Color-hierarchies in executive control of monkeys' behavior

Attentional Correlates of Colored Lights: Considerations for Cognitive Testing

Attention, an important index of cognitive function, can be affected amidst colored lights. This work investigated the effects of colored lights on the performance in attention task. Participants (N = 42) performed in one, two, and three letter cancellation task (LCT) during four lighting conditions. The order of LCT and the colored light sessions were randomized. The performance in LCT was evaluated through % accuracy, % omission, and % error. A repeated measures ANOVA showed a statistically significant difference in % accuracy in one LCT (F(2.46, 100.8) = 24.45, p < 0.001), two LCT (F(2.57, 105.4) = 20.53, p < 0.001), and three LCT (F(2.66, 109.22) = 17.96, p < 0.001) among the four colored lights. In addition, % omission revealed a statistically significant difference in one LCT (F(2.46, 100.8) = 24.43, p < 0.001), two LCT (F(2.57, 105.4) = 20.57, p < 0.001), and three LCT (F(2.66, 109.16) = 18.21, p < 0.001) among the four lights. There was no statistically significant difference in % error in one LCT (F(2.05, 84.1) = 1.23, p = 0.3), two LCT (F(2.66, 109.06) = 0.62, p = 0.971), three LCT (F(2.62, 107.53) = 0.97, p = 0.4) among the four lighting conditions. Colored lights affect attention-related cognitive processing. The attentional correlates of white and red lights are more compared to green, and blue lights. Lighting condition should be an important consideration for cognitive testing, for designing workspaces, educational settings, and other environments where attention plays a crucial role.

Morphine exposure modulates dimensional bias and set formation in anthropoids

Humans demonstrate significant behavioural advantages with particular perceptual dimensions (such as colour or shape) and when the relevant dimension is repeated in consecutive trials. These dimension-related behavioural modulations are significantly altered in neuropsychological and addiction disorders; however, their underlying mechanisms remain unclear. Here, we studied whether these behavioural modulations exist in other trichromatic primate species and whether repeated exposure to opioids influences them. In a target detection task where the target-defining dimension (colour or shape) changed trial by trial, humans exhibited shorter response time (RT) and smaller event-related electrodermal activity with colour dimension; however, macaque monkeys had shorter RT with shape dimension. Although the dimensional biases were in the opposite directions, both species were faster when the relevant dimension was repeated, compared with conditions when it changed, across consecutive trials. These indicate that both species formed dimensional sets and that resulted in a significant 'switch cost'. Scheduled and repeated exposures to morphine, which is analogous to its clinical and recreational use, significantly augmented the dimensional bias in monkeys and also changed the switch cost depending on the relevant dimension. These cognitive effects occurred when monkeys were in abstinence periods (not under acute morphine effects) but expressing significant morphine-induced conditioned place preference. These findings indicate that significant dimensional biases and set formation are evolutionarily preserved in humans' and monkeys' cognition and that repeated exposure to morphine interacts with their manifestation. Shared neural mechanisms might be involved in the long-lasting effects of morphine and expression of dimensional biases and set formation in anthropoids.

Mapping causal links between prefrontal cortical regions and intra-individual behavioral variability

Intra-individual behavioral variability is significantly heightened by aging or neuropsychological disorders, however it is unknown which brain regions are causally linked to such variabilities. We examine response time (RT) variability in 21 macaque monkeys performing a rule-guided decision-making task. In monkeys with selective-bilateral lesions in the anterior cingulate cortex (ACC) or in the dorsolateral prefrontal cortex, cognitive flexibility is impaired, but the RT variability is significantly diminished. Bilateral lesions within the frontopolar cortex or within the mid-dorsolateral prefrontal cortex, has no significant effect on cognitive flexibility or RT variability. In monkeys with lesions in the posterior cingulate cortex, the RT variability significantly increases without any deficit in cognitive flexibility. The effect of lesions in the orbitofrontal cortex (OFC) is unique in that it leads to deficits in cognitive flexibility and a significant increase in RT variability. Our findings indicate remarkable dissociations in contribution of frontal cortical regions to behavioral variability. They suggest that the altered variability in OFC-lesioned monkeys is related to deficits in assessing and accumulating evidence to inform a rule-guided decision, whereas in ACC-lesioned monkeys it results from a non-adaptive decrease in decision threshold and consequently immature impulsive responses.

Dynamic modulation of inhibition ability following repeated exposures to morphine in macaque monkey

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.

