Brain responses associated with different hierarchical effects on cues and targets during rule shifting

Neuroelectrophysiological alteration associated with cognitive flexibility after 24 h sleep deprivation in adolescents

The cognitive neural mechanisms by which sleep deprivation affects cognitive flexibility are poorly understood. Therefore, the study investigated the neuroelectrophysiological basis of the effect of 24 h sleep deprivation on cognitive flexibility in adolescents. 72 participants (36 females, mean age ± SD=20.46 ± 2.385 years old) participated in the study and were randomly assigned to the sleep deprivation group and control group. They were instructed to complete a task switch paradigm, during which participants' behavioral and electroencephalographic data were recorded. Behaviorally, there were significant between-group differences in accuracy. The results of event-related potential showed that the P2, N2 and P3 components had significant group effects or interaction effects. At the time-frequency level, there were statistically significant differences between the delta and theta bands. These results suggested that 24 h sleep deprivation affected problem-solving effectiveness rather than efficiency, mainly because it systematically impaired cognitive processing associated with cognitive flexibility.

Relationship Between the Parietal Cortex and Task Switching: Transcranial Direct Current Stimulation Combined with an Event-related Potential Study

Task switching refers to a set of cognitive processes involved in shifting attention from one task to another. In recent years, researchers have applied transcranial direct current stimulation (tDCS) to investigate the causal relationship between the parietal cortex and task switching. However, results from available studies are highly inconsistent. This may be due to the unclear understanding of the underlying mechanisms. Therefore, the current study utilized event-related potential (ERP) analysis to investigate the modulatory effects of tDCS on task-switching processes. Twenty-four subjects were recruited to perform both predictable and unpredictable parity/magnitude tasks under anodal (RA) and sham conditions. The results showed no significant changes in behavioral performance. However, marked tDCS-induced ERP changes were observed. Specifically, for the predictable task switching, compared with the sham condition, the target-N2 component occurred significantly earlier for switch trials than repeat trials under the RA condition in males, while no difference was found in females. For unpredictable task switching, under the sham condition, the P2 peak was significantly larger for switch trials compared with repeat trials, whereas this difference was not observed under the RA condition. These results indicated the causal relationship between the right parietal cortex and exogenous adjustment processes involved in task switching. Moreover, anodal tDCS over the right parietal cortex may lead to the manifestation of gender differences.

Consequences of scarcity: the impact of perceived scarcity on executive functioning and its neural basis

Introduction

Previous studies have found a causal relationship between scarcity and the adverse impact it has on executive functioning. However, few studies have directly examined perceived scarcity, and cognitive flexibility (the third component of executive functions) has rarely been included.

Methods

Using a 2 (group: scarcity group vs. control group) × 2 (trial type: repeat trial vs. switch trial) mixed design, this study directly explored perceived scarcity's impact on cognitive flexibility and revealed its neural basis in the switching tasks. Seventy college students participated in this study through open recruitment in China. A priming task was used to induce perceived scarcity, thus exploring the impact of perceived scarcity on participants' performance in switching tasks and enabling the analysis of the neural activity of the brain, combined with electroencephalograph (EEG) technology.

Results

In terms of behavioral outcomes, perceived scarcity led to poorer performance and a greater switching cost of reaction time in the switching tasks. Regarding neural activity, perceived scarcity led to an increase in the amplitude of P3 differential wave (repeat trials minus switch trials) in the parietal cortex during the target-locked epochs in the switching tasks.

Discussion

Perceived scarcity can lead to changes in the neural activity of the brain regions related to executive functioning, resulting in a temporary decrease in cognitive flexibility. It may lead to individuals unable to adapt well to the changing environment, unable to quickly devote themselves to new tasks, and reduce work and learning efficiency in daily life.

