Pharmacologically induced changes in arousal: effects on behavioral and electrophysiologic measures of alertness and attention

Assessing attention orienting in mice: a novel touchscreen adaptation of the Posner-style cueing task

Atypical attention orienting has been found to be impaired in many neuropsychological disorders, but the underlying neural mechanism remains unclear. Attention can be oriented exogenously (i.e., driven by salient stimuli) or endogenously (i.e., driven by one's goals or intentions). Genetic mouse models are useful tools to investigate the neurobiology of cognition, but a well-established assessment of attention orienting in mice is missing. This study aimed to adapt the Posner task, a widely used attention orienting task in humans, for use in mice using touchscreen technology and to test the effects of two attention-modulating drugs, methylphenidate (MPH) and atomoxetine (ATX), on the performance of mice during this task. In accordance with human performance, mice responded more quickly and more accurately to validly cued targets compared to invalidly cued targets, thus supporting mice as a valid animal model to study the neural mechanisms of attention orienting. This is the first evidence that mice can be trained to voluntarily maintain their nose-poke on a touchscreen and to complete attention orienting tasks using exogenous peripheral cues and endogenous symbolic cues. The results also showed no significant effects of MPH and ATX on attention orienting, although MPH improved overall response times in mice during the exogenous orienting task. In summary, the current study provides a critical translational task for assessing attention orienting in mice and to investigate the effects of attention-modulating drugs on attention orienting.

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.

Prescription Stimulants' Effects on Healthy Inhibitory Control, Working Memory, and Episodic Memory: A Meta-analysis

The use of prescription stimulants to enhance healthy cognition has significant social, ethical, and public health implications. The large number of enhancement users across various ages and occupations emphasizes the importance of examining these drugs' efficacy in a nonclinical sample. The present meta-analysis was conducted to estimate the magnitude of the effects of methylphenidate and amphetamine on cognitive functions central to academic and occupational functioning, including inhibitory control, working memory, short-term episodic memory, and delayed episodic memory. In addition, we examined the evidence for publication bias. Forty-eight studies (total of 1,409 participants) were included in the analyses. We found evidence for small but significant stimulant enhancement effects on inhibitory control and short-term episodic memory. Small effects on working memory reached significance, based on one of our two analytical approaches. Effects on delayed episodic memory were medium in size. However, because the effects on long-term and working memory were qualified by evidence for publication bias, we conclude that the effect of amphetamine and methylphenidate on the examined facets of healthy cognition is probably modest overall. In some situations, a small advantage may be valuable, although it is also possible that healthy users resort to stimulants to enhance their energy and motivation more than their cognition.

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

Methylphenidate (MPH), a stimulant drug with dopamine and noradrenaline reuptake inhibition properties, is mainly prescribed in attention deficit hyperactivity disorder, is increasingly used by the general population, intending to enhance their cognitive function. In this literature review, we aim to answer whether this is effective. We present a novel way to determine the extent to which MPH enhances cognitive performance in a certain domain. Namely, we quantify this by a percentage that reflects the number of studies showing performance enhancing effects of MPH. To evaluate whether the dose-response relationship follows an inverted-U-shaped curve, MPH effects on cognition are also quantified for low, medium and high doses, respectively. The studies reviewed here show that single doses of MPH improve cognitive performance in the healthy population in the domains of working memory (65% of included studies) and speed of processing (48%), and to a lesser extent may also improve verbal learning and memory (31%), attention and vigilance (29%) and reasoning and problem solving (18%), but does not have an effect on visual learning and memory. MPH effects are dose-dependent and the dose-response relationship differs between cognitive domains. MPH use is associated with side effects and other adverse consequences, such as potential abuse. Future studies should focus on MPH specifically to adequately asses its benefits in relation to the risks specific to this drug.

