The role of the dorsolateral prefrontal cortex in random number generation: a study with positron emission tomography

Individualised Transcranial Magnetic Stimulation Targeting of the Left Dorsolateral Prefrontal Cortex for Enhancing Cognition: A Randomised Controlled Trial

Repetitive transcranial magnetic stimulation (rTMS) has been demonstrated to produce cognitive enhancing effects across different neuropsychiatric disorders; however, so far, these effects have been limited. This trial investigated the efficacy of using a novel individualised approach to target the left dorsolateral prefrontal cortex (L-DLPFC) for enhancing cognitive flexibility based on performance on a cognitive task. First, forty healthy participants had their single target site at the L-DLPFC determined based on each individual's performance on a random letter generation task. Participants then received, in a cross-over single-blinded experimental design, a single session of intermittent theta burst stimulation (iTBS) to their individualised DLPFC target site, an active control site and sham iTBS. Following each treatment condition, participants completed the Task Switching task and Colour-Word Stroop test. There was no significant main effect of treatment condition on the primary outcome measure of switch reaction times from the Task Switching task [F = 1.16 (2, 21.6), p = 0.33] or for any of the secondary cognitive outcome measures. The current results do not support the use of our novel individualised targeting methodology for enhancing cognitive flexibility in healthy participants. Research into alternative methodological targeting approaches is required to further improve rTMS's cognitive enhancing effects.

Autonomous behaviour and the limits of human volition

Humans and some other animals can autonomously generate action choices that contribute to solving complex problems. However, experimental investigations of the cognitive bases of human autonomy are challenging, because experimental paradigms typically constrain behaviour using controlled contexts, and elicit behaviour by external triggers. In contrast, autonomy and freedom imply unconstrained behaviour initiated by endogenous triggers. Here we propose a new theoretical construct of adaptive autonomy, meaning the capacity to make behavioural choices that are free from constraints of both immediate external triggers and of routine response patterns, but nevertheless show appropriate coordination with the environment. Participants (N = 152) played a competitive game in which they had to choose the right time to act, in the face of an opponent who punished (in separate blocks) either choice biases (such as always responding early), sequential patterns of action timing across trials (such as early, late, early, late…), or predictable action-outcome dependence (such as win-stay, lose-shift). Adaptive autonomy was quantified as the ability to maintain performance when each of these influences on action selection was punished. We found that participants could become free from habitual choices regarding when to act and could also become free from sequential action patterns. However, they were not able to free themselves from influences of action-outcome dependence, even when these resulted in poor performance. These results point to a new concept of autonomous behaviour as flexible adaptation of voluntary action choices in a way that avoids stereotypy. In a sequential analysis, we also demonstrated that participants increased their reliance on belief learning in which they attempt to understand the competitor's beliefs and intentions, when transition bias and reinforcement bias were punished. Taken together, our study points to a cognitive mechanism of adaptive autonomy in which competitive interactions with other agents could promote both social cognition and volition in the form of non-stereotyped action choices.

Three-phase temporal dynamics in random number generation

"Inhibition of return" (IOR) was originally described in the field of spatial attention, but it has also been observed in random number generation tasks. Subjects showed a tendency of "repetition avoidance," which can be considered as equivalent to IOR in another cognitive domain. As temporal factors have been suspected to play an important role in random number generation, we aimed to examine how such factors might influence regularities such as repetition avoidance in random number generation tasks. Participants were instructed to verbally generate a sequence of numbers at a certain pace, that is, with either 0.5, 1.5, 3 or 4 s between each response. Each number in the sequence should have the same probability of appearance and should be independent from the others. However, it was observed that the human-generated sequences differed drastically from computer-simulated pseudo-random sequences. The distribution of the repetition gap, which indicates how many different numbers are reported between two identical numbers in the generated sequences, showed a "three-phase" characteristic: a phase of avoidance of the same number, an oscillatory component for coming back to the same number, and finally an exponential decay of number selection frequencies. This three-phase characteristic was independent of the time interval between responses. These observations indicate an item-based process in random number generation, making a time-based control in this task rather unlikely as has been hypothetically assumed.

EEG coherence before and after giving birth

During pregnancy and the postpartum period, changes in brain volume and in motivational, sensory, cognitive, and emotional processes have been described. However, to date, longitudinal modifications of brain function have been understudied. To explore regional cortical coupling, in pregnancy and at 3 months postpartum, we analyzed resting-state electroencephalographic (EEG) coherence in the delta, theta, alpha1, alpha2, beta1, and beta2 frequency bands across frontal and parietal regions of the maternal brain (Fp1, Fp2, F3, F4, P3, and P4). We found that from pregnancy to the postpartum period, mothers showed less intrahemispheric EEG coherence between the frontal and parietal regions in the alpha1 and alpha2 bands, as well as greater interhemispheric EEG coherence between frontopolar regions in the beta2 band. These changes suggest decreased inhibition of neural circuits. These neurophysiological changes may represent an adaptive process characteristic of motherhood.

Syndromes associated with frontotemporal lobar degeneration change response patterns on visual analogue scales

Self-report scales are widely used in cognitive neuroscience and psychology. However, they rest on the central assumption that respondents engage meaningfully. We hypothesise that this assumption does not hold for many patients, especially those with syndromes associated with frontotemporal lobar degeneration. In this study we investigated differences in response patterns on a visual analogue scale between people with frontotemporal degeneration and controls. We found that people with syndromes associated with frontotemporal lobar degeneration respond with more invariance and less internal consistency than controls, with Bayes Factors = 15.2 and 14.5 respectively indicating strong evidence for a group difference. There was also evidence that patient responses feature lower entropy. These results have important implications for the interpretation of self-report data in clinical populations. Meta-response markers related to response patterns, rather than the values reported on individual items, may be an informative addition to future research and clinical practise.

Counting on random number generation: Uncovering mild executive dysfunction in congenital heart disease

Congenital heart disease (CHD) is associated with various neurocognitive deficits, particularly targeting executive functions (EFs), of which random number generation (RNG) is one indicator. RNG has, however, never been investigated in CHD. We administered the Mental Dice Task (MDT) to 67 young adults with CHD and 55 healthy controls. This 1-minute-task requires the generation of numbers 1 to 6 in a random sequence. RNG performance was correlated with a global EF score. Participants underwent MRI to examine structural-volumetric correlates of RNG. Compared to controls, CHD patients showed increased backward counting, reflecting deficient inhibition of automatized behavior. They also lacked a small-number bias (higher frequency of small relative to large numbers). RNG performance was associated with global EF scores in both groups. In CHD patients, MRI revealed an inverse association of counting bias with most of the volumetric measurements and the amount of small numbers was positively associated with corpus callosum volume, suggesting callosal involvement in the "pseudoneglect in number space". In conclusion, we found an impaired RNG performance in CHD patients, which is associated with brain volumetric measures. RNG, reportedly resistant to learning effects, may be an ideal task for the longitudinal assessment of EFs in patients with CHD.

