Neuron, Volume 77 Supplemental Information Gamma and the Coordination of Spiking Activity in Early Visual Cortex Xiaoxuan Jia, Seiji Tanabe, and Adam Kohn Supplemental Information Inventory: Supplementary Figure 1: Analysis of data arising from well-isolated single units. Related to Figures 1, 2, 3, 4 and 7. Supplementary Figure 2: Effects of stimulus size on spike-spike coherence in V1 and spikefield coherence between V1 and V2. Related to Figures 3 and 4. Supplementary Figure 3 Event-based analysis of V1 LFP and V1-V2 coupling. Related to Figures 3 and 4. Supplementary Figure 4 Properties of the low frequency components of the LFP. Related to Figures 3 and 4. Supplementary Figure 5 Properties of gamma power in V2. Related to Figures 4, 5, 7, and 8. Supplementary Figure 6 Analysis of trial-to-trial fluctuations in gamma power and their relationship to the coordination of spiking activity. Related to Figures 3 and 4. Supplementary Figure 7 Comparison of effects across animals. Related to Figures 1, 2, 3, 4, and 5. Supplementary Figure 8 Analysis of gamma and the coordination of spiking activity in awake monkey V1. Related to Figures 1, 2 and 3. 1
Supplementary Figure 1 Analysis of data arising from well-isolated single units, those with a waveform signal-to-noise ratio (snr) larger than 3.5 (Kelly et al., 27). (A) V1 spike-v1 LFP coherence for gratings of different sizes, as in Figure 1. Coherence is highest for the large grating, and there is a shift towards lower peak frequencies. The difference between the largest and smallest stimulus condition was high significant (.85±.3 vs..65±.1, p<.1, n=16). (B) The average V1-V1 jitter-corrected CCG for activity driven by large (red) and small (black) grating stimuli. Synchrony increased about 2.2 fold for activity driven by large (n=3,47 pairs) compared to small (n=3,232 pairs) gratings (3.85±.58E-4 vs. 1.77±.35E-4; p=.2). (C) Gamma phase modulation of V1 spiking activity, as in Figure 7. Spikes were clustered at the preferred gamma phase (F=41.2; p<.1, n=151). V1-V2 coupling was highest near the preferred gamma phase, but the modulation was not significant due to the substantially smaller number of pairs (data not shown, F=.44, p=.8). (D) Coherence between V1 spiking activity and V2 LFPs, for large (red) and small (black) gratings. Coherence is significantly stronger for the larger grating (.366±.1 vs.222±.4; p<.1). (E) The average V1-V2 jittercorrected CCGs for activity driven by large (red; n=1,327 pairs) and small gratings (black; n=1,9 pairs). The sharp peak of jittered CCG increased 5% for large gratings compared to small (1.9±.12E-4 v.s..72±.11e-4; p=.3). (F) V2 spiking as a function of V2 gamma phase. Spike times were weakly modulated by gamma phase (F=4.35, p=.1, n=93 cells), as also observed in the full data set (Figure 7D). V1-V2 coupling was strongest for phases 9 degrees offset from the V2 preferred phase, as in the full data set, but the modulation was not statistically significant given the relatively small number of observations (data not shown; F=.9, p=.5). Together these results show that similar effects to those shown in the main text were observed when the analysis was limited to well-isolated single units. 2
Supplementary Figure 1 A SFC.11.8 V1-V1 1 deg 2 deg 4 deg 6 deg 8 deg 1 deg.5 n = 16 sites 2 4 6 8 1 D V1 spikes V2 LFP sfcerence.6.3 V1-V2 <3.5 deg 1 deg n = 773 pairs 2 4 6 8 1 B 6 x 1 4 Jitter-corrected CCG E 2 x 1 4 Jitter-corrected CCG (coin/spk) 4 2 <3.5 deg 1 deg (coin/spk) 1 2 n = 347 3232 1 n = 1327 19 1 1 1 1 Time (ms) Time (ms) C Normalized spike counts.135 V1 spikes on V1 gamma.125 n = 151 cells.115 φ-36 φ -18 φ V1 phase (deg) F Normalized spike counts V2 spikes on V2 gamma.135.125.115 φ-36 φ -18 φ V2 phase (deg) 3
