Figure 4.

Object–space novelty during SR and not OR per se determines SC—CA1 synaptic depression. (a) Stable baseline recording was obtained when only test-pulses were applied to the Schaffer collateral—CA1 stratum radiatum synapses in the freely moving mice (n = 14). When test-pulse stimulation was paired with spatial object recognition (SR), a progressive decrease in synaptic strength that plateaued and lasted for at least 24 h (1440 min) was observed (ANOVA, P < 0.0001). No decrease in synaptic strength was observed when the mice were reexposed to the same objects at the same locations the next day. When a novel spatial configuration of the same objects was presented, however, the synaptic depression reemerged (ANOVA, P < 0.0001). (b) Analog traces illustrate the Schaffer collateral—CA1 field potentials at pretask, 5 min and 24 h (1440 min). Vertical scale bar corresponds to 2 mV and horizontal scale bar corresponds to 5 ms. (c) Behavioral analysis showed that the mice explored the objects significantly less during reexposure at the old positions but explored to a much greater extent when the objects were arranged in a novel configuration. Reexposure and novel configuration data are expressed as a percentage of novelty exploration. *t-test, P < 0.0001. (d) Analysis of the discrimination ratio revealed that the mice showed a decreased preference when the objects where presented at the familiar locations during reexposure and a strong increment in preference when the objects were relocated during novel configuration (ANOVA, P < 0.0001).