Scientists are surprised to find that primate neurons have fewer synapses in the visual cortex than mice

A study analyzing the synapses of individual macaques and mice showed that primate neurons have 2 to 5 times fewer synapses in the visual cortex than mice
.

A study by the University of Chicago and Argonne National Laboratory analyzed more than 15,000 individual synapses in macaques and mice, and found that primate neurons have 2 to 5 times fewer synapses in the visual cortex than in mice.
The difference may be due to the metabolic cost of maintaining synapses
.

Primates are generally considered smarter than mice
.

In a study comparing the levels of synapses in the brains of macaques and mice, researchers found that compared with rodents, primates have much fewer synapses per neuron, whether in the primary visual cortex.
The excitatory neurons in layer /3 are also inhibitory neurons
.

The research team consists of scientists from the laboratories of Dr.
David Friedman from the University of Chicago and Dr.
Narayanan Kasuri from Argonne University.
They use the latest advances in electron microscopy and the existing publicly available data sets , To compare the connectivity of two species
.

After reconstructing the microscope images and measuring the shapes of 107 rhesus monkey neurons and 81 mouse neurons, the researchers identified nearly 6,000 synapses in the rhesus monkey samples and more than 9,700 synapses in the mouse samples
.

Dr.
Gregg Wildenberg, a scientist in the Kasthuri laboratory, said: "The reason for this is surprising is that neuroscientists and ordinary people have a quiet hypothesis that having more neuronal connections means you are smarter
.

After discovering this amazing discovery, Wildenberg contacted Matt Rosen, a graduate student in Friedman's lab, hoping that Rosen could use his computer expertise to better understand the difference in the number of synapses.
And its possible reasons
.

"We have always expected that the synaptic density of primates will be similar to that of rodents, and possibly even higher, because primates have more space and more neurons in their brains.
It was surprising to find that we thought about why primates have fewer neurons than expected
.

This model considers two potential metabolic costs: one is the cost of a single electrical signal sent by a neuron, called an action potential, which is very expensive in terms of energy; the other is the establishment and maintenance of the processes between different cells.
Cost of touching
.

Wildenberg said: "The brain only accounts for 2.
5% of our total body mass, but it requires 20% of the body's total energy
.

The researchers said that this result will help future studies of primates and mice, as well as comparisons between the two
.
Wildenberg said: "Fundamentally, I think all neuroscientists want to understand what makes us humans and what makes us different from other primates and mice
.
" "We are studying connectomics, focusing on Understanding neuroanatomy
at the level of individual connections .
Prior to this, people did not describe well whether there are differences at the level of connections, which may give us clues about how evolution builds different types of brains
.
Every brain is Neurons, each neuron connects and communicates with other neurons in a stereotyped way
.
How does evolution build different kinds of brains under these constraints? You have to study mice, primates, and many others The species can really begin to understand what's going on here
.
"

Rosen also pointed out that understanding the differences between species can help clarify the general principles of the brain to better understand behavior
.
He said: "Comparative methods allow us to think carefully about the anatomy of the brain in the context of the specific behavior of organisms
.
" "No one treats mice and primates in the same way; their behavior is different
.
These pairs The basic observation of the anatomical differences between these two animals may allow us to extract general principles that apply to different species, as well as the uniqueness of each animal
.
"

For example, understanding the density of synapses—especially the ratio of excitatory synapses to inhibitory synapses—can provide information for research on neurological diseases such as Parkinson's disease and autism
.
"If we only measure the excitement/inhibition ratio of mice, and assume that the excitement/inhibition ratio is the same for all species, how will this affect our understanding of this disease?" Wildenberg said
.
"We found primates.
There is a difference in the excitability/inhibition ratio between animals and mice; how do we apply these models to humans, and what does this mean?"

Future research will include studying similar problems during brain development, trying to understand how the number and density of synapses affect neural networks over time, as well as the developmental differences between mice and primates
.

references:

" Primate neuronal connections are sparse in cortex as compared to mouse" by Gregg A.
Wildenberg, Matt R.
Rosen, Jack Lundell, Dawn Paukner, David J.
Freedman and Narayanan Kasthuri, 14 September 2021, Cell Reports .

DOI: 10.
1016/j .
celrep.
2021.
109709