FIGURE 1.

Searching strategies used by rodents during spatial learning in the Morris water maze. (A) Spatial allocentric strategy (object to object) is characterized by the ability to navigate using distal cues located outside the maze and at some distance from the rodent. The bottom panel shows representative examples of three allocentric search strategies listed from most precise to least precise (direct swim→ focal swim → directed search), which have been related to AHN. (B) Non-spatial egocentric strategy (self to object) characterized by the ability to navigate using internal cues independent of external cues based on a sequence of bodily movements. The bottom panel presents representative examples of six spatially imprecise egocentric search strategies (chaining, scanning, random, thigmotaxis, and perseverance). The decrease in AHN has been related to more imprecise search strategies. (C,D) Example of the search strategies adopted by rodents with normal (C) and low levels of neurogenesis (D). The bottom bar charts illustrate the percentage of search strategies employed by rodents across training. Green bar: spatially precise search. Blue bar: spatially imprecise search. Gray bar: perseverance search. Rodents with low hippocampal neurogenesis require more training days before they begin to use spatially precise search strategies (green) than rodents with normal neurogenesis. When the platform changes to a new location, rodents with low neurogenesis spend more time searching over the old platform location (perseverance; gray bar) and adopt more imprecise search strategies (blue) than controls.