Brain scan (illustrative).
(photo credit: ING IMAGE/ASAP)
The brain learns in a completely different way than what has been thought for seven decades, according to researchers at Bar-Ilan University.
This theory contradicts the most common assumption in neuroscience and will transform our understanding of brain function, said Prof. Ido Kanter of the physics department and the Gonda (Goldschmied) Multidisciplinary Brain Research Center at the Ramat Gan university.
The brain is a complex network containing billions of neurons, where each of these neurons communicates simultaneously with thousands of others via their synapses (structures that allow the nerve cell to pass an electrical or chemical signal to another neuron).
However, the nerve cell actually collects its many synaptic incoming signals through several extremely long ramified “arms” called “dendritic trees.”
Pioneering work by the late Canadian psychologist Prof. Donald Hebb in 1949 suggested that learning occurs in the brain by modifying the strength of the synapses, whereas neurons function as the computational elements in the brain.
This has remained the belief until today.
But using new theoretical results and experiments on neuronal cultures, a group of scientists led by Kanter has shown the 70-year-old central assumption that learning occurs only in the synapses to be erroneous.
In an article recently published in the journal Scientific Reports, the Israeli researchers defy conventional wisdom and show that learning is actually done by several dendrites, similar to the slow-learning mechanism currently attributed to the synapses.
Hebb’s theory has been so deeply rooted in the scientific world for so many years that no one ever proposed such a different approach.
Moreover, synapses and dendrites are connected to the neuron in a series, so the exact localized site of the learning process seemed irrelevant, explained Kanter.
“The newly discovered process of learning in the dendrites occurs at a much faster rate than in the old scenario that suggested learning occurs solely in the synapses.”
The new theory maintains that learning occurs in a few dendrites that are in much closer proximity to the neuron, contrary to the previous notion.
“Does it make sense to measure the quality of air we breathe via many tiny, distant satellite sensors at the elevation of a skyscraper or by using one or several sensors in close proximity to the nose? Similarly, it is more efficient for the neuron to estimate its incoming signals close to its computational unit, the neuron,” said Kanter.
Another important finding of the study is that weak synapses, previously thought to be insignificant even though they comprise the majority of our brain, play an important role in the dynamics of our brain.
They induce oscillations of the learning parameters rather than pushing them to unrealistic fixed extremes, as suggested in the current synaptic learning scenario, the BIU researchers said.
The discovery shows that learning occurs in different sites of the brain and therefore calls for a reevaluation of current treatments for disordered brain functionality.
Therefore, the popular phrase “neurons that fire together wire together” (summarizing Hebb’s hypothesis) must now be rephrased.
In addition, the learning mechanism is at the basis of recently advanced machine-learning and deep-learning achievements.
The change in the learning paradigm opens new horizons for different types of deep-learning algorithms and artificial intelligence-based applications that imitate our brain functions, to take on advanced features at a much faster speed.