Fig. 6.

Final categorizations of the FEF layer IV neurons and their physiological properties. A: distribution of Inhibitory Indices, calculated as a vote over all of the literature-based width measurements, showing the value for every neuron. The distribution was segmented into quartiles that defined putative excitatory neurons (blue circles), putative inhibitory neurons (orange circles), and ambiguous neuron (multicolored hatched circles). B: average action-potential waveforms for the 3 classes of layer IV neurons. For comparison, the average action-potential waveform of known pyramidal (identified layer V) neurons is shown with a dashed line. The waveforms were height normalized by matching the peaks and the baseline levels. C: sensitivity of the putative excitatory and inhibitory neurons to orthodromic stimulation. Distributions of current thresholds (left) and activation latencies (right) are plotted with the use of 100-μA and 0.5-ms bins, respectively. Numbers show medians. Data for ambiguous neurons are not shown, but they were similar to the putative excitatory neurons: their median current threshold was 396 μA and activation latency, 3.1 ms. *P < .05 by Mann-Whitney rank sum test.