Effects of transcranial static magnetic field stimulation over the left dorsolateral prefrontal cortex on random number generation

OBJECTIVE

Focal application of transcranial static magnetic field stimulation (tSMS) is a neuromodulation technique, with predominantly inhibitory effects when applied to the motor, somatosensory or visual cortex. Whether this approach can also transiently interact with dorsolateral prefrontal cortex (DLPFC) function remains unclear. The suppression of habitual or competitive responses is one of the core executive functions linked to DLPFC function. This study aimed to assess the impact of tSMS on the prefrontal contributions to inhibitory control and response selection by means of a RNG task.

METHODS

We applied 20 min of tSMS over the left DLPFC of healthy subjects, using a real/sham cross-over design, during performance of a RNG task. We used an index of randomness calculated with the measures of entropy and correlation to assess the impact of stimulation on DLPFC function.

RESULTS

The randomness index of the sequences generated during the tSMS intervention was significantly higher compared to those produced in the sham condition.

CONCLUSIONS

Our results indicate that application of tSMS transiently modulates specific functional brain networks in DLPFC, which indicate a potential use of tSMS for treatment of neuropsychiatric disorders.

SIGNIFICANCE

This study provides evidence for the capacity of tSMS for modulating DLPFC function.

Exercise-Induced Elevated BDNF Concentration Seems to Prevent Cognitive Impairment after Acute Exposure to Moderate Normobaric Hypoxia among Young Men

Memory impairment, reduced learning ability, decreased concentration, and psychomotor performance can be all signs of deleterious impact of hypoxia on cognitive functioning. In turn, physical exercise can improve performance and enhance cognitive functions. The purpose of this study was to investigate whether the potential positive effects of exercise performed under normobaric hypoxia can counteract the negative effects of hypoxia on cognitive function, and whether these changes correlate with brain-derived neurotrophic factor (BDNF) concentrations. Seventeen healthy subjects participated in a crossover study where they performed two sessions of single breathing bouts combined with moderate intensity exercise under two conditions: normoxia (NOR EX) and normobaric hypoxia (NH EX). To assess cognitive function, Stroop test was applied. There were no significant differences in any part of the Stroop interference test regardless of the conditions (NOR, NH), despite a statistical decrease in SpO2 (p < 0.0001) under normobaric hypoxic conditions. In addition, a statistical increase (p < 0.0001) in BDNF concentration was observed after both conditions. Acute exercise under normobaric hypoxia did not impair cognitive function despite a significant decrease in SpO2. Exercise in such conditions may offset the negative effects of hypoxia alone on cognitive function. This may be related to the significant increase in BDNF concentration and, as a consequence, positively affect the executive functions.

Instruction effects on randomness in sequence generation

Randomness is a fundamental property of human behavior. It occurs both in the form of intrinsic random variability, say when repetitions of a task yield slightly different behavioral outcomes, or in the form of explicit randomness, say when a person tries to avoid being predicted in a game of rock, paper and scissors. Randomness has frequently been studied using random sequence generation tasks (RSG). A key finding has been that humans are poor at deliberately producing random behavior. At the same time, it has been shown that people might be better randomizers if randomness is only an implicit (rather than an explicit) requirement of the task. We therefore hypothesized that randomization performance might vary with the exact instructions with which randomness is elicited. To test this, we acquired data from a large online sample (n = 388), where every participant made 1,000 binary choices based on one of the following instructions: choose either randomly, freely, irregularly, according to an imaginary coin toss or perform a perceptual guessing task. Our results show significant differences in randomness between the conditions as quantified by conditional entropy and estimated Markov order. The randomization scores were highest in the conditions where people were asked to be irregular or mentally simulate a random event (coin toss) thus yielding recommendations for future studies on randomization behavior.

Load-Dependent Prefrontal Cortex Activation Assessed by Continuous-Wave Near-Infrared Spectroscopy during Two Executive Tasks with Three Cognitive Loads in Young Adults

The present study examined the evolution of the behavioral performance, subjectively perceived difficulty, and hemodynamic activity of the prefrontal cortex as a function of cognitive load during two different cognitive tasks tapping executive functions. Additionally, it investigated the relationships between these behavioral, subjective, and neuroimaging data. Nineteen right-handed young adults (18–22 years) were scanned using continuous-wave functional near-infrared spectroscopy during the performance of n-back and random number generation tasks in three cognitive load conditions. Four emitter and four receptor optodes were fixed bilaterally over the ventrolateral and dorsolateral prefrontal cortices to record the hemodynamic changes. A self-reported scale measured the perceived difficulty. The findings of this study showed that an increasing cognitive load deteriorated the behavioral performance and increased the perceived difficulty. The hemodynamic activity increased parametrically for the three cognitive loads of the random number generation task and in a two-back and three-back compared to a one-back condition. In addition, the hemodynamic activity was specifically greater in the ventrolateral prefrontal cortex than in the dorsolateral prefrontal cortex for both cognitive tasks (random number generation and n-back tasks). Finally, the results highlighted some links between cerebral oxygenation and the behavioral performance, but not the subjectively perceived difficulty. Our results suggest that cognitive load affects the executive performance and perceived difficulty and that fNIRS can be used to specify the prefrontal cortex’s implications for executive tasks involving inhibition and working memory updating.

Could direct and generative retrieval be two flips of the same coin? A dual-task paradigm study

Autobiographical memories are thought to be retrieved using two possible ways: a generative one, which is effortful and follows a general-to-specific pathway, and a direct one, which is automatic and relatively effortless. These two retrieve processes are known to differ on the quantitative side (especially considering retrieval times), from a qualitative point of view; however, evidence is missing. Here, we aimed to disentangle this question by taking advantage of a dual-task paradigm in which the different tasks tax different executive functions. Participants were asked to perform an autobiographical memory task under three different conditions: no cognitive load, non-visual cognitive load and visual cognitive load. On the quantitative side, results replicated previous findings with generative processes being slower compared with direct ones. Conversely, on the qualitative side, results indicated that the retrieval times of both direct and generative retrieval processes varied similarly according to the dual-task condition, thus supporting the idea that the same memory process could underlie both retrievals.

