Figure 3.

Relative prevalence of different search strategies identified on trial 1 of the working memory experiment.

Search strategies were classified under blind conditions by two independent experimenters according to the qualitative system described by Brody and Holtzman (2006). Only six out of the nine strategies defined by these authors could be clearly identified here because short swim paths characterized by a direct trajectory to the platform were only meaningfully interpretable in a reference memory task or at least when the animals were expected to know the platform location. This was not the case here for swim paths derived only from trial 1 of each day's working memory test.

The three strategies under the category of Systematic search are: ‘scanning’ (searching randomly in the interior portion of the pool), ‘random’ (searching randomly in the entire pool), and ‘focal incorrect’ (searching intently in a quadrant that does not contain the platform before moving to another area of the pool). Under the category of Looping is: ‘chaining’ (circular swimming at a fixed distance from the wall) ‘peripheral looping’ (persistent swimming around the outer 15 cm of the pool), and ‘circling’ (swimming in tight circles with some net directional movement). Search paths that did not conform to any of the above descriptions were classified collectively as “other”.

Each pie chart illustrates the proportion (expressed in percent) of the different search strategies in mutants and controls, separately for the 15-s (A) and the 10-min (B) delay conditions. Separate χ² test of independence conducted at each delay condition did not reveal any significant difference in the relative deployment of different strategies between mutant and control mice; and both did not yield a significant association. An additional χ² test of independence was used to gauge the impact of delay on strategy use between the two delay conditions, which also failed to reveal a significant association.