Cognitive impairment in depression: a systematic review and meta-analysis

BACKGROUND

This review aimed to address the question of whether cognitive impairment should be considered a core feature of depression that may be a valuable target for treatment.

METHOD

We conducted a systematic review and meta-analysis of cognitive function, assessed with a single neuropsychological test battery, the Cambridge Neuropsychological Test Automated Battery (CANTAB), in patients with depression during symptomatic and remitted states. Inclusion of studies comparing patients remitted from depression and controls enabled us to investigate whether cognitive impairment persists beyond episodes of low mood in depression.

RESULTS

Our meta-analysis revealed significant moderate cognitive deficits in executive function, memory and attention in patients with depression relative to controls (Cohen's d effect sizes ranging from -0.34 to -0.65). Significant moderate deficits in executive function and attention (Cohen's d ranging from -0.52 to -0.61) and non-significant small/moderate deficits in memory (Cohen's d ranging from -0.22 to -0.54) were found to persist in patients whose depressive symptoms had remitted, indicating that cognitive impairment occurs separately from episodes of low mood in depression.

CONCLUSIONS

Both low mood and cognitive impairment are associated with poor psychosocial functioning. Therefore, we argue that remediation of cognitive impairment and alleviation of depressive symptoms each play an important role in improving outcome for patients with depression. In conclusion, this systematic review and meta-analysis demonstrates that cognitive impairment represents a core feature of depression that cannot be considered an epiphenomenon that is entirely secondary to symptoms of low mood and that may be a valuable target for future interventions.

Cognitive effects of methylphenidate and levodopa in healthy volunteers

Our previous study showed enhanced declarative memory consolidation after acute methylphenidate (MPH) administration. The primary aim of the current study was to investigate the duration of this effect. Secondary, the dopaminergic contribution of MPH effects, the electrophysiological correlates of declarative memory, and the specificity of memory enhancing effects of MPH to declarative memory were assessed. Effects of 40 mg of MPH on memory performance were compared to 100mg of levodopa (LEV) in a placebo-controlled crossover study with 30 healthy volunteers. Memory performance testing included a word learning test, the Sternberg memory scanning task, a paired associates learning task, and a spatial working memory task. During the word learning test, event-related brain potentials (ERPs) were measured. MPH failed to enhance retention of words at a 30 min delay, but it improved 24 h delayed memory recall relative to PLA and LEV. Furthermore, during encoding, the P3b and P600 ERP latencies were prolonged and the P600 amplitude was larger after LEV compared to PLA and MPH. MPH speeded response times on the Sternberg Memory Scanning task and improved performance on the Paired Associates Learning task, relative to LEV, but not PLA. Performance on the Spatial working memory task was not affected by the treatments. These findings suggest that MPH and LEV might have opposite effects on memory.

Residual effects of zopiclone 7.5 mg on highway driving performance in insomnia patients and healthy controls: a placebo controlled crossover study

RATIONALE

Residual effects of hypnotics on driving performance have been mainly determined in studies using a standardized driving test with healthy good sleepers. Responses to effects may differ, however, between insomniacs and healthy volunteers due to the underlying sleep disorder. In addition, a majority of insomniacs uses hypnotics chronically resulting in the development of tolerance to impairing effects. Impaired driving performance in healthy volunteers may then be an overestimation of the actual effects in insomniacs.

OBJECTIVES

The present study aims to compare the residual effects of zopiclone 7.5 mg on on-the-road driving performance of 16 middle-aged insomniacs chronically using hypnotics (chronic users), 16 middle-aged insomniacs not or infrequently using hypnotics (infrequent users), and 16 healthy, age matched, good sleepers (controls).

METHODS

The study was conducted according to a 3 × 2 double-blind, placebo controlled crossover design, with three groups and two treatment conditions. Treatments were single oral doses of zopiclone 7.5 mg and placebo administered at bedtime (2330 hours). Between 10 and 11 h after administration subjects performed a standardized highway driving test.

