Fig. 1: Task paradigm, behavior, and recordings.

a Task structure (see “Behavioral task” subsection of Methods). Tn, the n^th target. The delay (2.5-4 s for M1 and M2; 1.15-1.50 s for M3 and M4) was randomized across trials. b Behavioral performance of each rank in different sequence lengths (from M1, see also Supplementary Fig. 1). Each subpanel shows averaged recall errors relative to target locations, Data and errorbars are presented as mean values and STD across recording sessions (n = 11 sessions). c Averaged correct rates on each rank of different sequence lengths. Error bars represent standard error of the mean (SEM) across recording sessions (n = 11). Line colors indicate ordinal ranks. d The averaged recall variabilities on each rank of different sequence lengths, error bars represent standard error of the mean (SEM) across recording sessions (n = 11). Same format as (c). e Rank error patterns of different sequence lengths (from top to bottom: length-2, -3, and -4). The rank error pattern is shown as a function of ordinal rank, averaged across spatial locations. Error bars represent standard deviation across recording sessions (n = 11). f Illustration of two-photon calcium imaging and high-throughput electrophysiological recording in monkeys’ LPFCs. The blue circles in the example FOV indicate the regions of interest (ROIs) with three example neurons, whose normalized calcium traces are on the lower left. ΔF/F, normalized fluorescence intensity. Red bar, cue on of single trial. The brown circles in the recording grid indicate the recording sites of three example neurons (activities shown in (g)). g Three example neurons exhibiting complex coding for spatial items across different ranks and sequence lengths during the late delay period (0 on time axes denoting onset of the ‘go’ cue). Each subpanel entitled with \({{{\rm{L}}}}_{{{\rm{i}}}}\)-\({{{\rm{R}}}}_{{{\rm{j}}}}\) represents one length i and rank j combination, with the top part being a spike raster plot and the bottom displaying averaged firing rates (shading: SEMs across trials during the late delay period). Line/dot colors correspond to spatial locations.