Cognitive enhancement effects of stimulants: a randomized controlled trial testing methylphenidate, modafinil, and caffeine

Methylphenidate differentially alters corticostriatal connectivity after traumatic brain injury

Traumatic brain injury commonly impairs attention and executive function and disrupts the large-scale brain networks that support these cognitive functions. Abnormalities of functional connectivity are seen in corticostriatal networks, which are associated with executive dysfunction and damage to neuromodulatory catecholaminergic systems caused by head injury. Methylphenidate, a stimulant medication that increases extracellular dopamine and noradrenaline, can improve cognitive function following traumatic brain injury. In this experimental medicine add-on study to a randomized, double-blind, placebo-controlled clinical trial, we test whether administration of methylphenidate alters corticostriatal network function and influences drug response. Forty-three moderate-severe traumatic brain injury patients received 0.3 mg/kg of methylphenidate or placebo twice a day in 2-week blocks. Twenty-eight patients were included in the neuropsychological and functional imaging analysis (four females, mean age 40.9 ± 12.7 years, range 20-65 years) and underwent functional MRI and neuropsychological assessment after each block. 123I-Ioflupane single-photon emission computed tomography dopamine transporter scans were performed, and specific binding ratios were extracted from caudate subdivisions. Functional connectivity and the relationship to cognition were compared between drug and placebo conditions. Methylphenidate increased caudate to anterior cingulate cortex functional connectivity compared with placebo and decreased connectivity from the caudate to the default mode network. Connectivity within the default mode network was also decreased by methylphenidate administration, and there was a significant relationship between caudate functional connectivity and dopamine transporter binding during methylphenidate administration. Methylphenidate significantly improved executive function in traumatic brain injury patients, and this was associated with alterations in the relationship between executive function and right anterior caudate functional connectivity. Functional connectivity is strengthened to brain regions, including the anterior cingulate, that are activated when attention is focused externally. These results show that methylphenidate alters caudate interactions with cortical brain networks involved in executive control. In contrast, caudate functional connectivity reduces to default mode network regions involved in internally focused attention and that deactivate during tasks that require externally focused attention. These results suggest that the beneficial cognitive effects of methylphenidate might be mediated through its impact on the caudate. Methylphenidate differentially influences how the caudate interacts with large-scale functional brain networks that exhibit co-ordinated but distinct patterns of activity required for attentionally demanding tasks.

Assessing acute effects of methylphenidate and modafinil on inhibitory capacity, time estimation, attentional lapses, and compulsive-like behavior in rats

Medications known as 'cognitive enhancers' are increasingly being consumed off-label by healthy people, raising concerns about their safety. The aim of our study was to profile behavioral performance upon oral administration of methylphenidate (2.5 mg/kg) and modafinil (64 mg/kg) - two popular cognitive enhancers - and upon their discontinuation. We modeled cognitively demanding challenges in neurotypical individuals using a behavioral task where Wistar - Lewis rats had to withhold responses for a specified time to obtain food rewards. This task allowed us to extract several measures of behavioral performance associated with clinically meaningful indices, such as compulsive-like responding, incapacity to wait (impulsivity), time estimation (precision and accuracy), and attentional lapses. Our study design involved examining these behavioral indices in subjects administered either methylphenidate, modafinil, or vehicle. We found that subjects administered modafinil obtained fewer rewards and were less efficient in reward pursuing than the vehicle group; this result was likely due to a drug-induced inability to wait. Upon modafinil discontinuation, subjects earned more rewards but did not entirely catch up with the vehicle group. As for methylphenidate, neither favorable nor unfavorable effects were found in our main analyses. However, an exploratory analysis of changes in behavioral performance within sessions suggested that methylphenidate fostered favorable, yet short-lived, effects. We discuss our results in terms of the risks and cost-benefits of doses above or below the effective dose of cognitive enhancement drugs.

Methylphenidate promotes a frontoparietal-dominant brain state improving cognitive performance: a randomized trial

Methylphenidate (MP) is a widely used stimulant medication for the treatment of attention deficit hyperactivity disorder that enhances brain dopamine signaling and improves attention. However, how dopamine stimulation alters brain state dynamics to support improved attention during task performance is still unclear. To address this, we employed a multimodal neuroimaging approach combining positron emission tomography, functional magnetic resonance imaging, and behavioral tasks, to discover associations between dopamine signaling, brain dynamics, and cognition. Multimodal images were collected from 37 healthy adults under a single-blind, counterbalanced, placebo-controlled crossover study. Dynamic functional analysis was used to compare the alterations in dynamic features of brain states before and after MP. Subsequently, we analyzed the correlation between these brain state changes and baseline striatal D1 and D2 dopamine receptor (D1R, D2R) availability. We also examined alterations in dynamic brain states and their effects on visuospatial tasks. The results showed that MP primarily affected frontoparietal-dominant activated (FPN+), somatomotor-dominant activated (SOM+), and visual-dominant suppressed (VIS-) brain states. Specifically, the dwell time and fractional occupancy exhibited significant increases within the FPN+ and VIS- and an opposite trend within the SOM+. Furthermore, the increase of dwell time in FPN+, which was positively correlated with baseline striatal D1R availability, was also associated with quicker response in the 2-ball-track task, but not significantly for the 3-ball-track task. The findings suggest that MP's enhancement of brain states with FPN+ and VIS- while decreasing SOM+, in part through D1R signaling might underlie MP's improvement of attention for low demanding tasks in healthy populations.Significance statement Methylphenidate (MP) is primarily prescribed for Attention-Deficit/Hyperactivity Disorder (ADHD), but it is also misused as a cognitive enhancer by individuals seeking to improve cognitive performance. Using advanced brain imaging and behavioral tasks, this study investigates how MP affects dopamine signaling, brain activity and cognitive performance. Our results demonstrate that MP promoted a frontoparietal-dominant brain state which linked to improved task performance and D1 receptor availability. This research also introduces a multi-level neuroimaging approach to studying drug effects, offering a foundation for tailoring interventions by predicting individual variations in responses to medicine.

