A. Left In all recordings (peripheral and cortical), 230 amplitude-frequency stimulus combinations were presented (3^rd panel from top), with dense sampling of 15 frequencies surrounding the vibrissa FRF (2^nd panel). Neural firing rate (FR) and vibrissa motion amplitude (VA) (1^st and 2^nd panels) are shown as a function of stimulus amplitude, with responses to larger input stimuli (e.g., 80µm) shown as darker gray scale lines. The ‘mid-point motion’ plot shows vibrissa motion measured with the opto-electrical device, while ‘tip motion’ indicates the stimulus input amplitude delivered to the distal vibrissa tip. Right Minimal amplitude tuning curves (MATC) were constructed using 6 threshold response criteria (most conservative the furthest panel on the right, most liberal on left, see ). Along the x-axis of each panel, the 15 sampled frequencies are plotted, from lowest frequency (Left) to highest (Right). Along the y-axis, MATCs are plotted on a motion amplitude level (MAL) decibel scale, referenced to 1µm motion. In this example, 5 of 6 criteria demonstrated frequency tuning, with well-defined characteristic frequencies (CF; marked by asterisks). The criteria level with the thickest box border (2^nd from right) shows the MATC resulting from the cut-off in activity indicated by the dashed line through the neural activation in the neural firing rate panel (FR) to the left. B. Three examples of MATCs in NV. The top row corresponds to the neural and vibrissa amplification plots as shown in 1A, with the thickest box marking the criteria indicated by the dashed line through the neural activity curves. Well-tuned responses with CFs corresponding to a tip motion of 8µm are shown in 1A and the example on the left in 1B.

Top An example of a minimal amplitude tuning curve (MATC) in SI. Each MATC corresponds to the neural and vibrissa amplification plots above them, with the thickest box marking the criteria indicated by the dashed line (see for details). Below The Left and Right columns show two examples of MATCs where tuning curves were simultaneously recorded for the primary vibrissa (PV) recording and for the surround electrode (SE). Tuning of both positions was observed, with well-tuned curves and CFs observed across a broader range of statistical criteria for PV driven responses.

A. Gain functions are shown for neural mean firing rates as a function of stimulus amplitude (8–80µm). Relative amplitude of response is shown for responses taken at the CF (black), FRF (dark gray), and at two frequencies ± 1 vibrissa motion bandwidth (±ω) from the FRF (lighter gray lines with filled and empty circle demarcations). Data were normalized to the peak evoked firing rate at the maximal stimulation amplitude (the best frequency at 80µm), and dashed lines indicate relative pre-stimulus activity levels. Top Panel NV single unit responses were taken from tuning curves defined requiring a minimum of 2 spikes/s (Criterion #3, see ). Middle Panel Cortical responses from recordings in the principal vibrissa barrel column (SI PV), taken from tuning curves defined requiring a minimal 128% increase above spontaneous firing rate (Criterion #4). Bottom Panel Cortical responses are shown from recordings taken simultaneously from a surround electrode (SI SE) located 350–1000µm lateral to the center (PV) representation. The same criterion was employed. B. For all peripheral and central recordings, the probability of significant neural activation at a given input amplitude is shown for the CF, FRF, and FRF + ω (gray scale scheme as in A). These curves demonstrate the relative gain in likelihood of a significant response for the stimulus input presented. Dashed gray horizontal lines indicate “stimulus detection” in 30% of recordings of neural activity using the described criteria. C. The minimal amplitude required to evoke a significant response in ≥ 30% of recordings for NV, SI PV, and SI SE sites (as in the dashed lines in B). For NV and SI PV sites, stimulation at the CF or FRF generated significant responses with motion amplitudes that were ~50% of those required when off-resonance frequencies (FRF ± ω) were presented. Further, off-resonance stimulation did not evoke consistent responses at SI SE sites, and CF or FRF stimuli required in turn about twice as much motion to drive 30% of the sample as was required at the SI PV site. The number of samples for (CF, FRF, FRF + ω, FRF − ω) were, in NV: (9, 15, 9, 9), SI PV: (10, 13, 8, 9) and SI SE: (10, 13, 8, 9). The FRF and FRF ± ω show different N due to edge effects of the sampled range.