Supplementary Figure 2 Effects of stimulus size on spike-spike coherence in V1 and spikefield coherence between V1 and V2. (A) To complement the CCG analysis of Figure 3, we calculated the spike-spike coherence (SSC) between all possible pairings of neurons. Gamma SSC was stronger for large gratings (.346±4E-5, n=51,98) than small gratings (.333±3.4E- 5, n=53,463; p<.1), and the peak frequency of SSC in the gamma band shifted from 47 Hz to 38 Hz when stimulus size was increased. The small bump at 1 Hz reflects a weak tendency of some neurons to fire with the monitor refresh; this modulation was not apparent in the LFP or in measure of spike-lfp coupling. (B) Given the interaction between V1 spike timing and V1 gamma, the gamma coherence of V1-V2 LFPs implies a relationship between V1 spikes and V2 gamma. We evaluated this by calculating the coherence between V1 spiking activity and V2 LFPs. Spike-field coherence was elevated at gamma frequencies and higher for responses to large (.346±.4; n=4,374 pairs; red trace) compared to small gratings (.221±.2, n=4,68 pairs; p<.1; black trace). (C) We next measured the relationship between V1 spikes and V2 LFPs for large gratings of different orientations for sites used in Figure 8D. The best orientation, which induced the most gamma power, showed higher V1 spike-v2 LFP coherence in the gamma band (.425±.7; n=3,981 pairs; red trace) than the worst orientation (.29±.4; black trace), although both conditions induced a clear peak in gamma SFC. 4
Supplementary Figure 2 A B C V1 spike-v2 LFP coherence V1 spikes-v2 LFP coherence V1 spike spike coherence.36.34.32.6.4.2.6.4.2 <3.5 deg 1 deg n = 51,98 53,463 pairs 2 4 6 8 1 <3.5 deg 1 deg n = 4374 468 pairs 2 4 6 8 1 Best ori Worst ori n = 3981 pairs 2 4 6 8 1 5
Supplementary Figure 3 Event-triggered averages of the global LFP. Our analysis shows that clustering of spike times in the gamma cycle is more consistent when gamma is more prominent. When driven by large gratings, spikes from individual neurons tend to cluster at the same phase. However, to determine how changes in gamma power affect the coordination of activity in a neuronal population, one must understand the timing relationships among large groups of neurons. We therefore examined the interaction between spike firing patterns in the population and the global gamma rhythm, defined as the average of the raw LFP signal across all electrodes at each point in time (see Jia et al., 211). (A) We computed event-triggered averages of the global LFP (ETA-LFP), where an event was defined as the number of neurons (regardless of identity) that fired in a 1 ms window. (B) Average global LFP triggered by events involving 1-7 neurons, for activity induced by a large grating (example data from one implant). The LFPs triggered on 1 neuron events (i.e. only 1 neuron in the recorded population firing a spike in a 1 ms epoch) showed little structure, but we observed a notable increase in the amplitude of ETA- LFP as the number of co-active neurons defining the trigger event increased. (C) The power spectrum of the ETA-LFPs was dominated by gamma frequencies when triggered by higher order events. (D) The average normalized gamma band power in the ETA-LFP increased from.17±.6 to.98±.1 (p<.1; n=8 implants), for events involving 1 neuron compared to those involving 7 neurons. This result suggests that higher-order synchrony occurs because spikes from individual neurons are more aligned at the same phase on the global gamma rhythm. (E) We next analyzed whether higher-order V1 events were more effective in driving downstream neurons in V2. Using responses to large gratings, we created a synthetic V1 spike train which consisted of 1 when a particular network event occurred (1 neuron firing by itself, or 2 or 3 neurons firing simultaneously, in a 1 ms bin) and a otherwise. We then computed the jitter-correct CCG between these events and the responses of V2 neurons, for V1 events consisting of one neuron firing by itself (blue), 2 neurons firing simultaneously (green), and 3 neurons firing together (red). There was a significant influence of the number of coactive neurons on V1-V2 coupling (ANOVA, F=26.9, p<.1), with higher order events more effective at driving V2 cells. These events became more frequent when gamma was elevated (Figure 3E,F). (F) V1 event-v2 LFP coherence, following the labeling convention in (E). Gamma coherence was higher between V1 and V2, when based on higher-order V1 events (.46±.4 for one neuron firing alone vs..91±.14 for 3 neurons firing together, p<.1). 6
