We calculated SXCorr that quantified how well the shape of LFPcal matched to that of LFPobs, irrespective of difference in response magnitudes between the two LFP profiles for individual tone frequencies. For the example shown in Figure 4A, SXCorr peaked at 1 kHz the frequency at which the amplitude of LFPobs response also peaked (Figure 4B). Up to 2.8 kHz, the SXCorr was above 0.8 and but it fell off at higher frequencies. Across all recording sites, SXCorr gradually

decreased as the tone frequency departed from the BFMUA (Figure 4C). At frequencies beyond 1 octave difference, median SXCorr were significantly different from that at BFMUA (bootstrap, two-tailed, p < 0.05). These results Hydroxychloroquine supplier can be explained by volume conduction. Tones at BFMUA evoke strong MUA and CSD responses (Figure 3C). CSD responses accompanied with MUA more likely reflect local activity than CSD responses without MUA concomitants (e.g., near the foot of tuning curve), and these are strong enough to generate similarly strong (and local) LFP responses like those to low frequency http://www.selleckchem.com/products/SB-203580.html tones shown in Figure 4A. Tones that are away from the BFMUA may still evoke weaker CSD responses. However, considering

the tonotopic organization of auditory cortex, concurrent strong CSD responses must occur somewhere else in either ascent or descent positions along the tonotopic gradient. In such cases, due to volume conduction, the LFP would still be strong. However, the LFPs generated by remote loci do not have correspondingly strong local responses in the CSD profile. In such cases, LFPcal should and does differ from LFPobs. Accordingly, LFPobs responses to tones more than 1 octave away from BFMUA could not be accounted for solely by electrical potentials generated by

the CSD Dichloromethane dehalogenase responses derived from LFPobs themselves. This conclusion is consistent with the idea that LFPobs responses are generated by a mixture of local and nonlocal electrophysiological events. The results described above reveal apparent volume conduction of LFP over relatively large distances traveling parallel to the cortical sheet, lateral to their site of generation. To get at volume conduction perpendicular to the cortical sheet in A1, we examined the spatial spread of the P30 component described in Figure 1 above. Figure 5A shows LFP responses to broad-band noise (BBN) recorded at recording depths with 200 μm intervals from the depth of A1 to the dura at the dorsal brain surface in one penetration. Near the bottom of the column, there is a polarity inversion of this component in supragranular A1, like that shown for the tone-evoked P30 in Figure 1. Above the inversion, the component is gradually attenuated over distance. Figure 5B shows the amplitude distribution of the P30 component in the LFP and CSD signals at the same timing.