Cognitive effects of methylphenidate in healthy volunteers: a review of single dose studies

Repetitive mild traumatic brain injury impairs norepinephrine system function and psychostimulant responsivity

Traumatic brain injury (TBI) is a complex pathophysiological process that results in a variety of neurotransmitter, behavioral, and cognitive deficits. The locus coeruleus-norepinephrine (LC-NE) system is a critical regulator of arousal levels and higher executive processes affected by TBI including attention, working memory, and decision making. LC-NE axon injury and impaired signaling within the prefrontal cortex (PFC) is a potential contributor to the neuropsychiatric symptoms after single, moderate to severe TBI. The majority of TBIs are mild, yet long-term cognitive deficits and increased susceptibility for further injury can accumulate after each repetitive mild TBI. As a potential treatment for restoring cognitive function and daytime sleepiness after injury psychostimulants, including methylphenidate (MPH) that increase levels of NE within the PFC, are being prescribed "off-label". The impact of mild and repetitive mild TBI on the LC-NE system remains limited. Therefore, we determined the extent of LC-NE and arousal dysfunction and response to therapeutic doses of MPH in rats following experimentally induced single and repetitive mild TBI. Microdialysis measures of basal NE efflux from the medial PFC and arousal measures were significantly lower after repetitive mild TBI. Females showed higher baseline PFC-NE efflux than males following single and repetitive mild TBI. In response to MPH challenge, males exhibited a blunted PFC-NE response and persistent arousal levels following repetitive mild TBI. These results provide critical insight into the role of catecholamine system dysfunction associated with cognitive deficits following repeated injury, outcome differences between sex/gender, and lack of success of MPH as an adjunctive therapy to improve cognitive function following injury.

Interactions of catecholamines and GABA+ in cognitive control: Insights from EEG and 1H-MRS

Catecholamines and amino acid transmitter systems are known to interact, the exact links and their impact on cognitive control functions have however remained unclear. Using a multi-modal imaging approach combining EEG and proton-magnetic resonance spectroscopy (1H-MRS), we investigated the effect of different degrees of pharmacological catecholaminergic enhancement onto theta band activity (TBA) as a measure of interference control during response inhibition and execution. It was central to our study to evaluate the predictive impact of in-vivo baseline GABA+ concentrations in the striatum, the anterior cingulate cortex (ACC) and the supplemental motor area (SMA) of healthy adults under varying degrees of methylphenidate (MPH) stimulation. We provide evidence for a predictive interrelation of baseline GABA+ concentrations in cognitive control relevant brain areas onto task-induced TBA during response control stimulated with MPH. Baseline GABA+ concentrations in the ACC, the striatum, and the SMA had a differential impact on predicting interference control-related TBA in response execution trials. GABA+ concentrations in the ACC appeared to be specifically important for TBA modulations when the cognitive effort needed for interference control was high - that is when no prior task experience exists, or in the absence of catecholaminergic enhancement with MPH. The study highlights the predictive role of baseline GABA+ concentrations in key brain areas influencing cognitive control and responsiveness to catecholaminergic enhancement, particularly in high-effort scenarios.

Can stimulants make you smarter, despite stealing your sleep?

Nonmedical use of psychostimulants for cognitive enhancement is widespread and growing in neurotypical individuals, despite mixed scientific evidence of their effectiveness. Sleep benefits cognition, yet the interaction between stimulants, sleep, and cognition in neurotypical adults has received little attention. We propose that one effect of psychostimulants, namely decreased sleep, may play an important and unconsidered role in the effect of stimulants on cognition. We discuss the role of sleep in cognition, the alerting effects of stimulants in the context of sleep loss, and the conflicting findings of stimulants for complex cognitive processes. Finally, we hypothesize that sleep may be one unconsidered factor in the mythology of stimulants as cognitive enhancers and propose a methodological approach to systematically assess this relation.

The Ability to Voluntarily Regulate Theta Band Activity Affects How Pharmacological Manipulation of the Catecholaminergic System Impacts Cognitive Control

BACKGROUND

The catecholaminergic system influences response inhibition, but the magnitude of the impact of catecholaminergic manipulation is heterogeneous. Theoretical considerations suggest that the voluntary modulability of theta band activity can explain this variance. The study aimed to investigate to what extent interindividual differences in catecholaminergic effects on response inhibition depend on voluntary theta band activity modulation.

METHODS

A total of 67 healthy adults were tested in a randomized, double-blind, cross-over study design. At each appointment, they received a single dose of methylphenidate or placebo and performed a Go/Nogo task with stimuli of varying complexity. Before the first appointment, the individual's ability to modulate theta band activity was measured. Recorded EEG data were analyzed using temporal decomposition and multivariate pattern analysis.

RESULTS

Methylphenidate effects and voluntary modulability of theta band activity showed an interactive effect on the false alarm rates of the different Nogo conditions. The multivariate pattern analysis revealed that methylphenidate effects interacted with voluntary modulability of theta band activity at a stimulus processing level, whereas during response selection methylphenidate effects interacted with the complexity of the Nogo condition.

CONCLUSIONS

The findings reveal that the individual's theta band modulability affects the responsiveness of an individual's catecholaminergic system to pharmacological modulation. Thus, the impact of pharmacological manipulation of the catecholaminergic system on cognitive control most likely depends on the existing ability to self-modulate relevant brain oscillatory patterns underlying the cognitive processes being targeted by pharmacological modulations.

Methylphenidate undermines or enhances divergent creativity depending on baseline dopamine synthesis capacity

Catecholamine-enhancing psychostimulants, such as methylphenidate have long been argued to undermine creative thinking. However, prior evidence for this is weak or contradictory, stemming from studies with small sample sizes that do not consider the well-established large variability in psychostimulant effects across different individuals and task demands. We aimed to definitively establish the link between psychostimulants and creative thinking by measuring effects of methylphenidate in 90 healthy participants on distinct creative tasks that measure convergent and divergent thinking, as a function of individuals' baseline dopamine synthesis capacity, indexed with 18F-FDOPA PET imaging. In a double-blind, within-subject design, participants were administered methylphenidate, placebo or selective D2 receptor antagonist sulpiride. The results showed that striatal dopamine synthesis capacity and/or methylphenidate administration did not affect divergent and convergent thinking. However, exploratory analysis demonstrated a baseline dopamine-dependent effect of methylphenidate on a measure of response divergence, a creativity measure that measures response variability. Response divergence was reduced by methylphenidate in participants with low dopamine synthesis capacity but enhanced in those with high dopamine synthesis capacity. No evidence of any effect of sulpiride was found. These results show that methylphenidate can undermine certain forms of divergent creativity but only in individuals with low baseline dopamine levels.

Role of environmental enrichment on social interaction, anxiety, locomotion, and memory in Wistar rats under chronic methylphenidate intake

Introduction

Chronic use of various compounds can have long-lasting effects on animal behavior, and some of these effects can be influenced by the environment. Many environmental enrichment protocols have the potential to induce behavioral changes.

Aim

The aim of the present study was to investigate how environmental enrichment can mitigate the effects of chronic methylphenidate consumption on the behavior of Wistar rats.

Methods

The animals were housed for 20 days under either an environmental enrichment protocol (which included tubes of different shapes) or standard housing conditions. After seven days, half of the rats received 13 days of oral administration of methylphenidate (2 mg/kg). After seven days, the rats underwent behavioral tests, including the elevated plus maze (anxiety), open field (locomotion), object-in-place recognition test (spatial memory), and a test for social interaction (social behavior).

Results

The results showed that the enriched environmental condition reversed the enhanced time in the open arms of the elevated plus maze induced by methylphenidate (F[1,43] = 4.275, p = 0.045). Methylphenidate also enhanced exploratory rearing in the open field (F[1,43] = 4.663, p = 0.036) and the time spent in the open area of the open field (H[3] = 8.786, p = 0.032). The enriched environment mitigated the inhibition of social interaction with peers induced by methylphenidate (H[3] = 16.755, p  < 0.001) as well as the preference for single exploratory behavior (H[3] = 9.041, p = 0.029).

Discussion

These findings suggest that environmental enrichment can counteract some of the effects of methylphenidate. These results are relevant for the clinical treatment of the long-lasting secondary effects associated with methylphenidate pharmacological treatment.