Catching Wandering Minds with Tapping Fingers: Neural and Behavioral Insights into Task-unrelated Cognition

When the human mind wanders, it engages in episodes during which attention is focused on self-generated thoughts rather than on external task demands. Although the sustained attention to response task is commonly used to examine relationships between mind wandering and executive functions, limited executive resources are required for optimal task performance. In the current study, we aimed to investigate the relationship between mind wandering and executive functions more closely by employing a recently developed finger-tapping task to monitor fluctuations in attention and executive control through task performance and periodical experience sampling during concurrent functional magnetic resonance imaging (fMRI) and pupillometry. Our results show that mind wandering was preceded by increases in finger-tapping variability, which was correlated with activity in dorsal and ventral attention networks. The entropy of random finger-tapping sequences was related to activity in frontoparietal regions associated with executive control, demonstrating the suitability of this paradigm for studying executive functioning. The neural correlates of behavioral performance, pupillary dynamics, and self-reported attentional state diverged, thus indicating a dissociation between direct and indirect markers of mind wandering. Together, the investigation of these relationships at both the behavioral and neural level provided novel insights into the identification of underlying mechanisms of mind wandering.

Random number generation and the ability of mentally reconstructing context in patients with organic amnesia

Studies investigating amnesic patients have shown the involvement of the medial temporal lobe during working memory (WM) tasks, especially when multiple items or features have to be associated. However, so far, no study has examined the relationship between episodic memory and WM components in patients with amnesia for comprehensive neuropsychological evaluation.

Objective

The objective of this study was to investigate whether the null retention relates to deficits in the episodic buffer (EB) or the central executive (CE) components of WM.

Methods

This study included 15 amnesic patients with mixed etiologies and 13 matched healthy controls. These 15 amnesic patients with mixed etiologies were divided into two subgroups: NUL subgroup (n=7) patients whose raw score was 0 (zero) on the Logical Memory delayed recall test and MOR subgroup (n=8) patients who recalled at least 1 item. The EB was assessed by complex span tasks, and the CE was assessed by random number generation (RNG) test.

Results

EB tasks were impaired in both subgroups compared with controls. RNG was impaired in NUL (p=0.03), but not in MOR (p=0.99), subgroup.

Conclusions

CE impairment hampers the retrieval mode action, preventing it from initiating the mental reconstruction of the context in which the to-be-remembered information was presented minutes ago.

Characterizing human random-sequence generation in competitive and non-competitive environments using Lempel-Ziv complexity

The human ability for random-sequence generation (RSG) is limited but improves in a competitive game environment with feedback. However, it remains unclear how random people can be during games and whether RSG during games can improve when explicitly informing people that they must be as random as possible to win the game. Nor is it known whether any such improvement in RSG transfers outside the game environment. To investigate this, we designed a pre/post intervention paradigm around a Rock-Paper-Scissors game followed by a questionnaire. During the game, we manipulated participants’ level of awareness of the computer’s strategy; they were either (a) not informed of the computer’s algorithm or (b) explicitly informed that the computer used patterns in their choice history against them, so they must be maximally random to win. Using a compressibility metric of randomness, our results demonstrate that human RSG can reach levels statistically indistinguishable from computer pseudo-random generators in a competitive-game setting. However, our results also suggest that human RSG cannot be further improved by explicitly informing participants that they need to be random to win. In addition, the higher RSG in the game setting does not transfer outside the game environment. Furthermore, we found that the underrepresentation of long repetitions of the same entry in the series explains up to 29% of the variability in human RSG, and we discuss what might make up the variance left unexplained.

A novel approach for targeting the left dorsolateral prefrontal cortex for transcranial magnetic stimulation using a cognitive task

Repetitive transcranial magnetic stimulation (rTMS) has the potential to be developed as a novel treatment for cognitive dysfunction. However, current methods of targeting rTMS for cognition fail to consider inter-individual functional variability. This study explored the use of a cognitive task to individualise the target site for rTMS administered to the left dorsolateral prefrontal cortex (L-DLPFC). Twenty-five healthy participants were enrolled in a sham-controlled, crossover study. Participants performed a random letter generation task under the following conditions: no stimulation, sham and active 'online' rTMS applied to F3 (International 10-20 System) and four standardised surrounding sites. Across all sites combined, active 'online' rTMS was associated with significantly reduced performance compared to sham rTMS for unique trigrams (p = 0.012), but not for unique digrams (p > 0.05). Using a novel localisation methodology based on performance outcomes from both measures, a single optimal individualised site was identified for 92% [n = 23] of participants. At the individualised site, performance was significantly poorer compared to a common standard site (F3) and both control conditions (ps < 0.01). The current results suggest that this localisation methodology using a cognitive task could be used to individualise the rTMS target site at the L-DLPFC for modulating and potentially enhancing cognitive functioning.

Mini-Review of Studies Testing the Cardiorespiratory Hypothesis With Near-Infrared Spectroscopy (NIRS): Overview and Perspectives

The cardiorespiratory hypothesis (CH) is one of the hypotheses used by researchers to explain the relationship between cardiorespiratory fitness and cognitive performance during executive functions. Despite the indubitable beneficial effect of training on brain blood flow and function that may explain the link between physical fitness and cognition and the recognition of the near-infrared spectroscopy (NIRS) as a reliable tool for measuring brain oxygenation, few studies investigated the CH with NIRS. It is still not well understood whether an increase in brain flow by training is translated into an increase in cerebral oxygenation. Thus, the objective of this mini-review was to summarize main results of studies that investigated the CH using the NIRS and to propose future research directions.

The Quest for Hemispheric Asymmetries Supporting and Predicting Executive Functioning

This narrative review addresses the neural bases of two executive functions: criterion setting, that is, the capacity to flexibly set up and select task rules and associations between stimuli, responses, and nonresponses, and monitoring, that is, the process of continuously evaluating whether task rules are being applied optimally. There is a documented tendency for criterion setting and monitoring to differentially recruit left and right lateral prefrontal regions and connected networks, respectively, above and beyond the specific task context. This model, known as the ROtman-Baycrest Battery to Investigate Attention (ROBBIA) model, initially sprung from extensive neuropsychological work led by Don Stuss. In subsequent years, multimodal lines of empirical investigation on both healthy individuals and patients with brain damage, coming from functional neuroimaging, EEG, neurostimulation, individual difference approaches, and, again, neuropsychology, so to "complete the circle," corroborated the functional mapping across the two hemispheres as predicted by the model. More recent electrophysiological evidence has further shown that hemispheric differences in intrinsic prefrontal dynamics are able to predict cognitive performance in tasks tapping these domain-general functions. These empirical contributions will be presented together with contrasting evidence, limits, and possible future directions to better fine-tune this model and extend its scope to new fields.

