tag:blogger.com,1999:blog-7328490230880147574.post6136220074623376148..comments2024-03-20T05:44:35.593-04:00Comments on Curious Neuroscientist: Young neurons in an old brainReza Shadmehrhttp://www.blogger.com/profile/07179384025713506624noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-7328490230880147574.post-76495349576039404802013-08-27T23:03:48.847-04:002013-08-27T23:03:48.847-04:00"Now it is possible that neurogenesis in the ..."Now it is possible that neurogenesis in the hippocampus is especially high, and other parts of the cerebral cortex may not have such a high turn-over. But the relative youth of the neurons in the hippocampus raises a fundamental question: what is memory if neurons are eliminated and replaced on a daily basis?" <br /><br />There's no paradox. Nearly all of the neurogenesis is in fact limited to the dentage gyrus, a subregion of the hippocampus. This fact is buried kind of deep in the paper you cite (more deeply buried than it should be, I think), and it's a generally accepted fact about neurogenesis now (with the exception of the newborn neurons of the olfactory system). If you subscribe to the idea that neurons in a network that support memory are fixed nodes, then you're just talking about neurons in the other two main sub-regions of the hippocampus. And in fact, those subregions (especially CA3) are the ones that modelers like to imagine are the substrate of memory. Empirically, those CA3 nodes are very fixed - as I think you would conclude they must be.<br /><br />If average neuron age being significantly lower than the human's age seems impossible to square with the idea that all neurogenesis is happening in the dentage gyrus - it's simply because there are so many more neurons in dentage gyrus than in the rest of the hippocampus. The cell type there (granule cells) are just tiny and more numerous - who knows why.. This is how it's possible that (surprisingly) half on the neurons in a human brain are in the much smaller cerebellum - cerebellum is packed with these tiny granule cells (50%, if I remember my brain trivia right).<br /> <br />Some models use the turnover of cells in dentate gyrus as a kind of time-stamp for memories during their formation. .. I don't know though. I'm very fond of the camp that denies LTP as the foundation of memory, anyway. http://www.ncbi.nlm.nih.gov/pubmed/10097007<br /><br />I do like Feynman's musing about constant atom turnover though :) It gives me hope for this notion of uploading the personal library. If the atoms don't need to be the same, the neurons don't need to be the same... maybe you could simulate it all in a big computer. I couldn't agree more - what a horrible waste it is, when so many years of experience and information disappear. Sorry for your loss.<br /><br />Thanks for your post! Thought provoking.Greg Halehttps://www.blogger.com/profile/00738091198701705503noreply@blogger.comtag:blogger.com,1999:blog-7328490230880147574.post-57316578567391753892013-08-26T14:43:48.831-04:002013-08-26T14:43:48.831-04:00Most of us do not remember being born, or much of ...Most of us do not remember being born, or much of anything from the first few years of life. The standard reason given for this is that the hippocampus, the region presumably critical for initially forming autobiographical memories, and the cerebral cortex, the region presumably critical for serving as the eventual storage site, are poorly developed at birth. But that doesn't mean that in infancy our brain is not forming memories. For example, there are memories that babies form when they are in the womb: a 3 day old infant can discriminate between the sounds of his mother and other women, and when given a choice, prefers to hear the sound of his mother. Perhaps we do not usually remember these early experiences because by the time we reach adulthood, there is so much neuronal turnover in the hippocampus. It is possible that if this turnover is not 100%, then some fraction of the very early experiences are still remembered.<br /><br />References<br />Anthony J. DeCasper and William P. Fifer (1980) Of human bonding: Newborns prefer their mothers' voices. Science 208:1174 - 1176.Reza Shadmehrhttps://www.blogger.com/profile/07179384025713506624noreply@blogger.comtag:blogger.com,1999:blog-7328490230880147574.post-87928412399133026752013-08-26T13:29:46.661-04:002013-08-26T13:29:46.661-04:00So I aak you this question: why do I remember bein...So I aak you this question: why do I remember being born?Zenniehttps://www.blogger.com/profile/05815765335808809176noreply@blogger.com