Prescription psychostimulants as a harm reduction and treatment intervention for methamphetamine use disorder and the implications for nursing clinical practice: A scoping review of the literature

The global rise in methamphetamine use and its negative effects warrants the need for research exploring harm reduction and treatment interventions for individuals with methamphetamine use disorder. Agonist medications have been utilized for years for the treatment of heroin and opioid addiction, but have yet to be incorporated into mainstream Canadian practice for methamphetamine dependence. This review aims to provide an overview of the current trends of prescription psychostimulant usage for individuals with methamphetamine use disorder from a Canadian perspective, identifies the barriers to accessing prescription psychostimulants for methamphetamine use disorder and highlights the nursing clinical practice implications in caring for individuals with the disorder. Discourse on the sustained abstinence and harm reduction debate is presented from the perspective of methamphetamine abuse is provided along with the neuropsychiatric complications of chronic methamphetamine use. The impacts of specific prescription psychostimulants on cognition are discussed as is the use of neuroimaging techniques to assess neuronal damage in methamphetamine users. Sign of toxicity, overdose and the contraindications for use of these prescription psychostimulants is also presented. The implications to nursing clinical practice in caring for this population is provided, touching on the clinical presentation of methamphetamine use, completing thorough assessment and screening and patient education. The findings of this review indicate the need for further research in this area exploring the benefits of prescription psychostimulants as a harm reduction and treatment intervention for the global problem of methamphetamine dependence.

Alpha/beta-gamma decoupling in methylphenidate medicated ADHD patients

There is much interest to understand how different neural rhythms function, interact and are regulated. Here, we focus on WM delay gamma to investigate its coupling with alpha/beta rhythms and its neuromodulation by methylphenidate. We address this through the use of human EEG conducted in healthy and ADHD subjects which revealed ADHD-specific electrophysiological deficits and MPH-induced normalization of gamma amplitude and its coupling with alpha/beta rhythms. Decreased alpha/beta-gamma coupling is known to facilitate memory representations via disinhibition of gamma ensembles coding the maintained stimuli. Here, we present EEG evidence which suggests that these dynamics are sensitive to catecholaminergic neuromodulation. MPH decreased alpha/beta-gamma coupling and this was related to the increase in delay-relevant gamma activity evoked by the same drug. These results add further to the neuromodulatory findings that reflect an electrophysiological dimension to the well-known link between WM delay and catecholaminergic transmission.

Pre-clinical evidence that methylphenidate increases motivation and/or reward preference to search for high value rewards

Methylphenidate is a stimulant used to treat attention deficit and hyperactivity disorder (ADHD). In the last decade, illicit use of methylphenidate has increased among healthy young adults, who consume the drug under the assumption that it will improve cognitive performance. However, the studies that aimed to assess the methylphenidate effects on memory are not consistent. Here, we tested whether the effect of methylphenidate on a spatial memory task can be explained as a motivational and/or a reward effect. We tested the effects of acute and chronic i.p. administration of 0.3, 1 or 3 mg/kg of methylphenidate on motivation, learning and memory by using the 8-arm radial maze task. Adult male Wistar rats learned that 3 of the 8 arms of the maze were consistently baited with 1, 3, or 6 sucrose pellets, and the number of entries and reentries into reinforced and non-reinforced arms of the maze were scored. Neither acute nor chronic (20 days) methylphenidate treatment affected the number of entries in the non-baited arms. However, chronic, but not acute, 1-3 mg/kg methylphenidate increased the number of reentries in the higher reward arms, which suggests a motivational/rewarding effect rather than a working memory deficit. In agreement with this hypothesis, the methylphenidate treatment also decreased the approach latency to the higher reward arms, increased the approach latency to the low reward arm, and increased the time spent in the high, but not low, reward arm. These findings suggest that methylphenidate may act more as a motivational enhancer rather than a cognitive enhancer in healthy people.

Cognitive enhancement: Effects of methylphenidate, modafinil, and caffeine on latent memory and resting state functional connectivity in healthy adults

Stimulants like methylphenidate, modafinil, and caffeine have repeatedly shown to enhance cognitive processes such as attention and memory. However, brain-functional mechanisms underlying such cognitive enhancing effects of stimulants are still poorly characterized. Here, we utilized behavioral and resting-state fMRI data from a double-blind randomized placebocontrolled study of methylphenidate, modafinil, and caffeine in 48 healthy male adults. The results show that performance in different memory tasks is enhanced, and functional connectivity (FC) specifically between the frontoparietal network (FPN) and default mode network (DMN) is modulated by the stimulants in comparison to placebo. Decreased negative connectivity between right prefrontal and medial parietal but also between medial temporal lobe and visual brain regions predicted stimulant-induced latent memory enhancement. We discuss dopamine's role in attention and memory as well as its ability to modulate FC between large-scale neural networks (e.g., FPN and DMN) as a potential cognitive enhancement mechanism.

Prevalence, profile and associations of cognitive impairment in Ugandan first-episode psychosis patients

Introduction

The MATRICS consensus cognitive battery (MCCB) is the gold standard for neuropsychological assessment in psychotic disorders but is rarely used in low resource settings. This study used the MCCB to determine the prevalence, profile and associations of various exposures with cognitive impairment in Ugandan first-episode psychosis patients.

Methods

Patients and matched healthy controls were recruited at Butabika Hospital in Uganda. Clinical variables were first collated, and after the resolution of psychotic symptoms, a neuropsychological assessment of seven cognitive domains was performed using the MCCB. Cognitive impairment was defined as two standard deviations (SD) below the mean in one domain or 1SD below the mean in two domains. Descriptive statistics determined the prevalence and profile of impairment while regression models determined the association between various exposures with cognitive scores while controlling for age, sex and education.

Results

Neuropsychological assessment with the MCCB found the burden of cognitive impairment in first-episode psychosis patients five times that of healthy controls. The visual learning and memory domain was most impaired in first-episode psychosis patients, while it was the working memory domain for the healthy controls. Increased age was associated with impairment in the domains of the speed of processing (p < 0.001) and visual learning and memory (p = 0.001). Cassava-rich diets and previous alternative and complementary therapy use were negatively associated with impairment in the visual learning (p = 0.04) and attention/vigilance domains (p = 0.012), respectively. There were no significant associations between sex, history of childhood trauma, or illness severity with any cognitive domain.

Conclusion

A significant burden of cognitive impairment in Ugandan first-episode psychosis patients is consistent with prior data from other contexts. However, the profile of and risk factors for impairment differ from that described in such work. Therefore, interventions to reduce cognitive impairment in FEP patients specific to this setting, including dietary modifications, are required.

Late-manifestation of attention-deficit/hyperactivity disorder in older adults: an observational study

BACKGROUND

The age of attention-deficit/hyperactivity disorder onset is usually during the first 12 years of life; however, there have been recent reports of late-onset attention-deficit/hyperactivity disorder. These reports have been limited to that of young adults, and details in older adults remain unknown. As such, we had previously presented the first case report of "very" late-onset attention-deficit/hyperactivity disorder, wherein the symptoms presented in senile age. In this observational study, we aimed to investigate the prevalence and clinical features of such attention-deficit/hyperactivity disorders in older adults visiting our dementia clinic.

METHODS

Four hundred forty-six consecutive patients visiting our specialty outpatient clinic for dementia during the 2-year period from April 1, 2015 to March 31, 2017 were included in this study. First, the patients were examined for the presence or absence of dementia in our specialty outpatient clinic for dementia. Those not diagnosed with dementia were examined for the presence or absence of attention-deficit/hyperactivity disorder in our specialty outpatient clinic for developmental disorders. Finally, these patients who were diagnosed with attention-deficit/hyperactivity disorder were investigated in detail to clarify their clinical characteristics.

RESULTS

Of 446 patients (246 women and 200 men), 7 patients were finally diagnosed with attention-deficit/hyperactivity disorder. Although these 7 patients were initially suspected to have Alzheimer's disease (considering their age, 6 of these 7 patients were suspected to have early onset Alzheimer's disease), it was found that these symptoms were due to attention-deficit/hyperactivity disorder. These patients had four characteristics in common: (1) they were significantly younger than the complete study population; (2) they predominantly showed inattention-related symptoms; (3) they showed latent manifestation; and (4) they experienced a stressful life event before manifestation.