Commonalities between mind wandering and task-set switching: An event-related potential study

Previous research has established that mind wandering does not necessarily disrupt one's task-switching performance. Here we investigated the effects of mind wandering on electrophysiological signatures, measured using event-related potentials (ERPs), during a switching task. In the current study, a final sample of 22 young adults performed a task-switching paradigm while electroencephalography was continuously recorded; mind wandering was assessed via thought probes at the end of each block. Consistent with previous research, we found no significant disruptive effects of mind wandering on task-switching performance. The ERP results showed that at the posterior electrode sites (P3, Pz, and P4), P3 amplitude was higher for mind-wandering switch trials than on-task switch trials, thus opposing the typical pattern of P3 attenuation during periods of mind wandering relative to on-task episodes. Considering that increased P3 amplitude during higher-order switch trials (e.g., response rule switching) may reflect the implementation of new higher-order task sets/rules, the current findings seem to indicate similar executive control processes underlie mind wandering and task-set switching, providing further evidence in favor of a role for switching in mind wandering.

Do after "not to do": Deinhibition in cognitive control

In daily life, we often need to inhibit a certain behavior or thought; however, sometimes we need to remove inhibition (deinhibition). Numerous studies have examined inhibition control, but it is unclear how deinhibition functions. In Experiment 1, we adopted a modified stop-signal task in which participants were instructed to immediately stop the prepared response to a stimulus appended by an accidental signal. The results showed that when the preceding trial was a stop-signal trial and participants successfully inhibited the action to the stimulus, the reaction time (RT) for the repeated stimuli in the current trial was significantly longer than that of the switched stimuli, reflecting the cost of deinhibition. Deinhibition ability is correlated with inhibitory control and cognitive flexibility. In Experiment 2, we manipulated stimulus onset asynchrony (SOA) between presentation of the stimuli and the stopping signals to exclude the interference of the signal preparation effect on the deinhibition cost. These findings suggest that an individual's deinhibition ability, as a previously ignored subcomponent of cognitive control, may play an important role in human adaptive behavior.

The neural mechanism of non-phase-locked EEG activity in task switching

Flexible switching between different tasks is an important cognitive ability for humans and it is often studied using the task-switching paradigm. Although the neural mechanisms of task switching have been extensively explored in previous studies using event-related potentials techniques, the activity and process mechanisms of non-phase-locked electroencephalography (EEG) have rarely been revealed. For this reason, this paper discusses the processing of non-phase-locked EEG oscillations in task switching based on frequency-band delineation. First, the roles of each frequency band in local brain regions were summarized. In particular, during the proactive control process (the cue-stimulus interval), delta, theta, and alpha oscillations played more roles in the switch condition while beta played more roles in repeat task. In the reactive control process (post-target), delta, alpha, and beta are all related to sensorimotor function. Then, utilizing the functional connectivity (FC) method, delta connections in the frontotemporal regions and theta connections located in the parietal-to-occipital sites are involved in the preparatory period before task switching, while alpha connections located in the sensorimotor areas and beta connections located in the frontal-parietal cortex are involved in response inhibition. Finally, cross-frequency coupling (CFC) play an important role in working memory among different band oscillation. The present study shows that in addition to the processing mechanisms specific to each frequency band, there are some shared and interactive neural mechanism in task switching by using different analysis techniques.

Cognitive control is modulated by hierarchical complexity of task switching: An event-related potential study

The study aimed to explore the effect of hierarchical complexity on task switching. The participants (n = 36) were asked to perform a magnitude or parity judgement on digits (1-9) in the hierarchical simple or complex block. In the simple block, participants made a numerical judgement on the presented digit (1-9) in each trial, whereas in the complex block, they had to first identify whether the digit in the current trial belonged to a predefined category (e.g., whether it was an even number), then perform a numerical judgment or not respond. The behavioural results revealed a significant interaction between hierarchical complexity and transition type (repeat vs. switch), with greater switch cost in the complex than in the simple block. Event-related potentials (ERPs) locked in the cue stage did not reveal this interaction, whereas the ERPs locked in the target stage revealed this interaction during the N2 and P3 time windows, with a larger switch negativity (switch minus repeat) in the complex than in the simple block. These findings demonstrate that an increase in hierarchical complexity triggers increased reactive control in the inhibition of the old task-set and reconfiguration of the new task-set during task switching.