Short- and long-term cognitive effects of deep brain stimulation in the caudal zona incerta versus best medical treatment in patients with Parkinson's disease

OBJECTIVE

A growing number of studies are showing positive effects of deep brain stimulation (DBS) in the caudal zona incerta (cZi) in various tremor disorders, as well as motor symptoms of Parkinson's disease (PD). The focus of the present study was to evaluate short- and long-term cognitive effects of bilateral cZi DBS in patients with PD.

METHODS

Twenty-five nondemented patients with advanced PD were recruited to participate in a randomized trial of cZi DBS versus best medical treatment (BMT). The patients in the BMT group were offered surgery after 6 months. Neuropsychological evaluations focusing on assessing verbal and visuospatial memory, attention, and executive function were conducted at baseline and at 6 and 24 months after surgery. Self-reported measures of depression, anxiety, and change in "frontal" behaviors were also completed at all assessment points.

RESULTS

Bilateral cZi DBS in patients with PD generated few adverse cognitive effects. At the short-term follow-up after 6 months, no differences were found between patients randomized to BMT and patients randomized to DBS with regard to most of the cognitive domains assessed. A transient improvement in anxiety was, however, found in the surgical group. At the long-term follow-up 24 months after cZi DBS, no major changes in global cognitive functioning were found, although a decline in attention and self-reported executive function was noted.

CONCLUSIONS

With the exception of a decline in attention and self-reported executive function, bilateral cZi DBS for PD in appropriately screened patients appears to be generally safe with regard to cognitive function, both in the short- and long-term perspective.

The Morra Game as a Naturalistic Test Bed for Investigating Automatic and Voluntary Processes in Random Sequence Generation

Morra is a 3,000-years-old hand game of prediction and numbers. The two players reveal their hand simultaneously, presenting a number of fingers between 1 and 5, while calling out a number between 2 and 10. Any player who successfully guesses the summation of fingers revealed by both players scores a point. While the game is extremely fast-paced, making it very difficult for players to achieve a conscious control of their game strategies, expert players regularly outperform non-experts, possibly with strategies residing out of conscious control. In this study, we used Morra as a naturalistic setting to investigate the necessity of attentive control in generation of sequence of items and the ability to proceduralize random number generation, which are both a crucial defensive strategy in Morra and a well-known empirical procedure to test the central executive capacity within the working memory model. We recorded the sequence of numbers generated by expert players in a Morra tournament in Sardinia (Italy) and by undergraduate students enrolled in a course-based research experience (CRE) course at Lawrence Technological University in the United States. Number sequences generated by non-expert and expert players both while playing Morra and in a random number generation task (RNGT) were compared in terms of randomness scores. Results indicate that expert players of Morra largely outperformed non-experts in the randomness scores only within Morra games, whereas in RNGT the two groups were very similar. Importantly, survey data acquired after the games indicate that expert players have very poor conscious recall of their number generation strategies used during the Morra game. Our results indicate that the ability of generating random sequences can be proceduralized and do not necessarily require attentive control. Results are discussed in the framework of the dual processing theory and its automatic-parallel-fast vs. controlled-sequential-slow polarities.

Cooperation Makes a Group be More Creative

This study investigated how cooperative and competitive interaction modes affect the group creative performance. The participants were recruited as dyads to solve 2 problems either demanding divergent thinking (alternative uses task, AUT) or not (object characteristic task, OCT). The dyads solved 1 of the 2 problems in the cooperative mode and the other in the competitive mode. Functional near-infrared spectroscopy (fNIRS)-based hyperscanning was used to record their neural activities in the prefrontal and right temporal-parietal junction (r-TPJ) regions. Results revealed the dyads showed higher AUT fluency, AUT originality, OCT fluency, and cooperation level in the cooperative mode than in the competitive mode. The fNIRS data revealed increased (task-baseline) interpersonal brain synchronization (IBS) in the right dorsolateral prefrontal cortex (r-DLPFC) and r-TPJ, only for dyads in the AUT/cooperation condition. In both r-DLPFC and r-TPJ, the IBS of dyads in the AUT/cooperation condition was stronger than in the AUT/competition and OCT/cooperation. Moreover, a stronger IBS was evoked between the regions in prefrontal and posterior temporal regions in the AUT/cooperation condition, as compared with the competition mode. These findings suggest that enhanced IBS may underlie the positive effects of cooperation as compared with the competition in terms of group creativity.

Single session high definition transcranial direct current stimulation to the cerebellum does not impact higher cognitive function

The prefrontal cortex is central to higher order cognitive function. However, the cerebellum, generally thought to be involved in motor control and learning, has also been implicated in higher order cognition. Recent work using transcranial direct current stimulation (tDCS) provides some support for right cerebellar involvement in higher order cognition, though the results are mixed, and often contradictory. Here, we used cathodal high definition tDCS (HD-tDCS) over the right cerebellum to assess the impact of HD-tDCS on modulating cognitive performance. We predicted that stimulation would result in performance decreases, which would suggest that optimal cerebellar function is necessary for cognitive performance, much like the prefrontal cortex. That is, it is not simply a structure that lends support to complete difficult tasks. While the expected cognitive behavioral effects were present, we did not find effects of stimulation. This has broad implications for cerebellar tDCS research, particularly for those who are interested in using HD-tDCS as a way of examining cerebellar function. Further implications, limitations, and future directions are discussed with particular emphasis on why null findings might be critical in developing a clear picture of the effects of tDCS on the cerebellum.

Divided Attention Selectively Impairs Value-Directed Encoding

In the present study, we examined the effect of value-directed encoding on recognition memory and how various divided attention tasks at encoding alter value-directed remembering. In the first experiment, participants encoded words that were assigned either high or low point values in multiple study-test phases. The points corresponded to the value the participants could earn by successfully recognizing the words in an upcoming recognition memory task. Importantly, participants were instructed that their goal was to maximize their score in this memory task. The second experiment was modified such that while studying the words participants simultaneously completed a divided attention task (either articulatory suppression or random number generation). The third experiment used a non-verbal tone detection divided attention task (easy or difficult versions). Subjective states of recollection (i.e., “Remember”) and familiarity (i.e., “Know”) were assessed at retrieval in all experiments. In Experiment 1, high value words were recognized more effectively than low value words, and this difference was primarily driven by increases in “Remember” responses with no difference in “Know” responses. In Experiment 2, the pattern of subjective judgment results from the articulatory suppression condition replicated Experiment 1. However, in the random number generation condition, the effect of value on recognition memory was lost. This same pattern of results was found in Experiment 3 which implemented a different variant of the divided attention task. Overall, these data suggest that executive processes are used when encoding valuable information and that value-directed improvements to memory are not merely the result of differential rehearsal.

