Transcranial direct current stimulation over the left posterior temporal lobe modulates semantic control: Evidence from episodic memory distortions.

Evidence accumulates to show that semantic cognition requires, in addition to semantic representations, control processes that regulate the accessibility and use of semantic knowledge in a task- and time-appropriate fashion. Semantic control has been recently proposed to rely on a distributed network that includes the posterior temporal cortex. Along these lines, recent meta-analyses of neuroimaging data and studies with patients suffering from semantic aphasia have suggested that the left posterior middle temporal gyrus (pMTG) is critically involved whenever situational context must constrain semantic retrieval. In the present experiment, we used transcranial direct current stimulation over the left posterior temporal lobe in an attempt to interfere with semantic control while participants performed a DRM task, a procedure for inducing conceptually-based false recognition that is contingent on both activation and control processes. Paralleling findings with patients suffering from brain damage restricted to the temporoparietal cortex, anodal stimulation (relative to sham stimulation) resulted in increased false recognition but intact true recognition. These findings fit well with the idea that the left pMTG is a key component of a semantic control network, the alteration of which results in memory performance that is affected by the intrusion of contextually-inappropriate semantic information.

Corrigendum: Understanding the effects of cortical gyrification in tACS: insights from experiments and computational models.

[This corrects the article DOI: 10.3389/fnins.2023.1223950.].

Understanding the effects of cortical gyrification in tACS: insights from experiments and computational models.

The alpha rhythm is often associated with relaxed wakefulness or idling and is altered by various factors. Abnormalities in the alpha rhythm have been linked to several neurological and psychiatric disorders, including Alzheimer's disease. Transcranial alternating current stimulation (tACS) has been proposed as a potential tool to restore a disrupted alpha rhythm in the brain by stimulating at the individual alpha frequency (IAF), although some research has produced contradictory results. In this study, we applied an IAF-tACS protocol over parieto-occipital areas to a sample of healthy subjects and measured its effects over the power spectra. Additionally, we used computational models to get a deeper understanding of the results observed in the experiment. Both experimental and numerical results showed an increase in alpha power of 8.02% with respect to the sham condition in a widespread set of regions in the cortex, excluding some expected parietal regions. This result could be partially explained by taking into account the orientation of the electric field with respect to the columnar structures of the cortex, showing that the gyrification in parietal regions could generate effects in opposite directions (hyper-/depolarization) at the same time in specific brain regions. Additionally, we used a network model of spiking neuronal populations to explore the effects that these opposite polarities could have on neural activity, and we found that the best predictor of alpha power was the average of the normal components of the electric field. To sum up, our study sheds light on the mechanisms underlying tACS brain activity modulation, using both empirical and computational approaches. Non-invasive brain stimulation techniques hold promise for treating brain disorders, but further research is needed to fully understand and control their effects on brain dynamics and cognition. Our findings contribute to this growing body of research and provide a foundation for future studies aimed at optimizing the use of non-invasive brain stimulation in clinical settings.

Electrophysiological correlates of dispositional mindfulness: A quantitative and complexity EEG study.

While growing evidence supports that dispositional mindfulness relates to psychological health and cognitive enhancement, to date there have been only a few attempts to characterize its neural underpinnings. In the present study, we aimed at exploring the electrophysiological (EEG) signature of dispositional mindfulness using quantitative and complexity measures of EEG during resting state and while performing a learning task. Hundred twenty participants were assessed with the Five Facet Mindfulness Questionnaire and underwent 5 min eyes-closed resting state and 5 min at task EEG recording. We hypothesized that high mindfulness individuals would show patterns of brain activity related to (a) lower involvement of the default mode network (DMN) at rest (reduced frontal gamma power) and (b) a state of 'task readiness' reflected in a more similar pattern from rest to task (reduced overall q-EEG power at rest but not at task), as compared to their low mindfulness counterparts. Dispositional mindfulness was significantly linked to reduced frontal gamma power at rest and lower overall power during rest but not at task. In addition, we found a trend towards higher entropy during task performance in mindful individuals, which has recently been reported during mindfulness meditation. Altogether, our results add to those from expert meditators to show that high (dispositional) mindfulness seems to have a specific electrophysiological pattern characteristic of less involvement of the DMN and mind-wandering processes.

