Everybody knows what the hippocampus is for: memory. And…maybe something about anxiety or depression? Yes – over the last 10 years or so many studies have been published showing that the hippocampus has these two roles and that the mnemonic and emotional functions of the hippocampus are associated with its septal (dorsal) and temporal (ventral) ends, respectively. This new knowledge means that we’ve had to reorient our perspective. What we see when we consider the septal hippocampus may not be the same if we only consider its temporal end. My goal here is not to provide a review of the memory vs. emotional functions of the hippocampus (btw this dichotomy is a vast oversimplification). Instead, I’d like to talk about how people have differentiated these two ends of the hippocampus in their analyses. I’m also happy to showcase a bunch of pretty anatomical images that will probably never be published in a traditional journal article. Continue reading Dorsoventral vs. Septotemporal hippocampus
And here we have the latest, craziest hypothesis of granule cell function. Crazy not because the authors have lost their minds but because the story of the dentate gyrus, where adult neurogenesis occurs, is becoming more peculiar every day. The underlying premise of this paper by Alme et al. (which we will examine later) is that granule neurons go through a critical period during their development when they are more likely to contribute to memory encoding. Here it’s hypothesized that, once the critical period is over, they shut down. Forever. Hundreds of thousands of neurons never to be used again. It’s not every day you get to read such bold and novel ideas. Their hypothesis has similarities with that proposed by Aimone 2006, that adult neurogenesis causes different cohorts of neurons to be immature at different phases of an animal’s life, thereby separating memories according to time. The question here is whether these neurons can be reactivated once their critical period is over. Continue reading Do new neurons go through a critical period and then retire, never to be used again?