Implicit Valuation of the Near-Miss is Dependent on Outcome Context

Gambling studies have described a "near-miss effect" wherein the experience of almost winning increases gambling persistence. The near-miss has been proposed to inflate the value of preceding actions through its perceptual similarity to wins. We demonstrate here, however, that it acts as a conditioned stimulus to positively or negatively influence valuation, dependent on reward expectation and cognitive engagement. When subjects are asked to choose between two simulated slot machines, near-misses increase valuation of machines with a low payout rate, whereas they decrease valuation of high payout machines. This contextual effect impairs decisions and persists regardless of manipulations to outcome feedback or financial incentive provided for good performance. It is consistent with proposals that near-misses cause frustration when wins are expected, and we propose that it increases choice stochasticity and overrides avoidance of low-valued options. Intriguingly, the near-miss effect disappears when subjects are required to explicitly value machines by placing bets, rather than choosing between them. We propose that this task increases cognitive engagement and recruits participation of brain regions involved in cognitive processing, causing inhibition of otherwise dominant systems of decision-making. Our results reveal that only implicit, rather than explicit strategies of decision-making are affected by near-misses, and that the brain can fluidly shift between these strategies according to task demands.

Lose-Shift Responding in Humans Is Promoted by Increased Cognitive Load

The propensity of animals to shift choices immediately after unexpectedly poor reinforcement outcomes is a pervasive strategy across species and tasks. We report here on the memory supporting such lose-shift responding in humans, assessed using a binary choice task in which random responding is the optimal strategy. Participants exhibited little lose-shift responding when fully attending to the task, but this increased by 30%–40% in participants that performed with additional cognitive load that is known to tax executive systems. Lose-shift responding in the cognitively loaded adults persisted throughout the testing session, despite being a sub-optimal strategy, but was less likely as the time increased between reinforcement and the subsequent choice. Furthermore, children (5–9 years old) without load performed similarly to the cognitively loaded adults. This effect disappeared in older children aged 11–13 years old. These data provide evidence supporting our hypothesis that lose-shift responding is a default and reflexive strategy in the mammalian brain, likely mediated by a decaying memory trace, and is normally suppressed by executive systems. Reducing the efficacy of executive control by cognitive load (adults) or underdevelopment (children) increases its prevalence. It may therefore be an important component to consider when interpreting choice data, and may serve as an objective behavioral assay of executive function in humans that is easy to measure.

Reappraisal inventiveness: impact of appropriate brain activation during efforts to generate alternative appraisals on the perception of chronic stress in women

BACKGROUND AND OBJECTIVES

Previous research indicated that more left-lateralized prefrontal activation during cognitive reappraisal efforts was linked to a greater capacity for generating reappraisals, which is a prerequisite for the effective implementation of cognitive reappraisal in everyday life. The present study examined whether the supposedly appropriate brain activation is relevant in terms of more distal outcomes, i.e., chronic stress perception.

DESIGN AND METHODS

Prefrontal EEG alpha asymmetry was recorded while female participants were generating reappraisals for stressful events and was correlated with their self-reported chronic stress levels in everyday life (n = 80).

RESULTS

Women showing less left-lateralized brain activity in the ventrolateral prefrontal cortex during cognitive reappraisal efforts reported experiencing more stress in their daily lives. This effect was independent of self-efficacy beliefs in managing negative emotions.

CONCLUSION

These findings underline the practical relevance of individual differences in appropriate brain activation during emotion regulation efforts and the assumedly related basic capacity for the generation of cognitive reappraisals to the feeling of being stressed. Implications include the selection of interventions for the improvement of coping with stress in women in whom the capability for appropriate brain activation during reappraisal efforts may be impaired, e.g., due to depression or old age.

The capacity for generating cognitive reappraisals is reflected in asymmetric activation of frontal brain regions

Encouraging patients to use cognitive reappraisal constitutes the core of modern psychotherapeutic approaches. However, evidence for specific neural correlates of the capacity for cognitive reappraisal, which is a necessary prerequisite for the effective implementation of cognitive reappraisal in everyday life, has been sparse to date. In the present study, the capacity for cognitive reappraisal was studied in terms of the participants’ inventiveness in generating alternative appraisals of anger-evoking events, and was correlated with frontal EEG alpha asymmetry recorded while the participants were generating reappraisals as well as during a common creative idea generation task. During cognitive reappraisal efforts, individuals higher on the capacity for generating cognitive reappraisals showed more left-lateralized activity in lateral prefrontal cortex, specifically in ventrolateral prefrontal cortex extending toward the frontal pole. This effect was observed independently from the activation during novel idea generation without emotional component, indicating that specific demands are implicated in the generation of reappraisals of emotional events. Taken together, the results indicate that individuals higher on the capacity for cognitive reappraisal are more capable or more prone to recruit appropriate brain regions when the situation demands coming up with alternative appraisals of stressful events. The findings may stimulate the development of more individually targeted interventions.

Joint cognition and the role of human agency in random number choices

Joint cognition refers to the mental systems that support group performance when carrying out a shared, or jointly owned task. We focused here on understanding the social configurations that underpin key phenomena in joint cognition, in particular, whether individual cognition in task-sharing environments is mostly shaped by social factors or not. To this end, we investigated, first and mainly, whether human presence is necessary for the creation of joint performance; second and separately, whether prior experience of task sharing has an adaptive influence on subsequent individual choices; and third and additionally, whether individual differences in a social trait mediate joint performance. We describe an experiment in which participants combined with another human or a computer as they attempted to generate a paired sequence that was as random as possible. First, we found little difference in joint performance with regard to whether a human or a computer was the co-participant, except for immediate repetitive response. Second, we found evidence for choice adaptation, but only under the lower time pressure. Third, we replicated previous research in which no systematic link was established between social desirability and joint performance. We conclude that joint cognition phenomena may be rooted primarily in turn-taking configurations rather than in social dynamics per se.

