Surgical procedure
In this study, we performed 3 experiments and collected data from two adult male rhesus monkeys (Macaca mulatta), referred to as Sp and Ph. All procedures were conducted in accordance with the guidelines of the National Institute of Mental Health Animal Use and Care Committee.
In a sterile surgery under general anesthesia we performed a craniotomy and a durotomy to access the surface of IT cortex (left hemisphere in Sp, right hemisphere in Ph). We then injected AAV5-C1V1(t/t)-EYFP (nominal titer: 8×1012 particles/ml) into the cortex. To ensure uniform viral expression and reduce anesthesia-controlled time, we used an injection array1 including four 31-gauge needles arranged in a 2×2 mm square. We placed the injection array four times, tiling central IT cortex with sixteen evenly spaced injection sites, resulting in a region of ~ 6mm x 6mm viral expression. Each needle was connected with flexible tubing to a 100 µl Hamilton syringe, and injection was controlled by a microinjection pump (Harvard Apparatus Pump 11 Elite). At each injection site, 10 µl of virus was injected at a 0.5 µl/min rate. Ten minutes were allowed to elapse after each injection before removing the array to allow the virus to diffuse into the cortical tissue.
Several weeks later (12 and 4 weeks in Sp and Ph respectively), in a second surgery, we confirmed the virus expression and implanted an Opto-Array (Blackrock Microsystems) on the injection site. To confirm the viral expression, we used the fluorescent signature of the enhanced yellow fluorescent protein (EYFP) coexpressed with the opsin in transfected cells, by shining a 490-515 nm wavelength light (with a NIGHTSEA Dual Fluorescent Protein Flashlight) and viewing the cortex through 550 nm longpass filter-goggles (NIGHTSEA). This fluorescent signature was confirmed in Monkey Sp, but not in Monkey Ph. Therefore, in Monkey Ph, before proceeding with the array implantation, we performed a second virus injection similar to the first injection procedure (3 injection array placements, yielding 12 injection sites in a region of 4 x 6 mm; 10 µl of virus injected into each site at 0.5 µl/min rate). Then we implanted an Opto-Array over the injection sites. The Opto-Array was placed directly on the pia mater and sutured to the neighboring dura. Following this, in the same surgery, we implanted a second Opto-Array on a similar area of the IT cortex in the opposite hemisphere (control site: right hemisphere in Sp, and left hemisphere in Ph) where no virus injection was performed.
Apparatus
The experiment was carried out with the monkey head fixed, positioned 57 cm from a 27 in, 3840x2160 pixel, 60 Hz, Dell P2715Qt monitor. Fluorescent room lights were turned on to avoid dark adaptation of the retinae. This was done to minimize the possibility that the monkey would detect the light from the Opto-Array through the skull. To guard against heating cortical tissue by LED activation, temperature on the LED die was monitored by a thermistor inside the Opto-Array at the beginning of each trial and trial delivery was paused if the temperature on the LED die rose more than 3° C above the baseline temperature, and restarted once they were less than 1° C above the baseline. 3° C at the LED die translates to approximately 0.5° C temperature change on the cortical surface; this temperature management regime is detailed in Rajalingham et al. 20212. The experiment was controlled with a custom MWorks script (The MWorks Project), running on a Mac Pro 2018. Opto-Arrays were controlled by a Blackrock LED Driver (Blackrock Microsystems) running a custom firmware version for compatibility with MWorks. Gaze was tracked with an Eyelink 1000 Plus (SR Research). Animals were water-restricted in their cages and received liquid rewards for successfully completing trials.
Behavioral task
Monkeys were trained to perform a detection task in which they were rewarded if they correctly identified whether a trial did or did not contain an optogenetic stimulation impulse. The subject started a trial by fixating on a central fixation point (black-on-white bullseye, 0.4° outer diameter and 0.2° inner diameter) for 500 ms on a gray background. Then, an image (scaled so the largest dimension spanned 8° for most images and 30° for four scenes during training and two scenes in experiment 1) appeared on the screen for 1000 ms while the animal held fixation on a central target. In half of the trials (randomly selected) 500 ms from the image onset, an LED on one of the Opto-Arrays was activated for 200ms. Then the image and central fixation point disappeared and two response targets appeared on the vertical midline (white, 0.4° diameter, 5° above and below center). The subject reported the existence of cortical stimulation by fixating for 100 ms on one of the response targets. Then, the response targets disappeared and a unique sound was played for correct and incorrect responses. The subject received a juice reward for a correct response or a punishment of 3.5 s delay before starting the next trial in case of an incorrect response. Trials with broken fixations or a latency of more than 3 s for choosing a response target were considered as an incorrect response during the experiment but excluded from further analysis. A ~300 ms tone played at the same time the image appeared to indicate that a trial had started.