Supplementary Figure 3 A B 2 Event triggered average (ETA) of global LFP Neuronal population Global LFP C 5 Example implant Amplitude (µv) 1 1 2 3 D 5 5 Time (ms) 1 1 spike 2 spikes 3 spikes 4 spikes 5 spikes 6 spikes 7 spikes Power 2.5 2 4 6 8 1 Normalized gamma power of ETA of global LFP.8.6.4.2 n = 8 implants 1 2 3 4 5 6 7 Number of synchronous neurons E V1 events - V2 CCG (coin/spk) x 1 4 1 Large gratings 5 hemispheres in V1 n =127 cells in V2 5 1 neuron 2 neurons 3 neurons 5 1 1 F V1 events-v2 LFP coherence.2.1 Large gratings 5 hemispheres in V1 n =3 sites in V2 2 4 6 8 1 Time (ms) 7
Supplementary Figure 4 Properties of the low frequency components of the LFP. (A) Our focus is on the gamma frequency components of the LFP, a well described and characterized frequency band linked to specific proposals of cortical function. However, we found that our manipulation of stimulus size also affected the lower frequency components of the LFP (<1 Hz), in a manner inverse to the modulation of gamma: increasing stimulus size led to a suppression of low frequency components. This is evident in (A) which shows the power spectrum of the V1 LFP for -2 Hz (n=236 sites as in Figure 1A). Power was strongest below ~5 Hz, and large gratings (red) induce less low-frequency LFP power than small gratings (black). (B) Although LFP low frequency power was suppressed for large gratings, we did not observe a striking decrease in V1 spike-field coherence. Coherence was reduced for the lowest frequency range (below roughly 8 Hz;.98±.2 vs..15±.3, p=.52), but it was elevated in the range 8-2 Hz (.79±.1 vs..69±.1, p<.1). (C) Similarly, V1-V2 field-field coherence was unaffected at the lowest frequencies, but elevated between 8-2 Hz (.393±.1 for large gratings compared to.364±.1 for small, p<.1). (D,E) Low frequency power in the V1- V1 CCG (D) and the V1-V2 CCG (E) were significantly reduced for large gratings (.74±.1 compared to.12±.1 for small gratings, p<.1;.11±.1 vs..146±.3, p<.1 for V1-V2 CCGs ). We conclude that large gratings suppress the lowfrequency coordination of spiking activity. This altered spiking coordination is not evident in the coherence between spikes and the LFP, but it is seen in the LFP itself. We also note that there are distinct behaviors for different frequencies in the range of -2 Hz. A full treatment of this frequency range falls outside the scope of the current study. 8
Supplementary Figure 4 A B C 2.12 V1 LFP power 1 1 2 V1-V1 SFC.9.6 2 V1 LFP V2 LFP coherence.6.5.4.3 2 D.15 E.3 V1-V1 CCG power.1.5 V1-V2 CCG power.2.1 2 2 9
Supplementary Figure 5 Properties of gamma power in V2. (A) Power spectra of V2 LFP for large and small gratings (n=5 sites). As in V1, increasing stimulus size induced more gamma power. (B) Upper panel shows the distribution of the gamma-preferred orientation at each site in V1, aligned so that the mean preferred orientation of each array is at degree (n=715 sites). Gamma orientation preference is shared across sites, as shown in Jia et al., 211. The lower panel shows the distribution of orientation preferences of MUA in V1, shifted according to the V1 gamma distribution. There is no apparent bias in the preferred orientation of the recorded units. (C) The upper panel shows the distribution of gamma preferred orientation at V2 sites (n=5 sites), aligned according to the mean preferred orientation of the simultaneously recorded V1 gamma. The preferred orientation of V2 gamma is also shared across V2 sites, and typically has the same preference as V1. The lower panel shows the distribution of orientation preferences of V2 neurons shifted according to the V1 gamma distribution. The preferred orientation of V2 neurons does not reflect the orientation tuning of the V1 or V2 gamma rhythm. 1