CONCLUSIONS

Our previous case report suggested that very late-onset attention-deficit/hyperactivity disorder patients could be incorrectly diagnosed with dementia. In this observational study, 1.6% of patients who were initially suspected of having dementia were actually diagnosed with attention-deficit/hyperactivity disorder. This study also showed that the "late-onset" described in our previous report would be better described as "late-manifestation." A clinician should consider late-manifestation of attention-deficit/hyperactivity disorder in the differential diagnosis when encountering dementia patients, especially early onset Alzheimer's disease.

Dorsal-to-ventral imbalance in the superior longitudinal fasciculus mediates methylphenidate's effect on beta oscillations in ADHD

While pharmacological treatment with methylphenidate (MPH) is a first line intervention for ADHD, its mechanisms of action have yet to be elucidated. We here seek to identify the white matter tracts that mediate MPH's effect on beta oscillations. We implemented a double-blind placebo-controlled crossover design, where boys diagnosed with ADHD underwent behavioral and MEG measurements during a spatial attention task while on and off MPH. The results were compared with an age/IQ-matched control group. Estimates of white matter tracts were obtained using diffusion tensor imaging (DTI). Via a stepwise model selection strategy, we identified the fiber tracts (regressors) significantly predicting values of the dependent variables of interest (i.e., oscillatory power, behavioral performance, and clinical symptoms): the anterior thalamic radiation (ATR), the superior longitudinal fasciculus ("parietal endings") (SLFp), and superior longitudinal fasciculus ("temporal endings") (SLFt). ADHD symptoms severity was associated with lower fractional anisotropy (FA) within the ATR. In addition, individuals with relatively higher FA in SLFp compared to SLFt, led to stronger behavioral effects of MPH in the form of faster and more accurate responses. Furthermore, the same parietotemporal FA gradient explained the effects of MPH on beta modulation: subjects with ADHD exhibiting higher FA in SLFp compared to SLFt also displayed greater effects of MPH on beta power during response preparation. Our data suggest that the behavioral deficits and aberrant oscillatory modulations observed in ADHD depend on a possibly detrimental structural connectivity imbalance within the SLF, caused by a diffusivity gradient in favor of parietal rather than temporal, fiber tracts.

Meta-analysis: Dose-Dependent Effects of Methylphenidate on Neurocognitive Functioning in Children With Attention-Deficit/Hyperactivity Disorder

OBJECTIVE

Neurocognitive deficits are at the heart of explanatory models of attention-deficit/hyperactivity disorder (ADHD), and lead to significant impairments in daily life. Determining the dosing effects of methylphenidate (MPH) on a broad range of neurocognitive functions and investigating possible impairing effects of high doses is therefore important.

METHOD

Placebo-controlled trials were included that investigated MPH dosing effects on neurocognitive functions in children and adolescents (aged 5-18 years) diagnosed with ADHD. Effect sizes (standardized mean differences [SMDs]) were calculated for different neurocognitive functions (baseline speed, variability in responding, nonexecutive memory and executive memory, inhibitory control, and cognitive flexibility) and, if available, for ADHD symptoms. Meta-regression analysis were used to investigate linear effects of dose (mg/kg/dose), and separate meta-analyses compared SMDs for 3 MPH dose ranges: low (0.10-0.30 mg/kg/dose), medium (0.31-0.60 mg/kg/dose), and high (0.61-1.00 mg/kg/dose).

RESULTS

A total of 31 studies fulfilled inclusion criteria, comprising 804 children with ADHD. Methylphenidate had beneficial effects on all neurocognitive functions (d = 0.20-0.73). Significant linear dosing effects were found for ADHD symptoms and lower-order neurocognitive functions (baseline speed, variability in responding, nonexecutive memory), with greater enhancement of functioning with increasing dose. No dosing effects were found for higher-order neurocognitive functions (executive memory, inhibitory control, and cognitive flexibility). No detrimental effects of MPH were found on any of the investigated functions.

CONCLUSION

Methylphenidate was superior to placebo in improving ADHD symptoms and a broad range of neurocognitive functions; however, effects sizes regarding the effects of dose vary substantially between functions. Our data highlight the importance of considering both neurocognitive and symptomatic aspects of ADHD in clinical practice.

Benefits and Harms of 'Smart Drugs' (Nootropics) in Healthy Individuals

'Smart drugs' (also known as 'nootropics' and 'cognitive enhancers' [CEs]) are being used by healthy subjects (i.e. students and workers) typically to improve memory, attention, learning, executive functions and vigilance, hence the reference to a 'pharmaceutical cognitive doping behaviour'. While the efficacy of known CEs in individuals with memory or learning deficits is well known, their effect on non-impaired brains is still to be fully assessed. This paper aims to provide an overview on the prevalence of use; putative neuroenhancement benefits and possible harms relating to the intake of the most popular CEs (e.g. amphetamine-type stimulants, methylphenidate, donepezil, selegiline, modafinil, piracetam, benzodiazepine inverse agonists, and unifiram analogues) in healthy individuals. CEs are generally perceived by the users as effective, with related enthusiastic anecdotal reports; however, their efficacy in healthy individuals is uncertain and any reported improvement temporary. Conversely, since most CEs are stimulants, the related modulation of central noradrenaline, glutamate, and dopamine levels may lead to cardiovascular, neurological and psychopathological complications. Furthermore, use of CEs can be associated with paradoxical short- and long-term cognitive decline; decreased potential for plastic learning; and addictive behaviour. Finally, the non-medical use of any potent psychotropic raises serious ethical and legal issues, with nootropics having the potential to become a major public health concern. Further studies investigating CE-associated social, psychological, and biological outcomes are urgently needed to allow firm conclusions to be drawn on the appropriateness of CE use in healthy individuals.

Extended-release methylphenidate for attention deficit hyperactivity disorder (ADHD) in adults

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is a psychiatric diagnosis increasingly used in adults. The recommended first-line pharmacological treatment is central nervous system (CNS) stimulants, such as methylphenidate, but uncertainty remains about its benefits and harms.

OBJECTIVES

To assess the beneficial and harmful effects of extended-release formulations of methylphenidate in adults diagnosed with ADHD.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, nine other databases and four clinical trial registries up to February 2021. We searched 12 drug regulatory databases for clinical trial data up to 13 May 2020. In addition, we cross-referenced all available trial identifiers, handsearched reference lists, searched pharmaceutical company databases, and contacted trial authors.

SELECTION CRITERIA

Randomised, double-blind, parallel-group trials comparing extended-release methylphenidate formulations at any dose versus placebo and other ADHD medications in adults diagnosed with ADHD.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data. We assessed dichotomous outcomes as risk ratios (RRs), and rating scales and continuous outcomes as mean differences (MDs) or standardised mean differences (SMDs). We used the Cochrane risk of bias tool to assess risks of bias, and GRADE to assess the certainty of the evidence. We meta-analysed the data using a random-effects model. We assessed three design characteristics that may impair the trial results' 'generalisability'; exclusion of participants with psychiatric comorbidity; responder selection based on previous experience with CNS stimulants; and risk of withdrawal effects. Our prespecified primary outcomes were functional outcomes, self-rated ADHD symptoms, and serious adverse events. Our secondary outcomes included quality of life, ADHD symptoms rated by investigators and by peers such as family members, cardiovascular variables, severe psychiatric adverse events, and other adverse events.

