FIGURE 1.

Exposure to novel allocentric space facilitates the induction of hippocampal LTP. (A) Insertion of a novel holeboard into a familiar environment (Ai) promotes the expression of LTP in the hippocampus of rats. In the graph shown, weak high frequency stimulation (wHFS) of perforant path (pp) synapses to the dentate gyrus (DG) triggers short-term potentiation (STP) that lasts for maximally 2 h (unfilled squares). Combination of wHFS (arrow) during exposure to a novel holeboard transforms STP into LTP that lasts for over 24 h (black squares). Inset: analogs show examples of field excitatory post synaptic potentials (fEPSPs) recorded prior to wHFS (iI), 5 min (ii) and 24 h(ii) after wHFS in animals that received wHFS only (top row) and animals that received wHFS during holeboard exploration (bottom row). Scale bar, vertical: 5 mV, horizontal, 5 ms. From Kemp and Manahan-Vaughan, 2008b. (B) Migration from a familiar environment to an adjacent novel environment 2 min after tetanic afferent stimulation (comprising exploration for 1 min, followed by a return to the familiar environment) promotes the expression of LTP at pp-DG synapses in rats. The graph describes how application of the tetanus alone resulted in STP (unfilled circles), compared to when the tetanus was applied in conjunction with novel environmental exposure (filled circles). Inset: analogs show examples of fEPSPs recorded at the time point signified by the digits in animals that received tetanus only (left) and that received tetanus followed by novel environment exploration (right). The graph shown (B) is from Straube et al., 2003, with permission.