Figure 2

Schematic representation of induction and recording of long-term potentation and long term depression in the hippocampus. Long-term potentiation (LTP) and long-term depression (LTD) can be induced by applying an electrical stimulus by placing an electrode placed in the Schaffer collateral-commissural (SCC) pathway and recording from the CA1 subfield. Upper panel shows a coronal section through the dorsal hippocampus, with schematic representation of intra-hippocampal connectivity. The CA1 pyramidal cell layer receives input from the entorhinal cortex through the dentate gyrus [DG] and the CA3 pyramidal layers and the SCC; the subiculum carries hippocampal efferents. Lower left-hand panel illustrates measurements of LTP as excitatory postsynaptic potentials (EPSP, peak amplitude or slope of the latter). Initially, low-frequency stimulation (LFS, usually less than 0.1 Hz) is applied to the Schaffer collaterals to establish a stable baseline (usually for 20-30 min), after which LTP is induced by high-frequency stimulation (HFS; usually 100 Hz), followed by LFS. Successful induction of LTP can be assumed when the post-HFS EPSP peak amplitude (or slope) exceeds that seen before HFS and is maintained for at least 60 min. ① depicts a single evoked EPSP; ② represents a potentiated EPSP after HFS. Lower right-hand panel shows that EPSP recordings also serve to detect LTD. After initial baseline recording, low-frequency stimulation (LFS, usually 1 or 5 Hz) is applied to the SCC; successfully induced LTD can be assumed when the post-LFS EPSP peak amplitude (or slope) is smaller than that observed before LFS. ① shows a single baseline EPSP; ② depicts a example of a depressed EPSP after LFS.