Researchers that have studied human hippocampal tissues found no new neurons there.
Even as we were struggling to come to terms with the fact that nerve cells – contrary to what is generally thought – are recoverable, is seems that we shall now take a complete opposite view. In early March 2018 researchers from University of California San Francisco have published the article about neurogenesis in Nature journal – results of their study on hippocampal tissues have planted seed of doubt as to long-standing dispute.
Analysis of 59 hippocampal samples of people of different ages (37 postmortem tissue samples and 22 surgically excised samples from patients who had been treated for epilepsy) has shown that, apparently, new neurons cannot emerge in the brain of adult person.
Thus, it has been found that newborns have an average 1,600 young neurons per square millimeter of brain tissue. However, the samples of hippocampal dentate gyrus from one-year-old children contained fivefold fewer new neurons than it was seen in samples from newborn infants. As children grow older, the number of new neurons is rapidly declining by 23-fold when a child is 7 years of age. When a child is reaching the age of 13 he is followed by a further fivefold decrease. The authors of the study have noticed that by that age neurons seem to be more mature than those of younger children.
Researchers have only about 2.4 new cells per square millimeter and found no evidence of them in the brain tissue of adult person.
Since the late 1990s it was believed that subgranular zone of hippocampus is the centerpiece of “adult” neurogenesis (emergence of new neurons) and therefore this very zone is associated with the “sorting” of memory, learning and new information retaining.
However, the authors of the study acknowledge that despite the extremely thorough analysis of hippocampal tissues conducted by them, it is still very controversial to say that new neurons do not emerge in the adult brain.
Nevertheless, work performed by them, gave rise to new discussions about neurogenesis and brought out lots of new questions. First, this is a serious challenge for experts that dealt with the search for treatment of diseases, with due regard for the constant regeneration of nerve cells. Secondly, if there is no “adult” neurogenesis, then scientists shall understand how it all works smoothly under such conditions and what are the means of obtaining new knowledge.