Over 12 years ago we posed a question on our lab website www.newneuron.com asking what are the functions of new cells in adult hippocampus? Still most recent articles on the functional role of adult neurogenesis begin with a statement saying that the functional role of new neurons remains unknown. Hundreds of studies have come and gone, each claiming one or another role for new neurons, and yet there is no consensus. An extensive, and still rapidly growing,
catalogue of such findings reflects continuing confusion in the field with no sign of resolution.
One seemingly logical approach to the above question is to consider only those learning tasks that have already been shown to be hippocampus-dependent, but this is a trap since for example the prototypical hippocampal spatial water maze task generated variable, inconsistent results. Another, more refined, approach is to consider only the Dentate Gyrus-dependent tasks but this can be deceptive since its predominantly mature granule neurons, may be concerned with entirely different matters than the new neurons generated in adulthood. A common explanation for a variety of behavioural effects seen after deletion or inactivation of the young neurons has been the variability of the methods and differences among species. An unwritten opinion expressed among the insiders in the field is that neurogenesis is important in any task that is “difficult”, leaving the easy stuff to the mature neurons but, the nature of this “difficulty” remains unknown. A recent example by Winocur et al., (2012, Behav. Brain Res. 227, p. 464) has shown that a visual discrimination learning task was disrupted by depletion of neurogenesis when the acquisition and recall phases were interrupted by an interfering activity, making the recall more difficult. This suggests that the previous studies may have used too large a yard stick to measure the role of new neurons and that more refined approaches are needed. Thus, in this Research Topic forum we welcome new approaches, new ways of thinking and novel techniques to approach the fundamental question of how neurogenesis participates in learning and memory. Some of the issues to consider are:
- Are lesions or cell deletions a valid way to test for functions?
- Can optogenetic techniques be of help?
- Are we misled by results from inbred laboratory species that may have little value in probing for real adaptive functions?
- Are we misled by thinking in terms of hypothetical concepts such as pattern separation?
- Is there a critical period for functional neurogenesis?
- Is context a critical component encoded by new neurons?
- How is memory interference dependent on new neurons?
- Can computational data-based models help in guiding the studies?
- Are the existing cell birthing techniques out of date?
