PMC

Percentage of sites showing an increased response (1st and 2nd rows: MUA and LFPs, respectively) or a decreased response by at least 20% (3rd and 4th rows: MUA and LFPs, respectively). Otherwise configuration is same as in .

Schematic representation of the acoustic stimuli used in the present study. A: time onsets (black dots) and long-term spectrum of control (ctrl; left) and attenuated frequency band (AFB) stimuli (right). B: time onsets (black dots) of tone pips for stimulus sequences alternating control stimulus and silence (ctrl-sil), AFB stimulus and silence (AFB-sil), or control stimulus and AFB stimulus (ctrl-AFB).

Medians of the cortical changes induced by the stimulus ensemble with AFB on awake animals. Each column corresponds to a position of the cortical BF relative to the AFB (see and ). 1st row: medians of the difference between the AFB conditions and the control conditions. Circles indicate statistically significant differences between control and AFB conditions. 2nd row: percentage of sites showing an increased response by at least 20%.

Effects of anesthesia on the neural enhancement produced by AFB stimulus. Five individual examples of cortical responses evoked by the stimulus ensemble without (1st and 2nd rows: MUA and LFPs, respectively) or with AFB (3rd and 4th rows: MUA and LFPs, respectively) obtained simultaneously in an awake animal. 5th and 6th rows: frequency profiles of cortical responses for MUA and LFPs, respectively. One observes a clear response enhancement at the edge-out frequencies, suggesting that anesthesia did not play a major role in our results.

Buildup and breakdown of neural changes produced by the AFB stimulus alternated with control stimulus or silence. Stimulus condition and time period (in parentheses) are indicated at top of each panel. The 10-s stimulation periods (ctrl or AFB) are divided into 3 time windows, i.e., 0–2.5, 2.5–5, and 5–10 s. 1st and 2nd rows: the neural changes for stimulus sequence with AFB of 1- or 0.5-octave bandwidth, respectively. The neural enhancement at the edge-out frequencies build up and break down within a few seconds (0–2.5 s) of stimulation.

Cortical responses evoked by stimulus ensembles with or without AFB for individual recordings where a single-unit activity over all the stimulus conditions could be obtained. Stimulus condition and time period (in parentheses) are indicated at top of each panel. 1st row: individual (and averaged; red line) waveforms of the single-unit activity. 2nd row: spectrotemporal receptive fields in all stimulus conditions. 3rd row: frequency profiles of cortical responses in all stimulus conditions. One observes a clear response enhancement at the edge-out frequencies, in particular on the upper edge of the spectral notch.

Time course of the neural changes produced by AFB stimulus with 1-octave-wide spectral notch in an awake animal. Each column corresponds to a stimulus condition and period (indicated at top of panels). 1st and 2nd rows: spectrotemporal receptive fields obtained from MUA and LFPs, respectively. 3rd and 4th rows: frequency profiles of neural responses for MUA and LFPs, respectively. The black and red lines represent the neural responses for the stimulus ensemble without AFB and with AFB, respectively. The enhancement of neural activity at the spectral edges is fast, i.e., it occurs within the 10-s presentation of the stimulus ensemble with AFB (3rd and 4th columns), and labile, i.e., it disappears within the following 10-s presentation of the stimulus ensemble without AFB (5th column). These results are comparable to those reported in anesthetized animals.

Medians of the difference between the AFB conditions and the control conditions for 3 positions of the AFB relative to the neural best frequency (BF), as a function of frequency. Each column represents a position of the AFB relative to the neural BF. 1st and 2nd rows: the average MUA and LFP, respectively. 1st column: average data for neurons with BF corresponding to the lower edge of the AFB. 2nd column: average data for neurons with BF corresponding to the AFB center. 3rd column: average data for neurons with BF corresponding to the upper edge of the AFB. Vertical dotted lines represent the edge frequencies of the notch. Circles indicate statistically significant differences between control and AFB conditions for MUA (results are identical for LFPs and are not shown). Neural responses are enhanced near and outside the notch, whereas they are reduced near and within the notch.

Medians of the difference between the various stimulus conditions and the control condition (ctrl-70) for 3 positions of the AFB relative to the neural BF, as a function of frequency and for the different stimulus conditions. Each column represents a position of the AFB relative to the neural BF (see ). 1st and 2nd rows: results for MUA at the 0.5- and 1-octave notch width (Nw), respectively. 3rd and 4th rows: results for LFPs at the 0.5- and 1-octave notch width, respectively. Vertical dotted lines represent the edge frequencies of the AFB. Circles indicate statistically significant differences for MUA (results are identical for LFPs and are not shown). Neural responses at both edges of the AFB are largely enhanced, whereas they are reduced within the AFB.

Neural changes produced by 10-s AFB stimulus alternated with 10-s silence or control stimulus. Stimulus condition and time period (in parentheses) are indicated at top of columns. 1st and 2nd rows: spectrotemporal receptive fields obtained from MUA and LFPs, respectively. 3rd and 4th rows: frequency profiles of neural responses for MUA and LFPs, respectively. AFB bandwidth (notch width, Nw; indicated at top) was 0.5 octave in the 3rd–5th columns and 1 octave in the 6th–8th columns. The black and red lines represent the neural responses for the stimulus ensemble without AFB and with AFB, respectively. The black lines from the 1st column (for MUA and LFPs) are replicated in the 2nd–8th columns for comparison. Neural responses are greatly enhanced at the edges of the notch and decreased within the notch. The neural changes at the spectral edges are fast, i.e., they occur within 10 s of the stimulus with AFB presentation (3rd–4th columns and 6th–7th columns), and labile, i.e., they disappear within the following 10 s of the stimulus ensemble without AFB presentation (5th and 8th columns).

Neural tuning of individual recordings obtained from a selected example at a given location in the primary auditory cortex. Each column corresponds to a stimulus condition (indicated at top). 1st and 2nd rows: spectrotemporal receptive fields obtained from control stimuli (multitone ensemble without AFB) for multiunit activity (MUA) and local field potentials (LFPs), respectively. 3rd and 4th rows: spectrotemporal receptive fields obtained from multitone ensemble with AFB for MUA and LFPs, respectively. Horizontal dotted lines represent the edge frequencies of the AFB. Neural activity in the spectrotemporal receptive field is represented by a color continuum from blue (minimum values) to red (maximum values). 5th and 6th rows: frequency profiles obtained by taking the maximum firing rate of MUA or the minimal amplitude of LFPs in the 10- to 30-ms time window, respectively. The red and black lines represent the neural responses for the stimulus ensemble with AFB and without AFB, respectively. Control conditions at 60, 50, and 40 dB are represented with a blue line. Vertical dotted lines represent the edge frequencies of the AFB. Neural responses are greatly enhanced at the edges of the AFB and decreased within the AFB.