Fig. 3.

RE-evoked spikes in the distal stratum radiatum and at the oriens/alveus border, indicative of the activation of local interneurons. A, A simultaneously recorded CA1 depth profile reveals that stimulus-triggered spikes (arrows) occurred only in the distal stratum radiatum (rad, *), in both the conditioning and test response, after high intensity stimulation of RE (0.13 Hz). pyr, stratum pyramidale;l-m, stratum lacunosum-moleculare; B,Magnification of recordings from the stratum radiatum.a, Radiatum spikes (arrows) shown inA (trace marked *). b, Radiatum field potentials to single pulses applied to RE at frequencies in the range from 0.13 to 2 Hz also exhibited spikes. c, Stimulus-triggered radiatum spikes (arrows) in both conditioning and test response, recorded in another rat. Notice that in all cases the latencies of the radiatum spikes were highly comparable.C, A synaptically driven neuron was encountered at the oriens/alveus border. A short latency action potential (black arrows) was recorded in both the conditioning and test response. D, The simultaneously recorded local field potential shows that the RE-evoked oriens/alveus spike (open arrows) preceded the postsynaptic pyramidal cell response. Stimulation moments in A–D are indicated bydots.