Figure 2. Low light conditions support the formation of short-term memory, which is independent of experience in a previous experiment.

Schematics depict experimental procedure; dark grey arenas denote low light (3 lux) conditions. Bar graphs show exploration time (as a percent of the total) for each object (mean ± SEM; n = 14 (A) or n = 15 (B); * p < 0.05). Total exploration time for each trial is indicated below the graphs. Scatter dot plots show individual discrimination ratios (open circles) and the group mean (horizontal line); positive values (>0) reflect a preference for the left-side object (familiarization trial) or the novel object (test trial). (A) In the first experiment, short-term memory in low light conditions was assessed using a 2-minute delay between the familiarization and test trials (A₁). No preference for object location (left or right side) was exhibited during the familiarization trial (A₂) but mice exhibited a significant preference for the novel object 2 minutes later during the test trial (A₃), indicative of short-term memory for the familiar object. (B) After a 2-week interval, the experiment was repeated using the same delay and light conditions (B₁). Importantly, however, the object assignments (familiar or novel) and locations (left or right side) were counterbalanced within subjects relative to the first experiment. Again there was no preference for object location (left or right side) during the familiarization trial (B₂). During the test trial 2 minutes later, mice exhibited a significant preference for the novel object (B₃), indicating that they formed a new short-term memory for the most recently experienced familiar object with no indication of savings from the previous exposure.