MAIN RESULTS

We included 24 trials (5066 participants), of which 21 reported outcome data for this review. We also identified one ongoing study. We included documents from six drug regulatory agencies covering eight trials. Twenty-one trials had an outpatient setting and three were conducted in prisons. They were primarily conducted in North America and Europe. The median participant age was 36 years. Twelve trials (76% of participants) were industry-sponsored, four (14% of participants) were publicly funded with industry involvement, seven (10% of participants) were publicly funded, and one had unclear funding. The median trial duration was eight weeks. One trial was rated at overall unclear risk of bias and 20 trials were rated at overall high risk of bias, primarily due to unclear blinding of participants and investigators, attrition bias, and selective outcome reporting. All trials were impaired in at least one of the three design characteristics related to 'generalisability'; for example, they excluded participants with psychiatric comorbidity such as depression or anxiety, or included participants only with a previous positive response to methylphenidate, or similar drugs. This may limit the trials' usefulness for clinical practice, as they may overestimate the benefits and underestimate the harms. Extended-release methylphenidate versus placebo (up to 26 weeks) For the primary outcomes, we found very low-certainty evidence that methylphenidate had no effect on 'days missed at work' at 13-week follow-up (mean difference (MD) -0.15 days, 95% confidence interval (CI) -2.11 to 1.81; 1 trial, 409 participants) or serious adverse events (risk ratio (RR) 1.43, CI 95% CI 0.85 to 2.43; 14 trials, 4078 participants), whereas methylphenidate improved self-rated ADHD symptoms (small-to-moderate effect; SMD -0.37, 95% CI -0.43 to -0.30; 16 trials, 3799 participants). For secondary outcomes, we found very low-certainty evidence that methylphenidate improved self-rated quality of life (small effect; SMD -0.15, 95% CI -0.25 to -0.05; 6 trials, 1888 participants), investigator-rated ADHD symptoms (small-to-moderate effect; SMD -0.42, 95% CI -0.49 to -0.36; 18 trials, 4183 participants), ADHD symptoms rated by peers such as family members (small-to-moderate effect; SMD -0.31, 95% CI -0.48 to -0.14; 3 trials, 1005 participants), and increased the risk of experiencing any adverse event (RR 1.27, 95% CI 1.19 to 1.37; 14 trials, 4214 participants). We rated the certainty of the evidence as 'very low' for all outcomes, primarily due to high risk of bias and 'indirectness of the evidence'. One trial (419 participants) had follow-up at 52 weeks and two trials (314 participants) included active comparators, hence long-term and comparative evidence is limited.

AUTHORS' CONCLUSIONS

We found very low-certainty evidence that extended-release methylphenidate compared to placebo improved ADHD symptoms (small-to-moderate effects) measured on rating scales reported by participants, investigators, and peers such as family members. Methylphenidate had no effect on 'days missed at work' or serious adverse events, the effect on quality of life was small, and it increased the risk of several adverse effects. We rated the certainty of the evidence as 'very low' for all outcomes, due to high risk of bias, short trial durations, and limitations to the generalisability of the results. The benefits and harms of extended-release methylphenidate therefore remain uncertain.

The effect of methylphenidate and mixed amphetamine salts on cognitive reflection: a field study

RATIONALE

Methylphenidate (MPH) and mixed D,L-amphetamine salts (MASs; Adderall) were previously found to have unreliable effects on judgment and decision processes.

OBJECTIVE

We predicted that MPH and MASs have a specific effect of reducing heuristic responses, which should lead to increased performance on the cognitive reflection test (CRT). The CRT is considered to be a testbed for heuristic versus deliberative response modes.

METHODS

We recruited a sample of 15,361 individuals using the Prolific Academic crowdsourcing platform. From this initial pool, our final sample consisted of 294 participants (125 MPH users and 169 MASs users) who conformed to the study criteria and completed the experimental tasks. Tasks were performed on days where participants were either medicated or not, allowing to assess the effect of medication status.

RESULTS

There was a strong positive effect of taking MPH on CRT scores (Cohen's d = 0.40) which was not qualified by frequency of MPH usage, ADHD symptoms, and demographic factors. There was also a somewhat weaker effect for MASs (Cohen's d = 0.07). No effects of MPH and MASs were recorded for risk-taking and numeracy.

CONCLUSIONS

The results indicate that MPH enhances decision-making in tasks where heuristic responses typically bias it.

Reduced prefrontal cortex and sympathetic nervous system activity correlate with fatigue after aHSCT

Long-term fatigue and cognitive dysfunction affects 35% of allogeneic haematopoietic stem cell transplantation (aHSCT) survivors, suggesting a dysfunctional prefrontal cortex. In this study, we assessed prefrontal cortex and sympathetic nervous system activity in aHSCT patients with fatigue (n = 12), non-fatigued patients (n = 12) and healthy controls (n = 27). Measurement of near-infrared spectroscopy and electrodermal activity was carried out at rest and during cognitive performance (Stroop, verbal fluency and emotion regulation tasks). Prefrontal cortex and sympathetic nervous system activity were also analyzed in response to dopamine and noradrenaline increase after a single dose of methylphenidate. Baseline cognitive performance was similar in the two patient groups. However, after methylphenidate, only non-fatigued patients improved in Stroop accuracy and had better verbal fluency task performance compared to the fatigued group. Task-related activation of prefrontal cortex in fatigued patients was lower compared to non-fatigued patients during all cognitive tests, both before and after methylphenidate administration. During the Stroop task, reaction time, prefrontal cortex activation, and sympathetic nervous system activity were all lower in fatigued patients compared to healthy controls, but similar in non-fatigued patients and healthy controls.Reduced prefrontal cortex activity and sympathetic arousal suggests novel treatment targets to improve fatigue after aHSCT.

Pharmacological Cognitive Enhancement and Cheapened Achievement: A New Dilemma

Recent discussions of cognitive enhancement often note that drugs and technologies that improve cognitive performance may do so at the risk of “cheapening” our resulting cognitive achievements (e.g., Kass, Life, liberty and the defense of dignity: the challenge for bioethics, Encounter Books, San Francisco, 2004; Agar, Humanity’s end: why we should reject radical enhancement, MIT Press, Cambridge, 2010; Sandel, The case against perfection. Harvard University Press, Cambridge, 2007; Sandel, The case against perfection: what’s wrong with designer children, bionic athletes, and genetic engineering?”. In: Holland (ed) Arguing about bioethics, Routledge, London, 2012; Harris in Bioethics 25:102–111, 2011). While there are several possible responses to this worry, we will highlight what we take to be one of the most promising—one which draws on a recent strand of thinking in social and virtue epistemology to construct an integrationist defence of cognitive enhancement. (e.g., Pritchard in Synthese 175:133–151, 2010; Palermos in Synthese 192:2955–2286, 2015; Clark in Synthese 192:3757–3375, 2015). According to such a line, there is—despite initial appearances to the contrary—no genuine tension between using enhancements to attain our goals and achieving these goals in a valuable way provided the relevant enhancement is appropriately integrated into the agent’s cognitive architecture (in some suitably specified way). In this paper, however, we show that the kind of integration recommended by such views will likely come at a high cost. More specifically, we highlight a dilemma for users of pharmacological cognitive enhancement: they can (1) meet the conditions for cognitive integration (and on this basis attain valuable achievements) at the significant risk of dangerous dependency, or (2) remain free of such dependency while foregoing integration and the valuable achievements that such integration enables. After motivating and clarifying the import of this dilemma, we offer recommendations for how future cognitive enhancement research may offer potential routes for navigating past it.

Methylphenidate for attention-deficit/hyperactivity disorder in adults: a narrative review

RATIONALE

Psychostimulants, including methylphenidate (MPH), are the mainstay of pharmacotherapy for attention-deficit/hyperactivity disorder (ADHD) in adults. Even though MPH is the most commonly used medication for ADHD these days, there are relatively few resources available that provide comprehensive insight into the pharmacological and clinical features of the compound.

OBJECTIVE

The aim of this paper is to provide an up-to-date outline of the pharmacology and clinical utility of MPH for ADHD in adult patients.

METHODS

While conducting the narrative review, we applied structured search strategies covering the two major online databases (MEDLINE and Cochrane Central Register of Controlled Trials). In addition, we performed handsearching of reference lists of relevant papers.

RESULTS

Methylphenidate exhibits multimodal mechanism of action, working primarily as a dopamine and noradrenaline reuptake inhibitor. It also protects the dopaminergic system against the ongoing 'wearing off' (by securing a substantial reserve pool of the neurotransmitter, stored in the presynaptic vesicles). In placebo-controlled trials, MPH was shown to be moderately effective both against the core ADHD symptoms (standardized mean difference [SMD], 0.49; 95% confidence interval [CI], 0.35-0.64), and the accompanying emotion regulation deficits (SMD, 0.34; 95% CI, 0.23-0.45). The most common adverse events related to long-term treatment with MPH are decreased appetite (~ 20%), dry mouth (15%), heart palpitations (13%), gastrointestinal infections (~ 10%), and agitation/feeling restless (~ 10%).

