight into the holy grail of neurobiology: decoding the neural code or language of the brain. If the eye receives the same visual information under identical conditions over and over again, one would expect that the signal, the series of generated spikes or bits, is essentially the same.
"But it's not known whether that happens under natural conditions, and it's technically very difficult to measure, " says senior researcher and co-author Donald Spencer, Ph.D. "That's where the power of computational neurobiology really comes to bear on otherwise intractable questions."
"Applying theories of engineering to the study of the brain has helped us gain new insight into how neurons communicate with each other," says Wang. "On the other hand, there are certain things that the brain does in unique ways that are completely different from how computers work. A better understanding of the brain allows us the capture these algorithms and could very well affect the things engineers do in everyday life."
Citation: Wang et al.,'Synchrony of Thalamocortical Inputs Maximizes Cortical Reliability', Science, April 2010, 328: 106-109;doi: 10.1126/science.1183108
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Schrödinger's Cat Is Not Just Alive And Dead, He's Both In 2 Places At Once
- Mindfulness Is Not A Waste Of Time
- Case For Moon: Humanity's Gateway To The Solar System - Open Ended Exploration With Planetary Protection At Its Heart
- B0 Meson Lifetime Difference Measured By ATLAS
- Voluntary Birth Control To Stop Climate Change - Or Else
- Arctic Ocean Methane Does Not Reach The Atmosphere
- Sweet Irony: The Environmental Impacts Of GMO Sugar Science Denial
- "this must be mystery, Cat Mystery. lol..."
- "Vampire are not real, and can never be. This stuff is limited to movies only...."
- "Milk is so tasty. Soy, Oy! CO2 is fertilizer for plants. We need more of it. Meat is tasty too..."
- "Both the Pacific Salmon Forum and the Cohen Commission agree there is scant evidence farming salmon..."
- "If interested in an electromagnetic model of the photon structure and its absorption process, as..."
- The Name Game: How Unethical Environmental Groups and Toxic Fanatics Scare You With Words
- Naturopathy: A Pre-holiday Rant
- Misdiagnosis of Dehydration in Older Folks
- The Amazing Things Poo Can Tell Us About Health
- This Dinner Plate Sucks—Literally
- Gwynn’s Appeal to Jury Could Overshadow Medical Science
- New meta-analysis shows ketamine effective against persistent post-surgical pain and could provide major cost-savings globally
- Refusing access to surgery recovery area at a UK hospital unless WHO Safe Surgery Checklist is fully complete
- Investment in energy storage vital if renewables to achieve full potential
- The Lancet Oncology: Teenagers and young adults still fare worse than children for many common cancers, according to Europe-wide
- Coping with active surveillance anxiety in prostate cancer