Throughout the training phase and all the experiments, 50% of the trials were ‘no-stimulation.’ The other 50% were trials in which an opto-array was activated. In ‘stimulation’ trials (40%-50% of all trials depending on the experiment and monkey, see experimental conditions for details), the opto-array on the virus-expressed site was activated and in ‘catch’ trials (0%-10% of all trials) the opto-array on the control site was activated. The catch trials used the same stimulation parameters and were rewarded the same as stimulation trials. Performance above chance level on the catch trials would indicate that the subjects did not truly perform the task by detecting the optogenetic activation of IT neurons. This controlled for the possibility that the subjects might be glimpsing light through the skull, or be detecting a potential perturbation of the neural activities caused by the heat3.
Behavioral Training
Both monkeys were operantly trained on the experimental task using a different set of images than would be used in the subsequent experiments (Extended Data Figure 1b). To maximize the signal that the monkey was learning to detect, we began training by activating five LEDs simultaneously with power of 10.6 mW and 12.1 mW per LED for Ph and Sp respectively in stimulation trials. To reduce choice bias, we employed a ‘correction loop’ procedure4. Under this protocol, if the monkey chose the same wrong response target more than three times in a row, every subsequently presented trial would be the opposite type until the monkey selected the correct response target. Data collected in correction loops were excluded from analysis. Ph. started the training phase with 2 images and the number of images was gradually increased to 22. Sp. started training with all 22 images, but we eventually reduced the number of images to 1 and slowly reintroduced the full training set like in Ph. Then, in both monkeys we reduced the number of activated LEDs to one, and illumination power to 4.5 mW in Ph and 9.1 mW in Sp. We introduced catch trials to Ph. after 17 sessions at an initial rate of 5% of all trials, then after 23 sessions increased the rate to 10% of all trials which continued for the rest of training. Catch trials comprising 10% of all trials were included for Sp. in all training sessions. In total, the subjects performed 42 and 48 sessions in the training phase, with 67,115 trials and 41,409 trials respectively for Ph and Sp. Part of the training data is reported in Rajalingham et al., 20212.
Experimental conditions and visual stimulus
Experiment 1 contained 40 images and 2 illumination sites for stimulation trials (see Extended Data Figure 1a for image set and inset in Figure 2b and Extended Data Figure 3 for schematic of illumination locations) with illumination power of 3.6 mW and 5.4 mW respectively for Ph and Sp. Catch trials were included at a rate of 10% and 2%, and 10 and 13 sessions were performed with a total of 17,033 trials and 16,125 trials, and an overall performance of 84.6% and 84.9% correct (catch trials excluded), respectively for Ph and Sp. Ph only received catch trials to one site on the control array while Sp received catch trials to two sites, randomly interleaved. The performances for detecting cortical stimulation were statistically significant for stimulation trials (Ph: X2 (1, N = 15320) = 7295.1, p < 0.001 and Sp: X2 (1, N = 15794) = 7714.7, p < 0.001) but not for catch trials (Ph: X2 (1, N = 10370) = 0.02, p = 0.879 and Sp: X2 (1, N = 8428) = 1.7, p = 0.190).
Experiment 2 contained 5 images, 2 stimulation sites and 7 intensity conditions. The stimulation sites were the same as in experiment 1. The images used in this experiment were a subset of the images used in experiment 1, with the two highest and two lowest d’ image conditions selected (average of the two cortical locations). The fifth image was chosen by calculating which image had the greatest difference in d’ between cortical location conditions in experiment 1. Illumination power for “stimulation” trials ranged from 0.4 mW to 5.4 mW for both monkeys and 9 and 12 sessions were performed with 14,941 and 14,056 trials collected with overall performance of 79.6% and 74.7% correct, respectively for Ph and Sp. This experiment included no catch trials.