The relative role of executive control and personality traits in grit.

Although grit is predictive of wellbeing, educational achievement, and success in life, it has been conceptualized as largely distinct from cognitive ability. The present study investigated the link between grit and executive functions since regulation abilities might underlie the expression of grit. A hundred thirty-four people were administered personality questionnaires (grit, impulsiveness, and mindfulness) and four experimental tasks tapping into Miyake's and Braver's models of executive functioning (including measures of flexibility, inhibition, working memory, and control mode dimensions). Multivariate analyses showed that two composite scores (trait and executive functioning) were reliably predictive of grit, although it was the trait composite (characterized by low impulsivity and high mindfulness) that explained more variance. Importantly, gritty participants did not demonstrate enhanced executive functioning. Instead, they exhibited a different pattern of performance that might be reflecting a cautious profile of control, characterized by paying attention to all available information, less reliance on previous contextual cues but sensitive to conflicting information of the current context. These findings converge with Duckworth's idea that high grit people do not necessarily have a greater cognitive capacity. Rather, they use it in a different way.

ERP Correlates of Prospective Memory and Cue Focality in Children.

Prospective memory (PM) is essential in the everyday activities of children because it involves remembering intentions for the future, such as doing their homework or bringing written parental permissions to school. Developmental studies have shown increases in PM performance throughout childhood, but the specific processes underlying this development are still under debate. In the present study, event-related potentials were used to examine whether the focality of the PM task is related to the PM increments by testing two groups of children (first and last cycle of primary school) and assessing differences in N300 (cue detection), frontal positivity (switching), parietal positivity (retrieval of the intention) and frontal slow waves (monitoring of the retrieved intention). The results showed significant differences in focality in the group of older children but no differences in any of the components for their younger counterparts. In addition, the differences between prospective and ongoing trials were smaller for younger than older children. These findings suggest that the ability to adjust attentional strategies, monitor, switch and retrieve the intention develops across childhood and affects PM performance in attentionally demanding conditions.

Baseline capacities and motivation in executive control training of healthy older adults.

OBJECTIVES: Normal aging involves progressive prefrontal declines and impairments in executive control. This study aimed to examine the efficacy of an executive-control training focusing on working memory and inhibition, in healthy older adults, and to explore the role of individual differences in baseline capacities and motivation in explaining training gains. METHODS: Forty-four healthy older adults were randomly assigned to an experimental (training executive control) or active control group (training processing speed). Participants completed six online training sessions distributed across two weeks. Transfer effects to working memory (Operation Span test), response inhibition (Stop-Signal test), processing speed (Pattern Comparison) and reasoning (Raven's Advanced Progressive Matrices and Cattell Culture Fair test) were evaluated. Furthermore, we explored individual differences in baseline capacities and assessed motivation during and after the intervention. RESULTS: The experimental group, but not the active control, showed significant transfer to response inhibition. Moreover, a general compensation effect was found: older adults with lower baseline capacities achieved higher levels of training improvement. Motivation was not related to training performance. CONCLUSION: Our results encourage the use of executive control training to improve cognitive functions, reveal the importance of individual differences in training-related gains, and provide further support for cognitive plasticity during healthy aging.

Selective directed forgetting is mediated by the lateral prefrontal cortex: Preliminary evidence with transcranial direct current stimulation.

