By following the activity of individual neurons in the heart of the brain, researchers believe they have discovered a significant difference between humans and other primates. This difference could partly explain the origin of our intelligence, but also several psychiatric disorders.
What makes the human brain so unique compared to other great apes is a central question in many studies. For decades, several important differences have been observed. Size is one of the most obvious factors, a human brain being on average three times larger than that of a chimpanzee.
There are also genetic differences as well as molecules expressed by the brain. Some neurotransmitters, such as dopamine, are found in higher concentrations in humans than in other great apes.
Israeli researchers have discovered a new element that could provide an explanation. By following the workings of individual neurons across the brain, they have shown that the secret of our intelligence could lie in the functioning of the neurons themselves.
More surprisingly, the characteristics that could have given us our intelligence could also be at the source of several psychiatric disorders, ranging from anxiety to post-traumatic stress disorder.
Follow the thought to a neuron near
For their comparison, the researchers looked at two important areas of the brain, both in humans and in macaque monkeys. The first is the cingulate cortex, a region responsible for several complex behaviors related in particular to the analysis of information and learning. The other is the amygdala, a region essential for emotional reactions, such as fear, as well as for memory.
To verify the differences between the neuronal functions of these regions, the researchers used an extremely delicate technique: recording the activity of individual neurons.
In humans, this method is sometimes used to determine the point of epileptic seizures in patients who do not respond to medication. This is done by implanting electrodes at various points in the brain to wait for the onset of a seizure to trace the origin of the electrical signals.
The researchers obtained electrical signal data from 750 neurons across the two regions of interest in seven patients who agreed to participate in the study during their follow-up. They then compared them to the signals obtained from five macaque monkeys.
Two properties interested scientists. The first was the robustness of the signal, that is, how much a signal traveled a path stably, repeatedly, and quickly. The other was efficiency, that is, the ability of a signal to spread through a large number of neurons and to multiply the possible responses.
Bugs in the system
By tracking how information moved in the brain, neuron by neuron, researchers found that human neurons sent signals more efficiently than those of monkeys or other primates, an observation confirming our greater ability to think. .
This advantage is not without consequence, because the researchers also noticed that the human signals were much less robust than in the monkeys.
This difference in signal quality explains the difference in response between our species. For example, the monkey will respond to a fear stimulus with a faster escape than a human who, for his part, will analyze the situation further before reacting. For researchers, the human brain may have sacrificed some of its robustness to increase its efficiency during the development of our intelligence.
However, according to the researchers, this difference increases the risk of errors in the human brain compared to that of other monkeys, errors that in brain regions related to emotions and memory, could lead to the appearance of survival reactions in inappropriate contexts, such as what happens in cases of high anxiety, depression or even post-traumatic stress.
At present, however, this conclusion is only a hypothesis. This one will have to be confirmed by other measures of brain activity, this time, while human and monkey carry out similar activities. However, it opens the door to a better understanding of the brain, which could eventually lead to new lines of treatment.