Electrophysiological correlates of the effect of set size on object switching in working memory

Previous studies have revealed the effect of set size (the number of activated items) on object switching in working memory, but the underlying neural mechanism remains unclear. In this study, participants were asked to first remember two (small size) or three (large size) two-digit numbers and the corresponding geometrical figures as different references for numerical comparison and then compare a series of numbers (10-99) to the reference numbers cued by different geometrical figures. The cue repeated or switched across trials. Behavioral results revealed that the switch cost was greater in the large-size condition than in the small-size condition. Event-related potential results showed that in the N2 component, an interaction was observed between set size and transition, with a significant transition effect (switch minus repeat) in the large-size condition and a non-significant transition effect in the small-size condition. The same interaction was observed in the P3 component, with a larger amplitude difference (switch minus repeat) in the large-size condition than in the small-size condition. These results suggested that when set size is increased, the effort to inhibit the irrelevant items increases, resulting in large cost of object switching in working memory.

Impact of hierarchical processing levels on division of labor: neural electrophysiological evidence from a joint rule shifting

OBJECTIVES

Although previous studies have revealed the behavioral and neural mechanisms underlying cognitive control, the neural electrophysiological process in joint task switching has rarely been discussed. Moreover, the hierarchy process remains unclear. Therefore, the present study aimed to explore the neural mechanism of a target when two actors use division of labor between action selections in a joint hierarchical rule-shifting situation.

METHODS

The present study employed a joint hierarchical rule shifting paradigm, and each participant was responsible for the selection of one type of action (left key and right key). The cue was the letter 'R' with three features, which indicated the hierarchical rule of the current trial. The target was an Arabic numeral (1-9, except 5). Participants made a magnitude judgement or a parity judgment based on the high and low hierarchical features of cues.

RESULTS

The P2 component was smaller in the high-shift condition than in the repeat condition; however, the high-shift condition elicited a larger N2 amplitude than the low-shift and repeat conditions. We believe that the current P2 is related to selective attention to the hierarchical features of rules, and N2 is related to conflict control. In addition, the high-shift condition had the largest P3 amplitude, which indicates that this condition has the largest extent of update and leads to the most unstable association between rule and stimuli.

CONCLUSIONS

The study demonstrated that participants had dynamic brain responses to target stimuli in the joint rule-shifting situation. In other words, participants first confirmed the actor of the current target and then processed the target stimuli themselves.

Proactive and reactive control differ between task switching and response rule switching: Event-related potential evidence

The distinction between task-switching (T-switch) and response-rule switching (RR-switch) has been reported in previous studies. However, it is unclear whether the neural correlates of proactive and reactive control differ between T-switch and RR-switch. In this study, a modified cue-target task was adopted. When the cue in the current trial differed from that in the preceding trial in shape (or color), the participants had to perform a T-switch (or RR-switch). Otherwise, they performed the same task following the same response rule. The behavioral results showed that the switch cost was greater for the RR-switch than for the T-switch. The event-related potential results indicated that (1) for cues, the switch-positivity in the late positive component (LPC) (500-800 ms) was more enhanced for the RR-switch than for the T-switch over the central to parietal regions, reflecting increased proactive control for the RR-switch compared with the T-switch; (2) for targets, the P3 amplitude was more attenuated in the RR-switch than the T-switch over the central and parietal regions, reflecting increased reactive control for the RR-switch; and (3) under the T-switch, the switch-positivity in the cue-LPC was negatively correlated with accuracy cost, while under the RR-switch, the switch negativity in the target-P3 was positively correlated with the reaction time cost. These findings suggest that similar proactive and reactive control are recruited in the T-switch and RR-switch, whereas cognitive control efforts clearly differ between them, perhaps due to different sub-processes.