SCH58261 effectively prevents the reduction in excitability of striatal MSNs in mice following 20 h of sleep deprivation

Adenosine, a sleep-associated neuromodulator, is crucial in various physiological and pathological processes. Previous studies have demonstrated that sleep deprivation (SD) alters striatal neuronal activity. In this study, we used in vitro electrophysiological recordings to investigate the effects of 20 h of SD on the neuronal excitability of mouse dorsal striatal medium spiny neurons (MSNs). Our findings revealed that SD resulted in altered action potential (AP) discharge properties and reduced neuronal excitability compared to the control group. Importantly, these changes were partially offset by the prophylactic injection of the A2A receptor (A2AR) antagonist SCH58261. Additionally, 20 h of SD caused a decrease in the amplitude and an increase in the interval of spontaneous excitatory postsynaptic currents (sEPSCs) compared to control. However, the prophylactic injection of the A2AR antagonism shortened the sEPSC interval, while the A1 receptor (A1R) antagonist DPCPX not only shortened the interval but also further reduced the amplitude of sEPSCs. Thus, it can be concluded that SCH58261 effectively prevents the reduction in excitability of striatal MSNs in mice following 20 h of sleep deprivation, whereas DPCPX does not.

Polyphenols, Alkaloids, and Terpenoids Against Neurodegeneration: Evaluating the Neuroprotective Effects of Phytocompounds Through a Comprehensive Review of the Current Evidence

Neurodegenerative diseases comprise a group of chronic, usually age-related, disorders characterized by progressive neuronal loss, deformation of neuronal structure, or loss of neuronal function, leading to a substantially reduced quality of life. They remain a significant focus of scientific and clinical interest due to their increasing medical and social importance. Most neurodegenerative diseases present intracellular protein aggregation or their extracellular deposition (plaques), such as α-synuclein in Parkinson's disease and amyloid beta (Aβ)/tau aggregates in Alzheimer's. Conventional treatments for neurodegenerative conditions incur high costs and are related to the development of several adverse effects. In addition, many patients are irresponsive to them. For these reasons, there is a growing tendency to find new therapeutic approaches to help patients. This review intends to investigate some phytocompounds' effects on neurodegenerative diseases. These conditions are generally related to increased oxidative stress and inflammation, so phytocompounds can help prevent or treat neurodegenerative diseases. To achieve our aim to provide a critical assessment of the current literature about phytochemicals targeting neurodegeneration, we reviewed reputable databases, including PubMed, EMBASE, and COCHRANE, seeking clinical trials that utilized phytochemicals against neurodegenerative conditions. A few clinical trials investigated the effects of phytocompounds in humans, and after screening, 13 clinical trials were ultimately included following PRISMA guidelines. These compounds include polyphenols (flavonoids such as luteolin and quercetin, phenolic acids such as rosmarinic acid, ferulic acid, and caffeic acid, and other polyphenols like resveratrol), alkaloids (such as berberine, huperzine A, and caffeine), and terpenoids (such as ginkgolides and limonene). The gathered evidence underscores that quercetin, caffeine, ginkgolides, and other phytochemicals are primarily anti-inflammatory, antioxidant, and neuroprotective, counteracting neuroinflammation, neuronal oxidation, and synaptic dysfunctions, which are crucial aspects of neurodegenerative disease intervention in various included conditions, such as Alzheimer's and other dementias, depression, and neuropsychiatric disorders. In summary, they show that the use of these compounds is related to significant improvements in cognition, memory, disinhibition, irritability/lability, aberrant behavior, hallucinations, and mood disorders.

Novel Perspective on Sevoflurane-Induced Cognitive Dysfunction: Implications of Neuronal SIRPα and Microglial Synaptic Remodeling

This study aims to investigate the role of neuronal SIRPα and microglial synaptic remodeling in sevoflurane-induced cognitive dysfunction in newborn mice. Newborn mice were exposed to sevoflurane, followed by behavioral assessments and single-cell transcriptome sequencing of cortical cells. Lentivirus-mediated overexpression of neuronal SIRPα and assessment of the microglial morphology and synaptic function were conducted. Sevoflurane exposure resulted in social cognitive impairments without affecting motor coordination. Transcriptomic analysis revealed no significant changes in cortical microglial cells or neurons. However, sevoflurane inhibited nonsynaptic synapse modification by microglia. Overexpression of neuronal SIRPα enhanced microglial function, promoted neuron development, and ameliorated cognitive impairments. SCENIC analysis identified a correlation between IRF8 and SIRPα expression. This study sheds light on the involvement of neuronal SIRPα and microglial synaptic remodeling in sevoflurane-induced cognitive dysfunction. Understanding these mechanisms offers new avenues for exploring cognitive impairment pathways and potential therapeutic targets.