Working memory capacity predicts effects of methylphenidate on reversal learning

Increased use of stimulant medication, such as methylphenidate, by healthy college students has raised questions about its cognitive-enhancing effects. Methylphenidate acts by increasing extracellular catecholamine levels and is generally accepted to remediate cognitive and reward deficits in patients with attention deficit hyperactivity disorder. However, the cognitive-enhancing effects of such 'smart drugs' in the healthy population are still unclear. Here, we investigated effects of methylphenidate (Ritalin, 20  mg) on reward and punishment learning in healthy students (N=19) in a within-subject, double-blind, placebo-controlled cross-over design. Results revealed that methylphenidate effects varied both as a function of task demands and as a function of baseline working memory capacity. Specifically, methylphenidate improved reward vs punishment learning in high-working memory subjects, whereas it impaired reward vs punishment learning in low-working memory subjects. These results contribute to our understanding of individual differences in the cognitive-enhancing effects of methylphenidate in the healthy population. Moreover, they highlight the importance of taking into account both inter- and intra-individual differences in dopaminergic drug research.

Can pharmaco-electroencephalography help improve survival of central nervous system drugs in early clinical development?

Pharmaco-electroencephalography has significant yet unrealised promise as a translatable intermediate biomarker of central pharmacodynamic activity that could help reduce Phase 2 attrition in the development of central nervous system drugs. In an effort to understand its true potential, a framework for decision-making was proposed and the utility of pharmaco-electroencephalography was assessed through several case studies. A key finding was that lack of standardisation reduces the value of data pooling and meta-analyses and renders assessment of translatability difficult, limiting utility in all but simple cases. Pre-competitive collaboration is essential both to improving understanding of translation and developing modern signal processing techniques.

Peak high-frequency HRV and peak alpha frequency higher in PTSD

Posttraumatic stress disorder (PTSD) is difficult to treat and current PTSD treatments are not effective for all people. Despite limited evidence for its efficacy, some clinicians have implemented biofeedback for PTSD treatment. As a first step in constructing an effective biofeedback treatment program, we assessed respiration, electroencephalography (EEG) and heart rate variability (HRV) as potential biofeedback parameters for a future clinical trial. This cross-sectional study included 86 veterans; 59 with and 27 without PTSD. Data were collected on EEG measures, HRV, and respiration rate during an attentive resting state. Measures were analyzed to assess sensitivity to PTSD status and the relationship to PTSD symptoms. Peak alpha frequency was higher in the PTSD group (F(1,84) = 6.14, p = 0.01). Peak high-frequency HRV was lower in the PTSD group (F(2,78) = 26.5, p < 0.00005) when adjusting for respiration rate. All other EEG and HRV measures and respiration were not different between groups. Peak high-frequency HRV and peak alpha frequency are sensitive to PTSD status and may be potential biofeedback parameters for future PTSD clinical trials.

Prescription stimulants in individuals with and without attention deficit hyperactivity disorder: misuse, cognitive impact, and adverse effects

Prescription stimulants are often used to treat attention deficit hyperactivity disorder (ADHD). Drugs like methylphenidate (Ritalin, Concerta), dextroamphetamine (Dexedrine), and dextroamphetamine-amphetamine (Adderall) help people with ADHD feel more focused. However, misuse of stimulants by ADHD and nonaffected individuals has dramatically increased over recent years based on students' misconceptions or simple lack of knowledge of associated risks. In this review, we discuss recent advances in the use and increasing misuse of prescription stimulants among high school and college students and athletes. Given the widespread belief that stimulants enhance performance, there are in fact only a few studies reporting the cognitive enhancing effects of stimulants in ADHD and nonaffected individuals. Student athletes should be apprised of the very serious consequences that can emerge when stimulants are used to improve sports performance. Moreover, misuse of stimulants is associated with dangers including psychosis, myocardial infarction, cardiomyopathy, and even sudden death. As ADHD medications are prescribed for long-term treatment, there is a need for long-term safety studies and education on the health risks associated with misuse is imperative.

Are prescription stimulants "smart pills"? The epidemiology and cognitive neuroscience of prescription stimulant use by normal healthy individuals

Use of prescription stimulants by normal healthy individuals to enhance cognition is said to be on the rise. Who is using these medications for cognitive enhancement, and how prevalent is this practice? Do prescription stimulants in fact enhance cognition for normal healthy people? We review the epidemiological and cognitive neuroscience literatures in search of answers to these questions. Epidemiological issues addressed include the prevalence of nonmedical stimulant use, user demographics, methods by which users obtain prescription stimulants, and motivations for use. Cognitive neuroscience issues addressed include the effects of prescription stimulants on learning and executive function, as well as the task and individual variables associated with these effects. Little is known about the prevalence of prescription stimulant use for cognitive enhancement outside of student populations. Among college students, estimates of use vary widely but, taken together, suggest that the practice is commonplace. The cognitive effects of stimulants on normal healthy people cannot yet be characterized definitively, despite the volume of research that has been carried out on these issues. Published evidence suggests that declarative memory can be improved by stimulants, with some evidence consistent with enhanced consolidation of memories. Effects on the executive functions of working memory and cognitive control are less reliable but have been found for at least some individuals on some tasks. In closing, we enumerate the many outstanding questions that remain to be addressed by future research and also identify obstacles facing this research.