Supplementary Figure 5 A 1 3 LFP power in V2 Small (<3.5 deg) Large (1 deg) 1 2 Power 1 1 n = 5 sites 1 2 4 6 8 1 B.8 Gamma in V1 C.4 Gamma in V2 Proportion of sites.6.4.2 n = 715 sites.3.2.1 n = 5 sites -9-45 45 9-9 -45 45 9.4 MUA in V1.4 MUA in V2 Proportion of sites.3.2.1.3.2.1-9 -45 45 9-9 -45 45 9 Preferred orientation (relative to mean V1 gamma preference; deg) 11
Supplementary Figure 6 Analysis of trial-to-trial fluctuations in gamma power and their relationship to the coordination of spiking activity. We analyzed responses to large gratings and ranked each trial by the amount of gamma induced. We then compared neuronal-neuronal and neuronal-field interactions, on trials in which strong gamma power was induced (top 1/3 of trials) and those in which there was little gamma power (bottom 1/3 of trials). This allowed us to dissociate changes in the coordination of spiking activity that were related to fluctuations in gamma power, from other influences that might occur with altering stimulus properties. Firing rates for the recorded V1 cells were indistinguishable on high and low gamma trials (9.64±.28 vs. 9.79±.29 sp/s, p =.72). (A) V1-V1 jitter-corrected CCGs for high (red) and low (blue) gamma power trials. High gamma trials were associated with an increase in V1- V1 synchrony (4.14±.6E-4 vs. 3.36±.6E-4 coin/spk; p<.1). (B) V1-V2 jitter-corrected CCGs for high (red) and low (blue) gamma power trials. Elevated gamma was associated with stronger inter-areal coupling of spiking activity (1.42±.8E-4 vs..97±.8 coin/spk; p=.1). V2 rates were indistinguishable on trials in which V1 gamma power was high and low (5.29±.35 vs. 5.±.37, p =.85). (C) V1 spike-v1 LFP coherence for high (red) and low (blue) gamma power trials. Elevated gamma was associated with stronger spike-field coupling in V1 (.8±.1 vs..113±.3; p<.1). (D) V1 spike-v2 LFP coherence for high (red) and low (blue) gamma power trials. Elevated gamma was associated with stronger spike-field coupling in V1 (.461±.4 vs..399±.3; p<.1). 12
Supplementary Figure 6 A 6 x 1 4 V1 V1 CCG Low gamma trials High gamma trials B 2 x 1 4 V1 V2 CCG Jitter-corrected CCG (coin/spk) 4 2 Jitter-corrected CCG (coin/spk) 1 C 2 1 1 Time (ms).15 V1 spikes V1 LFP coherence D 1 1 1 Time (ms) V1 spikes V2 LFP coherence.6 V1-V2 SFC.1 V1-V2 SFC.4.2.5 2 4 6 8 1 2 4 6 8 1 13
Supplementary Figure 7 We found that the degree to which gamma power increased with stimulus size varied across animals. We wondered whether there was a relationship between the modulation of LFP gamma power and the strength of altered spike-spike or spike-field effects. This figure shows the results of this analysis, with each dot representing data from a single animal; the horizontal and vertical error bars indicate 95% confidence intervals, calculate by bootstrapping. (A) Relationship between change in V1 LFP gamma power and V1 SFC. (B) Relationship between change in V1 LFP gamma power and V1 gamma phase spike bias. (C) Relationship between change in LFP gamma power and V1 synchrony. (D) Relationship between change in V1 LFP gamma power and V1-V2 field-field coherence. (E) Relationship between change in V1 LFP gamma power and modulation of V1-V2 coupling by V1 gamma phase. (F) Relationship between changes in LFP gamma power and modulation of V1-V2 coupling by V1 gamma phase. We draw the following conclusions from this analysis: (1) For analyses involving LFPs (A, E), the effects were significant in every individual animal or all but one animal (the increase LFP gamma power for large stimuli evident by all points but one having a power ratio greater than 1). (2) For population based measures of spiking activity, the effects are statistically significant in most individual animals (all but one animal for the effects on V1 synchrony shown in C; 5 of 7 animals for the effects on V1-V2 coupling shown in D). (3) For single site spiking analysis, the effects were more variable. This is not surprising as they involve typically ~3 sites