Figure 4A (left column) shows laminar-temporal profiles of LFPobs responses to tones, in a penetration site tuned toward low frequencies. The profiles maintained common patterns across tone frequencies: the predominant onset negativity in the bottom two thirds of channels and positivity in the top one third of channels across tone frequencies. Other later features, like the strong positivity around 50 ms in the bottom of the profile, were preserved only for responses to lower frequency tones. CSD responses (Fig. 4A, second column) are similar to LFPobs in terms of their strength across frequencies below 1.4 kHz. However, CSD responses are nearly abolished at high stimulus frequencies. Tuning curves in Figure 4B also show that CSD responses were nearly zero at high stimulus frequencies where LFPobs responses still had amplitudes about 20% of peak values. Figure 4A (third column) shows laminar-temporal profiles of LFPcal derived from CSD profiles using Equation 1 (methods). Note that our simultaneous recording from single arrays orthogonal to cortical layers cannot resolve the fine details of spatial distributions for sinks/sources. For example, lateral spread of activity may
