Volume 74, Issue 5, Pages 899-910 (June 2012) Spontaneous High-Gamma Band Activity Reflects Functional Organization of Auditory Cortex in the Awake Macaque  Makoto Fukushima, Richard C. Saunders, David A. Leopold, Mortimer Mishkin, Bruno B. Averbeck  Neuron  Volume 74, Issue 5, Pages 899-910 (June 2012) DOI: 10.1016/j.neuron.2012.04.014 Copyright © 2012 Elsevier Inc. Terms and Conditions

Figure 1 Microelectrocorticographic (μECoG) Arrays and Implanted Locations (A) μECoG array designed for this study (figure courtesy of Neuronexus Inc.) consists of 32 electrodes in a 4 × 8 pattern (small yellow dots) fabricated on a 20 μm thick polyimide film. The large white circles are holes in the array designed for microinjections. (B) Implanted locations of five arrays (numbered 1–5) in monkey M. Three arrays (1, 2, and 3) were inserted in the lateral sulcus and positioned on the supratemporal plane. The two other arrays were placed on the lateral surface of the superior temporal gyrus. (C) Lateral view of the right hemisphere reproduced from the postmortem brain of monkey M after removing the upper bank of the lateral sulcus and frontoparietal operculum to visualize the location of the three arrays (1–3) on the supratemporal plane, on which we focused in the current study. Fifth array is not drawn in this figure. (D) Nissl-stained coronal section taken from the approximate location of the dashed line in (C). The brain was serially sectioned with the implanted array in place; a piece of the array is visible on the STP in this section. Abbreviations: ls, lateral sulcus; STP, supratemporal plane; sts, superior temporal sulcus. Neuron 2012 74, 899-910DOI: (10.1016/j.neuron.2012.04.014) Copyright © 2012 Elsevier Inc. Terms and Conditions

Figure 2 Examples of the Auditory Evoked Potential and the Characteristic Frequency (A) Upper panels: trial-averaged spectrograms to a tone stimulus. The spectrograms were normalized by the prestimulus period activity. Lower panels: trial-averaged auditory evoked potential to the same tone stimulus in Upper panel. Left panels from Ch 8 in the most caudal array; Right panels from Ch 92 in the most rostral array, both from monkey M). (B) Frequency-intensity tuning curve. The average evoked high-gamma power from the first 150 ms is plotted for each of the 180 tone stimuli (30 frequencies × 6 intensity levels). The unit of power is (μV)2. The log (base 10) of the power is color coded. The characteristic frequency (CF) is indicated by the arrow on the frequency axis. See also Figure S3 for supplemental information for this figure. Neuron 2012 74, 899-910DOI: (10.1016/j.neuron.2012.04.014) Copyright © 2012 Elsevier Inc. Terms and Conditions

Figure 3 Tonotopic Map on the STP Obtained with High-Gamma Power (A) The spatial map of the estimated CFs for each monkey (Left, monkey M; right, monkey B). The CFs are color coded. White indicates site without significant frequency tuning. (B) The CFs projected onto their caudorostral locations. Each CF from (A) is plotted on the vertical axis and its corresponding caudorostral location is plotted on the horizontal axis. Abbreviation: Sec, sector (see main text for definition of each sector). See also Figures S1 and S3 and Table S1 for supplemental information for this figure. Neuron 2012 74, 899-910DOI: (10.1016/j.neuron.2012.04.014) Copyright © 2012 Elsevier Inc. Terms and Conditions

Figure 4 The Spatial Structure of the Spontaneous High-Gamma-Band Voltage Is Correlated with the CF Map (A) Two time frames from spontaneous high-gamma voltage illustrating the significant correlations between spontaneous activity and the CF map (monkey M: top, r = 0.67; bottom, r = 0.44). The dashed lines indicate the boundaries of different sectors as defined in Figure 3A. (B) Distributions of correlation between the CF map and spontaneous activity (left, monkey M; right, monkey B). Red, the distribution of correlation coefficients between the CF map and spontaneous-voltage time frames over the entire recording session. Black, the control distribution created by correlating with randomized CF maps (with 10 different randomizations). Each distribution was fitted by a Gaussian, indicated by the lines. The significance level was computed from the control distribution for p < 0.01 (two-sided, p < 0.005 on each side). The gray area indicates the correlation coefficients satisfying this significance level. Neuron 2012 74, 899-910DOI: (10.1016/j.neuron.2012.04.014) Copyright © 2012 Elsevier Inc. Terms and Conditions

Figure 5 The Amount of Variance Explained by Each Principal Component from the Spontaneous Activity Left: monkey M; right: monkey B. Bar plot with the ordinate labeling on the left side: the percentage of variance explained by each principal component. Red curve with the ordinate labeling on the right side: The cumulative proportion of the variance explained. The vertical dotted line indicates the number of principal components necessary to explain 80% of the total variance of the data (22 for monkey M, 32 for monkey B). The gray dashed line indicates the percentage of variance explained by uniformly distributed eigenvalues. Neuron 2012 74, 899-910DOI: (10.1016/j.neuron.2012.04.014) Copyright © 2012 Elsevier Inc. Terms and Conditions

Figure 6 Principal Components from the Spontaneous Activity Correlated with the Functional Architecture of the Auditory Cortex (A) The highest order PCs that correlated with the areal map. The first PCs provide the eigenvector with the highest correlation for both monkey M (left) and monkey B (right). (B) The highest-order PCs that correlated with the tonotopic map. The second PC for monkey M (left) and the fourth PC for monkey B (right). (C) The scatter plot showing the correlation between the normalized CFs and eigenvalues plotted in (B) for significant frequency-tuned sites in Figure 3A. Each circle corresponds to one of the significantly tuned sites. See also Figure S2 and Table S2 for supplemental information for this figure. Neuron 2012 74, 899-910DOI: (10.1016/j.neuron.2012.04.014) Copyright © 2012 Elsevier Inc. Terms and Conditions