Oculomotor system can differentially process red and green colors during saccade programming in the presence of a competing distractor

Selective attention filters irrelevant information entering our brain to allow for fine-tuning of the relevant information processing. In the visual domain, shifts of attention are most often followed by a saccadic eye movement to objects and places of high relevance. Recent studies have shown that the stimulus color can affect saccade target selection and saccade trajectories. While those saccade modulations are based on perceptual color space, the level in the visual processing hierarchy at which color selection biases saccade programming remains unclear. As color has also been shown to influence manual response inhibition which is a key function of the prefrontal cortex, we hypothesized that the effects of color on executive functions would also inherently affect saccade programming. To test this hypothesis, we measured behavioral performance and saccade metrics during a modified saccadic Stroop task which reflects competition between color words ("RED" and "GREEN") and their color at the level of the prefrontal cortex. Our results revealed that the oculomotor system can differentially process red and green colors when planning a saccade in the presence of a competing distractor.

The marmoset as a model for investigating the neural basis of social cognition in health and disease

Social-cognitive processes facilitate the use of environmental cues to understand others, and to be understood by others. Animal models provide vital insights into the neural underpinning of social behaviours. To understand social cognition at even deeper behavioural, cognitive, neural, and molecular levels, we need to develop more representative study models, which allow testing of novel hypotheses using human-relevant cognitive tasks. Due to their cooperative breeding system and relatively small size, common marmosets (Callithrix jacchus) offer a promising translational model for such endeavours. In addition to having social behavioural patterns and group dynamics analogous to those of humans, marmosets have cortical brain areas relevant for the mechanistic analysis of human social cognition, albeit in simplified form. Thus, they are likely suitable animal models for deciphering the physiological processes, connectivity and molecular mechanisms supporting advanced cognitive functions. Here, we review findings emerging from marmoset social and behavioural studies, which have already provided significant insights into executive, motivational, social, and emotional dysfunction associated with neurological and psychiatric disorders.

Color Modulates Feature Integration

Bayesian models of object recognition propose the resolution of ambiguity through probabilistic integration of prior experience with available sensory information. Color, even when task-irrelevant, has been shown to modulate high-level cognitive control tasks. However, it remains unclear how color modulations affect lower-level perceptual processing. We investigated whether color affects feature integration using the flash-jump illusion. This illusion occurs when an apparent motion stimulus, a rectangular bar appearing at different locations along a motion trajectory, changes color at a single position. Observers misperceive this color change as occurring farther along the trajectory of motion. This mislocalization error is proposed to be produced by a Bayesian perceptual framework dependent on responses in area V4. Our results demonstrated that the color of the flash modulated the magnitude of the flash-jump illusion such that participants reported less of a shift, i.e., a more veridical flash location, for both red and blue flashes, as compared to green and yellow. Our findings extend color-dependent modulation effects found in higher-order executive functions into lower-level Bayesian perceptual processes. Our results also support the theory that feature integration is a Bayesian process. In this framework, color modulations play an inherent and automatic role as different colors have different weights in Bayesian perceptual processing.

Dimensional bias and adaptive adjustments in inhibitory control of monkeys

Humans and macaque monkeys, performing a Wisconsin Card Sorting Test (WCST), show a significant behavioral bias to a particular sensory dimension (e.g. color or shape); however, lesions in prefrontal cortical regions do not abolish the dimensional biases in monkeys and, therefore, it has been proposed that these biases emerge in earlier stages of visual information processing. It remains unclear whether such dimensional biases are unique to the WCST, in which attention-shifting between dimensions are required, or affect other aspects of executive functions such as 'response inhibition' and 'error-induced behavioral adjustments'. To address this question, we trained six monkeys (Macaca mulatta) to perform a stop-signal task in which they had to inhibit their response when an instruction for inhibition was given by changing the color or shape of a visual stimulus. Stop Signal Reaction Time (SSRT) is an index of inhibitory processes. In all monkeys, SSRT was significantly shorter, and the probability of a successful inhibition was significantly higher, when a change in the shape dimension acted as the stop-cue. Humans show a response slowing following a failure in response inhibition and also adapt a proactive slowing after facing demands for response inhibition. We found such adaptive behavioral adjustments, with the same pattern, in monkeys' behavior; however, the dimensional bias did not modulate them. Our findings, showing dimensional bias in monkey, with the same pattern, in two different executive control tasks support the hypothesis that the bias to shape dimension emerges in early stages of visual information processing.