Pharmacological Cognitive Enhancement Among International Medical Students: Assessing Study Habits as a Novel Factor

Introduction

Pharmacological cognitive enhancement (PCE) among healthy individuals with off-label use of medications raises ethical and safety concerns in academia. Among the few studies that have examined this phenomenon in medical students, the desire to improve performance and cope with high levels of stress are the most common associated factors implicated. Our main objective was to update current literature by exploring a novel factor by investigating the association between PCE use and student learning approaches among a cohort of international medical students.

Methods

We conducted a cross-sectional study with an anonymous, online survey, distributed to year 1 US international medical students at Universidad Autónoma de Guadalajara. Participants reported PCE medication use, underlying motivators, and answered items characterizing their study habits via the Approaches to Learning and Studying Inventory (ALSI).

Results

A total of 103 student responses were included, with 18 students (17.3%) reporting PCE use and a majority (61.1%) of whom were female. PCE users were less likely to adopt deep or strategic study approaches and were mainly motivated to improve academic performance.

Discussion

We encourage universities to have open discussions about medication risks and forms to improve an active learning without its use, which might be beneficial in curbing the perceived need for pharmacologic enhancement. Further explorations are required to confirm if certain study habits are truly associated with PCE use.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40670-024-02113-w.

Effects of different doses of caffeine on cognitive performance in healthy physically active individuals

PURPOSE

Caffeine is a potent central nervous system stimulant that increases the activity of the prefrontal cortex and can improve various cognitive skills. An improvement in these cognitive skills can lead to further benefits in athletic performance. Therefore, it is necessary to clarify the dose-response of caffeine on cognitive performance. This study aimed to determine the effects of different doses of caffeine on sport-related cognitive aspects.

METHODS

Twenty-nine healthy physically active young adults were recruited. All participants completed three trials under the following conditions: (a) placebo, (b) 3 mg/kg, or (c) 6 mg/kg body mass of caffeine. In each trial, different cognitive abilities were evaluated with the following battery of tests: reaction time (Dynavision™ D2), anticipation (Bassin Anticipation Timer), sustained attention (Go/No-Go and Eriksen Flanker Test) and memory tests. Moreover, the side effects and the perceived sensation index were recorded 24 h after each test.

RESULTS

Reaction time only improved following 6 mg/kg of caffeine intake (Physical reaction time: -0.04 s, 95% CI -0.08 to -0.01 s, P = 0.036, d = 0.5; Motor reaction time: -0.04 s, 95% CI -0.07 to -0.01 s, P = 0.008, d = 0.6) compared to the placebo condition. Anticipation, sustained attention, and memory were not affected after either caffeine dose intake (all P > 0.05). In addition, the 6 mg/kg dose of caffeine augmented the occurrence of the side effects of increased activeness (P = 0.046) and nervousness (P = 0.001).

CONCLUSION

Acute intake of 6 mg/kg caffeine is effective in improving reaction time despite increasing the occurrence of side effects in healthy physically active young adults.

STUDY REGISTRATION

This study has been registered in ClinicalTrials whose ID is: NCT05995314 (2023-08-08).

Caffeine and modafinil modulate the effects of sleep deprivation on thalamic resting-state functional connectivity: A double-blind pilot study

BACKGROUND

Studies have found that the use of clinically approved caffeine and modafinil can alleviate cognitive impairment due to sleep deprivation (SD) to some extent. However, the neural mechanisms by which these two cognitive enhancers work to counteract the effects of SD on cognitive impairment remain unclear.

METHODS

A double-blind within-subjects experiment using resting-state functional magnetic resonance imaging (rs-fMRI) was designed. Participants underwent three 36-h SD trials, each of which involved taking 200 mg of caffeine, modafinil, or placebo at the 28th and 32 nd h of SD. Sixteen subregions of the thalamus were selected as the regions of interest and changes in functional connectivity (FC) between the thalamus and the other brain regions were explored after the participants took caffeine or modafinil.

RESULTS

The subjective sleepiness of the participants increased with the duration of SD. compared with placebo, modafinil and caffeine had insignificant effects on wakefulness or sleepiness. However, in terms of neural FC, we found varying degrees of attenuation or enhancement of the FC between the thalamus and other regions. Taking caffeine during SD weakened the FC between the right rostral temporal thalamus (rTtha) subregion and the left lingual gyrus compared with placebo. Caffeine enhanced the FC between three subregions of the thalamus, namely the left sensory thalamus, the left rTtha, and the right lateral pre-frontal thalamus, and the right inferior temporal, left orbitofrontal, and right superior occipital gyris. Modafinil weakened the FC between the right posterior parietal thalamus and left middle temporal gyrus, and enhanced the FC between the left medial pre-frontal thalamus, left rTtha, and right occipital thalamus and left middle frontal gyrus.

