Article Figures & Data
Figures
- Figure 1.
Tasks and areas for neurophysiological recordings. A, Frames represent the sequence of event during the MSNG task, in which they were required to report whether two visual stimuli appeared at a matching spatial location, by either continuing to fixate on the center fixation point (match trials), or by saccading to the location (nonmatch trials) of the second stimulus. B, The possible locations of stimuli were arranged in an invisible half circle with 10° of visual angle eccentricity, and the presentations of the stimuli were separated by a 3-s delay period in which no stimuli were displayed. The first stimulus could appear pseudo-randomly at one of nine possible spatial locations. Possible cue locations included a reference location (shown here at the top location) and eight locations deviating from the reference location by an angular distance of 11.25°, 22.5°, 45°, and 90°, either clockwise or counterclockwise. The reference location was changed from session to session and could appear in eight locations 45° apart around the fixation point (see Materials and Methods). This cue was followed by a second stimulus (henceforth referred to as the match or nonmatch). The match would appear at the same location as the cue in approximately half the trials (9/17 conditions). Similarly, the nonmatch would appear at the reference location in approximately half the trials (8/17 conditions). The reference location varied from session to session. C, Neurophysiological recordings were performed in two cortical areas: the dlPFC, including areas 8 and 46, and the PPC, including areas 7a and LIP. IPS, intraparietal sulcus; STS, superior temporal sulcus; AS, arcuate sulcus; PS, principal sulcus.
- Figure 2.
Exemplar neural responses from the MSNG task. Examples of four dlPFC neurons are shown, exhibiting CS, LMS, and NMS cells, defined by the task variables of stimulus location and task epoch. The x-axes represent the relative location to the center reference location. The y-axes represent the spiking rates during two 500-ms stimulus presentation epochs. Error bars indicate SE.
- Figure 3.
Proportion of NMS neurons in PFC and PPC. A, Bar graphs show the proportions of cells tuned to stimulus location, task epoch and their interaction (i.e., NMS), in the dlPFC (N = 404) and PPC (N = 654). Increased selectivity to single task variables does not fully explain the increased levels of NMS in the dlPFC. This area continued to display a higher proportion of NMS cells compared with the PPC, even after a permutation test was used to control for different levels of CS (see Materials and Methods). B, Probability and cumulative density function for the F-scores in the ANOVA test on factor of location, epoch and their interaction. C, Classification of NMS cells shows that in dlPFC, the NMS is mainly contributed by cells that shows location selectivity only during the match period. All crosses (black, red, purple, and green) represent NMS cells with color coding for different selectivity categories. Gray dots indicate all other cells.
- Figure 4.
Population responses in PCA space. Each point represents responses of dlPFC (top) and PPC (bottom) neurons to one stimulus location. Numbers in points denote the eight possible locations of cue and match stimuli in Figure 1B, right, ordered in clockwise fashion. Red planes, Best-fit planes for the representations mean firing rate of neurons in the cue period. Blue planes, Best-fit planes in the match period. PC1, PC2, and PC3 are the first three principal components of the response space.
- Figure 5.
Behavior performance during each session. Mean correct behavior performance is plotted in successive 40-trial blocks. Top, Performance in match trials, when the match appeared to a position deviating from the reference location by the angle indicated. Bottom, Performance in nonmatch trials, when the cue appeared at the reference location and nonmatch stimulus appeared at the position deviating by the angle indicated. Error bars indicate SEM.
- Figure 6.
Changes in cell selectivity across a single experimental session. A, Average F-score for the interaction term in the ANOVA test for dlPFC and PPC neurons plotted as a function of trial order across sessions. B, Average F-score for location factor in the AVOVA in either the cue or the match period, is plotted against trial order in a session. dlPFC cells developed selectivity to location over the course of a single session more obviously, compared with PPC. C, Permutation tests demonstrate that both dlPFC and PPC, displayed statistically significant changes in degree of nonlinearity, measured by F-ratio for the interaction term in ANOVA test. x-axes of the plots represent slopes for linear regression of trial-order-dependent F-score change. Vertical lines indicate empirical values form unshuffled data.
- Figure 7.
Neuronal selectivity in correct and error trials. Selectivity is plotted in the dlPFC and PPC, after controlling for the number of trials and the location pairs that were examined. No decrease in the mean F-score of the interaction term (i.e., NMS) was observed. Box boundaries represent 25−75% data range, whiskers indicate 1.5 interquartile range, and squares indicate means across each brain area.
- Figure 8.
Location selectivity in the cue and the delay period. A, Left, Bar graphs show the proportions of cells tuned to stimulus location, task epoch (cue vs delay) and their interaction in the dlPFC (N = 362) and PPC (N = 624). dlPFC exhibited a higher proportion of cells showing NMS (the interaction bar) defined by location selectivity during the cue and the delay period. Right, Increased selectivity to single task variables does not fully explain the increased levels of NMS in the dlPFC. This area continued to display a higher proportion of NMS cells compared with the PPC, even after a permutation test was used to control for different levels of CS (see Materials and Methods). B, Three representative cells that showed cue, delay, and both period selectivity for the locations of stimuli. Shaded area represents standard error of the mean firing rate. C, Scatter plot for location selectivity in the cue and the delay period, for PFC and PPC populations. D, Scatter plot indicating the preferred location for the cue (abscissa) and delay period (ordinate) for cells that showed location selectivity in both periods. Each circle represents one neuron. Only neurons with responses that could be fitted by a Gaussian function were included in this analysis (N = 23 in PFC, N = 7 in PPC).
- Figure 9.
Mixed selectivity for cue location and reward. A, An example cell that reversed its location preference in rewarded versus nonrewarded conditions. Black line represents the time that reward was expected. Shaded area represents standard error of the mean firing rate. B, Bar graphs show the proportions of cells tuned to stimulus location, reward, and their interaction (i.e., NMS), in the dlPFC (N = 314) and PPC (N = 500). Error bar represents standard deviation in 50 resamples.
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