Impaired math achievement in patients with acute vestibular neuritis

Broad cognitive difficulties have been reported in patients with peripheral vestibular deficit, especially in the domain of spatial cognition. Processing and manipulating numbers relies on the ability to use the inherent spatial features of numbers. It is thus conceivable that patients with acute peripheral vestibular deficit show impaired numerical cognition. Using the number Stroop task and a short math achievement test, we tested 20 patients with acute vestibular neuritis and 20 healthy, age-matched controls. On the one hand, patients showed normal congruency and distance effects in the number Stroop task, which is indicative of normal number magnitude processing. On the other hand, patients scored lower than healthy controls in the math achievement test. We provide evidence that the lower performance cannot be explained by either differences in prior math knowledge (i.e., education) or slower processing speed. Our results suggest that peripheral vestibular deficit negatively affects numerical cognition in terms of the efficient manipulation of numbers. We discuss the role of executive functions in math performance and argue that previously reported executive deficits in patients with peripheral vestibular deficit provide a plausible explanation for the lower math achievement scores. In light of the handicapping effects of impaired numerical cognition in daily living, it is crucial to further investigate the mechanisms that cause mathematical deficits in acute PVD and eventually develop adequate means for cognitive interventions.

Age-related differences in inhibitory control and memory updating in boys with Asperger syndrome

Deficits in specific executive domains are highly prevalent in autism spectrum disorder; however, age-related improvements in executive functions (reflecting prefrontal maturational changes) have been reported even in individuals diagnosed with autism. The current study examined two components of cognitive flexibility (inhibition of prepotent responses and memory monitoring/updating) by using a random-motor-generation task (MPT) in a group of 23 boys with Asperger syndrome (AS) and 23 matched healthy controls. We found poorer inhibition and more repetitive responses in younger AS children solely, but comparable memory monitoring/updating skills across groups. Overall, our findings correspond well with previous studies and reveal that even in AS specific EFs may improve with age and, thus, call for a more differentiated view of executive (dys) function profiles in children diagnosed with AS. Tests such as the random-motor-generation task may help to disentangle more specific processes of executive deficits in autism spectrum disorder as compared to the more classical tests.

Executive control and working memory are involved in sub-second repetitive motor timing

The nature of the relationship between timing and cognition remains poorly understood. Cognitive control is known to be involved in discrete timing tasks involving durations above 1 s, but has not yet been demonstrated for repetitive motor timing below 1 s. We examined the latter in two continuation tapping experiments, by varying the cognitive load in a concurrent task. In Experiment 1, participants repeated a fixed three finger sequence (low executive load) or a pseudorandom sequence (high load) with either 524-, 733-, 1024- or 1431-ms inter-onset intervals (IOIs). High load increased timing variability for 524 and 733-ms IOIs but not for the longer IOIs. Experiment 2 attempted to replicate this finding for a concurrent memory task. Participants retained three letters (low working memory load) or seven letters (high load) while producing intervals (524- and 733-ms IOIs) with a drum stick. High load increased timing variability for both IOIs. Taken together, the experiments demonstrate that cognitive control processes influence sub-second repetitive motor timing.

Acute peripheral vestibular deficit increases redundancy in random number generation

Unilateral peripheral vestibular deficit leads to broad cognitive difficulties and biases in spatial orientation. More specifically, vestibular patients typically show a spatial bias toward their affected ear in the subjective visual vertical, head and trunk orientation, fall tendency, and walking trajectory. By means of a random number generation task, we set out to investigate how an acute peripheral vestibular deficit affects the mental representation of numbers in space. Furthermore, the random number generation task allowed us to test if patients with peripheral vestibular deficit show evidence of impaired executive functions while keeping the head straight and while performing active head turns. Previous research using galvanic vestibular stimulation in healthy people has shown no effects on number space, but revealed increased redundancy of the generated numbers. Other studies reported a spatial bias in number representation during active and passive head turns. In this experiment, we tested 43 patients with acute vestibular neuritis (18 patients with left-sided and 25 with right-sided vestibular deficit) and 28 age-matched healthy controls. We found no bias in number space in patients with peripheral vestibular deficit but showed increased redundancy in patients during active head turns. Patients showed worse performance in generating sequences of random numbers, which indicates a deficit in the updating component of executive functions. We argue that RNG is a promising candidate for a time- and cost-effective assessment of executive functions in patients suffering from a peripheral vestibular deficit.

Brain structure links everyday creativity to creative achievement

Although creativity is commonly considered to be a cornerstone of human progress and vital to all realms of our lives, its neural basis remains elusive, partly due to the different tasks and measurement methods applied in research. In particular, the neural correlates of everyday creativity that can be experienced by everyone, to some extent, are still unexplored. The present study was designed to investigate the brain structure underlying individual differences in everyday creativity, as measured by the Creative Behavioral Inventory (CBI) (N=163). The results revealed that more creative activities were significantly and positively associated with larger gray matter volume (GMV) in the regional premotor cortex (PMC), which is a motor planning area involved in the creation and selection of novel actions and inhibition. In addition, the gray volume of the PMC had a significant positive relationship with creative achievement and Art scores, which supports the notion that training and practice may induce changes in brain structures. These results indicate that everyday creativity is linked to the PMC and that PMC volume can predict creative achievement, supporting the view that motor planning may play a crucial role in creative behavior.

Linking cognitive abilities with the propensity for risk-taking: the balloon analogue risk task

There is great interest about the individual differences that influence the ability of dealing with risky decisions. In this light, an intriguing question is whether decision-making during risk is related to other cognitive abilities, especially executive functions. To investigate, in healthy subjects, the existence of a possible correlation between risk-taking and cognitive abilities, the balloon analogue risk task (BART) has been exploited to assess risk-taking propensity and the random number generation (RNG), to investigate cognitive functions. The risk-taking propensity is significantly correlated with the Cycling factor, a feature of RNG performance specifically related to the ability of updating and monitoring information. In particular, an excessive activity of monitoring (expressed by lower values of Cycling factor) is related to a more risk-averse behavior. An overlapping between the circuits involved in both RNG and BART, centered on the dorsolateral prefrontal cortex, could be the possible neurophysiological substrate for this correlation. This study suggests a relevant contribution of executive functions in risk-taking behavior. This could have relevant implications in neuroeconomics and neuropsychiatry of addiction and pathological gambling.

Load-Dependent Interference of Deep Brain Stimulation of the Subthalamic Nucleus with Switching from Automatic to Controlled Processing During Random Number Generation in Parkinson's Disease

BACKGROUND

Deep brain stimulation of the subthalamic nucleus (STN DBS) ameliorates the motor symptoms of Parkinson's disease (PD). However, some aspects of executive control are impaired with STN DBS.

