Fig. S1. Left panel: the typical two first positions chosen for placing the electrode array in the guinea pig auditory cortex. The first position was along the large blood vessels filling the dorso-ventral Sylvian pseudo-sulcus, which was easily found in all animals. The lowest best frequencies were found close to this sulcus (Edeline et al. 1993; Manunta and Edeline 1999; Wallace et al. 2000). The second position was perpendicular to the first one and reached higher frequencies, some of them possibly belonging to the tonotopic DC area known to have very similar properties to the AI area regarding the STRFs (Rutkowski et al. 2002). If a third position was tried, it was parallel to the second one, more ventral or dorsal. Thus, the sampling covered the whole tonotopic map of AI. Right panel: first position of the electrode array in an aged animal (#4) along the Sylvian pseudo-sulcus. Black dots indicate the penetration localization for the 16 electrodes. Note that despite this anterior position very close to the sulcus, no low CF or cortical response to low frequency tones <1.5kHz was found in this animal at 75dB SPL (Fig. 2).

Fig. S2. Individual example of ABR, MU and LFP recording from an old animal (#5) and some of the quantified parameters (in bold italic).

Fig. S3. Latency shift for a 10dB decrease as a function of the intensity level for ABR (A), Multi-unit activity (B) and LFP (C).

Fig. S4. Averaged group results on effects of hearing loss or aging on several features of peaks in receptive fields of cortical neurons.

Fig. S5. Averaged group results on effects of hearing loss or aging in the case of a 10dB intensity level decrease for a SPL above 70dB (left panels) or 10/20dB above threshold (right panels).

Fig. S6. Evolution of ABR threshold in the traumatized animals.

Table S1. Size of sets of MUs and LFPs (in parenthesis) used in each figure, for each group and each frequency band

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