Science Bytes: A Fresh Look at Dendrites

New research shows that dendrites (shown here in green) are not just passive conduits for electrical currents between neurons.

A fundamental belief in neuroscience has been that neurons are digital devices. They either generate a spike or not. (Our study’s) results show that the dendrites do not behave purely like a digital device. Dendrites do generate digital, all-or-none spikes, but they also show large analog fluctuations that are not all or none. This is a major departure from what neuroscientists have believed for about 60 years.”

– Mayank Mehta, UCLA professor of physics and astronomy, neurology and neurobiology.


Descartes famously said: “I think, therefore I am.” But just how do we think? Does the brain “think” by processing signals digitally the way a computer does, in discrete pulses of binary digits (“bits”). Or does it operate in an old-fashioned analog way?

It turns out that the brain is both digital and analog, according to a recent study by a UCLA team of scientists. The study, led by Mayank Mehta, a physicist and neuroscientist, examined the role of dendrites – the branch-like extensions of neurons – in generating electrical signals in brains of laboratory rats [1]

Dendrites has long been thought to play a passive role compared to the body of neurons (known as soma). The original belief was that most of the electrical impulses are generated by the soma, and that dendrites merely transmit these currents from the neuron’s synapse. To their surprise, the UCLA team found that dendrites generate nearly 10 times more spikes than somas. Moreover, since dendrites make up more than 90 percent of neural tissue, this finding challenges the conventional thinking that animals underutilize their brains.

There’s more. First, because dendrites are nearly 100 times larger in volume than the neuronal centers, the large number of dendritic spikes taking place indicate that the brain has more than 100 times the computational capacity than was previously thought! Second, dendrites can process both digital and analog signals. A long-held belief, now driven by buzz words like Artificial Intelligence, is that the brain is basically a “soft computer” whose workings can be simulated given sufficiently powerful computers and algorithms. The UCLA study completely debunks this idea. The new discovery tells us that if we consider the brain to be a masterpiece of nature (and no one argues with that), it’s also clear that nature has wisely chosen to equip the brain with both digital and analog capabilities. Digital signal processing may be the defining technology of our age, but analog devices (such as hard drives) have one important redeeming feature – they process continuous information which has an infinite number of possible values, the only limitation being the accuracy of the analog device itself.

At the end of the day, we shouldn’t be surprised that nature loves infinity. Infinity confers a richness to life that discrete computation cannot match. We are truly wonderfully made.

Notes:

[1] Mehta is a UCLA professor of physics and astronomy, of neurology and of neurobiology. The study’s other authors are Pascal Ravassard, David Ho, Lavanya Archarya, Ashley Kees and Cliff Vuong, all of UCLA. Funding was provided by the University of California.  The research is reported in the March 9 issue of the journal Science.

[2] A further discussion on the impossibility of simulating the brain by digital computers can be found in Ronald Cicurel and Miguel L. Nicholis, The Relativistic Brain, 2015.

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