Article Figures & Data
Figures
- Figure 1.
Concurrent auditory competition and regions of interest for simultaneous dual region recordings. A, Experimental design: The driver stimulus (blue) was played from a speaker located at the preferred location of recorded OT units at a fixed level. The competitor stimulus (green) was played from a speaker outside OT's receptive field >50° away from the driver speaker. Sound level of the competitor varied from −15 to 10 dB relative to the driver level. Chronic 16-channel linear electrodes were implanted in OT and a downstream forebrain thalamic region, nRt. B, C, Spatial receptive fields of example OT (B) and nRt (C) units that were simultaneously recorded. Color intensity in each circle represents the spike response rate measured for stimuli played from that speaker location.
- Figure 2.
Despite broad spatial tuning, most nRt units represent frontal locations robustly. A, Heat map of azimuth tuning for all nRt units computed by taking the maximum normalized spike response at each azimuth across all elevations· B, Average azimuth tuning curve across the population. Positive and negative azimuths indicate contralateral and ipsilateral space respectively. C, Heat map of elevation tuning for all nRt units computed by taking the maximum normalized spike response at each elevation across all azimuths. D, Average elevation tuning curve across the population. For each unit, the spike response in each trial was normalized by the maximum spike response observed across all trials. Units on the y-axis of heat maps are sorted chronologically according to recording site date.
- Figure 3.
Spike response rate increases and STS does not change in nRt with competition of flat noise stimuli. A, Percent change in spike response rates for each relative level during competition. B, Example raster plots for two relative level conditions when the driver was stronger (−15 dB) and when the competitor was stronger (+10 dB). Spike times of two simultaneously recorded units (green and orange) with coincident spikes between the two units indicated as (black) ticks. C, Cross-correlograms from competing sounds, averaged across all simultaneously recorded unit pairs for each relative level condition (same order as in D). The number of unit pairs with significant STS is indicated above each correlogram. The horizontal colored line indicates the peak height of the average cross-correlogram computed from when a driver stimulus was presented alone. D, Population competition synchrony index (CSI) measuring the change in STS with competition relative to presentation of a single driver stimulus, across relative levels. Box plots show the interquartile range (25th–75th percentile) with whiskers indicating 5–95% confidence interval, and circles represent individual units. ANOVA p value and relevant post hoc p values reported for each pairwise comparison.
- Figure 4.
nRt units exhibit variations in their response patterns to competition depending on whether the varying competitor stimulus resides in their preferred location. A, Histogram of tuning selectivity indices measured for each unit across the nRt population based on responses to frontal and lateral stimuli alone. Values above and below zero (dashed line) indicate preference toward frontal and lateral driver locations, respectively. B, Normalized response rates to average binaural level (ABL) for single stimuli presented at either a frontal driver location (orange) or lateral driver location (blue) curves for frontal driver-selective units. The range of relative levels at which concurrent sounds were presented is highlighted in pink. C, Percent change in spike response rates for each relative level during competition for frontal driver-selective units when presented either frontal driver/lateral competitor pairs (yellow curve) or lateral driver/frontal competitor pairs (blue curve). ANOVA p value for each tuning selectivity category indicated in legend. Error bars indicate standard error of mean.
- Figure 5.
Modeling OT responses across the map during competition predicts that nRt linearly sums OT inputs from distant locations of the map. A, B, Modeling symmetric and opposing OT response changes (A) to competition at driver (orange) and competitor (blue) positions to observe invariant responses in nRt (B). C, D, Modeling asymmetric and opposing OT response changes (C) to competition at driver and competitor positions to observe increasing responses in nRt (D).
- Figure 6.
nRt units with extreme selectivity exhibit response patterns expected from their dominant OT input. A, Percent change in spike response rates for each relative level during sound competition with a frontal driver and lateral competitor for nRt units with extreme frontal driver selectivity (tuning selectivity index >0.30, n = 3). B, Percent change in spike response rates for each relative level during sound competition with a frontal driver and lateral competitor for nRt units with extreme lateral driver selectivity (tuning selectivity index <−0.50, n = 2). Error bars indicate standard error of mean.
- Figure 7.
Lateral OT responses exhibit faster transitions than frontal OT responses. Percent change in spike response rates for each relative level during competition for OT units that prefer frontal (<45°, A) and lateral (>45°, B) azimuths. Box plots show the interquartile range (25th–75th percentile) with whiskers indicating 5–95% confidence interval, and circles represent individual units. ANOVA p value and relevant post hoc p values reported for each pairwise comparison.
- Figure 8.