Recent research has shown that providing a cue to selectively forget one subset of previously learned facts may result in specific forgetting of this information. Behavioral evidence suggests that this selective directed forgetting effect relies on executive control and is a direct consequence of active, rather than passive, mechanisms. To date, however, no previous research has addressed the neural underpinnings of selective directed forgetting. Since the lateral prefrontal cortex is thought to mediate motivated forgetting by exerting top-down control over the brain structures that underpin memory representations, the present study aimed to test the hypothesis that selective directed forgetting is prefrontally driven. Specifically, we used transcranial direct current stimulation to disrupt activity in the dorsolateral prefrontal cortex, using a stimulation protocol that has already been shown to be effective in this regard. Our results reveal that, in contrast to sham stimulation, real stimulation abolished selective directed forgetting. Additionally, real stimulation hindered performance in an updating working memory task thought to recruit the lateral prefrontal cortex. These findings, complementing others obtained with a variety of memory control tasks, support the hypothesis that memory downregulation is achieved by control processes mediated by the right lateral prefrontal cortex.

Electrophysiological Prints of Grit.

While scientific interest in understanding the grit trait has grown exponentially in recent years, one important gap in the grit literature relates to its biological and neural substrate. In the present study, we adopted a hypotheses-driven approach in a large sample of young adults (N = 120) with diverse educational backgrounds and work experiences in order to investigate the electrophysiological correlates of grit both during rest and while performing a learning task. Additionally, we selected a measure of impulsiveness to better understand the neural similarities and differences between grit and related self-control constructs. Based on previous work that implicated the prefrontal cortex in grit, we hypothesized that high grit participants would have lower frontal theta/beta ratio (a broadly used index that reflects prefrontally-mediated top-down processes, which might indicate better control over subcortical information). Furthermore, we expected the perseverance of effort facet of grit to be linked to higher complexity during task engagement because previous research has shown complexity indexes (entropy and fractal dimension) to be linked to effort while performing cognitive tasks. Our results revealed that although there were no differences at rest as a function of grit, the participants with high grit and high consistency of interest scores exhibited lower frontal theta/beta ratios during the learning task. This pattern suggests that individual differences in grit might be more evident when top-down control processes are at work. Furthermore, there was a positive association between perseverance of effort and entropy at task, which might indicate more effort and engagement in the task. Finally, no association was found between the neural indexes (frontal theta/beta ratio, entropy, or fractal dimension) and impulsiveness, neither impulsiveness mediated between grit and brain measures. Finally, when controlling for impulsiveness and demographic variables (gender, age, education, and work experience) the effects at the facet level remained statistically significant. While there is still a long way to fully understand the neural mechanisms of grit, the present work constitutes a step toward unveiling the electrophysiological prints of grit.

Transcranial Direct Current Stimulation Over the Right Anterior Temporal Lobe Does Not Modulate False Recognition.

Non-invasive transcranial direct current stimulation (tDCS) over the left anterior temporal lobe (ATL) has been shown to cause a reduction in the rate of false memories with semantically related words. Such a reduction seems to be specific to false memories induced by the study of associative lists, but is not observed when the studied lists are categorical in nature. These findings are interpreted as evidence that the left ATL functions as an integration hub that is crucial for the binding of semantic information into coherent representations of concepts. In order to investigate whether the right ATL might also contribute to semantic integration in the processing of verbal associative material, a follow-up tDCS study was conducted with the stimulation at study lateralized on the right ATL. A sample of 75 undergraduate students participated in an experiment in which they studied 8 associative lists and 8 categorical lists. One third of the participants studied all their word lists under anodal stimulation, another third studied under cathodal stimulation and the other third under sham stimulation. Results showed that stimulation of the right ATL by tDCS does not modulate false recognition for either association-related critical words or category-related critical words. These results provide preliminary support to views positing asymmetric connectivity between the anterior temporal lobes and the semantic representational network, and provide evidence for understanding bilateral brain dynamics and the nature of semantically induced memory distortions.

Dual mechanisms of cognitive control in mindful individuals.

