Figure 2.

Spiking properties of anteroventral units. A, B, Head-directional properties of HD-by-theta units (A) and HD units (B). The spiking of HD-by-theta (A, top, left; marked with purple symbols) and HD (B, top, left; marked with red symbols) follows equivalent directional pattern. The experiments are conducted in rectangular recording arena and the animal's path is marked with black line. The polar plot examples reveal the head directionality of HD-by-theta (A, top, right) and HD (B, top, right) units. The polar plot for each cell represents the distribution of time heading in different directions across all time bins of the trial (blue) and the distribution of head directions for time bins when a spike was recorded from the cell (black). The coordinate system denotes maximal firing frequency of the recorded unit with 0 Hz in the center and 104.15/70.30 Hz in the periphery. The same signal can be plotted as firing rate versus head direction tuning plot for HD-by-theta (A, bottom) and HD (B, bottom) units. C, D, The spike waveform (left) and the autocorrelogram of spiking activity (right) for eight anteroventral HD-by-theta units (C) and four HD units (D). For the spike waveform, the solid curve represents the mean, and the dashed curve represents the SD. Autocorrelation histograms were calculated for −10/10 ms. The clear isolation of the neuronal extracellular response was identified by the absence of correlations within the first 2 ms of the refractory period.