Fig. 1.

Induction of late-phase long-term potentiation (L-LTP) in the superficial layer of the insular cortex (IC). A: schematic diagram showing location of 1 MED64 probe on the coronal IC slice (left; adapted from Paxinos and Franklin 2001 with permission) as well as arrangement of the 8 × 8 recording array (interelectrode distance: 150 μm, electrode size: 50 × 50 μm; right). B: light microscopy photograph showing relative location of IC with the MED64 probe and the layer designation. Red dot indicates stimulation site in deep layer (layer V-VI). C: overview of multisite synaptic responses recorded at baseline (black) and 3 h after theta burst stimulation (TBS) (red). Red open circle denotes the stimulated channel (Ch. 36), while red and black filled circles mark the superficial channels undergoing (Ch. 47) and not undergoing (Ch. 22) L-LTP, respectively. Black rectangle represents the channel not exhibiting any response in the baseline state (Ch. 56). Vertical lines demarcate different layers. D: example traces of Ch. 47, Ch. 22, and Ch. 56 from C shown in an enlarged scale for the baseline state. E: results of 1 channel showing L-LTP (Ch. 47) and the other channel not showing L-LTP (Ch. 22) in 1 slice. Inset: representative field excitatory postsynaptic potentials (fEPSPs) at time points indicated by numbers in graph. F: summary of averaged data from 5 superficial channels in each category within the same slice. G: pooled data from 9 slices from 9 mice, separately illustrating the results of LTP-occurring channels and LTP-not occurring channels in the superficial layer. TBS application in the deep layer resulted in an enduring synaptic potentiation that could last for at least 3 h. However, some channels did not undergo LTP in response to the same protocol. Arrows in E–G indicate starting point of TBS application. Calibration in C–E: 100 μV, 10 ms. Error bars in G represent SE.