Not much research has adopted a multicomponent approach to examine the relationship between mindfulness and cognitive control. Studies addressing this issue have produced mixed results that may be due to the incorporation of different questionnaires to assess mindfulness and to the assessment of different stages and types of mindfulness itself. In the present study, we aimed to investigate to which extent dispositional mindfulness relates to a dynamic use of control modes as understood from the dual mechanisms of control theory. Further, we aimed to test this hypothesis by including two different frequently used mindfulness questionnaires in order to explore their confluence. Hundred thirty young adults completed two well-established assessment tools of mindfulness (Mindful Attention Awareness Scale and Five Facets Mindfulness Questionnaire) and two well-validated experimental tasks measuring proactive/reactive control modes (AX-Continuous Performance Task and Cued Task-Switching Paradigm). The data analyses were performed considering the continuous values in multiple regression analyses, as it is thought to better capture individual differences. The results replicate the previous findings suggesting that mindful individuals tend to use proactive and reactive control in a balanced manner in comparison to low mindfulness individuals, who tend to rely more on proactive control. Moreover, mindful individuals showed greater flexibility when the two processing modes were available. Hence, the major effects were found by using the two questionnaires. Altogether our findings indicate that mindful individuals, who have been characterized by an enhanced focus on the present moment without judgment, are less attached to the previous contextual information, which allows them to exhibit a more flexible performance.

Electrophysiological correlates of interference control at retrieval predict performance on a subsequent analogical reasoning task.

Previous research has shown that variations in the accessibility of relevant information that stem from retrieval practice may impair analogical reasoning. In the present study, we sought to examine the neural signatures of inhibitory control during selective retrieval and its effects on a subsequent analogical reasoning task by employing electrophysiological measures. At a behavioral level, we found that selective retrieval of a subset of potential solutions led to impaired performance on the analogy test. ERPs analyses during selective retrieval revealed that (1) the repeated presentation of retrieval cues was associated with decreased amplitudes for the FN400 ERP effect, possibly reflecting reduced reactivation of competitor associates and interference across retrieval attempts; (2) this effect correlated positively with the retrieval-related impairment in analogical reasoning performance. During the analogy test, the production of control solutions (non-affected by prior retrieval practice) was characterized by more positive modulations of anterior frontal and parietal ERPs than the production of unstudied solutions, whereas inhibited solutions elicited similar amplitudes to unstudied solutions. This effect was restricted to the retrieval phase of the analogy where the actual solutions had to be retrieved, but it did not affect the mapping phase where the accessibility status of the possible solutions failed to reveal significant amplitude differences. These findings suggest that control during selective retrieval may lead to the downregulation of competing memory representations and advance our understanding of the neural correlates of analogical thinking.

Both High Cognitive Load and Transcranial Direct Current Stimulation Over the Right Inferior Frontal Cortex Make Truth and Lie Responses More Similar.

Deception scholars have argued that increasing the liar's cognitive system artificially can produce deception cues. However, if too much load is imposed, the truth tellers' performance can also be impaired. To address this issue, we designed a veracity task that incorporated a secondary task to increase cognitive load gradually. Also, because deception has been associated with activity in the inferior frontal cortex (IFC), we examined the influence of transcranial direct current stimulation (tDCS) of the IFC on performance. During stimulation, participants truthfully or deceptively indicated whether each of a number of statements shown on screen was true or not. Higher load decreased recall but not general compliance or response times (RTs). Truthful trials yielded higher compliance rates and faster RTs than deceptive trials except for the highest load level. Anodal right stimulation decreased compliance in truthful trials when participants were not overloaded. Truth telling was more vulnerable to cognitive load and tDCS than lying.

Cathodal transcranial direct current stimulation over the right dorsolateral prefrontal cortex cancels out the cost of selective retrieval on subsequent analogical reasoning.

Analogical reasoning involves mapping the relation between two concepts within a specific field into a new domain to selectively retrieve a possible solution. Neuroimaging studies have shown that both selective retrieval and reasoning by analogy are related to activity in prefrontal regions such as the dorsolateral prefrontal cortex (DLPFC). In the present study, we investigate the role of the right DLPFC in modulating memory accessibility and its impact on analogical reasoning by using transcranial direct current stimulation (tDCS). Participants performed a four-term reasoning task after performing repeated selective retrieval of previously presented items, some of which could be used as solutions in the analogical test. During selective retrieval, half of the participants received cathodal tDCS over the right DLPFC and the other half received sham stimulation. The results reveal that whereas the sham group showed the expected cost in performance that is associated with selective retrieval, the cathodal group did not exhibit such an impairment in reasoning. No general effects of tDCS on analogical performance were observed. Altogether, our results support the involvement of the right DLPFC as a core component of a control network that selectively contributes to the retrieval component of analogical reasoning, but with little role in mapping relations between different domains.