Cognitive domains affected by histamine H(1)-antagonism in humans: a literature review

The neurotransmitter histamine has been suggested to be involved in cognitive functioning. Generally, studies in animals have shown a decrease in performance after decreasing histamine neurotransmission and improved performance after increasing histamine neurotransmission. It is unclear, however, what role histamine plays in cognition in humans. Up until now, most data are derived from studies and reviews that aimed to assess the sedative potential of H(1)-antagonists and not the effects on cognition in particular. The objective of this paper is specifically to review which cognitive domains are affected by H(1)-antagonists. Taken together, 90 experimental studies on the performance effects of sedative H(1)-antagonists published between 1973 and 2009 were reviewed. Results showed that psychomotor skills and attention are most frequently impaired and memory the least. Tasks assessing memory that were affected usually required rapid responses. It was concluded that both the complexity of the task as well as the demand for information processing speed determines the sensitivity to the effects of central H(1)-antagonism. The importance of the sensitive cognitive domains to histaminergic dysfunction, as well as the relation between histamine related decrease in arousal and task performance deserve further research.

Pharmacological manipulations of arousal and memory for emotional material: effects of a single dose of methylphenidate or lorazepam

Benzodiazepines produce robust impairments of memory alongside global decreases in physiological and subjective arousal. Recently one benzodiazepine (triazolam) has been found to disproportionately impair memory for emotionally arousing material (Buchanan et al., 2003). The extent to which this effect may be mediated by the drug's sedative action is unclear. The present study aimed to assess how pharmacologically decreasing physiological arousal with a benzodiazepine and increasing arousal with a stimulant impact on memory for emotional material. A double-blind placebo controlled trial with 48 volunteers was used to investigate the effects of methylphenidate (40 mg) and Lorazepam (1.5 mg) on incidental memory for emotional material in Cahill and McGaugh's (1995) slide-story task. The slide-story was presented to participants administered either active drug or placebo and retrieval was assessed one week later. Methylphenidate produced stimulant effects and Lorazepam produced sedative effects. Significantly enhanced memory for emotional material was observed in participants given placebo, but not in those given either methylphenidate or Lorazepam. Despite producing opposite effects upon arousal, both methylphenidate and Lorazepam lessen the impact of emotionally arousing material on memory. The effects of Lorazepam add to a growing literature that benzodiazepines may exert their clinical, anxiolytic effects in part via altering emotionaL cognitive function.

An integrative approach to determine the best behavioral and biological markers of methylphenidate

AIMS

To distinguish the most sensitive markers of methylphenidate (MPH) effects on behavior and underlying biology using an integrated cognitive and brain function test battery.

METHODS

A randomized placebo-controlled trial with 32 healthy adult males. Subjects were tested on MPH doses across 18 sessions with subjective mood, objective behavioral and biological endpoints. From a computerized battery of tests, behavioral measures were cognitive performance scores, while biological measures of brain function included electroencephalographs (EEG) and event-related potentials (ERPs) with complementary measures of autonomic arousal. Using mixed modeling analyses; we determined which measures were most affected by MPH dose and correlation analyses determined the associations among them.

RESULTS

MPH dose had the most pronounced effect on cognitive performance (sustained attention/vigilance), baseline autonomic arousal (heart rate, blood pressure) and baseline brain activity (EEG theta power). The faster reaction time, reduced errors, increased autonomic arousal and reductions in theta showed strong to moderate inter-correlations. MPH least affected subjective mood measures and early sensory ERP components.

DISCUSSION

These findings suggest that MPH increases cortical and autonomic arousal, facilitating vigilance. The combination of behavioral and biological measures may provide an objective set of markers of MPH response.

