Figure 6.
The action potential waveforms from the multiple place fields of a single unit could not be discriminated in the multidimensional waveform parameter space used for single-unit isolation. Examples from two cells are shown in A and B. These cells fired clear complex spikes. They were chosen because they also had three or four clear place fields on the chamber floor, which was the average for the population. The firing rate map of each unit is shown with the locations of the fields on the chamber floor indicated by ellipses. Action potentials in the different fields were discriminated using the location of the rat when the spike was emitted. Below the rate map, a set of six waveform parameter two-dimensional projections are shown. This is only a subset of the projections that were used to isolate the unitary waveform. The action potentials at the different field positions are indicated in colors that correspond to the ellipse color that marks the field location (the black ellipse corresponds to blue events). All other events recorded by the tetrode are indicated in gray. Two blowups of a waveform parameter projection are given to the left and right of each rate map. The blowups only show the isolated waveform events. This depicts that the waveforms strongly overlap in waveform parameter space. The average waveforms of the action potentials in each field are given in the bottom row. The waveforms on tetrode wires 1 through 4 are drawn in black, red, green, and blue, respectively. The cell in A discharged 1100 action potentials during the recording. The isolation quality measures for the highlighted single unit are as follows: Iiso(background) = 12.6; Iiso(neighbor) = 14.9. The cell depicted in B discharged 3580 action potentials during the recording. The isolation quality measures are as follows: Iiso(background) = 7.9; Iiso(neighbor) = 7.1, which is approximately the average isolation quality of the single units that were analyzed for this study.