Forward suppression in the auditory cortex is frequency-specific.
Bottom Line: The temporal order and frequency proximity of sounds influence both their perception and neuronal responses.These effects are larger when the two sounds are spectrally similar.These data are consistent with the idea that cortical neurons receive convergent inputs with a wide range of tuning properties that can adapt independently.
Affiliation: MRC Institute of Hearing Research, University Park, Nottingham NG7 2RD, UK.Show MeSH
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Mentions: A total of 156 units were recorded (53 SU and 103 MU). Figure 1 shows several example units where we measured SRFs for several different probe tone frequencies. In these examples the probe immediately follows the conditioning tone (i.e. an ISI of 0). The first row shows the excitatory RF of each unit and beneath it are the SRFs for each probe condition. Figure 1A shows a SU in which the tuning of suppression is profoundly affected by the choice of probe. In this example, two probe tone frequencies were presented (indicated by crosses): one at 20 kHz, close to the CF; and one at 12 kHz, away from the CF. When the probe frequency was 20 kHz, near to the unit CF, the SRF had a similar shape to the RF, and both the SCF and SBF are at the probe tone frequency. When the probe tone frequency was at 12 kHz, well below the unit's CF, the SRF shifted to lower frequencies. The tuning near threshold (0.4 criterion; white line) and near maximum suppression (0.9 criterion; grey line) clearly showed a shift in tuning. Suppression also had a lower threshold and a wider bandwidth for the off-CF probe. Two further examples are given in Fig. 1, both of which show differences in the tuning of forward suppression when the probe tone frequency is not at CF. Notice that the tuning is not necessarily centred on the probe frequency. In some cases, the region of maximal suppression (grey lines) is centred on the probe frequency whilst threshold tuning resembles the excitatory tuning curve (Fig. 1B; 0.6-kHz probe).
Affiliation: MRC Institute of Hearing Research, University Park, Nottingham NG7 2RD, UK.