CONCLUSIONS

After 36 h of total SD, modafinil and caffeine administration enhanced or attenuated the time-domain correlations between various subregions of the thalamus and brain regions of the frontal and temporal lobes in healthy adults, compared with placebo. These results provide valuable evidence for further unraveling the neuropharmacological mechanisms of caffeine and modafinil, as well as important insights for exploring effective pharmacological intervention strategies against SD.

A dataset for fatigue estimation during shoulder internal and external rotation movements using wearables

Wearable sensors have recently been extensively used in sports science, physical rehabilitation, and industry providing feedback on physical fatigue. Information obtained from wearable sensors can be analyzed by predictive analytics methods, such as machine learning algorithms, to determine fatigue during shoulder joint movements, which have complex biomechanics. The presented dataset aims to provide data collected via wearable sensors during a fatigue protocol involving dynamic shoulder internal rotation (IR) and external rotation (ER) movements. Thirty-four healthy subjects performed shoulder IR and ER movements with different percentages of maximal voluntary isometric contraction (MVIC) force until they reached the maximal exertion. The dataset includes demographic information, anthropometric measurements, MVIC force measurements, and digital data captured via surface electromyography, inertial measurement unit, and photoplethysmography, as well as self-reported assessments using the Borg rating scale of perceived exertion and the Karolinska sleepiness scale. This comprehensive dataset provides valuable insights into physical fatigue assessment, allowing the development of fatigue detection/prediction algorithms and the study of human biomechanical characteristics during shoulder movements within a fatigue protocol.

Armodafinil as a Potential Pharmacological Treatment for Attention Deficit Hyperactivity Disorder in Adults: A Review

INTRODUCTION

Armodafinil is a psychostimulant that promotes alertness, and it has been shown to improve attention, memory, and fatigue in healthy adults and adults with neurodevelopmental conditions that share symptoms with Attention Deficit Hyperactivity Disorder (ADHD). It is generally well tolerated and safe, and most of the adverse events reported are considered not serious. However, the available evidence on the efficacy of armodafinil for the treatment of ADHD in adults is scarce.

OBJECTIVE

The present review aims to perform a systematized search of the available evidence on the possible therapeutic benefit of armodafinil treatment in adult patients with ADHD.

METHODS

A literature review using PubMed was conducted to compile and summarize the available clinical and scientific evidence on the possible use of armodafinil as a pharmacological treatment in adult patients with ADHD.

RESULTS

From the 86 articles reviewed, the available evidence showed that both acute and chronic treatment with armodafinil can improve wakefulness, memory, impulse control, and executive functions in adults with sleep disorders and other conditions. In addition, evidence of improvement in cognitive functions and mood alterations in other neuropsychiatric conditions was shown.

CONCLUSION

Armodafinil could be useful for the treatment of ADHD in adults, according to the review of the literature from both pre-clinical and clinical studies.

Effects of Caffeine on Main Symptoms in Children with ADHD: A Systematic Review and Meta-Analysis of Randomized Trials

(1) Background: Attention-deficit/hyperactivity disorder (ADHD) is typically treated with stimulant medications, which may lead to several adverse effects. Recent animal studies have shown that caffeine can improve the symptoms of ADHD. This systematic review and meta-analysis sought to evaluate the effect of caffeine on ADHD symptoms in children. (2) Methods: PubMed, Embase, and Cochrane databases were searched for randomized controlled trials comparing caffeine with placebo in children, comparing overall symptoms of ADHD, inattention, hyperactivity, and impulsivity. (3) Results: We included seven RCTs in the systematic review for qualitative assessment, with 104 patients aged 5 to 15 years. Four of these studies (n = 76) were included in the meta-analysis. After qualitative analysis, four studies indicated no improvement in any of the ADHD symptoms compared with placebo. One study showed improvement in ADHD symptoms based on 1 of 5 scales applied. One study indicated significant improvement in general symptoms, inattention, and hyperactivity. One study indicated improvement in sustained attention but a worsening of impulsivity. In contrast, when using a quantitative analysis of the general symptoms of ADHD, the data showed no significant difference when comparing placebo with caffeine (standardized mean difference -0.12; 95% CI -0.44 to 0.20; p = 0.45; I2 = 0%). (4) Conclusion: overall, the totality of the evidence suggests no significant benefit of caffeine over placebo in the treatment of children with ADHD.

Novel pharmacotherapy targeting the positive symptoms of schizophrenia

INTRODUCTION

The severity of positive symptoms in schizophrenia is associated with poor prognosis. About one-third of schizophrenia patients partially respond to treatment with available antipsychotics. The purpose of the present manuscript is to provide an updated overview of novel pharmacotherapy targeting positive symptoms in schizophrenia.

AREAS COVERED

A comprehensive research on the main database sources (PubMed, PsychINFO, Isi Web of Knowledge, MEDLINE, and EMBASE) was performed to obtain original articles published till 31st January 2023 about new pharmacological strategies for the treatment of positive symptoms in schizophrenia.