per animal as opposed to 5-1 pairs. Nevertheless, the single neuron gamma phase bias (B) was significant in two animals, and higher when gamma was elevated in 5 of the 6 animals. The modulation of V1-V2 coupling by gamma phase (D) was significant in three animals, and similar in nature in 6 of the 7 animals. No animal showed a significant effect in the opposite direction. (4) A portion of the variability in the effects across animals could be explained by the variability in the gamma power induced. Generally, in animals in which larger gratings resulted in only a slight elevation of gamma power, there was a weaker change in spiking coordination. The correlations ranged from.3 (where measurements were based on a small number of individual sites) to a remarkable.7-.8 for our measurements of V1-V2 coupling, and these correlations were highly statistically significant. The sole exception to this trend was V1 synchrony, which showed a small but significant negative correlation. This was driven by one array which showed a strong enhancement of synchrony but little change in gamma power. In fact, in this animal, even the smaller grating (3.5 deg) induced substantial gamma power so that the increase in gamma for the large grating was limited. Among the remaining 5 arrays, the correlation between the change in gamma power and synchrony was.57 (p<.1). (5) No effect we report is driven by an "outlier" response from a single animal. These analyses show that much of the variability in spiking coordination was related to differences across animals in gamma power, consistent with the primary conclusion of our study. 14
Supplementary Figure 7 A.8 V1 spike-field coherence B.3 V1 gamma phase bias SFC difference (big small).6.4.2 r=.3 p=.5 Phase bias difference (big small).2.1.1 r=.48 p=.5. 8 1 3 6. 8 1 3 6 C 8 x1-4 V1-V1 synchrony D 12 x1-4 V1-V2 coupling Synchrony difference (big-small; coin/spk) 6 4 2 r=-.23 p<.1 Coupling difference (big-small; coin/spk) 1 8 6 4 2 r=.84 p<.1. 8 1 3 6. 8 1 3 6 E V1-V2 coherence F 1 x1-3 Modulation of V1-V2 coupling with V1 gamma phase Coherence difference (big-small).1.5 r=.73 p=.3 -.5.8 1 3 6 Gamma power ratio (big/small) V1-V2 coupling (pref-opposite phase) 5 5 r=.73 p<.1. 8 1 3 6 Gamma power ratio (big/small) 15
Supplementary Figure 8 Analysis of gamma and the coordination of spiking activity in awake monkey V1. Methods: We recorded in 5 sessions from a male macaque monkey (macaca fascicularis). The animal was headposted and trained to fixate in a 1 deg x 1 deg window. Eye position was monitored with a high speed infrared camera (Eyelink, 1 Hz). 5 ms after the establishment of fixation, a drifting grating appeared over the aggregate receptive field of the recorded units. We presented stimuli 2 degrees and 8 degrees in diameter, at 4 stimulus orientations (45 degree steps). The receptive fields of the recorded units were roughly 2 degrees away from the point of fixation, in the lower visual field. Gratings had a spatial frequency of 1 cycle/deg and a drift rate of 6.25 Hz. Gratings were presented for 1 s at full contrast. If the animal broke fixation, the trial was aborted and the data discarded. The animal was rewarded with a drop of water for successfully completed trials, typically ~5-8 per session. All procedures were approved by the Institutional Animal Care and Use Committee at the Albert Einstein College of Medicine. Neural activity was recorded using a 48 channel microelectrode array (Blackrock, 6x8 configuration, 4 micron spacing, electrode length 1 mm). Events crossing a user-defined threshold were digitized (3 khz), saved, and sorted offline, using the same equipment, filter settings, and procedures as in the experiments with anesthetized animals. All analysis was performed in an identical manner to that recorded in anesthetized animals. (A) LFP power induced by small (black) and large (red) gratings. Gamma power was significantly higher for large gratings (3.48±.15 vs. 2.69±.15; p=.8, n=75 sites) for frequencies between 4-6 