RESULTS

Zopiclone 7.5 mg significantly impaired on-the-road driving performance in both insomnia groups and healthy controls. The magnitude of impairment was significantly less in the chronic users group as compared with the controls.

CONCLUSIONS

The smaller magnitude of effects suggests that investigating residual effects of hypnotics in healthy volunteers may yield a minor overestimation of the actual effects in insomnia patients.

On-the-road driving performance and driving-related skills in older untreated insomnia patients and chronic users of hypnotics

RATIONALE

Many older adults report sleep problems and use of hypnotics. Several studies have shown that hypnotics can have acute adverse effects on driving the next morning. It is unclear however whether driving of chronic hypnotic users is impaired. Therapeutic effects on insomnia and development of tolerance may reduce the residual effects on driving.

OBJECTIVES

The present study aimed to compare actual driving performance and driving-related skills of chronic hypnotic users to good sleepers. To determine whether insomnia itself affects driving performance, driving and driving-related skills were compared between insomnia patients who do not or infrequently use hypnotics and good sleepers.

METHODS

Twenty-two frequent users of hypnotics (using hypnotics ≥ 4 nights per week for more than 3 months), 20 infrequent users (using hypnotics ≤ 3 nights per week), and 21 healthy, age-matched controls participated in this study. On the night before testing, all subjects were hospitalized for an 8-h sleep recorded by polysomnography. Frequent hypnotic users used their regular medication at bedtime (2330 hours), while infrequent users and controls received no medication. Cognitive performance (word learning, digit span, tracking, divided attention, vigilance, and inhibitory control) was assessed 8.5 h and driving performance between 10 and 11 h after bedtime and dosing.

RESULTS

Polysomnographic recordings did not significantly differ between the groups, but the insomnia patients, treated or untreated, still reported subjective sleep complaints. Results show no differences in driving performance and driving-related skills between both groups of insomnia patients and controls.

CONCLUSIONS

Driving performance in chronic users of hypnotics and untreated insomnia patients is not impaired. For chronic users, this may be due to prescription of relatively safe drugs and low doses. For untreated insomniacs, this corroborates previous findings showing an absence of neuropsychological deficits in this group of patients.

Methylphenidate produces selective enhancement of declarative memory consolidation in healthy volunteers

RATIONALE

Methylphenidate inhibits the reuptake of dopamine and noradrenaline and is used to treat children with attention deficit hyperactivity disorder (ADHD). Besides reducing behavioral symptoms, it improves their cognitive function. There are also observations of methylphenidate-induced cognition enhancement in healthy adults, although studies in this area are relatively sparse. We assessed the possible memory-enhancing properties of methylphenidate.

OBJECTIVE

In the current study, the possible enhancing effects of three doses of methylphenidate on declarative and working memory, attention, response inhibition and planning were investigated in healthy volunteers.

METHODS

In a double blind placebo-controlled crossover study, 19 healthy young male volunteers were tested after a single dose of placebo or 10, 20 or 40 mg of methylphenidate. Cognitive performance testing included a word learning test as a measure of declarative memory, a spatial working memory test, a set-shifting test, a stop signal test and a computerized version of the Tower of London planning test.

RESULTS

Declarative memory consolidation was significantly improved relative to placebo after 20 and 40 mg of methylphenidate. Methylphenidate also improved set shifting and stopped signal task performance but did not affect spatial working memory or planning.

CONCLUSIONS

To the best of our knowledge, this is the first study reporting enhanced declarative memory consolidation after methylphenidate in a dose-related fashion over a dose range that is presumed to reflect a wide range of dopamine reuptake inhibition.

Histamine H1 receptor antagonist cetirizine impairs working memory processing speed, but not episodic memory

BACKGROUND AND PURPOSE

The histaminergic neurotransmitter system is currently under investigation as a target for drug treatment of cognitive deficits in clinical disorders. The therapeutic potential of new drugs may initially be screened using a model of histaminergic dysfunction, for example, as associated with the use of centrally active antihistamines. Of the selective second generation antihistamines, cetirizine has been found to have central nervous system effects. The aim of the present study was to determine whether cetirizine can be used as a tool to model cognitive deficits associated with histaminergic hypofunction.

