A group of Swedish and Italian researchers recently found that most parts of the brain are involved in processing signals arising from touch. Thus they determined that the brain does not operate like a set of switches, as we used to think:
“We immediately realised that our findings deviated strongly from the accepted view that different parts of the brain are responsible for different specific functions,” says Henrik Jörntell, one of the researchers behind the study…
“According to a prevailing view of the brain, known as functional localisation, the brain works like a set of switches: different parts of the brain are responsible for different functions. This theory is certainly easy to comprehend, but when we measure the activity levels in individual neurons, we get a different picture, which indicates that functions are in fact processed more globally by the whole brain,” says Henrik Jörntell.
The experiment, conducted on anesthetized rats, may help us understand brain injury better:
“Each individual neuron is involved in a large number of different functions. As it is closely tied to a very large number of other neurons, the function that one neuron has in a specific situation will be determined by what the other neurons with which it is connected are doing at the time,” says Henrik Jörntell.
He thinks this could explain the previously baffling observation that minor brain injuries or loss of neurons often go unnoticed.
“The brain’s network learns to solve the same tasks by creating partly new collaborative groups of neurons, which enables it to bypass damaged neural tissue with no measurable loss of function. I believe that these findings could mean a new world of promising treatment potential for many different conditions. As there is often an extensive latent brain capacity left in cases of major brain injury, one can imagine that a greater recovery could be achieved if we could teach the brain to form new collaborative groups of neurons,” says Henrik Jörntell.
Paper. (open access) – Jonas M.D. Enander, Henrik Jörntell. Somatosensory Cortical Neurons Decode Tactile Input Patterns and Location from Both Dominant and Non-dominant Digits. Cell Reports, 2019; 26 (13): 3551 DOI: 10.1016/j.celrep.2019.02.099 More.
The image of the human brain operating as a series of switches makes its way into discussions of AI projects where the machines do operate that way:
Researchers at the U.S. National Institute of Standards and Technology (NIST) explain that, much like a biological brain, the switch “learns” by processing the electrical signals it receives and producing appropriate output signals. The process mirrors the function of biological synapses in the brain, which allow neurons to communicate with each other.
Lou Del Bello, “Scientists Are Closer to Making Artificial Brains That Operate Like Ours Do” at Futurism
But not only do new findings shake up old assumptions, some longstanding questions have been hotly contested recently, like whether the adult human brain creates new neurons:
In 1928, Santiago Ramón y Cajal, the father of modern neuroscience, proclaimed that the brains of adult humans never make new neurons. “Once development was ended,” he wrote, “the founts of growth and regeneration … dried up irrevocably. In the adult centers the nerve paths are something fixed, ended and immutable. Everything must die, nothing may be regenerated.”
Ed Yong, “Do Adult Brains Make New Neurons? A Contentious New Study Says No” at The Atlantic
More recent evidence suggested otherwise and the view shifted to a more promising one for treatments:
Humans continue to produce new neurons in a part of their brain involved in learning, memory and emotion throughout adulthood, scientists have revealed, countering previous theories that production stopped after adolescence. The findings could help in developing treatments for neurological conditions such as dementia.
Many new neurons are produced in the hippocampus in babies, but it has been a matter of hot debate whether this continues into adulthood – and if so, whether this rate drops with age as seen in mice and nonhuman primates.
Nicola Davis, “Humans produce new brain cells throughout their lives” at The Guardian
And then, thanks to a recent study, back again:
In a new study, and one of the biggest yet, a team led by Arturo Alvarez-Buylla at the University of California at San Francisco completely failed to find any trace of young neurons in dozens of hippocampus samples, collected from adult humans. “If neurogenesis continues in adult humans, it’s extremely rare,” says Alvarez-Buylla. “It’s not as robust as what people have said, where you could go running and pump up the number of neurons.”
Ed Yong, “Do Adult Brains Make New Neurons? A Contentious New Study Says No” at The Atlantic
But wait! Yet another recent study (open access) says, yes, the adult human brain does grow new neurons:
Now another group of scientists have published research that pushes back, revealing the new neurons are produced in this brain region in human adults and does not drop off with age. The findings, they say, could help in the hunt for ways to treat conditions ranging from Alzheimer’s to psychiatric problems.
“The exciting part is that the neurons are there throughout a lifetime,” said Dr Maura Boldrini from Columbia University in New York and first author of the new study published in the journal Cell Stem Cell. “It seems that indeed humans are different from mice – where [neuron production] goes down with age really fast – and this could mean that we need these neurons for our complex learning abilities and cognitive behavioural responses to emotions,” she said.
Nicola Davis, “Humans produce new brain cells throughout their lives” at The Guardian
Sounds quite a tangle.
The bottom line is that when we read, for example, that “Scientists Are Closer to Making Artificial Brains That Operate Like Ours Do” (as above), we might ask: If career researchers dispute the question of how the brain works at basic levels, how can non-experts be so sure they have replicated it?
Maybe it’s worse than they fear. Perhaps the brain doesn’t and can’t operate like a piece of machinery at all. And vice-versa.
See also: Brains are not billions of little computers
and
Researchers identify a new form of brain communication