OBJECTIVE

We tested the prediction that (i) STN DBS interferes with switching from automatic to controlled processing during fast-paced random number generation (RNG) (ii) STN DBS-induced cognitive control changes are load-dependent.

METHODS

Fifteen PD patients with bilateral STN DBS performed paced-RNG, under three levels of cognitive load synchronised with a pacing stimulus presented at 1, 0.5 and 0.33 Hz (faster rates require greater cognitive control), with DBS on or off. Measures of output randomness were calculated. Countscore 1 (CS1) indicates habitual counting in steps of one (CS1). Countscore 2 (CS2) indicates a more controlled strategy of counting in twos.

RESULTS

The fastest rate was associated with an increased CS1 score with STN DBS on compared to off. At the slowest rate, patients had higher CS2 scores with DBS off than on, such that the differences between CS1 and CS2 scores disappeared.

CONCLUSIONS

We provide evidence for a load-dependent effect of STN DBS on paced RNG in PD. Patients could switch to more controlled RNG strategies during conditions of low cognitive load at slower rates only when the STN stimulators were off, but when STN stimulation was on, they engaged in more automatic habitual counting under increased cognitive load. These findings are consistent with the proposal that the STN implements a switch signal from the medial frontal cortex which enables a shift from automatic to controlled processing.

Bidirectional Modulation of Numerical Magnitude

Numerical cognition is critical for modern life; however, the precise neural mechanisms underpinning numerical magnitude allocation in humans remain obscure. Based upon previous reports demonstrating the close behavioral and neuro-anatomical relationship between number allocation and spatial attention, we hypothesized that these systems would be subject to similar control mechanisms, namely dynamic interhemispheric competition. We employed a physiological paradigm, combining visual and vestibular stimulation, to induce interhemispheric conflict and subsequent unihemispheric inhibition, as confirmed by transcranial direct current stimulation (tDCS). This allowed us to demonstrate the first systematic bidirectional modulation of numerical magnitude toward either higher or lower numbers, independently of either eye movements or spatial attention mediated biases. We incorporated both our findings and those from the most widely accepted theoretical framework for numerical cognition to present a novel unifying computational model that describes how numerical magnitude allocation is subject to dynamic interhemispheric competition. That is, numerical allocation is continually updated in a contextual manner based upon relative magnitude, with the right hemisphere responsible for smaller magnitudes and the left hemisphere for larger magnitudes.

Abnormal fronto-striatal functional connectivity in Parkinson's disease

Parkinson's disease (PD) is characterized by the relatively selective depletion of dopamine in the striatum, which consequently leads to dysfunctions in cortico-striatal-thalamic-cortical circuitries. It has been shown that the most common cognitive deficits in PD patients are related to the fronto-striatal circuits. In PD, most previous functional connectivity studies have been performed using seed-based methods to identify the brain regions that are abnormally connected to one or more seeds, but these cannot be used to quantify the interactions between one region and all other regions in a particular network. Functional connectivity degree, which is a measurement that can be used to quantify the functional or structural connectivity of a complex brain network, was adopted in this study to assess the interactions of the fronto-striatal network. Compared to healthy controls, PD patients had significantly decreased total functional connectivity degree for the left putamen and the right globus pallidum in fronto-striatal networks. Additionally, negative correlations between the fronto-pallial functional connectivity degree (i.e., the right globus pallidum with the left middle frontal gyrus, and with the right triangular part of inferior frontal gyrus) and disease duration were observed in PD patients. The results of this study demonstrate that fronto-striatal functional connectivity is abnormal in patients with PD and indicate that these deficits might be the result of motor and cognitive dysfunctions in PD patients.

The Anterior Insula Tracks Behavioral Entropy during an Interpersonal Competitive Game

In competitive situations, individuals need to adjust their behavioral strategy dynamically in response to their opponent’s behavior. In the present study, we investigated the neural basis of how individuals adjust their strategy during a simple, competitive game of matching pennies. We used entropy as a behavioral index of randomness in decision-making, because maximizing randomness is thought to be an optimal strategy in the game, according to game theory. While undergoing functional magnetic resonance imaging (fMRI), subjects played matching pennies with either a human or computer opponent in each block, although in reality they played the game with the same computer algorithm under both conditions. The winning rate of each block was also manipulated. Both the opponent (human or computer), and the winning rate, independently affected subjects’ block-wise entropy during the game. The fMRI results revealed that activity in the bilateral anterior insula was positively correlated with subjects’ (not opponent’s) behavioral entropy during the game, which indicates that during an interpersonal competitive game, the anterior insula tracked how uncertain subjects’ behavior was, rather than how uncertain subjects felt their opponent's behavior was. Our results suggest that intuitive or automatic processes based on somatic markers may be a key to optimally adjusting behavioral strategies in competitive situations.

Neural substrates of levodopa-responsive gait disorders and freezing in advanced Parkinson's disease: a kinesthetic imagery approach

Gait disturbances, including freezing of gait, are frequent and disabling symptoms of Parkinson's disease. They often respond poorly to dopaminergic treatments. Although recent studies have shed some light on their neural correlates, their modulation by dopaminergic treatment remains quite unknown. Specifically, the influence of levodopa on the networks involved in motor imagery (MI) of parkinsonian gait has not been directly studied, comparing the off and on medication states in the same patients. We therefore conducted an [H2 (15) 0] Positron emission tomography study in eight advanced parkinsonian patients (mean disease duration: 12.3 ± 3.8 years) presenting with levodopa-responsive gait disorders and FoG, and eight age-matched healthy subjects. All participants performed three tasks (MI of gait, visual imagery and a control task). Patients were tested off, after an overnight withdrawal of all antiparkinsonian treatment, and on medication, during consecutive mornings. The order of conditions was counterbalanced between subjects and sessions. Results showed that imagined gait elicited activations within motor and frontal associative areas, thalamus, basal ganglia and cerebellum in controls. Off medication, patients mainly activated premotor-parietal and pontomesencephalic regions. Levodopa increased activation in motor regions, putamen, thalamus, and cerebellum, and reduced premotor-parietal and brainstem involvement. Areas activated when patients are off medication may represent compensatory mechanisms. The recruitment of these accessory circuits has also been reported for upper-limb movements in Parkinson's disease, suggesting a partly overlapping pathophysiology between imagined levodopa-responsive gait disorders and appendicular signs. Our results also highlight a possible cerebellar contribution in the pathophysiology of parkinsonian gait disorders through kinesthetic imagery.

