According to this framework, continuous neurogenesis results in a combination of buy AP24534 signals from the DG to the CA3 that consists of two separate populations (Figure 3): (1) A population of broadly tuned GCs that weakly encode most of the features of the environment (Figure 3A). By itself, the latter population is most similar to the classic pattern-separating DG network; however, while its encoding may be nearly orthogonal, it may not relay enough information to allow

subsequent discrimination (Figure 2). Likewise, on its own, the first population may contain information about the remembered event, but this information is in a sense “noisy” in that it lacks specificity. Combined, however, the two populations are capable of maximizing

the information encoded while preserving the sparse coding of the overall active population (Figure 3C). We propose that neurogenesis is actually capable of affecting this process in several ways. Clearly, the presence of “hyperexcitable” immature neurons provides a population of broadly tuned neurons, such as shown in Figure 3A. Due to their physiology and low connectivity, these immature neurons will be responsive to a wide range of inputs and overlap considerably with one another. While individually they are PCI-32765 cell line SPTLC1 not as informative as mature cells (by virtue of their responding to many inputs), as a population they can still contain some specificity about their inputs. Importantly, because these neurons are responsive to a wide range of inputs, not as many young neurons

are required to ensure that at least a few are responsive to any potential input to the DG. For this reason, the population of immature neurons does not need to be very large relative to the more sparsely active, sharply tuned mature neurons. Less obvious, but equally as important, is the proposed role of neurogenesis in forming the sharply tuned GC population (Figure 3B). A sparse population is thought to be necessary for memory encoding in the hippocampus: attractor formation in the CA3 requires fairly separate inputs to adequately form memories that do not interfere with one another (Treves and Rolls, 1992). However, although the DG is large relative to other regions, there are not enough neurons available to ensure an ability to encode every possible input that may be experienced. For this reason, the experience-dependent specialization of maturing neurons to features of their environment is important to ensure that the mature GC population consists of neurons that are capable of responding to the key features of most environments.