Article Figures & Data
Figures
- Figure 1.
Memory-guided anti-reach task with precuing. a, The left sequence shows an example of a pro-trial, and the right, an example of an anti-trial. Subjects had to maintain eye fixation (central dark spot) throughout the trial and hand fixation (central white spot) until the go instruction (disappearance of the white spot). The reach goal was defined by the combination of a context cue (colored central frame), indicating the pro/anti transformation rule, and a color-neutral spatial cue, which was presented at any of four different peripheral screen positions (0, 90, 180, 270°). Cues could be presented before (precue period) or after a variable memory period (go cue period), simultaneously or separately. In the example, the context and the spatial cue are both presented during the precue period. To be rewarded, the subject had to make a reach toward the previous spatial cue position (pro-reach) or to the opposite side (anti-reach). The arrows and dotted circles are for demonstration purpose only and were not shown to the subjects. b, In this study, we compare conditions in which the subjects either had full information on the upcoming motor goal (transformation rule and spatial cue presented as precue; RS condition) or only the context information available (transformation rule presented as precue, spatial cue during go cue period; R condition). c, Extracellular signals from multiple individual neurons were recorded simultaneously in PRR and PMd (regions of interest for monkey S) while the monkeys performed the task.
- Figure 2.
Motor-goal tuning in PRR and PMd during the late planning phase of reach movements. The example cell (a) shows classical motor-goal tuning, characterized by a PD depending on the motor goal and not the cue (DD not significantly different from 180°), as shown in the polar plot (middle). The response strength and selectivity were independent of the behavioral context (GM and SM not different from zero). Raster plots and spike density functions for pro (light gray) and anti (dark) trials are shown for the two most active directions (here, 90 and 270°) during the late memory period. Time 0 marks the onset of the go cue period. The mean firing rate during the fixation period is provided for comparison (dashed line). Spike density curves are smoothed with a Gaussian kernel (σ = 50 ms; dark lines, mean; light area, SE) for presentation purposes only. Also, polar tuning functions are interpolated for presentation purposes only, whereas all analyses are conducted nonparametrically on the original spike data. b, Tuning DDs in PRR (top) and PMd (bottom) indicate that neurons in these areas are preferentially motor-goal tuned. Most individual neurons do not deviate significantly from 180° (light gray bars); a few do according to their bootstrap confidence limits (dark bars). The circular distributions of the DD for all neurons in each area do not significantly deviate from 180°. Note that because of symmetry the distribution of absolute values (|DD|) are plotted, whereas circular statistics are applied to the original DD values.
- Figure 3.
Contextual gain modulation of motor-goal tuning in PRR and PMd. a, Examples of neurons with a high absolute GM indicating stronger activity for either pro-reaches (top) or anti-reaches (bottom), with invariant motor-goal tuning preference (DD not significantly different from 180°) and selectivity (SM not significantly different from zero; conventions are as in Fig. 2a). The anti-preferring neuron (bottom) was also one that fulfilled the strict criteria for an ideal contextual gain modulation of motor-goal tuning: the neuron was significantly tuned in pro and anti trials, had a significant GM, the DD was not significantly different from 180°, and the SM not significantly different from zero. (Note that the tuning vectors shown in the polar plot are not normalized, resulting in unequal length for pro and anti trials despite equally strong tuning; the SM is computed with normalized tuning vectors.) b, Distribution of GM across the neuronal populations (conventions are as in Fig. 2b). In PMd (bottom), there was a significant bias toward negative values (mean, −0.08; gray triangle; t test) indicating on average stronger antipreference in PMd, but not in PRR (top; white triangle). The GM distributions in both areas were broader than for the shuffled data (dashed line; σd > σs; Bartlett's test) indicating significant modulation effects in both areas. Significance levels were as follows: *p < 0.05, **p < 0.01, ***p < 0.001.
- Figure 4.
Contextual selectivity modulation of motor-goal tuning in PRR and PMd. a, Examples of cells with a high absolute SM, indicating stronger directional selectivity for either pro-reaches or anti-reaches, but having the same response strength for both conditions on average across all reach directions (GM not significantly different from zero; conventions are as in Fig. 2a). The modulation resulted in different forms of tuning [e.g., bimodal (top) or nonselective (bottom) tuning functions during anti-reach planning]. b, Distribution of SM across the neuronal populations (conventions are as in Fig. 2b). There was a significant bias for positive (pro-preferring) values in PRR (top), but not in PMd (bottom), indicating on average stronger directional selectivity during pro-reach planning in PRR, like the examples shown in a. The SM distributions in both areas were broader than those of the shuffled data (dashed line; σd > σs; Bartlett's test) indicating significant modulation effects in both areas (conventions are as in Fig. 3).
- Figure 5.
Direct context modulation in PRR and PMd independent of spatial tuning. a, Examples show a pro-preferring cell (left), which was continuously more active in the memory period of pro-trials than during anti-trials (R condition). In the anti-preferring cell (right), the contextual modulation appeared later (i.e., only ∼500 ms before the go cue). b, Distribution of DM across the neuron populations. In PRR (top) as in PMd (bottom), the distributions were unbiased (i.e., centered at zero). The distribution of DM in both areas was broader than that of the shuffled data (dashed line; σd > σs; Bartlett's test) indicating contextual modulation effects (all conventions are as in Fig. 3).
- Figure 6.
Summary of the strength and bias of contextual modulations in PRR (black) and PMd (gray). a, Strength of contextual modulations. Both areas showed contextual modulations of all three types (GM, SM, and DM; Bartlett's test; significance levels are as in Fig. 3), with GM being the strongest. The σ ratio indicates the width of the distribution of modulation indices relative to the width of the distribution of the shuffled data (see Materials and Methods) (Figs. 3⇑–5). b, Pro/anti bias in the population mean. PRR and PMd showed complementary pro/anti biases in the mean contextual gain and selectivity modulation (GM and SM; mean ± SEM; t test). c, Pro/anti bias in the number of modulated neurons. The relative number of neurons with a propreference versus an antipreference was higher in PRR for GM and SM, but balanced otherwise (χ2 test).
- Figure 7.
Interdependence of contextual modulations in PRR and PMd. a–c, Pairwise cross-correlations between the three modulation indices. The Pearson correlation of the three modulation indices (r and p values given at the bottom of the diagrams) across neurons shows that none of the indices in either PRR or PMd were significantly correlated. d–f, Pairwise cross-correlation of the absolute values of the modulation indices for PRR (top) and PMd (bottom) separately. In PRR, SM–DM (f; top) and SM–GM (e; top) were negatively correlated [i.e., strong GM and DM modulations implied weak SM modulations, and vice versa (Spearman's rank correlation)]. In PMd, only SM and DM showed negative correlations (f). The underlying rose plots (gray circular histograms) illustrate the frequencies of relative modulation strengths.
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