EXPERT OPINION

The most promising compounds include: lamotrigine, pro-cognitive-compounds (donepezil - in the short term, idazoxan and piracetam) and drugs acting partially or totally outside the Central Nervous System (CNS) (anti-inflammatory drugs: celecoxib, methotrexate; cardiovascular compounds: L-theanine, mononitrate isosorbide, propentofylline, sodium nitroprusside; metabolic regulators: diazoxide, allopurinol; others: bexarotene, raloxifene [in women]). The effectiveness of the latter compounds indicates that other biological systems, such as immunity or metabolism can be object of future research to identify pharmacological targets for positive symptoms of schizophrenia. Mirtazapine could be useful for treating negative symptoms without increasing the risk of a worsening of delusions/hallucinations. Nevertheless, the lack of replication of studies prevents to draw definitive conclusions and future studies are needed to confirm the findings presented in this overview.

Do Medical Universities Students Use Cognitive Enhancers while Learning?—Conclusions from the Study in Poland

Background: Stress and everyday problems may impact memory and cognition. Therefore, many people use cognitive enhancers (CEs), sold for prescription, as over-the-counter drugs, or dietary supplements, believing they may help with everyday functioning. Our study was designed to answer whether taking CEs is common among Medical University students and to identify which substances are mainly used. Methods and Results: An anonymous online questionnaire was answered by 479 students of Medical (88%) and Dentistry (12%) Faculties in Poland. Women constituted the majority of respondents (63%). CEs were used by 53% of respondents, with the most frequent being caffeine, ginseng, nicotine, theanine, ginkgo, and lecithin. Some persons used CEs that are available only with a prescription. The most important reasons for the use of CEs were to increase arousal and improve concentration (mentioned by 81% and 73%, respectively). Over 65% of students experienced some undesired/adverse effects after taking CEs, with tachycardia being the most common, followed by sleep disturbances (reported by 51% and 40%, respectively). Conclusions: More than half of the respondents from the Medical and Dentistry Faculties reported using CEs, despite their unproven efficacy and not-well-established safety. This raises significant concern about the knowledge of young persons regarding CEs and should encourage universities to undertake educational actions.

The mitigation of the executive vigilance decrement via HD-tDCS over the right posterior parietal cortex and its association with neural oscillations

Vigilance-maintaining a prolonged state of preparation to detect and respond to specific yet unpredictable environmental changes-usually decreases across prolonged tasks, causing potentially severe real-life consequences, which could be mitigated through transcranial direct current stimulation (tDCS). The present study aimed at replicating previous mitigatory effects observed with anodal high-definition tDCS (HD-tDCS) over the right posterior parietal cortex (rPPC) while extending the analyses on electrophysiological measures associated with vigilance. In sum, 60 participants completed the ANTI-Vea task while receiving anodal (1.5 mA, n = 30) or sham (0 mA, n = 30) HD-tDCS over the rPPC for ~ 28 min. EEG recordings were completed before and after stimulation. Anodal HD-tDCS specifically mitigated executive vigilance (EV) and reduced the alpha power increment across time-on-task while increasing the gamma power increment. To further account for the observed behavioral and physiological outcomes, a new index of Alphaparietal/Gammafrontal is proposed. Interestingly, the increment of this Alphaparietal/Gammafrontal Index with time-on-task is associated with a steeper EV decrement in the sham group, which was mitigated by anodal HD-tDCS. We highlight the relevance of replicating mitigatory effects of tDCS and the need to integrate conventional and novel physiological measures to account for how anodal HD-tDCS can be used to modulate cognitive performance.

Stimulant abuse as a coping strategy-Forensic and criminal consequences of stimulant abuse for neuroenhancement

Pharmacological neuroenhancement (PN) describes the use of divergent psychoactive substances to enhance mental performance (cognition) without medical need. This kind of substance abuse takes place predominantly in stressful situations. Users implicitly-or even explicitly-describe this kind of drug abuse to be a coping strategy. Regarding the decision making process whether to use PN drugs or not, users indicate that legal aspects to be decisive. However, the legal situation has been neglected so far. To elucidate the German legal situation, PN substances have to be divided into over-the-counter drugs, prescription drugs and illegal drugs. Amphetamines have the highest cognition-enhancing potential, followed by modafinil and caffeine-containing substances. It is pointed out that the use of both freely available and prescription PN substances and narcotics without medical indication have so far been largely exempt from punishment under German law. However, individuals (physicians, bus and truck drivers, etc.) taking PN substances may expose others at risk due to wrong decisions (driving or treatment), errors based on side effects of the used substances. Therefore, the protection of life and health of others could legitimize criminal regulation.

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.

Effects of modafinil on electroencephalographic microstates in healthy adults

RATIONALE

Modafinil has been proposed as a potentially effective clinical treatment for neuropsychiatric disorders characterized by cognitive control deficits. However, the precise effects of modafinil, particularly on brain network functions, are not completely understood.

OBJECTIVES

To address this gap, we examined the effects of modafinil on resting-state brain activity in 30 healthy adults using microstate analysis. Electroencephalographic (EEG) microstates are discrete voltage topographies generated from resting-state network activity.

