No abstract

Processing advantages for particular colors (color-hierarchies) influence emotional regulation and cognitive functions in humans and manifest as an advantage of the red color, compared with the green color, in triggering response inhibition but not in response execution. It remains unknown how such color-hierarchies emerge in human cognition and whether they are the unique properties of human brain with advanced trichromatic vision. Dominant models propose that color-hierarchies are formed as experience-dependent learning that associates various colors with different human-made conventions and concepts (e.g., traffic lights). We hypothesized that if color-hierarchies modulate cognitive functions in trichromatic nonhuman primates, it would indicate a preserved neurobiological basis for such colorhierarchies. We trained six macaque monkeys to perform cognitive tasks that required behavioral control based on colored cues. Color-hierarchies significantly influenced monkeys' behavior and appeared as an advantage of the red color, compared to the green, in triggering response inhibition but not response execution. For all monkeys, the order of color-hierarchies, in response inhibition and also execution, was similar to that in humans. In addition, the cognitive effects of colorhierarchies were not limited to the trial in which the colored cues were encountered but also persisted in the following trials in which there was no colored cue on the visual scene. These findings suggest that color-hierarchies are not resulting from association of colors with human-made conventions and that simple processing advantage in retina or early visual pathways does not explain the cognitive effects of color-hierarchies. The discovery of color-hierarchies in cognitive repertoire of monkeys indicates that although the evolution of humans and monkeys diverged in about 25 million years ago, the color-hierarchies are evolutionary preserved, with the same order, in trichromatic primates and exert overarching effects on the executive control of behavior.

Background: Deficits in cognitive control, particularly inhibition ability, play crucial roles in susceptibility, progress, and relapse to opioid addiction. However, it is unclear when and how such deficits develop and interact with repeated exposures to prescribed opioids. Aim: Using macaque monkey ( Macaca mulatta), as an animal model with high translational merits in cognitive neuroscience, we tried to delineate alterations of inhibition ability in the course of repeated exposures to morphine. Methods: Monkeys were trained to perform stop-signal task and then we closely monitored their inhibition ability before exposure, after initial exposure, and following repeated exposures to morphine when they experienced abstinent periods. We also assessed morphine-induced conditioned place preference (CPP) in these monkeys to monitor the long-lasting effects of morphine on other behaviors. Results: Compared to the baseline level, monkeys’ inhibition ability was significantly enhanced after initial exposure to morphine (early phase); however, it became significantly attenuated after repeated exposures (late phase). These alterations occurred while monkeys consistently expressed the morphine-induced CPP over the course of morphine exposure. Conclusions: Our findings indicate that repeated and scheduled exposures to morphine, which is akin to its clinical and recreational use, lead to dynamic alterations in primates’ cognitive control depending on the extent of exposure. Enhancement of inhibition after limited exposure might provide opportunities to intervene and prevent the progress and culmination of opioid addiction, which is characterized by disinhibited drug-seeking and consumption.

No abstract

We do not fully understand the resolution at which temporal information is processed by different species. Here we employed a temporal order judgment (TOJ) task in rats and humans to test the temporal precision with which these species can detect the order of presentation of simple stimuli across two modalities of vision and audition. Both species reported the order of audiovisual stimuli when they were presented from a central location at a range of stimulus onset asynchronies (SOA)s. While both species could reliably distinguish the temporal order of stimuli based on their sensory content (i.e., the modality label), rats outperformed humans at short SOAs (less than 100 ms) whereas humans outperformed rats at long SOAs (greater than 100 ms). Moreover, rats produced faster responses compared to humans. The reaction time data further revealed key differences in decision process across the two species: at longer SOAs, reaction times increased in rats but decreased in humans. Finally, drift-diffusion modeling allowed us to isolate the contribution of various parameters including evidence accumulation rates, lapse and bias to the sensory decision. Consistent with the psychophysical findings, the model revealed higher temporal sensitivity and a higher lapse rate in rats compared to humans. These findings suggest that these species applied different strategies for making perceptual decisions in the context of a multimodal TOJ task.