The Higher, More Complicated: The Neural Mechanism of Hierarchical Task Switching on Prefrontal Cortex

Cognitive control is essential to daily life. Task switching is a classical paradigm used to study cognitive control. Previous researchers have studied the representation of different abstract hierarchical rules in the prefrontal cortex and explored the process mechanisms of task switching. However, the differences between the different hierarchical levels of task switching, especially the related neural mechanisms in the prefrontal cortex, are still unclear. This review focuses on and summarizes this issue. The present study suggests that the higher the hierarchical rule shifting or task switching, the more anterior the activation is on the prefrontal cortex. In addition, a high hierarchy of rules or tasks is more abstract, which leads to a larger switching cost.

Reconfiguration of response rule is more difficult than that of task goal: Behavior and electrophysiological evidence

Previous studies have investigated the neural mechanisms underlying cognitive control by using the task-switching paradigm, but differentiation from response rule switching (RR-switch) remains poorly explored. In this study, a partial voluntary task-switching (VTS) paradigm was used to explore the electrophysiological differences between task switching (T-switch) and RR-switching. Participants were sequentially presented with Arabic numerals colored red or green. If the color in the current trial was the same as that in the previous trial, the participants had to perform the same task following the same response rule. Otherwise, they had to voluntarily switch tasks (e.g., from parity task to magnitude task) or switch response rules (e.g., from "pressing F for odd and J for even number' to 'pressing J for odd and F for even number"). The behavioral results indicated that RR-switch was infrequently selected, and the performance was less efficient than that of the T-switch. Event-related potential results showed that both T- and RR-switches elicited a larger switch-positivity in the P2 and P3 time windows than that in the repeat condition. Switch-positivity was larger for RR-switch than for T-switch over the frontal sites, suggesting that more attention and cognitive resources were required to update information for the RR-switch than for the T-switch. These findings suggest that in the VTS, the hierarchical relationship between task goals and response rules is relatively loose, resulting in the neural disassociation of task reconfiguration and response change.

Neural Dynamics of Context-sensitive Adjustments in Cognitive Flexibility

To adaptively interact with the uncertainties of daily life, we must match our level of cognitive flexibility to situations that place different demands on our ability to focus on the current task while remaining sensitive to cues that signal other, more urgent tasks. Such cognitive-flexibility adjustments in response to changing contextual demands (metaflexibility) have been observed in cued task-switching paradigms, where the performance cost incurred by switching versus repeating tasks (switch cost) scales inversely with the proportion of switches (PS) within a block of trials. However, the neural underpinnings of these adjustments in cognitive flexibility are not well understood. Here, we recorded 64-channel EEG measures of electrical brain activity as participants switched between letter and digit categorization tasks in varying PS contexts, from which we extracted ERPs elicited by the task cue and EEG alpha-power differences during both the cue-to-target interval and the resting precue period. The temporal resolution of EEG/ERPs allowed us to test whether contextual adjustments in cognitive flexibility are mediated by tonic changes in processing mode, or by changes in phasic, task-cue-triggered processes. We observed reliable modulation of behavioral switch cost by PS context that were mirrored in both cue-evoked ERP and time-frequency effects, but not in blockwide precue EEG changes. These results indicate that different levels of cognitive flexibility are instantiated in response to the presentation of task cues, rather than by being maintained as a tonic neural-activity state difference between low- and high-switch contexts.