METHODS

Using a placebo-controlled, within-subjects design, we examined changes to microstate parameters following placebo (0 mg), low (100 mg), and high (200 mg) modafinil doses. We also examined the functional significance of these microstates via associations between microstate parameters and event-related potential indexes of conflict monitoring and automatic error processing (N2 and error-related negativity) and behavioral responses (accuracy and RT) from a subsequent flanker interference task.

RESULTS

Five microstates emerged following each treatment condition, including four canonical microstates (A-D). Modafinil increased microstate C proportion and occurrence regardless of dose, relative to placebo. Modafinil also decreased microstate A proportion and microstate B proportion and occurrence relative to placebo. These modafinil-related changes in microstate parameters were not associated with similar changes in flanker ERPs or behavior. Finally, modafinil made transitions between microstates A and B less likely and transitions from A and B to C more likely.

CONCLUSIONS

Previous fMRI work has correlated microstates A and B with auditory and visual networks and microstate C with a salience network. Thus, our results suggest modafinil may deactivate large-scale sensory networks in favor of a higher order functional network during resting-state in healthy adults.

Hypothesis: Amelioration of obesity-induced cognitive dysfunction via a lorcaserin-betahistine combination treatment

The prolonged exposure to obesogenic diets disrupts the mesocortical dopaminergic input to the prefrontal cortex (PFC). This leads to suboptimal dopamine levels in this brain region, which affects cognition and control of food intake. Treatments that restore mesocortical dopaminergic neurotransmission may improve obesity‐associated cognitive dysfunction and modulate food intake to induce weight loss. Given the complexity and multifactorial nature of obesity, combination treatments would likely achieve sizeable and sustained body weight loss and improve obesity‐linked outcomes, such as cognitive dysfunction. Given this background, we hypothesize that concomitant activation of serotonin 5‐HT2C and histamine H1 receptors, coupled with antagonism of histamine H3 receptors, synergistically modulates mesocortical dopamine neurotransmission and ameliorates obesity‐induced cognitive dysfunction. We propose to test the hypothesis in a diet‐induced obesity (DIO) rat model by treating animals with the 5‐HT2C agonist lorcaserin and the H1 agonist and H3 antagonist betahistine. Consistent with our hypothesis, both lorcaserin and betahistine have been shown to reduce body weight in humans with obesity and animals. Both drugs have been demonstrated to improve cognitive functions by influencing dopaminergic signaling in the PFC. The proposed combination treatment addresses the paucity of studies on obesity treatments that improve cognitive function. This research may also help identify a potential targetable mechanism connecting obesity and neurocognitive outcomes.

Non-invasive brain stimulation and neuroenhancement

Attempts to enhance human memory and learning ability have a long tradition in science. This topic has recently gained substantial attention because of the increasing percentage of older individuals worldwide and the predicted rise of age-associated cognitive decline in brain functions. Transcranial brain stimulation methods, such as transcranial magnetic (TMS) and transcranial electric (tES) stimulation, have been extensively used in an effort to improve cognitive functions in humans. Here we summarize the available data on low-intensity tES for this purpose, in comparison to repetitive TMS and some pharmacological agents, such as caffeine and nicotine. There is no single area in the brain stimulation field in which only positive outcomes have been reported. For self-directed tES devices, how to restrict variability with regard to efficacy is an essential aspect of device design and function. As with any technique, reproducible outcomes depend on the equipment and how well this is matched to the experience and skill of the operator. For self-administered non-invasive brain stimulation, this requires device designs that rigorously incorporate human operator factors. The wide parameter space of non-invasive brain stimulation, including dose (e.g., duration, intensity (current density), number of repetitions), inclusion/exclusion (e.g., subject's age), and homeostatic effects, administration of tasks before and during stimulation, and, most importantly, placebo or nocebo effects, have to be taken into account. The outcomes of stimulation are expected to depend on these parameters and should be strictly controlled. The consensus among experts is that low-intensity tES is safe as long as tested and accepted protocols (including, for example, dose, inclusion/exclusion) are followed and devices are used which follow established engineering risk-management procedures. Devices and protocols that allow stimulation outside these parameters cannot claim to be "safe" where they are applying stimulation beyond that examined in published studies that also investigated potential side effects. Brain stimulation devices marketed for consumer use are distinct from medical devices because they do not make medical claims and are therefore not necessarily subject to the same level of regulation as medical devices (i.e., by government agencies tasked with regulating medical devices). Manufacturers must follow ethical and best practices in marketing tES stimulators, including not misleading users by referencing effects from human trials using devices and protocols not similar to theirs.

The impact and causal directions for the associations between diagnosis of ADHD, socioeconomic status, and intelligence by use of a bi-directional two-sample Mendelian randomization design

BACKGROUND

Previous studies have reported associations between attention-deficit/hyperactivity disorder (ADHD) and lower socioeconomic status and intelligence. We aimed to evaluate the causal directions and strengths for these associations by use of a bi-directional two-sample Mendelian randomization (MR) design.

METHODS

We used summary-level data from the largest available genome-wide association studies (GWAS) to identify genetic instruments for ADHD, intelligence, and markers of socioeconomic status including the Townsend deprivation index, household income, and educational attainment. Effect estimates from individual genetic variants were combined using inverse-variance weighted regression.

