Quantifying the behavioural relevance of hippocampal neurogenesis

TL;DR

This study systematically reviews and reanalyzes existing research to quantify how much hippocampal neurogenesis actually influences behavior, finding it has a negligible effect compared to other mechanisms.

Contribution

It applies causal mediation analysis and meta-analysis to rigorously assess the behavioral role of hippocampal neurogenesis, clarifying its true contribution.

Findings

Neurogenesis has a negligible effect on behavior (effect size ~0.15).

Most behavioral effects are explained by other mechanisms.

Meta-analysis increases the precision of the estimated effects.

Abstract

Few studies that examine the neurogenesis--behaviour relationship formally establish covariation between neurogenesis and behaviour or rule out competing explanations. The behavioural relevance of neurogenesis might therefore be overestimated if other mechanisms account for some, or even all, of the experimental effects. A systematic review of the literature was conducted and the data reanalysed using causal mediation analysis, which can estimate the behavioural contribution of new hippocampal neurons separately from other mechanisms that might be operating. Results from eleven eligible individual studies were then combined in a meta-analysis to increase precision (representing data from 215 animals) and showed that neurogenesis made a negligible contribution to behaviour (standarised effect = 0.15; 95% CI = -0.04 to 0.34; p = 0.128); other mechanisms accounted for the majority of experimental effects (standardised effect = 1.06; 95% CI = 0.74 to 1.38; p = 1.7 $\times 10^{-11}$).