New brain cell synthesis supports new memories? It isn't that simple.

Several laboratories have performed experiments suggesting that our ability to store new memories might be related to the generation of new nerve cells in the hippocampus, which is essential to forming episodic memories. Now Kandel's laboratory now offers the contrary finding that reducing new nerve cell synthesis can enhance working memory. Their abstract:

To explore the function of adult hippocampal neurogenesis, we ablated cell proliferation by using two independent and complementary methods: (i) a focal hippocampal irradiation and (ii) an inducible and reversible genetic elimination of neural progenitor cells. Previous studies using these methods found a weakening of contextual fear conditioning but no change in spatial reference memory, suggesting a supportive role for neurogenesis in some, but not all, hippocampal-dependent memory tasks. In the present study, we examined hippocampal-dependent and -independent working memory using different radial maze tasks. Surprisingly, ablating neurogenesis caused an improvement of hippocampal-dependent working memory when repetitive information was presented in a single day. These findings suggest that adult-born cells in the dentate gyrus have different, and in some cases, opposite roles in distinct types of memory.

Their full paper (PDF download HERE) has a nice illustration of the techniques used.