INTEGRATIVE SIGNIFICANCE

This approach has provided additional insight into the mechanism of the stimulant medication, MPH, which would not be achieved by using such measures in isolation.

Topiramate effects on the EEG and alertness in healthy volunteers: a different profile of antiepileptic drug neurotoxicity

OBJECTIVE

Previous quantitative EEG (QEEG) studies of carbamazepine (CBZ), oxcarbazepine (OXC), and phenytoin (PHT) revealed a pattern of EEG slowing and an increase in drowsiness on the awake maintenance task (AMT). EEG slowing has been shown to correlate with negative effects on cognitive tests. Topiramate (TPM) is a novel AED with relatively large negative effects on cognitive function. We tested the hypothesis that TPM would induce significant slowing of EEG background rhythms and an increase in AMT drowsiness.

METHODS

Forty healthy volunteers were randomized to TPM, gabapentin (GBP), or placebo. Doses were escalated as tolerated to a maximum of 400mg/day for TPM or 3600 mg/day for GBP, over a 10-week period, followed by a minimum 2-week plateau period. Volunteers underwent an EEG, cognitive tests, and the AMT prior to starting an AED and again 12 weeks later. The EEG was captured using a structured recording protocol and quantified using the fast Fourier transform. Four target measures were derived from the averaged occipital electrodes (peak frequency of the dominant posterior rhythm, median frequency, percentage theta, and percentage delta). Test-retest changes for all measures were scored against similar test-retest distributions previously obtained from untreated healthy volunteers.

RESULTS

TPM produced no significant change in any of the four target EEG measures or on the AMT, even though several target cognitive tests revealed moderate or greater negative effects. There were also no significant changes in the placebo group. GBP slowed the peak and median frequency EEG measures and increased the percentage of theta and delta activity. Neither TPM, GBP, nor placebo caused a significant increase in drowsiness on the AMT.

CONCLUSIONS

TPM has a unique neurotoxicity profile. It has no effect on EEG background measures or on the AMT, but induces moderate to large negative changes in many cognitive test scores. This profile differs from those of CBZ, OXC, PHT, and GBP.

24 hour ambulatory research system supporting multiple physiologic sensors

The design and development of a 24-hour ambulatory physiological data collection system is reported. The system was designed specifically to support the needs of investigators studying mind-body interventions but could be used for a variety of research needs. The system is novel in that it supports a wide variety of physiologic sensors with a relatively high sample rate, full data storage, and standalone run-time of greater than 24 hours. Experience with data acquisition and methods for post-acquisition data analysis are also discussed.

Memory function in women with premenstrual complaints and the effect of serotonergic stimulation by acute administration of an alpha-lactalbumin protein

Serotonergic hypofunction may underlie at least part of the symptoms that are experienced by women with premenstrual complaints, including memory deficits. In the current study we investigated changes in memory functions in the premenstrual phase compared to the early postmenstrual phase in 16 women with premenstrual complaints. In addition, the effect of an acute serotonergic stimulation by administration of an alpha-lactalbumin protein on premenstrual memory performance was assessed using a double-blind placebo-controlled crossover design. It was found that both short-term and long-term memory for words (30-word learning task) and abstract figures (abstract visual learning task) were mildly impaired in the premenstrual phase. Administration of alpha-lactalbumin during the premenstrual phase could only partially attenuate the memory performance decrements that are seen in the premenstrual phase. Specifically, alphalactalbumin improved long-term memory for abstract figures, but not for words. There were no effects of menstrual phase or alpha-lactalbumin on planning functions (computerized Tower of London). The data suggest that serotonergic hypofunction may play a role in premenstrual memory decline, but serotonergic mechanisms cannot fully account for observed cognitive changes in the premenstrual phase.

Where arousal meets attention: a simultaneous fMRI and EEG recording study

In this fMRI study, we looked for the regions supporting interaction between cortical arousal and attention during three conditions: detection, observation, and rest. Arousal measurements were obtained from the EEG low-frequency (LF) power (5-9.5 Hz) recorded continuously together with fMRI. Whatever the condition, arousal was positively correlated with the fMRI signal of the right dorsal-lateral prefrontal and superior parietal cortices, closely overlapping regions involved in the maintenance of attention. Although the inferior temporal areas also presented a correlation with arousal during detection, path analysis suggests that this influence may be indirect, through the top-down influence of the previously mentioned network. However, those visual-processing areas could account for the correlation between arousal and performances. Lastly, the medial frontal cortex, frontal opercula, and thalamus were inversely correlated with arousal but only during detection and observation so that they could account for the control of arousal.