Selective directed forgetting: Eliminating output order and demand characteristics explanations.

Previous research has shown that giving an instruction to forget part of a studied list of items impairs the subsequent retrieval of these items compared with those not cued to be forgotten. This selective directed forgetting (SDF) effect has been found with slightly different procedures and in adolescents and young adults. While recent research has suggested that executive control might underlie SDF, alternative explanations that rely on procedural issues still have not been investigated. Specifically, SDF might essentially reflect output interference from the items cued to be remembered, so that the earlier recalled items interfere with the later recalled items. The effect could also result from demand characteristics: Participants might withhold the to-be-forgotten items to comply with the experimenter's implicit goals or might not be willing to engage in the effort of retrieving all studied information. The results from two experiments showed that (1) the to-be-forgotten items were less accessible and were not influenced by output interference from to-be-remembered items (Experiment 1), and (2) SDF was still present when participants were offered monetary reward for retrieving as many items as possible (Experiment 2). Hence, the findings do not provide support to explanations of SDF based on output interference and demand characteristics.

Inhibitory control during selective retrieval may hinder subsequent analogical thinking.

Analogical reasoning is a complex cognitive activity that involves access and retrieval of pre-existing knowledge in order to find a suitable solution. Prior work has shown that analogical transfer and reasoning can be influenced by unconscious activation of relevant information. Based on this idea, we report two experiments that examine whether reduced access to relevant information in memory may further disrupt analogical reasoning unwittingly. In both experiments, we use an adaptation of the retrieval practice paradigm [1] to modulate memory accessibility of potential solutions to a subsequent set of analogy problems of the type 'A is to B as C is to ?'. Experiment 1 showed a retrieval-induced impairment in analogical problem solving. Experiment 2 replicated this finding and demonstrated that it cannot be due to the deliberative episodic retrieval of the solutions to the analogies. These findings, predictable from an inhibitory framework of memory control, provide a new focus for theories of analogical transfer and highlight the importance of unconscious memory processes that may modulate problem solving.

EEG Multiscale Complexity in Schizophrenia During Picture Naming.

Introduction: Patients with schizophrenia show cognitive deficits that are evident both behaviourally and with EEG recordings. Recent studies have suggested that non-linear analyses of EEG might more adequately reflect the complex, irregular, non-stationary behavior of neural processes than more traditional ERP measures. Non-linear analyses have been mainly applied to EEGs from patients at rest, whereas differences in complexity might be more evident during task performance. Objective: We aimed to investigate changes in non-linear brain dynamics of patients with schizophrenia during cognitive processing. Method: 18 patients and 17 matched healthy controls were asked to name pictures. EEG data were collected at rest and while they were performing a naming task. EEGs were analyzed with the classical Lempel-Ziv Complexity (LZC) and with the Multiscale LZC. Electrodes were grouped in seven regions of interest (ROI). Results: As expected, controls had fewer naming errors than patients. Regarding EEG complexity, the interaction between Group, Task and ROI indicated that patients showed higher complexity values in right frontal regions only at rest, where no differences in complexity between patients and controls were found during the naming task. EEG complexity increased from rest to task in controls in left temporal-parietal regions, while no changes from rest to task were observed in patients. Finally, differences in complexity between patients and controls depended on the frequency bands: higher values of complexity in patients at rest were only observed in fast bands, indicating greater heterogeneity in patients in local dynamics of neuronal assemblies. Conclusion: Consistent with previous studies, schizophrenic patients showed higher complexity than controls in frontal regions at rest. Interestingly, we found different modulations of brain complexity during a simple cognitive task between patients and controls. These data can be interpreted as indicating schizophrenia-related failures to adapt brain functioning to the task, which is reflected in poorer behavioral performance. HIGHLIGHTS:     - We measured classical and multiscale Lempel-Ziv Complexity (LZCN and MLZC) of the EEG signal of patients with schizophrenia and controls at rest and while performing a cognitive task.    - We found that patients and controls showed a different pattern of brain complexity depending on their cognitive state (at rest or under cognitive challenge).    - Our results illustrate the value of the MLZC in the characterization of the pattern of brain complexity in schizophrenia on function of frequency bands.    - Nonlinear methodologies of EEG analysis can help to characterize brain dysfunction in schizophrenia.

