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Unique Processing During a Period of High Excitation/Inhibition Balance in Adult-Born Neurons

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Science  09 Mar 2012:
Vol. 335, Issue 6073, pp. 1238-1242
DOI: 10.1126/science.1214956

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Neurogenesis and Pattern Integration

The adult hippocampus continuously produces new neurons that integrate into the dentate gyrus network and contribute to information processing. What features of adult-born neurons are important for information processing in the dentate gyrus? Marín-Burgin et al. (p. 1238, published online 26 January; see the Perspective by Kempermann) labeled newborn neurons and used sophisticated electrophysiological and imaging techniques to show that immature neurons integrated a broader variety of synaptic inputs from different origins compared with mature neurons, which were highly input specific. Thus, immature neurons may represent a population of integrators that are broadly tuned during a transient period and may encode most features of incoming information. After maturation, new granule cells display a high activation threshold and input specificity to become good pattern separators.

Abstract

The adult dentate gyrus generates new granule cells (GCs) that develop over several weeks and integrate into the preexisting network. Although adult hippocampal neurogenesis has been implicated in learning and memory, the specific role of new GCs remains unclear. We examined whether immature adult-born neurons contribute to information encoding. By combining calcium imaging and electrophysiology in acute slices, we found that weak afferent activity recruits few mature GCs while activating a substantial proportion of the immature neurons. These different activation thresholds are dictated by an enhanced excitation/inhibition balance transiently expressed in immature GCs. Immature GCs exhibit low input specificity that switches with time toward a highly specific responsiveness. Therefore, activity patterns entering the dentate gyrus can undergo differential decoding by a heterogeneous population of GCs originated at different times.

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