Fig. 1: Experimental approach.
From: Functional architecture of executive control and associated event-related potentials in macaques
a Saccade countermanding task. Monkeys earned fluid reward for shifting gaze (dashed circle) to a visual target unless a stop-signal appeared after a variable stop-signal delay (SSD) adjusted to achieve ~50% canceled trials. Successful no-stop-signal or canceled trial outcome was signaled by a high-pitched tone after Ttone preceding fluid delivery. Noncanceled errors were signaled by a low-pitched tone. Monkeys could shift gaze and blink after Ttone, which equaled 1500 ms - SSD. Noncanceled trials with RT > SSD were explicit errors. Noncanceled trials with RT < SSD were premature responses. Details in text. b Neural sampling. Neural spiking was recorded across all layers of agranular SEF (NeuN stain) using Plexon U-probe. Neurons with both broad (black) and narrow (red) spikes were sampled. Spiking modulation was measured relative to the presentation of task events (thin solid, visual target; thick solid, stop-signal) and performance measures like SSRT (dashed vertical). Simultaneously, EEG was recorded from an electrode in the cranial surface over the MFC (10–20 location Fz). The yellow rectangle portrays the cortical area sampled in a T1 MR image. c Neuron classification. Among 575 sampled neurons 271 were classified by their modulation during successful stopping. Their respective spike density functions (SDF) were submitted to an unsupervised consensus clustering pipeline27 yielding the composite similarity matrix (z-score color map) and associated dendrogram. The color coding in this figure bears no relation to colors used in other figures. Consensus clustering yielded 5 clusters with 2 clusters containing >80% of the neurons. The different modulation patterns are evident in the average SDF aligned on SSRT of each cluster. Following manual curation, 129 facilitated and 84 suppressed neurons were analyzed further based on heterogeneity in modulation latency, duration, and pattern with the feedback tone. K-means clustering further divided facilitated neurons into sustained and transient classes (right panel). The inset in the right panel shows that k = 2 clusters were chosen based on the Elbow method and the Silhouette score. Therefore, three classes of neurons were analyzed in this study.