Neural and sympathetic activity associated with exploration in decision-making: further evidence for involvement of insula

We previously reported that sympathetic activity was associated with exploration in decision-making indexed by entropy, which is a concept in information theory and indexes randomness of choices or the degree of deviation from sticking to recent experiences of gains and losses, and that activation of the anterior insula mediated this association. The current study aims to replicate and to expand these findings in a situation where contingency between options and outcomes is manipulated. Sixteen participants performed a stochastic decision-making task in which we manipulated a condition with low uncertainty of gain/loss (contingent-reward condition) and a condition with high uncertainty of gain/loss (random-reward condition). Regional cerebral blood flow was measured by (15)O-water positron emission tomography (PET), and cardiovascular parameters and catecholamine in the peripheral blood were measured, during the task. In the contingent-reward condition, norepinephrine as an index of sympathetic activity was positively correlated with entropy indicating exploration in decision-making. Norepinephrine was negatively correlated with neural activity in the right posterior insula, rostral anterior cingulate cortex, and dorsal pons, suggesting neural bases for detecting changes of bodily states. Furthermore, right anterior insular activity was negatively correlated with entropy, suggesting influences on exploration in decision-making. By contrast, in the random-reward condition, entropy correlated with activity in the dorsolateral prefrontal and parietal cortices but not with sympathetic activity. These findings suggest that influences of sympathetic activity on exploration in decision-making and its underlying neural mechanisms might be dependent on the degree of uncertainty of situations.

Improved cerebral oxygenation response and executive performance as a function of cardiorespiratory fitness in older women: a fNIRS study

Cardiorespiratory fitness has been shown to protect and enhance cognitive and brain functions, but little is known about the cortical mechanisms that underlie these changes in older adults. In this study, functional near infrared spectroscopy (fNIRS) was used to investigate variations in oxyhemoglobin [HbO2] and in deoxyhemoglobin [HHb] in the dorsolateral prefrontal cortex (DLPFC) during the performance of an executive control task in older women with different levels of cardiorespiratory fitness (VO2max). Thirty-four women aged 60-77 years were classified as high-fit and low-fit based on VO2max measures. They all performed a control counting (CNT) task and the Random Number Generation (RNG) task at two different paces (1 number/1 s and 1 number/1.5 s), allowing to manipulate task difficulty, while hemodynamic responses in the bilateral DLPFCs were recorded using continuous-wave NIRS. The behavioral data revealed that the high-fit women showed significantly better performance on the RNG tasks compared with the low-fit women. The high-fit women showed significant increases in [HbO2] responses in both left and right DLPFCs during the RNG task, while the low-fit women showed significantly less activation in the right DLPFC compared with the right DLPFC of the high-fit women and compared with their own left DLPFC. At the level of the whole sample, increases in the [HbO2] responses in the right DLPFC were found to mediate in part the relationship between VO2max level and executive performance during the RNG task at 1.5 s but not at 1 s. These results provide support for the cardiorespiratory fitness hypothesis and suggest that higher levels of aerobic fitness in older women are related to increased cerebral oxygen supply to the DLPFC, sustaining better cognitive performance.

Rhythmic complexity and predictive coding: a novel approach to modeling rhythm and meter perception in music

Musical rhythm, consisting of apparently abstract intervals of accented temporal events, has a remarkable capacity to move our minds and bodies. How does the cognitive system enable our experiences of rhythmically complex music? In this paper, we describe some common forms of rhythmic complexity in music and propose the theory of predictive coding (PC) as a framework for understanding how rhythm and rhythmic complexity are processed in the brain. We also consider why we feel so compelled by rhythmic tension in music. First, we consider theories of rhythm and meter perception, which provide hierarchical and computational approaches to modeling. Second, we present the theory of PC, which posits a hierarchical organization of brain responses reflecting fundamental, survival-related mechanisms associated with predicting future events. According to this theory, perception and learning is manifested through the brain’s Bayesian minimization of the error between the input to the brain and the brain’s prior expectations. Third, we develop a PC model of musical rhythm, in which rhythm perception is conceptualized as an interaction between what is heard (“rhythm”) and the brain’s anticipatory structuring of music (“meter”). Finally, we review empirical studies of the neural and behavioral effects of syncopation, polyrhythm and groove, and propose how these studies can be seen as special cases of the PC theory. We argue that musical rhythm exploits the brain’s general principles of prediction and propose that pleasure and desire for sensorimotor synchronization from musical rhythm may be a result of such mechanisms.

An architecturally constrained model of random number generation and its application to modeling the effect of generation rate

Random number generation (RNG) is a complex cognitive task for human subjects, requiring deliberative control to avoid production of habitual, stereotyped sequences. Under various manipulations (e.g., speeded responding, transcranial magnetic stimulation, or neurological damage) the performance of human subjects deteriorates, as reflected in a number of qualitatively distinct, dissociable biases. For example, the intrusion of stereotyped behavior (e.g., counting) increases at faster rates of generation. Theoretical accounts of the task postulate that it requires the integrated operation of multiple, computationally heterogeneous cognitive control (“executive”) processes. We present a computational model of RNG, within the framework of a novel, neuropsychologically-inspired cognitive architecture, ESPro. Manipulating the rate of sequence generation in the model reproduced a number of key effects observed in empirical studies, including increasing sequence stereotypy at faster rates. Within the model, this was due to time limitations on the interaction of supervisory control processes, namely, task setting, proposal of responses, monitoring, and response inhibition. The model thus supports the fractionation of executive function into multiple, computationally heterogeneous processes.

The effect of practice on random number generation task: a transcranial direct current stimulation study

Random number generation (RNG) is a procedurally-simple task related to specific executive functions, such as updating and monitoring of information and inhibition of automatic responses. The effect of practice on executive functions has been widely investigated, however little is known on the impact of practice on RNG. Transcranial direct current stimulation (tDCS) allows to modulate, non-invasively, brain activity and to enhance the effects of training on executive functions. Hence, this study aims to investigate the effect of practice on RNG and to explore the possibility to influence it by tDCS applied over dorsolateral prefrontal cortex. Twenty-six healthy volunteers have been evaluated within single session and between different sessions of RNG using several measures of randomness, which are informative of separable cognitive components servicing random behavior. We found that repetition measures significantly change within single session, seriation measures significantly change both within and between sessions, while cycling measures are not affected by practice. tDCS does not produce any additional effect, however a sub-analysis limited to the first session revealed an increasing trend in seriation measure after anodal compared to cathodal stimulation. Our findings support the hypothesis that practice selectively and consistently influences specific cognitive components related to random behavior, while tDCS transiently affects RNG performance.