“As the stories of BDNF and exercise developed in parallel, it became clear that BDNF was important not merely for the survival of neurons but also for their growth (sprouting new branches) and thus for learning. Eero Castrén, as well as Susan Patterson from Kandel’s lab at Columbia, found that if you stimulate LTP in mice by making them learn, BDNF levels increase. Looking inside their brains, researchers determined that mice without BDNF lose their capacity for LTP; conversely, injecting BDNF directly into the brains of rats encouraged LTP.”