RESULTS

A genetically predicted one standard deviation (SD) increment in the Townsend deprivation index conferred an odds ratio (OR) of 5.29 (95% confidence interval (CI) 1.89-14.76) for an ADHD diagnosis (p<0.001). A genetically predicted one SD higher education level conferred an OR of 0.30 (95% CI 0.25-0.37) (p<0.001), and a genetically predicted one SD higher family income provided an OR of 0.35 (95% CI 0.25-0.49; p<0.001). The associations remained after adjustment for intelligence whereas the lower odds of an ADHD diagnosis with higher intelligence did not persist after adjustment for liability to greater educational attainment (adjusted OR 1.03, 95% CI 0.68-1.56; p=0.87). The MR analysis of the effect of ADHD on socioeconomic markers found that genetic liability to ADHD was statistically associated with each of them (p<0.001) but not intelligence. However, the average change in the socioeconomic markers per doubling of the prevalence of ADHD corresponded only to 0.05-0.06 SD changes.

CONCLUSIONS

Our results indicate that an ADHD diagnosis may be a direct and strong intelligence-independent consequence of socioeconomic related factors, whereas ADHD appears to lead only to modestly lowered socioeconomic status. Low intelligence seems not to be a major independent cause or consequence of ADHD.

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.

Impact of Caffeine on Alzheimer’s Disease Pathogenesis—Protective or Risk Factor?

Alzheimer’s disease (AD), the most common dementia worldwide, remains without an effective treatment to this day despite intensive research conducted during the last decades. In this context, researchers have turned their attention towards the prevention of this pathology, focusing on early detection and better control of the most important risk factors, concomitantly with trying to find potentially protective factors that may delay the onset of AD. From the multitude of factors studied, coffee (especially its main component, caffeine) is a current interesting research topic, taking into consideration the contradictory results of recent years’ studies. On the one hand, much of the evidence from fundamental research suggests the potentially protective trait of caffeine in AD, while other data mainly from human studies lean toward no correlation or even suggesting that caffeine is a veritable risk factor for dementia. Given the methodological heterogeneity of the studies, this review aims to bring new evidence regarding this topic and to try to clearly establish a correlation between the two entities. Thus, in the first part, the authors make a clear distinction between the effects of coffee and the effects of caffeine in AD, presenting a rich basis of clinical trials on both animal models and the human subject. Subsequently, the main pathophysiological mechanisms that would explain the action of caffeine in the etiopathogenesis of AD are reviewed. Finally, the role of computational models is presented, having beneficial impact on both better understanding of the disease mechanism and the development of new therapeutic approaches for AD prevention.

Influence of modafinil on early ejaculation - Results from a double-blind randomized clinical trial

BACKGROUND

For men, early ejaculation is a serious health concern. Here, we tested the influence of modafinil (Profinil®) on early ejaculation. To this end, we performed a double-blind randomized clinical trial among men with early ejaculation.

METHODS

A total of 46 men with early ejaculation (mean age: 37.35 years) and in stable marital relationships with regular weekly penile-vaginal intercourse were randomly assigned either to the modafinil (100 mg) or to the placebo condition. Compounds were taken about 4-6h before intended penile-vaginal intercourse. At baseline and four weeks later at the end of the study, participants completed a series of self-rating questionnaires covering early ejaculation. Female partners also rated their male partners' early ejaculation profile.

RESULTS

Dimensions of early ejaculation improved over time, but only so in the modafinil condition, while no improvements were observed in the placebo condition.

CONCLUSIONS

Among male adults in stable marital relationships with regular weekly penile-vaginal intercourse modafinil improved dimensions of early ejaculation, always compared to placebo. Given the strong effect of modafinil on cognitive-executive processes, it is conceivable, that modafinil acted both via physiological and cognitive-executive pathways.

A State-of-the-Art Review on the Use of Modafinil as A Performance-enhancing Drug in the Context of Military Operationality

INTRODUCTION

Modafinil is an eugeroic drug that has been examined to maintain or recover wakefulness, alertness, and cognitive performance when sleep deprived. In a nonmilitary context, the use of modafinil as a nootropic or smart drug, i.e., to improve cognitive performance without being sleep deprived, increases. Although cognitive performance is receiving more explicit attention in a military context, research into the impact of modafinil as a smart drug in function of operationality is lacking. Therefore, the current review aimed at presenting a current state-of-the-art and research agenda on modafinil as a smart drug. Beside the question whether modafinil has an effect or not on cognitive performance, we examined four research questions based on the knowledge on modafinil in sleep-deprived subjects: (1) Is there a difference between the effect of modafinil as a smart drug when administered in repeated doses versus one single dose?; (2) Is the effect of modafinil as a smart drug dose-dependent?; (3) Are there individual-related and/or task-related impact factors?; and (4) What are the reported mental and/or somatic side effects of modafinil as a smart drug?

METHOD

We conducted a systematic search of the literature in the databases PubMed, Web of Science, and Scopus, using the search terms "Modafinil" and "Cognitive enhance*" in combination with specific terms related to the research questions. The inclusion criteria were studies on healthy human subjects with quantifiable cognitive outcome based on cognitive tasks.

