Popelus

(I am going to sleep now, but tomorrow I'll write a bigger post.) Everytime I follow the citations' chain from articles which talk about the "second wave of synaptogenesis", I see that they end up citating the 1999 seminal paper by Giedd et al., which has been citated almost 4000 times. It was one of the first MRI studies to notice that gray matter volume in the Prefrontal Cortex increases until 12 years of age and then starts decreasing. Here is what Giedd et al. say in that article: I feel like this has been taken too literally by most authors. After this Giedd paper, most papers simply assume that changes in gray matter volume are changes in synaptic density, and therefore they say that there is a second synaptogenesis... because they see that there is a peak of gray matter volume several years after the synaptic density peak that Huttenbacher found histologically (4-5 years).

That would be very nice if you could find the link. I haven't found any refererence saying that synaptic pruning occurs in sleep. The glymphatic system looks really interesting, and it makes sense that it could be related to synaptic pruning (many authors question themselves what happens to the gray matter that decays during synaptic pruning, and perhaps it is removed by the glymphatic system). I'm currently having a new doubt... as I've ran into some papers that state that during adolescence a new "second wave" of synaptogenesis occurs. For instance, in this paper they mention a second surge of synaptogenesis in adolescence. And in this paper (the link will let you download it) it is stated that a "second wave" of synaptogenesis occurs. I've checked all the papers they citate, and none of them seems to say so. I think these two papers I linked are misunderstanding the synaptic rewiring or remodeling that takes place in adolescence, thinking that it's actually a new synaptogenesis. What do you think?

Hello DrmDoc! Thanks for your reply. I do have access to that article and I had it already in my Mendeley database. I've been researching non-stop since I published my original post, and all I have to say is I am disappointed by scientists. Several papers say in their abstracts that they've researched the synaptic pruning process, when actually all they've measured is gray matter volume. Likewise, several papers say that they've researched the myelination process, but all they've measured is white matter volume. As the paper that you quoted states, there are many factors that can alter the white and gray matter volumes. One of the most obvious is intra-cortical myelination, which leads to (when measured) more white matter volume and less gray matter volume. Although white matter volume does keep increasing even into adulthood, several articles disagree on whether myelination is what causes this increase. Check this and this to see opposite results using different indirect techniques to measure myelination separatedly from white matter volume. The first paper finds that myelination does increase and decrease more or less at the same rate as white matter volume. The second paper states that "The MTR results suggest that this growth [in white matter volume of male adolescents] is not related to myelination". Whatever factors underlie growth and decay of white and gray matter volumes, we should clearly stop carelessly assuming that these are the same as myelination/demyelination and synaptogenese/synaptic pruning respectively.

Hello everyone! I'm currently working on the final project of my Psychology's degree, and the topic I've chosen is the relation between the maturation of the PFC and the development of executive functions. As you will see, my work is quite simplistic, as I'm mainly focusing on brain morphology. Although I'm finding very nice papers to work with, there's something that particularly bothers me about the different methods to measure PFC maturation. On the one hand, several studies show that synaptic density peaks at around 4-5 years of age in the PFC. On the other hand, it's widely known that the volume of gray matter peaks at around 11-12 years of age in the PFC. So, I know these two measures are compatible. I know that gray matter volume is only partially related to synaptic density. Gogtay et al. (2004) say: Selemon (2013) also says: Okay, so it seems like the synaptic pruning in the PFC becomes noticeable at around 4-5 years, and at 11-12 years this process speeds up, so much that it leads to a decrease in gray matter volume. However, as I said at the beginning of this post, something about this really bothers me. My question is: What's making the gray matter volume of the PFC steadily increase from 5 to 11 years of age, if synaptic density is decreasing during this period? I couldn't find any papers researching this, although it seems intuitive that it's due to the growth of glial cells and other non-neuronal cells. Most papers either focus on gray matter volume, or on synaptic density, and they hardly ever analyze the factors that account for the differences between these two measures. There must be something that I am missing... Thank you very much! EDIT: found this very interesting article ( http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2762785/ ) that answers my question. Seems like indeed scientists may be overestimating the relation between synaptic density and gray matter volume.