tracking the course of hippocampal representations during learning: when is the map required?

How long did rats train for eyeblink?

Following recovery from surgery to implant eyelid wires (and also implant hyperdrives in six rats in each of the young and old groups), rats were trained in the spatial eyeblink conditioning task for 31 days as described in Figure 1. As shown in Figure 3, A and C, EMG activity increased significantly in both age groups over the 20 cm approach to the stimulus locations during days 1–10 of training (Position 1, Friedman test (effect of distance from stimulus): χ 2 (19) = 63.492, p < 0.001; Position 2, Friedman test (effect of distance from stimulus): χ 2 (19) = 110.298, p < 0.001). EMG activity increased significantly and to higher levels in both age groups during days 21–30 of training ( Fig. 3 B, D; Position 1, Friedman test (effect of distance from stimulus): χ 2 (19) = 221.768, p < 0.001; Position 2, Friedman test (effect of distance from stimulus: χ 2 (19) = 234.723, p < 0.001). There were no significant differences in EMG activity between age groups during days 1–10 or days 21–30 of training. On trials in which no eyeblink stimuli were given, young and old rats exhibited a similar decay in blink activity as they left the stimulus positions (data not shown), indicating that there was no effect of age on accuracy of the blink response.

What kind of wires are used in rats eyelids?

The right eyelids of five young adult and four old rats were implanted with four insulated annealed 0.005” stainless steel wires for monitoring of spatial eyeblink conditioning behavior. A second cohort of six young adult and six old rats received eyelid wire implantations as just described, and also the attachment of a hyperdrive manipulator device ( Wilson and McNaughton, 1993) that holds an array of 12 independently adjustable tetrode recording probes ( McNaughton et al., 1983b; Recce and O'Keefe, 1989 ).

Does hippocampal spontaneous remapping occur later in life?

Four primary findings emerge from the experiments reported here: (1) confirmation that hippocampal spontaneous remapping occurs more frequently later in the lifespan ( Barnes et al., 1997 ); (2) during an initially novel place conditioning task, remapping emerges only after at least 2 weeks of bi-daily training sessions; (3) although spatial memory measured using the Morris water task is impaired in old rats, there is no effect of age on spatial eyeblink conditioning; (4) place field stability correlated positively with water maze learning and negatively with spatial conditioning. At least two interpretations may combine to explain these results: (1) the hippocampus has a time-limited role in spatial eyeblink conditioning; (2) because poor hippocampus-dependent learning correlates with more remapping in aged rats, yet these animals exhibit good place conditioning, older rats may use behavioral strategies that rely less on the hippocampus and more on other structures that can sustain this behavior.