Hz, a range overlapping with that seen in anesthetized data. It is unlikely this difference in frequencies is due to anesthesia, as peak frequency has been shown to vary across subjects (Edden et al., 29) and other awake studies have described a gamma bump in the 3-5 Hz range. (B) V1 spike-field coherence for activity driven by small (black) and large (red) gratings. Gamma SFC was significantly higher for large gratings (.361±.2 vs..345±.2, p<.1). (C) Left: V1 spike timing, as a function of gamma phase, for an example site. Center: Phase bias for activity driven by small (gray) and large (red) gratings. Bias was stronger for responses to large gratings (.493±.6 vs..349±.41, p=.55). Because bias can be difficult to measure at low rates, which were prevalent in the data set (mean rate of 3.6±.5 spk/s, compared to 9.7±.2 in the anesthetized data), we also analyzed a subset of conditions for which the mean firing rate was at least 2 spk/s. In this subset, the phase bias was lower than for the full population, and significantly higher for responses to large gratings (.27±.2 vs..21±.2, p=.376). (D) Jitter-corrected CCGs for responses to large or small gratings were not significantly different (1.3±.5E-4 vs 9.2±.5E-4 coin/spk; p=.13, n=1938 pairs). This can be attributed to the low spike count contributing to these measurements, due both to lower firing rates arising from the coarse sampling of orientation and significantly fewer trials. When we analyzed a subset of our pairs recorded in anesthetized animals, chosen to match the distribution of spike counts in the awake data, the difference between synchrony for large and small gratings was also not significant (3.6±.7 vs 3.6±.6 E-4 coin/spk; p=.9). To determine whether enhanced gamma in awake animals was also associated with greater coordination of spike timing, we therefore compared the rate of occurrence of events consisting of 1 neuron firing alone, or 2, 3 or 4 neurons firing in a 1 ms window, for activity driven by large and small 16
gratings. Activity driven by large gratings (red) had a significantly higher rate of 2, 3, or 4 neurons firing simultaneously. This is most easily seen in the ratio of occurrence rate (big/small), shown to the right. The ratio is very near 1 for events consisting of 1 neuron firing alone; this is because responses to large and small gratings were rate matched and nearly all of the events consisted of 1 neuron firing alone. For events consisting of 2, 3 or 4 neurons firing simultaneously there is a marked increase in rate of occurrence. The error bars indicate 95% confidence intervals (based on bootstrap samples from the original distribution) and these do not include a ratio of 1 (no effect), except for the 4-neuron events which were very rare (only a total of 11 cases). We also evaluated significance using a binomial test. This showed the probability of the observed difference (assuming patterns were equally likely to occur for the two stimulus conditions) was highly significant for 2- and 3-neuron events, as indicated by the p-values. In addition to confirming our V1 findings in an awake animal, there are a number of additional similarities between our findings and previous reports in awake animals that indicate our results are not due to or strongly influenced by anesthesia: -First, the size-dependent properties of the gamma components of the LFP we report are remarkably similar to the work of Ray and Maunsell (211) and of Gieselmann and Thiele (28) in awake monkey, both in gamma power and the shift in peak frequency. For instance, Ray and Maunsell (211) state that the power in the gamma range (4 6 Hz, peak at ~5 Hz) increased with size (page 2, column 2, paragraph 2), a range very similar to that of our study (3-5 Hz). Ray and Maunsell (21) also shows a robust gamma spectral bump at frequencies between 3 and 6 Hz, depending on contrast. Gieselmann and Thiele (28) show that the peak gamma frequency of the LFP spectra shift from ~5 Hz to ~3 Hz as stimulus size increases (Figure 