CONCLUSIONS

There is substantial body of evidence to suggest that MPH is an effective and safe treatment option for adults with ADHD.

Acute drug effects differentially predict desire to take dextroamphetamine again for work and recreation

RATIONALE

Misuse of dextroamphetamine occurs in work and recreational contexts. While acute drug effects broadly predict abuse liability, few studies have considered the relationship between acute effects and context.

OBJECTIVES

This study examined how individual differences in acute effects of dextroamphetamine relate to desire to take dextroamphetamine again in different contexts.

METHODS

This secondary analysis used data from healthy adults with no history of moderate-to-severe substance use disorder, who received oral doses of placebo and dextroamphetamine (10 and 20 mg) over 3 sessions under double-blind, randomized conditions. Subjects rated subjective effects and completed reward-related behavioral tasks. Subjects rated their desire to take dextroamphetamine again in hypothetical work and recreational contexts. Multilevel models examined within-subjects change scores (10 mg-placebo; 20 mg-placebo) to determine how subjective effects and behavioral outcomes predicted desire to take dextroamphetamine again for work versus recreation.

RESULTS

Subjects reported more desire to take 20 mg dextroamphetamine again for work than for recreation. At 20 mg, there was an interaction between context and liking/wanting, such that liking/wanting predicted desire to use dextroamphetamine for work only. There was also an interaction at 20 mg between context and psychomotor speed, such that psychomotor speed predicted interest in using dextroamphetamine for recreation only.

CONCLUSIONS

We found that positive subjective effects predicted desire to use dextroamphetamine again for work, while increased motor effects predicted desire to use dextroamphetamine recreationally. Hedonic effects may be perceived as advantageous when working, while increased physical energy may be preferred during recreation, suggesting that context of intended use is important when examining abuse liability.

Examining the roles of cognitive flexibility, emotion recognition, and metacognitions in adult Attention Deficit and Hyperactivity Disorder with predominantly inattentive presentation

The evaluation of cognitive functions in Attention Deficit and Hyperactivity Disorder (ADHD) is fundamental to improve the efficacy of therapeutic interventions. However, the role of specific higher-order cognitive functions in adult ADHD, including cognitive flexibility, emotion recognition, and metacognitions, remains unclear. Therefore, in the current study, we aimed to examine these three distinct higher-order cognitive functions among adult ADHD individuals. Forty patients with ADHD with predominantly inattentive presentation and 42 healthy controls participated in the study. The Adult Attention Deficit and Hyperactivity Disorder Scale (AADHDS), the Wisconsin Card Sorting Test (WCST), the Reading the Mind in the Eyes Test (RMET), and the Metacognitions Questionnaire-30 (MCQ-30) were administered. Results indicated that patients with ADHD had worse metacognitions scores, in specific subdimensions, relative to healthy controls. However, cognitive flexibility and emotion recognition did not differ between the groups. Moreover, the cognitive confidence subdimension of the MCQ-30 was found to be sole significant predictor in the attention deficit subdimension of the AADHDS. Our findings suggest that lack of cognitive confidence may contribute to ADHD symptomatology despite regularly functioning cognitive flexibility and emotion recognition. Therefore, metacognitions could be a suitable target to alleviate the severity of ADHD symptoms.

Dopamine modulations of reward-driven music memory consolidation

Music listening provides one of the most significant abstract rewards for humans because hearing music activates the dopaminergic mesolimbic system. Given the strong link between reward, dopamine, and memory, we aimed here to investigate the hypothesis that dopamine-dependent musical reward can drive memory improvements. Twenty-nine healthy participants of both sexes provided reward ratings of unfamiliar musical excerpts that had to be remembered following a consolidation period under three separate conditions: after the ingestion of a dopaminergic antagonist, a dopaminergic precursor, or a placebo. Linear mixed modeling of the intervention data showed that the effect of reward on memory-i.e., the greater the reward experienced while listening to the musical excerpts, the better the memory recollection performance-was modulated by both dopaminergic signaling and individual differences in reward processing. Greater pleasure was consistently associated with better memory outcomes in participants with high sensitivity to musical reward, but this effect was lost when dopaminergic signaling was disrupted in participants with average or low musical hedonia. Our work highlights the flexibility of the human dopaminergic system, which can enhance memory formation not only through explicit and/or primary reinforcers but also via abstract and aesthetic rewards such as music.

Social Justice Theories as the Basis for Public Policy on Psychopharmacological Cognitive Enhancement

Psychopharmacological cognitive enhancements could lead to a higher quality of life of healthy individuals with lower cognitive capacities, but the current regulatory framework does not seem to enable access to this group. This article discusses why Sen’s Capability Approach could open up such access, while two other modern social justice theories – utilitarianism and Rawls’ Justice as Fairness – could not. In short, the utilitarian approach is proven to be inadequate, due to practical reasons and having a low chance of real-world success. Rawls’ Justice as Fairness seems to be problematic because of conflicting stances that follow from his First Principle of Justice. The Capability Approach has the greatest chance of success in the context of these substances, because of arguments that can be identified under the banners of agency/self-respect and the way the public views those who take the capability path out of their poor situation. The article also discusses general and practical problems with psychopharmacological cognitive enhancement that should be addressed when writing new policy on this topic.

Supplementation with Matured Hop Bitter Acids Improves Cognitive Performance and Mood State in Healthy Older Adults with Subjective Cognitive Decline

BACKGROUND

Prevention of age-related cognitive decline and depression is becoming urgent because of rapid growing aging populations. Effects of vagal nerve activation on brain function by food ingredients are inadequately investigated; matured hop bitter acid (MHBA) administration reportedly improves cognitive function and depression via vagal nerve activation in model mice.

OBJECTIVE

We investigated the effects of MHBA supplementation on cognitive function and mood state in healthy older adults with perceived subjective cognitive decline.

METHODS

Using a randomized double-blind placebo-controlled trial design, 100 subjects (aged 45-69 years) were randomly assigned into placebo (n = 50) and MHBA (n = 50) groups, and received placebo or MHBA capsules daily for 12 weeks.

RESULTS

Symbol Digit Modalities Test (SDMT) score assessing divided attention at week 12 was significantly higher (p = 0.045) and β-endorphin at week 12 was significantly lower (p = 0.043) in the subjects receiving MHBA. Transthyretin in serum, a putative mild cognitive impairment marker, was significantly higher at week 12 in the MHBA group than in the placebo group (p = 0.048). Subgroup analysis classified by the subjective cognitive decline questionnaire revealed that in addition to improved SDMT scores, memory retrieval assessed using the standard verbal paired-associate learning tests and the Ray Verbal Learning Test at week 12 had significantly improved in the subgroup with perceived subjective cognitive decline and without requirement for medical assistance in the MHBA group compared with that in the placebo group.

CONCLUSION

This study suggested that MHBA intake improves cognitive function, attention, and mood state in older adults.

Attention-deficit/hyperactivity disorder and the explore/exploit trade-off

The ability to maximize rewards and minimize the costs of obtaining them is vital to making advantageous explore/exploit decisions. Exploratory decisions are theorized to be greater among individuals with attention-deficit/hyperactivity disorder (ADHD), potentially due to deficient catecholamine transmission. Here, we examined the effects of ADHD status and methylphenidate, a common ADHD medication, on explore/exploit decisions using a 6-armed bandit task. We hypothesized that ADHD participants would make more exploratory decisions than controls, and that MPH would reduce group differences. On separate study days, adults with (n = 26) and without (n = 23) ADHD completed the bandit task at baseline, and after methylphenidate or placebo in counter-balanced order. Explore/exploit decisions were modeled using reinforcement learning algorithms. ADHD participants made more exploratory decisions (i.e., chose options without the highest expected reward value) and earned fewer points than controls in all three study days, and methylphenidate did not affect these outcomes. Baseline exploratory choices were positively associated with hyperactive ADHD symptoms across all participants. These results support several theoretical models of increased exploratory choices in ADHD and suggest the unexplained variance in ADHD decisions may be due to less value tracking. The inability to suppress actions with little to no reward value may be a key feature of hyperactive ADHD symptoms.

