The correct answer is growth of new neurons
We are able to create new neurons, even in adulthood. The discovery is relatively new, because it was thought that we were born with a certain “neuron bank” that was decreasing with time and that we were not able to increase. However, the latest findings in neuroscience have overturned that belief. Our brain is plastic: we can create different connections and even, in some areas, like the hippocampus, we can make new neurons be born.