Spike response rate increases but STS does not change in nRt with competition of amplitude-modulated stimuli. Competition between stimuli with different modulation frequencies (left column: driver fAM = 55 Hz, competitor fAM = 75 Hz; right column: driver fAM = 75 Hz, competitor fAM = 55 Hz). A, B, Percent change in spike response rates for each relative level during competition. C, D, Example raster plots for two relative conditions when the driver was stronger (−15 dB) and when the competitor was stronger (+10 dB). Spike times of two simultaneously recorded units (green and orange) with coincident spikes between the two units (black) indicated as ticks. E, F, Cross-correlograms from competing sounds, averaged across all simultaneously recorded unit pairs for each relative level condition. Number of unit pairs with significant STS indicated above each correlogram. Horizontal colored lines indicate the peak height of the average cross-correlogram computed from when a driver stimulus was presented alone. G, H, Competition synchrony index (CSI) measuring change in STS with competition relative to presentation of a single driver stimulus, across relative levels. Box plots show the interquartile range (25th–75th percentile) with whiskers indicating 5–95% confidence interval, and circles represent individual units. ANOVA p value and relevant post hoc p values reported for each pairwise comparison.
- Figure 9.
STS in nRt reflects the amplitude modulation frequency of the strongest stimulus. Competition between stimuli with different modulation frequencies (left column: driver fAM = 55 Hz, competitor fAM = 75 Hz; right column: driver fAM = 75 Hz, competitor fAM = 55 Hz). A, E, Cross-correlograms from competing sounds, averaged across all simultaneously recorded unit pairs for each relative level condition. Number of unit pairs with significant STS indicated above each correlogram. Horizontal colored lines indicate the peak height of the average cross-correlogram computed from when a driver stimulus was presented alone. B, F, Power spectra of cross-correlograms, averaged across all simultaneously recorded unit pairs. Colored arrows indicate the frequency corresponding to the maximum peak observed in the power spectra. C, G, Scatterplots of vector strength (VS) to the competitor as a function of the VS to the driver with competition across relative levels. Each dot represents one unit, gray dots show units that did not phase lock to the driver (Rayleigh's test of uniformity, percentage of units that significantly phase lock to the driver indicated within each subplot, green and blue dots), black dashed lines indicate unity. D, H, Mean VS to the driver and competitor as a function of relative level.
- Figure 10.
Distribution of spatial tuning correlation values between simultaneously recorded OT and nRt units. A, Histogram of spatial tuning correlation values between OT and forebrain units where colors indicate interquartile ranges. Example OT (B) and nRt (C) unit pair exhibiting low spatial tuning correlation below the 25th percentile range (gray bars in A). Example OT (D) and nRt (E) unit pair exhibiting high spatial tuning correlation above the 75th percentile range (navy bars in A). F, Histogram of spatial tuning correlation values between OT and nRt contributed by frontal OT units with preferred location magnitudes less than 45° (blue) and lateral OT units with preferred location magnitudes greater than 45° (red). p value from t test on the frontal and peripheral histogram distributions reported in the top left corner indicates frontal OT units exhibited larger spatial tuning correlation values with nRt units than lateral OT units.
- Figure 11.
Interregional STS between OT and nRt during competition is most prominent when unit pairs across regions exhibit similar spatial tuning and the driver is strongest. A, Cross-correlograms computed from spike trains of units in OT and nRT for competing sounds, averaged across all simultaneously recorded unit pairs belonging to spatial tuning correlation quartiles, as indicated in Figure 10A colors and color bar (rows), and each relative level condition (columns). Number of unit pairs indicated in each subplot. B, C, Competition synchrony index (CSI) measuring change in STS with competition relative to presentation of a single driver stimulus across all relative levels (B) and for unit pairs exhibiting spatial tuning correlation values across all quartiles for relative level conditions −15 and −10 (left 2 columns) (C). Box plots show the interquartile range (25th–75th percentile) with whiskers indicating 5–95% confidence interval, and circles represent individual units. ANOVA p value and relevant post hoc p values reported for each pairwise comparison.
- Figure 12.
Cross-regional power of gamma oscillations and STS between OT and nRt is strongest during competition when the driver is strongest. A–C, Heat map of average gamma power within OT (A), within nRt (B), and between OT and nRt (C) for each spatial tuning correlation quartile, as indicated in Figure 10A (rows), as a function of relative level conditions (columns). Color bars indicate the average gamma power in each condition observed within OT (A), nRt (B), and between OT and nRT for simultaneously recorded units (C). D–F, Scatterplot of cross-regional STS as a function of average gamma power within OT (D), within nRt (E), and between OT and nRt (F). Pearson’s correlation coefficient indicated top left.
- Figure 13.
Midbrain and forebrain spikes are coherent with different frequency bands of LFP gamma oscillations. A, B, Spike field coherence in OT (A) and nRt (B) during competition when the driver was strongest (−15), the driver and competitor were equal (0), and when the competitor was strongest (+10). C, D, Histogram of the difference between spike phases and preferred phase relative to the LFP bandpass filtered within the low gamma range (20–50 Hz) in OT (C) and nRt (D) during competition. E, F, Histogram of the difference between spike phases and preferred phase relative to the LFP bandpass filtered within the high gamma range (50–75 Hz) in OT (E) and nRt (F) during competition. Vector strengths (VS) indicated in each subplot. Gray curve in all plots constructed from estimating spike field coherence and spike phase from trial shuffled data.
