Big brain evolution: adult neurogenesis? II (Evolution)

by David Turell @, Thursday, March 08, 2018, 22:00 (109 days ago) @ David Turell

New research casts doubt on much adult development of new neurons in one area:

There are many doubters about this new study, who did a different type of study in the past:

"The observation that the human brain churns out new neurons throughout life is one of the biggest neuroscience discoveries of the past 20 years. The idea has captured immense popular and scientific interest—not least, because of hopes the brain’s regenerative capacity might be harnessed to boost cognition or to treat injury or disease. In nonhuman animals the continued production of new neurons has been linked to improved learning and memory, and possibly even mood regulation.

"But new findings in humans, reported online in Nature on Wednesday, pump the brakes on this idea. In a direct challenge to earlier studies, the authors report adults produce no new cells in the hippocampus, a key hub for processing memories.


"Yet others argue it is too early to change course based on the new results. Jonas Frisén, senior author of the 2013 study, stands by his original findings. “Since it is a rare phenomenon they are looking for, they may just not have looked carefully enough,” he says. The 1,400 neurons Frisén’s team estimated arise daily comprise a small fraction of the tens of millions of hippocampal cells. To find them, his group at the Karolinska Institute in Stockholm studied people who were exposed to cold war nuclear bomb testing, and incorporated a radioactive carbon isotope into their dividing cells over many years. This cumulative measure, Frisén argues, can detect neurogenesis better than antibodies that label new neurons at a single time point.

"The U.C.S.F.-led group is “not really measuring neurogenesis in this study,” adds neuroscientist Fred Gage at the Salk Institute for Biological Studies. “Neurogenesis is a process, not an event. They just took dead tissue and looked at it at that moment in time.” In their seminal 1998 study Gage and his colleagues studied the brains of people who had received as part of cancer treatment an imaging molecule that became integrated into the DNA of actively dividing cells. Gage also believes the authors used overly restrictive criteria for counting neural progenitor cells, further reducing the chances of seeing them in adults. Far from settling the debate, Gage predicts this provocative paper will intensify interest in this area of study. “There will be lots and lots more papers,” he says."

Comment: Reminder, this debate is about a deeper structure than the pre-frontal cortex where most of the brain enlargement in Erectus and afterward occurred. If the pre-frontal cortex in adults cannot produce more neurons, the argument that concepts forced an enlargement of the brain by making new neurons and new networks falls by the wayside. I would trust the earlier studies based on exposure to isotopes more than this study.

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