3 of their paper), very similar to the results we observe. In fact, even studies of attentiondriven increase in gamma power show a similar frequency range: Fries et al. (28; cited in the manuscript) show that attention leads to an increase in power in the 3-1 Hz range, with a peak frequency of roughly 56 Hz. Thus, studies in awake animals show that both stimulusinduced and attention-induced gamma power involve peak frequencies very similar to those that we report. -Second, the orientation-dependent properties of the gamma component of the LFP (Figure 8) are also observed in awake monkeys (reported in Figure 1 of Jia et al., 211; see also Berens et al. 28). -Third, the magnitude of spike-field coherence we report (Figure 1) is similar to those reported in awake animals. Chalk et al (21) reported awake V1 SFC values of.2-.3 (Figure 5; Neuron 66: 114-125), as did Lima et al. (21; cited in the manuscript). Hansen and Dragoi (211) found values of ~.1 in the superficial layers of awake V1 cortex. Fries et al. (28; cited in manuscript) reported V4 SFC values of.5-.1 (Chalk found values of ~.2 in V4). Strong conclusions cannot be drawn from these comparisons since SFC can be affected by numerous factors both in recording (filtering, impedance, isolation quality) and analysis (number of tapers, number of trials, number of spikes). Nevertheless, they show the relationship between LFP and spikes is similar in our data and the available awake data. 17
-Fourth, the magnitude of the V1-V1 LFP coherence we observe (~.7; Figure 8B) is similar to that reported in awake monkey V1 (Figure 9 of Lima et al., 21 or Figure 5 of Ray and Maunsell, 21). -Fifth, we measured responses in opiate (sufentanil) anesthetized monkeys. A comparison of responses in awake, opiate-anesthetized (fentanyl, a close analogue of the sufentanil we use), and isoflurane anesthetized rats showed that responses under opiate anesthesia were much more similar to awake responses than to isoflurane anesthesia (Constantinople and Bruno, 211). -Sixth, spike synchrony and gamma-fluctuations in the CCG have of course been reported in awake animals (e.g. Lima et al., 211, Roelfsema et al., 24). Thus, while we cannot exclude the possibility that there would be some quantitative difference between our results and those one would obtain by repeating the experiment in awake animals (if this were feasible, given the requirement of having many spikes and extremely stable and reproducible presentation of stimuli across trials), the available evidence suggests that gamma, spiking activity, and their relationship are similar in opiate-anesthetized and awake animals. 18
Supplementary Figure 8 A 1 2 Large (8 deg) Small (2 deg) B.5 LFP power 1 1 1 SFC.4 n=75 sites 1 1 2 4 6 8 1.3 2 4 6 8 1 C Normalized spike counts.2.1 18 Example site 9 9 18 Phase (deg) Gamma phase bias.5.4.3.2.1 p=.55 (n=75) Small Large.5.4.3.2.1 p=.38 (n=56) Small Large D Occurence (# of events/sec) 1 2 1 1 1 1-1 1-2 1-3 1-4 Total events: 228,85 987 349 11 1 2 3 4 Number of active neurons (in 1 ms bin) Rate of occurence (large/small) 3 p=n.s. p=.4 2 p<.1 p=n.s. 1 1 2 3 4 Number of active neurons (in 1 ms bin) 19
Supplemental References Constantinople CM, Bruno RM (211) Effects and mechanisms of wakefulness on local cortical networks. Neuron 69: 161-168. Edden RA, Muthukumaraswamy SD, Freeman TC, Singh KD (29) Orientation discrimination performance is predicted by GABA concentration and gamma oscillation frequency in human primary visual cortex. J Neurosci 29: 15721 15726. Hansen BJ, Dragoi V (211) Adaptation-induced synchronization in laminar cortical circuits. Proc Natl Acad Sci USA 18: 172-1725. Kelly RC, Smith MA, Samonds JM, Kohn A, Bonds AB, Movshon JA, Lee TS (27) Comparison of recordings from microelectrode arrays and single electrodes in the visual cortex. J Neurosci. 27: 261-264. Roelfsema PR, Lamme VA, Spekreijse H (24) Synchrony and covariation of firing rates in the primary visual cortex during contour grouping. Nat Neurosci. 7: 982-991. 2