Figure 1.

The method. A, Extracellular recordings were obtained from one or more LGNd neurons in awake rabbits. Field potentials were recorded from the retinotopically aligned region of V1 using a 16-channel silicone probe (vertical spacing, 100 μm). B, LGNd neurons were identified as sustained or transient based on the poststimulus time histogram (PSTH) generated by a light or dark spot over the receptive field center. The PSTH of a sustained LGNd neuron after a 1 s presentation of a white spot over its receptive field center is shown. C, Receptive fields were mapped with sparse noise, and retinotopic alignment of LGNd (blue) with a layer 4 cortical site (black) was quantified (in this case, sites were misaligned by approximately one-third of the LGNd receptive field center diameter). D, A spike-triggered average of the field potential elicited from one of the cortical sites in layer 4 (channel 7 in E), showing the axon terminal potential and the postsynaptic response. E, F, Depth profiles of the spike-triggered field potentials were examined on all cortical recording sites (E), and the CSD depth profile of these averages was derived (F). These spike-triggered field and CSD profiles were based on all of the spikes generated by this LGNd neuron (>42,000). G, A color map of the spike-triggered CSD from F. In this and in subsequent figures, the solid horizontal arrows in CSD tracings indicate the channel that corresponded to the reversal point of the field potential generated by a diffuse flash stimulus. Brackets indicate our estimate of the upper and lower boundaries of layer 4 (see Materials and Methods).