Neural correlates of executive control functions in the monkey

Abstract

Executive control functions (ECFs) have become an important topic in the cognitive sciences in the past 40 years. The number of publications has steadily increased, and in the last decade, studies have been conducted in one of the best models of human cognition: the old-world macaque monkey. Here, we review recent studies in the monkey that have contributed to our understanding of the neuronal implementation of ECFs, with a focus on task-switching paradigms. These paradigms have revealed that ECFs are distributed across both the parietal and frontal lobes.

Figure I

The approximate location of each of the techniques in the spatial and temporal domains (after Ref. [56]).

Figure 1

Example trials of four paradigms. Panels are read from left to right. Not all events are illustrated, such as error signals, which have an essential role in panels (a) and (b). Screen touches are indicated by a star-burst, liquid rewards with drops and lack thereof with crossed out drops. (a) Analogue of WCST [15]. Monkeys alternated between blocks of matching shape and blocks of matching color. Changes in task were not cued; monkeys used error feedback to switch between tasks. In high conflict trials (top two rows), knowledge of the task rule was necessary to perform the task; in low conflict trials either rule resulted in the same answer (bottom row). (b) Another WCST analogue [19]. Monkeys alternated between saccade and anti-saccade blocks. ~ character seperates trials [also in panel (d)]. (c) A task-switching paradigm analogue [22]. One of two possible matching rules was cued on each trial: respond on match or respond on non-match. The task cue (screen color and presence or absence of a drop of liquid) was presented simultaneously with a sample image. Animals judged whether a second image was a match or non-match, and combined this information with the current rule to release or refrain from releasing a bar. (d) Another task-switching paradigm analog [28]. On each trial, the animal first viewed a task-cue, instructing it to respond to the color or orientation of the following stimulus. There were two distinct cues for each task, to distinguish sensory and task related signals. In the color task, red and green stimuli required a left or right button press, respectively; in the orientation task, vertical and horizontal lines required a left or right response, respectively. A delay period between the task cue and imperative stimulus allowed for the measurement of task-specific neuronal signals.

Figure 2

Schematic view of monkey brain with relevant parts labeled. (a) Lateral view. AS, Arcuate; CS, Central; IPS, Intraparietal sulcus; PS, Principal. Areas and regions on the lateral cortical surface: DLPFC and VLPFC, Dorsolateral and Ventrolateral prefrontal cortex; FEF, Frontal eye fields; PPC, Posterior parietal cortex; SEF, supplemental eye fields. (b) Medial view with a portion of the anterior cingulate cortex (ACC) indicated. (c) Orbital (bottom) view. OPFC, Orbital and ventrolateral prefrontal cortex are indicated.