The role of the substantia nigra in cognitive activity in cats

The role of the substantia nigra in cognitive processes of different levels of complexity was studied using an original method. Neurosurgical or neurochemical exclusion of the substantia nigra in cats led to significant impairment of conditioned reflex activity, generalization and abstraction processes; these recovered with pharmacological treatment directed to the dopaminergic system, with partial recovery after treatment directed to the GABAergic and cholinergic systems. Treatment directed to the serotoninergic system was ineffective.

Additional dopamine reuptake inhibition attenuates vigilance impairment induced by serotonin reuptake inhibition in man

There is evidence for a specific impairment of human vigilance following enhancement of serotonergic activity by antidepressant drugs. In the present study, we investigated the putative role of serotonergic-dopaminergic interactions in diminished vigilance by comparing the attentional effects of sertraline, a selective serotonin reuptake inhibitor (SSRI) with additional mild dopamine stimulating effects, with those of paroxetine, a SSRI without dopamine activity, using a placebo-controlled, double-blind, three-way cross-over design. Twenty-one (of 24) healthy middle-aged subjects completed the three treatment periods of 2 weeks in which sertraline (50 mg, days 1-7; 100 mg, days 8-14), paroxetine (20 mg, days 1-7; 40 mg, days 8-14) and placebo were administered. Vigilance (Mackworth Clock Test), selective (Stroop, Dichotic Listening) and divided attention (Dichotic Listening) were assessed at baseline and on days 7 and 14 of each treatment period. Selective and divided attention were unaffected by SSRI treatment. Subchronic administration of paroxetine impaired vigilance performance at each investigated dose. Sertraline did not produce a significant decline in vigilance performance, presumably due to its concomitant effects on dopamine activity, counteracting the negative effects of serotonin on dopamine neurotransmission. It is concluded that a serotonergically mediated reduction of dopamine activity plays an important role in the reduction of human vigilance following SSRI administration.

Methylphenidate increases the motor effects of L-Dopa in Parkinson's disease: a pilot study

We determined whether methylphenidate, a dopamine transporter blocker, modifies motor, cognitive, or affective responses to L-Dopa in Parkinson's disease (PD). Five patients who reported benefit from L-Dopa/carbidopa and motor fluctuations were admitted and withdrawn from their usual antiparkinsonian medications. On 3 consecutive days in a randomized double-blinded fashion, they took 0.2 mg/kg oral methylphenidate or placebo followed 30 minutes later by a 1-hour intravenous L-Dopa (2 mg/kg per h) or placebo infusion. Vital signs, tapping, walking, dyskinesias, mood, anxiety, concentration, and arousal were monitored every 30 minutes. Cognitive testing was performed before and following the infusion. Methylphenidate combined with L-Dopa led to greater peak right-hand tapping speed than either alone. Dyskinesia severity increased most when methylphenidate and L-Dopa were co-administered. There were no differences between conditions on the Stroop test, digit ordering, simple reaction time, or covert orienting of attention validity effect. Methylphenidate alone led to improvement in choice reaction time. Change in self-assessed analogue ratings of mood, anxiety, arousal, or concentration did not differ between conditions. Methylphenidate increased the motor effects of L-Dopa with minimal effects on cognitive or affective functions, suggesting a physiologic role for the dopamine transporter in patients with PD with motor fluctuations.

Verbal fluency task affects gait in Parkinson's disease with motor freezing

We examined the effects of a simultaneous verbal fluency task on walking in Parkinson's disease (PD) patients with freezing of gait (PD-F) compared to nonfreezing patients (PD-NF) or control subjects (C). Effects of antiparkinsonian medications on gait in PD-F were examined. PD-F patients exhibited a greater increase in the number of steps to complete the walk with verbal fluency, even when the effect of medication was taken into account (mean increase +/- SD): PD-F = 4.2 +/- 4.6, n = 10; PD-NF = 0.1 +/- 1.6, n = 9; C = 1.5 +/- 1.5, n = 19; P = .007. Medications improved walking in PD-F patients by decreasing the number of steps, the time to walk, and freezing. PD-F patients may be more dependent on attention for walking.