Response variations can promote the efficiency of task switching: Electrophysiological evidence

Previous studies have investigated sequence effect on task switching and found that increased cognitive control in preceding trials would transfer to the current trial. However, it remains unclear whether response variations during task repetition can enhance cognitive control and promote task switching. In the present study, we designed two sequence contexts, the response-change (r-change) and response-repeat (r-repeat) contexts, by adopting a classical task-switching paradigm in which participants were asked to make an odd-even or large-small judgment of the presented digit. The only difference between the two sequence contexts was whether responses varied frequently during task repetition. Behavioral results showed that the r-change context induced smaller switch costs and higher accuracy for task switching than the r-repeat context. Event-related potential (ERP) results revealed (1) the effect of context on N2 amplitudes, with greater N2 in the r-change context than the r-repeat context at frontal-central regions; (2) the interaction between context and transition type during the stimulus-locked P3 component, with a marked context effect for the task-switch trials; (3) non-significant context effect on task switching during the response-locked P3 component. These findings suggest that response variations during a sequence of task-repeat trials can trigger the increase in cognitive control that promotes the efficiency of followed task switching.

Neural electrophysiological mechanism of joint hierarchical rule shifting: an event-related potential study

Although previous studies have explored the brain mechanism by which an individual independently accomplishes task switching or rule shifting with different hierarchical structures, electrophysiological evidence indicating that two actors cooperate to complete the hierarchical rule shift remains unclear. This study adopts a modified joint hierarchical rule shifting paradigm in which one actor judged the parity task and the other decided the magnitude task. Results demonstrated that cues in high- and low-shift conditions elicited larger P2 amplitudes and that low-shift had a larger P3 amplitude than high-shift. Results further indicated that participants required more attention resources to ascertain who would make a judgment for the current trial and that low hierarchical features were superior in reconfiguring changed rules. Regarding the target, the high-shift condition evoked smaller P2 and larger N2 amplitudes when compared to low-shift and repeat conditions, whereas when compared to high- and low-shifts, the repeat condition elicited a larger P3 amplitude. The findings revealed that participants required more control resources to process the varied features and that repeat condition required the least cognitive resources to update rules. Thus, participants had different process patterns between cues and targets when cooperating with their co-actors.

More change in task repetition, less cost in task switching: Behavioral and event-related potential evidence

Previous studies have shown that the probability of task switching can vary the level of cognitive control and modulate the size of switch costs. However, it is unclear whether switch costs would be affected by a task-repetition context formed by varying the degree of response (and task-relevant stimulus property) change within the task repetition sequences while the probability of task switching remains constant. In the present study, participants were presented with a string of digits (e.g., ②②②). Basing on stimulus color, they were required to indicate either the presented digit, or the number of presented digits. Before task switching, stimulus and response in consecutive task-repeat trials varied more or less frequently. Behavioral results showed that the frequent-change context elicited smaller switch costs than the rare-change context. Event-related potential (ERP) results indicated that: (1) the frequent-change context evoked greater fronto-central N2 amplitudes for both task-repeat and task-switch trials, implying that cognitive control increased due to the variation of stimulus and response associations; (2) for the task switch trials, smaller P300 amplitudes were evoked in the frequent-change context than the rare-change context, reflecting the promoted task-set reconfiguration. These findings suggest that, the more change in stimulus and response during task repetition, the higher the overall level of cognitive control and the higher efficiency of task-switching.

SNARC effect modulated by central executive control: revealed in a cue-based trisection task

People respond to small numbers faster with the left hand and respond to large numbers faster with the right hand, a phenomenon known as the Spatial-Numerical Association of Response Codes (SNARC) effect. Whether the SNARC effect originates from culturally determined long-term experience or the task-set-influenced temporary associations among spaces, locations, and numerical magnitudes in working memory (WM) is still controversial. In the present study, we used a trisection paradigm in which numbers were divided into three categories (small: 1, 2; middle: 4, 5, 6; and large: 8, 9) to explore whether the central executive control can modulate the SNARC effect. Participants were serially presented with a cue and a target number. The cue denoted a task rule, which informed participants to compare the target number with either 3 or 7. The cue was either switched or repeated across trials. We found that the SNARC effects were observed in the cue-switching condition. In the cue-repeat condition, the SNARC effect disappeared. These findings suggest that the SNARC effect is modulated by set-shifting-related central executive control in WM, supporting the view that the SNARC effect is WM-dependent.