Effects of methylphenidate on reinforcement learning depend on working memory capacity

RATIONALE

Brain catecholamines have long been implicated in reinforcement learning, exemplified by catecholamine drug and genetic effects on probabilistic reversal learning. However, the mechanisms underlying such effects are unclear.

OBJECTIVES AND METHODS

Here we investigated effects of an acute catecholamine challenge with methylphenidate (20 mg, oral) on a novel probabilistic reversal learning paradigm in a within-subject, double-blind randomised design. The paradigm was designed to disentangle effects on punishment avoidance from effects on reward perseveration. Given the known large individual variability in methylphenidate's effects, we stratified our effects by working memory capacity and trait impulsivity, putatively modulating the effects of methylphenidate, in a large sample (n = 102) of healthy volunteers.

RESULTS

Contrary to our prediction, methylphenidate did not alter performance in the reversal phase of the task. Our key finding is that methylphenidate altered learning of choice-outcome contingencies in a manner that depended on individual variability in working memory span. Specifically, methylphenidate improved performance by adaptively reducing the effective learning rate in participants with higher working memory capacity.

CONCLUSIONS

This finding emphasises the important role of working memory in reinforcement learning, as reported in influential recent computational modelling and behavioural work, and highlights the dependence of this interplay on catecholaminergic function.

Neurobiologic Rationale for Treatment of Apathy in Alzheimer's Disease With Methylphenidate

The public health burden of Alzheimer's disease (AD) is related not only to cognitive symptoms, but also to neuropsychiatric symptoms, including apathy. Apathy is defined as a quantitative reduction of goal-directed activity in comparison to a previous level of functioning and affects 30%-70% of persons with AD. Previous attempts to treat apathy in AD-both nonpharmacologically and pharmacologically-have been wanting. Catecholaminergic treatment with methylphenidate has shown encouraging results in initial trials of apathy in AD. Understanding the neuronal circuits underlying motivated behavior and their reliance on catecholamine actions helps provide a rationale for methylphenidate actions in the treatment of apathy in patients with AD. Anatomical, physiological, and behavioral studies have identified parallel, cortical-basal ganglia circuits that govern action, cognition, and emotion and play key roles in motivated behavior. Understanding the distinct contributions to motivated behavior of subregions of the prefrontal cortex-dorsolateral, orbital-ventromedial, and dorsomedial-helps to explain why degeneration of these areas in AD results in apathetic behaviors. We propose that the degeneration of the prefrontal cortex in AD produces symptoms of apathy. We further propose that methylphenidate treatment may ameliorate those symptoms by boosting norepinephrine and dopamine actions in prefrontal-striatal-thalamocortical circuits.

A Single Low-Dose of Methylphenidate Improves Abnormal Visual Field Testing

PURPOSE

To evaluate the effect of methylphenidate on visual field testing in healthy adults with abnormal visual field results.

METHODS

This prospective, randomized, controlled interventional clinical trial comprised all patients who had abnormal visual field test results and normal eye examination and ophthalmic history. Eligible patients were randomly assigned to either the study group or the control group. All patients repeated their visual field testing. Study group patients received a single dose of 10 mg methylphenidate prior to that. The main outcome measures were the percent difference in mean deviation and pattern standard deviation between the second and first visual fields.

RESULTS

The methylphenidate group had greater improvement in all parameters. Mean deviation improved by median 68% (IQR 19%-78%) in the methylphenidate group vs. 27% [-5% to 55%] in the controls. However, this was not statistically significant (p = .83). Pattern standard deviation improved by median 49% (22%-59%) vs. 7% [-9% to 45%], respectively (p = .012). The visual fields were also reviewed by 3 masked experienced ophthalmologists. They indicated that the second visual field improved in 76.2% of the methylphenidate group vs. 48.5% of the controls (p = .04). A normal repeat visual field occurred in 57.7% vs. 21.2%, respectively. A subgroup analysis of patients with prior experience in visual field testing yielded an even more striking improvement in the methylphenidate group vs. controls.

CONCLUSIONS

A single low dose of methylphenidate can improve visual field testing in subjects without ocular pathology, and even more in those with prior experience in perimetry.

Acting Before; A Combined Strategy to Counteract the Onset and Progression of Dementia

Brain aging and aging-related neurodegenerative disorders are posing a significant challenge for health systems worldwide. To date, most of the therapeutic efforts aimed at counteracting dementiarelated behavioral and cognitive impairment have been focused on addressing putative determinants of the disease, such as β-amyloid or tau. In contrast, relatively little attention has been paid to pharmacological interventions aimed at restoring or promoting the synaptic plasticity of the aging brain. The review will explore and discuss the most recent molecular, structural/functional, and behavioral evidence that supports the use of non-pharmacological approaches as well as cognitive-enhancing drugs to counteract brain aging and early-stage dementia.

Catecholaminergic Modulation of Semantic Processing in Sentence Comprehension

Catecholamine (CA) function has been widely implicated in cognitive functions that are tied to the prefrontal cortex and striatal areas. The present study investigated the effects of methylphenidate, which is a CA agonist, on the electroencephalogram (EEG) response related to semantic processing using a double-blind, placebo-controlled, randomized, crossover, within-subject design. Forty-eight healthy participants read semantically congruent or incongruent sentences after receiving 20-mg methylphenidate or a placebo while their brain activity was monitored with EEG. To probe whether the catecholaminergic modulation is task-dependent, in one condition participants had to focus on comprehending the sentences, while in the other condition, they only had to attend to the font size of the sentence. The results demonstrate that methylphenidate has a task-dependent effect on semantic processing. Compared to placebo, when semantic processing was task-irrelevant, methylphenidate enhanced the detection of semantic incongruence as indexed by a larger N400 amplitude in the incongruent sentences; when semantic processing was task-relevant, methylphenidate induced a larger N400 amplitude in the semantically congruent condition, which was followed by a larger late positive complex effect. These results suggest that CA-related neurotransmitters influence language processing, possibly through the projections between the prefrontal cortex and the striatum, which contain many CA receptors.

Creativity and ADHD: A review of behavioral studies, the effect of psychostimulants and neural underpinnings

Attention deficit/hyperactivity disorder (ADHD) is a debilitating disorder and most research therefore focuses on its deficits and its treatment. Research on the potential positive sides of ADHD is limited, and although a comprehensive overview of empirical studies on this subject is missing, it has been suggested that ADHD is associated with enhanced creativity. To identify important relations, trends and gaps in the literature, we review 31 behavioral studies on creativity and ADHD, distinguishing different research designs, age groups, creativity measurements and effects of psychostimulants, as well as reflecting the potential underlying neural mechanisms of creativity and ADHD. Most studies find evidence for increased divergent thinking for those with high ADHD scores (subclinical) but not for those with the disorder (clinical). The rates of creative abilities/achievements were high among both clinical and subclinical groups. We found no evidence for increased convergent thinking abilities in ADHD, nor did we find an overall negative effect of psychostimulants on creativity. Neuroscientific findings suggest candidate regions as well as mechanisms that should be studied further to increase our understanding of the relationship between creativity and ADHD. We propose research opportunities to boost the knowledge needed to better understand the potential positive side of ADHD.

Is Methylphenidate Beneficial and Safe in Pharmacological Cognitive Enhancement?

Nootropics are drugs used to either treat or benefit cognition deficits. Among this class, methylphenidate is a popular agent, which acts through indirect dopaminergic and noradrenergic agonism and, therefore, is proposed to enhance performance in catecholamine-dependent cognitive domains such as attention, memory and prefrontal cortex-dependent executive functions. However, investigation into the efficacy of methylphenidate as a cognitive enhancer has yielded variable results across all domains, leading to debate within the scientific community surrounding its off-label use in healthy individuals seeking scholaristic benefit or increased productivity. Through analysis of experimental data and methodological evaluation, it is apparent that there are dose-, task- and domain-dependent considerations surrounding the use of methylphenidate in healthy individuals, whereby tailored dose administration is likely to provide benefit on an individual basis dependent on the domain of cognition in which benefit is required. Additionally, it is apparent that there are subjective effects of methylphenidate, which may increase user productivity irrespective of cognitive benefit. Whilst there is not extensive study in healthy older adults, it is plausible that there are dose-dependent benefits to methylphenidate in older adults in selective cognitive domains that might improve quality of life and reduce fall risk. Methylphenidate appears to produce dose-dependent benefits to individuals with attention-deficit/hyperactivity disorder, but the evidence for benefit in Parkinson's disease and schizophrenia is inconclusive. As with any off-label use of pharmacological agents, and especially regarding drugs with neuromodulatory effects, there are inherent safety concerns; epidemiological and experimental evidence suggests there are sympathomimetic, cardiovascular and addictive considerations, which might further restrict their use within certain demographics.