Neuropsychopharmacological mechanisms of stimulant drug action in attention-deficit hyperactivity disorder: a review and integration

The psychostimulants, D-amphetamine (D-AMP) and methylphenidate (MPH), are widely used to treat attention-deficit hyperactivity disorder (ADHD) in both children and adults. The purpose of this paper is to integrate results of basic and clinical research with stimulants in order to enhance understanding of the neuropharmacological mechanisms of therapeutic action of these drugs. Neurochemical, neurophysiological and neuroimaging studies in animals reveal that the facilitative effects of stimulants on locomotor activity, reinforcement processes, and rate-dependency are mediated by dopaminergic effects at the nucleus accumbens, whereas effects on delayed responding and working memory are mediated by noradrenergic afferents from the locus coeruleus (LC) to prefrontal cortex (PFC). Enhancing effects of the stimulants on attention and stimulus control of behavior are mediated by both dopaminergic and noradrenergic systems. In humans, stimulants appear to exert rate-dependent effects on activity levels, and primarily enhance the motor output, rather than stimulus evaluation stages of information-processing. Similarity of response of individuals with and without ADHD suggests that the stimulants do not target a specific neurobiological deficit in ADHD, but rather exert compensatory effects. Integration of evidence from pre-clinical and clinical research suggests that these effects may involve stimulation of pre-synaptic inhibitory autoreceptors, resulting in reduced activity in dopaminergic and noradrenergic pathways. The implications of these and other hypotheses for further pre-clinical and clinical research are discussed.

Quantitative electro-oculography and electroencephalography as indices of alertness

Even though both electro-oculography (EOG) and EEG have been widely used for assessing alertness, the relationship between these two measures has not yet been clarified at various alertness levels. We estimated the frequencies of eye movements faster than 15 degrees/s (NoEM15) and EEG power at every 0.5 Hz step frequency point, quantitatively as well as continuously from alert to very light sleep (Stage 1) in 14 healthy adults. We devised a new EOG derivation for a computerized analysis, because conventional EOG recordings suffer from EEG contamination and have been analyzed manually. EOG electrodes were attached to the left orbitale in this study. The eye movements were detected as peaks in differentiated EOG signals. Significant correlations were found between NoEM15 and EEG powers at several frequency points, mainly in the alpha and beta bands. Though fluctuating EEG components in close correspondence to the frequency of the eye movements varied depending on the individual, EEG power at the peak frequency of the awake state was most closely associated with the eye movements. A broad band power that centers at the peak frequency may be a better measure for alertness assessment than powers in fixed bands.

Cholinergic modulation, visual function and Alzheimer's dementia

Electrophysiological evidence at a cellular level and in vivo macroelectrode recordings converge in indicating a degree of specificity of acetylcholine action in vision. Acetylcholine (ACh) function is also thought to play a significant role in memory, learning and other cognitive processes. In this respect, ACh action is suggested to serve in both sensory and cognitive processes. The pharmacological blocking of brain muscarinic transmission has been proposed as a model of geriatric memory impairment and Alzheimer's dementia. Visual electrophysiological testing is deemed of diagnostic specificity for this disease. ACh brain neurotransmission, however, mostly contributes to the modulation of nonspecific aspects of cognition, such as arousal or attention. Alzheimer's dementia results from complex neuron alterations [which also affect muscarinic receptors among other (sub)cellular structures] rather than simply reflecting ACh impoverishment. A substantial loss of retinal ganglion cells is documented in patients with Alzheimer's disease and is consistent with electrophysiological observations. However, it is unclear to what extent the dysfunction of the visual system observable in Alzheimer's dementia is qualitatively different from that occurring spontaneously during aging. The dissimilarities between the effect of acute muscarinic blocking (e.g. by scopolamine) and dementia outnumber the similarities. Accordingly, the conventional ACh agonist-antagonist model of dementia now appears questionable, and replacement treatment with compounds enhancing ACh function proved disappointing. It is suggested that (nonspecific) ACh action becomes function-specific, as determined by the architecture of local brain circuits in which it is involved.