RESULTS

We found no literature on the impact of a repeated intake of modafinil as a smart drug, although, in users, intake occurs on a regular basis. Moreover, although modafinil was initially said to comprise no risk for abuse, there are now indications that modafinil works on the same neurobiological mechanisms as other addictive stimulants. There is also no thorough research into a potential risk for overconfidence, whereas this risk was identified in sleep-deprived subjects. Furthermore, eventual enhancing effects were beneficial only in persons with an initial lower performance level and/or performing more difficult tasks and modafinil has an adverse effect when used under time pressure and may negatively impact physical performance. Finally, time-on-task may interact with the dose taken.

DISCUSSION

The use of modafinil as a smart drug should be examined in function of different military profiles considering their individual performance level and the task characteristics in terms of cognitive demands, physical demands, and sleep availability. It is not yet clear to what extent an improvement in one component (e.g., cognitive performance) may negatively affect another component (e.g., physical performance). Moreover, potential risks for abuse and overconfidence in both regular and occasional intake should be thoroughly investigated to depict the trade-off between user benefits and unwanted side effects. We identified that there is a current risk to the field, as this trade-off has been deemed acceptable for sleep-deprived subjects (considering the risk of sleep deprivation to performance) but this reasoning cannot and should not be readily transposed to non-sleep-deprived individuals. We thus conclude against the use of modafinil as a cognitive enhancer in military contexts that do not involve sleep deprivation.

Memory enhancement with stimulants: Differential neural effects of methylphenidate, modafinil, and caffeine. A pilot study

Human memory is susceptible to manipulation in many respects. While consolidation is well known to be prone to disruption, there is also growing evidence for the enhancement of memory function. Beside cognitive strategies and mnemonic training, the use of stimulants may improve memory processing in healthy adults. In this single-dose, double-blind, within-subject, randomized, placebo-controlled pilot study, 20 mg methylphenidate (N = 13) or 200 mg modafinil (N = 12) or 200 mg caffeine (N = 14) were administrated to in total 39 healthy participants while performing a declarative memory task. Each participant received only one substance and functional magnetic resonance imaging (fMRI) was used to assess drug-dependent memory effects of the substance for encoding and recognition compared to task-related activation under placebo. While methylphenidate showed some behavioral effect regarding memory recall performance, on the neural level, methylphenidate-dependent deactivations were found in fronto-parietal and temporal regions during recognition of previously learned words. No BOLD alterations were seen during encoding. Caffeine led to deactivations in the precentral gyrus during encoding whereas modafinil did not show any BOLD signal alterations at all. These results should be interpreted with caution since this a pilot study with several limitations, most importantly the small number of participants per group. However, our main finding of task-related deactivations may point to a drug-dependent increase of efficiency in physiological response to memory processing.

Role of the Dopaminergic System in the Striatum and Its Association With Functional Recovery or Rehabilitation After Brain Injury

Disabilities are estimated to occur in approximately 2% of survivors of traumatic brain injury (TBI) worldwide, and disability may persist even decades after brain injury. Facilitation or modulation of functional recovery is an important goal of rehabilitation in all patients who survive severe TBI. However, this recovery tends to vary among patients because it is affected by the biological and physical characteristics of the patients; the types, doses, and application regimens of the drugs used; and clinical indications. In clinical practice, diverse dopaminergic drugs with various dosing and application procedures are used for TBI. Previous studies have shown that dopamine (DA) neurotransmission is disrupted following moderate to severe TBI and have reported beneficial effects of drugs that affect the dopaminergic system. However, the mechanisms of action of dopaminergic drugs have not been completely clarified, partly because dopaminergic receptor activation can lead to restoration of the pathway of the corticobasal ganglia after injury in brain structures with high densities of these receptors. This review aims to provide an overview of the functionality of the dopaminergic system in the striatum and its roles in functional recovery or rehabilitation after TBI.

The Neurophysiology of Caffeine as a Central Nervous System Stimulant and the Resultant Effects on Cognitive Function

Caffeine is one of the world’s most consumed drugs. According to the Washington Post (2015), two billion cups of coffee are consumed per day worldwide. Caffeine is classified as a central nervous system (CNS) stimulant and an organic molecule called methylxanthine. Caffeine has three notable mechanisms of action on the CNS that produce a psychostimulant effect. These effects are responsible for the effect that caffeine has on cognitive function. The effects of caffeine consumption on cognitive function have been demonstrated across several studies involving humans and animals. With the immense number of people consuming caffeine around the world, it is of vital importance to study the effects that this drug has on people’s cognitive function. This literature review provides useful insights on this question through the analysis of caffeine’s effects on cognitive function, along with information on caffeine’s three modes of action. The findings of recent studies show mixed results regarding the effects of caffeine on mood, attention, processing speed, and memory. Current research suggests that if caffeine does have an effect on mood, the most significant changes may be anxiety. Studies did not support caffeine as having any significant effect on attention, but that it did play a role in enhancing processing speed. The majority of the studies reviewed suggest caffeine as having a significant positive effect on both short and long-term memory in adults and the elderly. Current findings warrant continued research on the association of caffeine and the resultant effects on cognitive function.