How effective are pharmaceuticals for cognitive enhancement in healthy adults? A series of meta-analyses of cognitive performance during acute administration of modafinil, methylphenidate and D-amphetamine

Modafinil, methyphenidate (MPH) and d-amphetamine (d-amph) are putative cognitive enhancers. However, efficacy of cognitive enhancement has yet to be fully established. We examined cognitive performance in healthy non-sleep-deprived adults following modafinil, MPH, or d-amph vs placebo in 3 meta-analyses, using subgroup analysis by cognitive domain; executive functions (updating, switching, inhibitory control, access to semantic/long term memory), spatial working memory, recall, selective attention, and sustained attention. We adhered to PRISMA. We identified k = 47 studies for analysis; k = 14 studies (64 effect sizes) for modafinil, k = 24 studies (47 effect sizes) for Methylphenidate, and k = 10 (27 effect sizes) for d-amph. There was an overall effect of modafinil (SMD=0.12, p=.01). Modafinil improved memory updating (SMD=0.28, p=.03). There was an overall effect of MPH (SMD=0.21, p=.0004) driven by improvements in recall (SMD=0.43, p=.0002), sustained attention (SMD=0.42, p=.0004), and inhibitory control (SMD=0.27, p=.03). There were no effects for d-amph. MPH and modafinil show enhancing effects in specific sub-domains of cognition. However, data with these stimulants is far from positive if we consider that effects are small, in experiments that do not accurately reflect their actual use in the wider population. There is a user perception that these drugs are effective cognitive enhancers, but this is not supported by the evidence so far.

Impaired error awareness in healthy older adults: an age group comparison study

Aging is associated with reduced conscious error detection but the brain regions mediating these changes have yet to be clarified. The present study examined the neural correlates of error awareness in healthy older adults. Sixteen older participants (mean age = 75.5 years) and sixteen younger controls (mean age = 27.9 years) were administered the error awareness task, a go/no-go response inhibition paradigm, in which participants were required to signal commission errors. Compared with young adults, older adults were significantly poorer at consciously detecting performance errors, despite both groups being matched for overall accuracy. This age-related behavioral effect was associated with differences in error-related dorsal anterior cingulate cortex and insula activation, with younger adults showing significant differences between errors made with versus without awareness compared with older adults. By contrast, an age-specific modulation in right inferior parietal lobule activation emerged, with increased right inferior parietal lobule activity occurring in older adults during errors made with awareness compared with younger adults. These findings are consistent with theories of age-related deterioration in error processing mechanisms.

Task experience eliminates catecholaminergic effects on inhibitory control - A randomized, double-blind cross-over neurophysiological study

Catecholaminergic neural transmission plays an important role during the inhibition of prepotent responses. Methylphenidate (MPH) is an important drug that modulates the catecholaminergic system. However, theoretical considerations suggest that the effects of drugs (e.g. MPH) on cognitive control may depend on prior learning effects. Here we investigate this in a conflict-modulated Go/Nogo task and evaluate neurophysiological processes associated with this dynamic using EEG signal decomposition methods and source localization analysis. The behavioral data show that prior learning experiences eliminate effects of MPH on response inhibition processes. On a neurophysiological level, we show that MPH modulates specific processes in medial frontal brain regions. Although MPH seems to consistently modulate neurophysiological processes associated with response inhibition, this is no longer sufficient to modulate behavioral performance once learning or task familiarization processes have taken place. An important consequence of this study finding is that it may be important to adjust MPH dosage depending on learning effects in a specific setting to constantly increase cognitive control functions in that setting. This has important implications for clinical practice, since MPH is the first-line pharmacological therapy in attention-deficit hyperactivity disorder (ADHD). Cross-over study designs with constant doses of MPH can mask effects on cognitive functions. The impact of learning needs careful consideration in cross-over study designs examining catecholaminergic drug effects.

Neuroethical issues in cognitive enhancement: Modafinil as the example of a workplace drug?

The use of cognitive-enhancing drugs by healthy individuals has been a feature for much of recorded history. Cocaine and amphetamine are modern cases of drugs initially enthusiastically acclaimed for enhancing cognition and mood. Today, an increasing number of healthy people are reported to use cognitive-enhancing drugs, as well as other interventions, such as non-invasive brain stimulation, to maintain or improve work performance. Cognitive-enhancing drugs, such as methylphenidate and modafinil, which were developed as treatments, are increasingly being used by healthy people. Modafinil not only affects ‘cold’ cognition, but also improves ‘hot’ cognition, such as emotion recognition and task-related motivation. The lifestyle use of ‘smart drugs’ raises both safety concerns as well as ethical issues, including coercion and increasing disparity in society. As a society, we need to consider which forms of cognitive enhancement (e.g. pharmacological, exercise, lifelong learning) are acceptable and for which groups under what conditions and by what methods we would wish to improve and flourish.

Learning Experience Reverses Catecholaminergic Effects on Adaptive Behavior

BACKGROUND

Catecholamines are important for cognitive control and the ability to adapt behavior (e.g., after response errors). A prominent drug that modulates the catecholaminergic system is methylphenidate. On the basis of theoretical consideration, we propose that the effects of methylphenidate on behavioral adaptation depend on prior learning experience.

METHODS

In a double-blind, randomized, placebo-controlled crossover study design, we examined the effect of methylphenidate (0.25 mg/kg) on post error behavioral adaptation processes in a group of n = 43 healthy young adults. Behavioral adaptation processes were examined in a working memory, modulated response selection task. The focus of the analysis was on order effects within the crossover study design to evaluate effects of prior learning/task experience.

RESULTS

The effect of methylphenidate/placebo on post-error behavioral adaptation processes reverses depending on prior task experience. When there was no prior experience with the task, methylphenidate increased post-error slowing and thus intensified behavioral adaptation processes. However, when there was prior task experience, (i.e., when the placebo session was conducted first in the crossover design), methylphenidate even decreased post-error slowing and behavioral adaptation. Effect sizes were large and the power of the observed effects was higher than 95%.

CONCLUSIONS

The data suggest that catecholaminergic effects on cognitive control functions vary as a function of prior learning/task experience. The data establish a close link between learning/task familiarization and catecholaminergic effects for executive functions, which has not yet been studied, to our knowledge, but is of considerable clinical relevance. Theoretical implications are discussed.

Paying attention to attention in depression

Attention is the gate through which sensory information enters our conscious experiences. Oftentimes, patients with major depressive disorder (MDD) complain of concentration difficulties that negatively impact their day-to-day function, and these attention problems are not alleviated by current first-line treatments. In spite of attention's influence on many aspects of cognitive and emotional functioning, and the inclusion of concentration difficulties in the diagnostic criteria for MDD, the focus of depression as a disease is typically on mood features, with attentional features considered less of an imperative for investigation. Here, we summarize the breadth and depth of findings from the cognitive neurosciences regarding the neural mechanisms supporting goal-directed attention in order to better understand how these might go awry in depression. First, we characterize behavioral impairments in selective, sustained, and divided attention in depressed individuals. We then discuss interactions between goal-directed attention and other aspects of cognition (cognitive control, perception, and decision-making) and emotional functioning (negative biases, internally-focused attention, and interactions of mood and attention). We then review evidence for neurobiological mechanisms supporting attention, including the organization of large-scale neural networks and electrophysiological synchrony. Finally, we discuss the failure of current first-line treatments to alleviate attention impairments in MDD and review evidence for more targeted pharmacological, brain stimulation, and behavioral interventions. By synthesizing findings across disciplines and delineating avenues for future research, we aim to provide a clearer outline of how attention impairments may arise in the context of MDD and how, mechanistically, they may negatively impact daily functioning across various domains.