The Cost of Prospective Memory in Children: The Role of Cue Focality.

Prospective memory (PM) is an essential ability in daily life, since it involves remembering to perform an intention. While PM largely develops during childhood and adolescence, its underlying mechanisms are still poorly understood. In general, age differences in PM have been found with tasks in which the prospective cues are not part of the ongoing activity (non-focal PM tasks). In the present study, we evaluated the cognitive cost produced by a PM task over the ongoing activity by comparing the performance of a single-task condition with that of an ongoing activity condition involving a prospective intention. Specifically, to determine the impact of cue focality on performance as a function of age, we tested two groups of children (6 and 11 years old) in three experimental conditions: single, focal and non-focal prospective cues. In the single-task condition, children were only asked to perform the ongoing task (to categorize images as animal or non-animal). In the focal condition, in addition to performing the ongoing activity, participants were asked to press different keys whenever the image appearing on the screen was a kite or a ball. In the non-focal condition, children were to press the keys if the color of the frame of the screen changed to magenta or gray. Although reaction times were greater for the non-focal conditions in both age groups, the results showed worse performance on the ongoing activity for both the focal and the non-focal conditions (relative to the single-task condition) in the younger children. This difference was less pronounced in older children so that response times for focal and non-focal cues differed from the single condition, but the difference in performance between focal and single task conditions was not reliable. These findings, which are partly in line with the dual process framework (McDaniel et al., 2015), suggest that while non-focal prospective cues compromise attentional control in younger and older children, focal cues seem to rely on less effortful processes in older children.

Tempering Proactive Cognitive Control by Transcranial Direct Current Stimulation of the Right (but Not the Left) Lateral Prefrontal Cortex.

Behavioral and neuroimaging data support the distinction of two different modes of cognitive control: proactive, which involves the active and sustained maintenance of task-relevant information to bias behavior in accordance with internal goals; and reactive, which entails the detection and resolution of interference at the time it occurs. Both control modes may be flexibly deployed depending on a variety of conditions (i.e., age, brain alterations, motivational factors, prior experience). Critically, and in line with specific predictions derived from the dual mechanisms of control account (Braver, 2012), findings from neuroimaging studies indicate that the same lateral prefrontal regions (i.e., left dorsolateral cortex and right inferior frontal junction) may implement different control modes on the basis of temporal dynamics of activity, which would be modulated in response to external or internal conditions. In the present study, we aimed to explore whether transcraneal direct current stimulation over either the left dorsolateral prefrontal cortex or the right inferior frontal junction would differentially modulate performance on the AX-CPT, a well-validated task that provides sensitive and reliable behavioral indices of proactive/reactive control. The study comprised six conditions of real stimulation [3 (site: left dorsolateral, right dorsolateral and right inferior frontal junction) × 2 (polarity: anodal and cathodal)], and one sham condition. The reference electrode was always placed extracephalically. Performance on the AX-CPT was assessed through two blocks of trials. The first block took place while stimulation was being delivered, whereas the second block was administered after stimulation completion. The results indicate that both offline cathodal stimulation of the right dorsolateral prefrontal cortex and online anodal stimulation of the right inferior frontal junction led participants to be much less proactive, with such a dissociation suggesting that both prefrontal regions differentially contribute to the adjustment of cognitive control modes. tDCS of the left-DLPFC failed to modulate cognitive control. These results partially support the predictions derived from the dual mechanisms of control account.