Experiment 3 contained 5 images and 4 image visibility conditions, plus one “no image” (uniform gray) condition (see Extended Data Figure 1c for this image set). The “no image” condition occurred as often as any one “image at a visibility” condition, creating 21 total conditions. One cortical site was used for this experiment (Site 1 for both monkeys). We selected the top 5 highest d’ images from experiment 1 at that cortical site for this imageset and degraded their visibility by reducing their contrast, saturation, and spatial frequency to near gray. To do this, the mean luminance of each image was adjusted to match that of the gray display background. Then, saturation was reduced by multiplying each pixel’s chromaticity coordinates (a* and b*, CIELAB 1976) by a scale factor of ⅓, 1/9, and 1/27 for the decreasing visibility levels. Image contrast was reduced by the same operation on the L* dimension (lightness) of the CIELAB color profile, but first the mean L* of the distribution was subtracted from each pixel, then re-added after multiplication by the scale factor, ensuring that the mean luminance of the distribution was unchanged. Finally, the spatial frequency of the Lab-scaled images was reduced by convolving each image with a 2D gaussian smoothing kernel with standard deviations of 0.39, 0.78, and 1.56° for the different visibility level. To ensure that the filtered images blended evenly into the background, padding was added to the edges of the images but care was taken to ensure the presented size was the same 8° as experiment 1 and 2. Each visibility condition was a combination of one CIELAB scaling factor and one gaussian filter. Illumination power was 3.5 mW and 5.4 mW, and 1 session was performed for each monkey with 2030 and 3193 trials collected with overall performance of 77.8% and 90.9% correct trials, respectively for Ph and Sp.
Data Analysis
Detection performance: we used d’ as a bias-free measure of performance for detecting cortical stimulation5 which is estimated by the following equation:
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Where Z is Z-transform, H is the animal’s hit rate for detecting stimulation, and F is the false alarm rate representing the proportion of trials where no stimulation was applied but the animals reported the trial as stimulated.
Effect of image on detectability (Experiment 1): first, we calculated a d’ for each image, indicating the detectability of cortical stimulation. This creates a ‘detection profile’ shown in Figure 2.a and Extended Data Figure 1. The 95% confidence intervals are estimated for each image by bootstrapping the data, resampling 10,000 times with replacement6 and the violin plots represent the distribution of the bootstrapped data. To statistically test the effect of image on detectability of cortical stimulation, we ran a permutation test in which first we calculated the standard deviation of the d’s across images (observed standard deviation). Then, we generated the null distribution by randomly assigning the images to the trials with 10,000 replications and compared the observed standard deviation to the distribution of standard deviations generated from the null model. The permutation tests showed that the effect of images on detection of cortical stimulation is statistically significant (p < 0.001 for all the detection profiles). Moreover, we ran the same permutation tests after excluding the no image trials from the data and the result remained statistically significant (p < 0.001 for all the detection profiles).
Effect of cortical stimulation location on image detection profile (Experiment 1): we used Pearson’s correlation to evaluate the similarity between the detection profiles derived from two neighboring stimulation sites. First we calculated a hit rate for each image and each stimulation site. The correlation between hit rate profiles at neighboring sites were statistically significant (Pearson’s r(39) = 0.91 and 0.82 respectively in Ph and SP; p < 0.001 for both subjects). To determine if there was a difference between the sites, we followed up these results with bootstrapped estimates of the correlations within each site and between them, resampled 10,000 times with replacement. The median correlation coefficients were 0.95 and 0.95 within the sites, and 0.86 between the sites for Ph (Figure 2.b) and 0.89 and 0.95 within and 0.75 between for Sp (Extended Data Figure 3). These results show that the detection profiles are more correlated within the sites compared with between them in both subjects. To test if this is a statistically significant difference, we generated a null distribution by randomly assigning sites to the stimulation trials with 10,000 replications; the results of this permutation test show that the observed correlation between the sites is smaller than the correlation between sites in the null distribution derived by randomly assigning sites to the trials (Ph: p =< 0.010, Sp: p < 0.001; Figure 2.b and Extended Data Figure 3).
Effect of Illumination power on image detection profile (Experiment 2): in Figure 2.c and Extended Data Figure 4, we plotted d’s as a function of illumination power for each image. We used the following formula to fit the data:
![](data:image/png;base64,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)
Where i is the trial number. x is illumination power, α, β, β1, …, βn are the fit coefficients. For each trial, the λ that matches the image index is assigned 1, and the rest are assigned 0. Therefore, β1, β2, …, β5 represent the effect of the image on the psychometric functions. The range of r2s are from 0.89 to 0.98 and 0.83 to 0.95 with the average of 0.94 and 0.89 for both stimulation sites respectively for Ph and Sp. Then we calculated the standard deviation of the coefficients β1, β2, …, β5. A permutation test was performed by assigning random image indices to the trials (10,000 times repetitions) to generate the null distribution of standard deviation for these coefficients. The results showed a significant effect of images on psychometric functions (p < 0.001 for both sites on both subjects).
Data availability
The data that support the findings of this study are available on request from the corresponding author.
Code availability
Code for experimental design and data analysis are available on request from the corresponding author.
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