Habit Expression and Disruption as a Function of Attention-Deficit/Hyperactivity Disorder Symptomology

Attention-deficit/hyperactivity disorder (ADHD) is associated with neurobehavioral reward system dysfunctions that pose debilitating impairments in adaptive decision-making. A candidate mechanism for such anomalies in ADHD may be a compromise in the control of motivated behaviors. Thus, demonstrating and restoring potential motivational control irregularities may serve significant clinical benefit. The motivational control of action guides goal-directed behaviors that are driven by outcome value, and habits that are inflexibly cue-triggered. We examined whether ADHD symptomology within the general population is linked to habitual control, and whether a motivation-based manipulation can break well-learned habits. We obtained symptom severity scores from 106 participants and administered a Go/NoGo task that capitalizes on familiar, well-learned associations (green-Go and red-NoGo) to demonstrate outcome-insensitivity when compared to newly learned Go/NoGo associations. We tested for outcome-insensitive habits by changing the Go and NoGo contingencies, such that Go signals became NoGo signals and vice versa. We found that generally, participants responded less accurately when green and red stimuli were mapped to color-response contingencies that were incongruent with daily experiences, whereas novel Go/NoGo stimuli evoked similar accuracy regardless of color-response mappings. Thus, our Go/NoGo task successfully elicited outcome-insensitive habits (i.e., persistent responses to familiar stimuli without regard for consequences); however, this effect was independent of ADHD symptomology. Nevertheless, we found an association between hyperactivity and congruent Go response latency, suggesting heightened pre-potency to perform habitual Go actions as hyperactivity increases. To examine habit disruption, participants returned to the lab and underwent the familiar version of the Go/NoGo task, but were given mid-experiment performance tracking information and a monetary incentive prior to contingency change. We found that this motivational boost via dual feedback prevented the incongruency-related accuracy impairment, effectively breaking the habit, albeit independent of ADHD symptomology. Our findings present only a modest link between ADHD symptomology and motivational control, which may be due to compensatory mechanisms in ADHD driving goal-directed control, or our task's potential insensitivity to individual differences in ADHD symptomology. Further investigations may be crucial for determining whether ADHD is related to motivational impairments.

Methylphenidate's effects on thalamic metabolism and functional connectivity in cannabis abusers and healthy controls

Methylphenidate (MPH) is a first line treatment for ADHD and is also misused as a purported cognitive enhancer, yet its effects on brain function are still poorly understood. Recent functional magnetic resonance imaging (fMRI) studies showed that MPH altered cortico-striatal resting functional connectivity (RFC). Here we investigated the effects of MPH in thalamic connectivity since the thalamus modulates striato-cortical signaling. We hypothesized that MPH would increase thalamic connectivity and metabolism, and that this response would be blunted in cannabis abusers. For this purpose, we measured RFC in seven thalamic nuclei using fMRI and brain glucose metabolism using positron emission tomography (PET) and ¹⁸F-fluorodeoxyglucose (FDG) in sixteen healthy controls and thirteen participants with cannabis use disorder (CUD) twice after placebo and after MPH (0.5 mg/kg, iv). MPH significantly increased thalamo-cerebellar connectivity and cerebellar metabolism to the same extent in both groups. Group comparisons revealed that in CUD compared to controls, metabolism in nucleus accumbens was lower for the placebo and MPH measures, that MPH-induced increases in thalamic metabolism were blunted, and that enhanced negative connectivity between thalamus and accumbens in CUD was normalized by MPH (reducing negative connectivity). Our findings identify the thalamus as a target of MPH, which increased its metabolism and connectivity. The reduced metabolism in nucleus accumbens and the disrupted thalamo-accumbens connectivity (enhanced negative connectivity) in CUD is consistent with impaired reactivity of the brain reward's circuit. MPH's normalization of thalamo-accumbens connectivity (reduced negative connectivity) brings forth its potential therapeutic value in CUD, which merits investigation.

Catecholaminergic effects on inhibitory control depend on the interplay of prior task experience and working memory demands

BACKGROUND

Catecholamines affect response inhibition, but the effects of methylphenidate on inhibitory control in healthy subjects are heterogenous. Theoretical considerations suggest that working memory demands and learning/familiarization processes are important factors to consider regarding catecholaminergic effects on response inhibition.

AIMS

The purpose of this study was to examine the role of working memory demands and familiarization for methylphenidate effects on response inhibition.

METHODS

Twenty-eight healthy adults received a single dose of methylphenidate (0.5 mg/kg) or placebo in a randomised, double-blind, crossover study design. The subjects were tested using a working memory-modulated response inhibition paradigm that combined a Go/Nogo task with a mental rotation task.

RESULTS

Methylphenidate effects were largest in the most challenging mental rotation condition. The direction of effects depended on the extent of the participants' task experience. When performing the task for the first time, methylphenidate impaired response inhibition performance in the most challenging mental rotation condition, as reflected by an increased false alarm rate. In sharp contrast to this, methylphenidate seemed to improve response execution performance in the most challenging condition when performing the task for the second time as reflected by reaction times on Go trials.

CONCLUSION

Effects of catecholamines on inhibitory control processes depend on the interplay of two factors: (a) working memory demands, and (b) learning or familiarization with a task. It seems that the net effect of increases in gain control and decreases in working memory processes determines the methylphenidate effect on response inhibition. Hence, crossover study designs likely underestimate methylphenidate effects on cognitive functions.

Catecholamine Modulation of Evidence Accumulation during Perceptual Decision Formation: A Randomized Trial

Recent behavioral modeling and pupillometry studies suggest that neuromodulatory arousal systems play a role in regulating decision formation but neurophysiological support for these observations is lacking. We employed a randomized, double-blinded, placebo-controlled, crossover design to probe the impact of pharmacological enhancement of catecholamine levels on perceptual decision-making. Catecholamine levels were manipulated using the clinically relevant drugs methylphenidate and atomoxetine, and their effects were compared with those of citalopram and placebo. Participants performed a classic EEG oddball paradigm that elicits the P3b, a centro-parietal potential that has been shown to trace evidence accumulation, under each of the four drug conditions. We found that methylphenidate and atomoxetine administration shortened RTs to the oddball targets. The neural basis of this behavioral effect was an earlier P3b peak latency, driven specifically by an increase in its buildup rate without any change in its time of onset or peak amplitude. This study provides neurophysiological evidence for the catecholaminergic enhancement of a discrete aspect of human decision-making, that is, evidence accumulation. Our results also support theoretical accounts suggesting that catecholamines may enhance cognition via increases in neural gain.

Single and Repeated Administration of Methylphenidate Modulates Synaptic Plasticity in Opposite Directions via Insertion of AMPA Receptors in Rat Hippocampal Neurons

Methylphenidate (MPH) is widely used in the treatment of Attention Deficit Hyperactivity Disorder. Several lines of evidence support that MPH can modulate learning and memory processes in different ways including improvement and impairment of test performances. A relevant factor in the efficacy of treatment is whether administration is performed once or several times. In this study we demonstrate opposite effects of MPH on performance of preadolescent rats in the Morris Water Maze test. Animals treated with a single dose (1 mg/kg) performed significantly better compared to controls, while in animals treated with repetitive administration at the same concentration performance was reduced. We found that hippocampal LTP in slices from rats treated with a single dose was increased, while LTP from rats treated with repetitive injections of MPH was lower than in controls. Using Western blot of CA1 areas from potentiated slices of rats treated with a single dose we found a significant increase of phosphorylation at Ser845 of GluA1 subunits, associated to an increased insertion of GluA1-containing AMPARs in the plasma membrane. These receptors were functional, because AMPA-dependent EPSCs recorded on CA1 were enhanced, associated to a significant increase in short-term plasticity. In contrast, CA1 samples from rats injected with MPH during six consecutive days, showed a significant decrease in the phosphorylation at Ser845 of GluA1 subunits associated to a lower insertion of GluA1-containing AMPARs. Accordingly, a reduction of the AMPA-mediated EPSCs and short-term plasticity was also observed. Taken together, our results demonstrate that single and repeated doses with MPH can induce opposite effects at behavioral, cellular, and molecular levels. The mechanisms demonstrated here in preadolescent rats are relevant to understand the effects of this psychostimulant in the treatment of ADHD.