EXPERIMENTAL APPROACH

The study was conducted according to a three-way, double-blind, cross-over design. Treatments were single oral doses of cetirizine 10 and 20 mg and placebo. Effects on cognition were assessed using tests of word learning, memory scanning, vigilance, divided attention, tracking and visual information processing speed.

KEY RESULTS

Cetirizine 10 mg impaired tracking performance and both doses impaired memory scanning speed. None of the other measures indicated impaired performance.

CONCLUSION AND IMPLICATIONS

Cetirizine affects information processing speed, but these effects were not sufficient to serve as a model for cognitive deficits in clinical disorders.

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.

Method development studies for repeatedly measuring anxiolytic drug effects in healthy humans

Human experimental models for anxiety may serve as translational tools for translating preclinical psychopharmacological investigations into human studies. For the evaluation of drugs of which pharmacokinetics and pharmacodynamics are unidentified, repeating measurements after drug administration is necessary for characterising the time course of drug effects. In experiment 1, a threat-of-shock paradigm and adaptations of the Trier mental arithmetic test and the Stroop colour naming test were repeated four times within a day to evaluate whether anxiety responses to this test battery remain stable after repeated testing. This procedure was repeated on 4 days in a second experiment to evaluate suitability of the paradigm for a crossover design with multiple sessions. Results indicate no reductions or changes in fear potentiated startle, the main outcome measure for the threat paradigm, over test sessions or days. Skin conductance responses and subjective ratings under threat-of-shock showed significant fluctuations but also no systematic decline over time. Finally, the threat paradigm and Stroop test resulted in small increases in reported state anxiety while mental arithmetic produced larger effects that diminished after the first test day. It is concluded that especially the startle paradigm could be a useful new instrument for screening new anxiolytic drugs.

Serotonin transporter polymorphisms (SLC6A4 insertion/deletion and rs25531) do not affect the availability of 5-HTT to [11C] DASB binding in the living human brain

Studies in vitro suggest that the expression of the serotonin transporter (5-HTT) is regulated by polymorphic variation in the promoter region of the 5-HTT gene (5-HTTLPR); however, results from human brain imaging studies examining the relation between 5-HTT genotype and 5-HTT radioligand binding in vivo have been inconsistent. This inconsistency could reflect small participant numbers or the use of sub-optimal radiotracer for measuring the 5-HTT. We used positron emission tomography in conjunction with the selective 5-HTT ligand [(11)C] DASB to examine the availability of the 5-HTT in seven brain regions in 63 healthy European caucasian volunteers who were genotyped for short (S) and long (L) variants (SLC6A4 and rs25531) of the 5-HTTLPR. [(11)C] DASB binding potential was not influenced by the allelic status of participants whether classified on a biallelic or triallelic basis in any of the regions studied. Our PET findings, in a relatively large sample with a near optimal radiotracer, suggest that 5-HTTLPR polymorphic variation does not affect the availability of 5-HTT to [(11)C] DASB binding in adult human brain. The reported impact of 5-HTTLPR polymorphic variation on emotional processing and vulnerability to depression are more likely therefore to be expressed through effects exerted during neurodevelopment.

Histamine H1 receptor blockade predominantly impairs sensory processes in human sensorimotor performance

BACKGROUND AND PURPOSE

Centrally active antihistamines impair cognitive performance, particularly sensorimotor performance. The aim of the present study was to further elucidate the scarcely studied subprocesses involved in sensorimotor performance, which may be affected by H1 receptor blockade. Better knowledge about the cognitive deficits associated with histamine dysfunction can contribute to better treatment of clinical disorders in which histamine hypofunction may be a contributing factor, such as in schizophrenia.

EXPERIMENTAL APPROACH

Interactions of dexchlorpheniramine with specific task manipulations in a choice reaction time task were studied. Task demands were increased at the level of sensory subprocesses by decreasing stimulus quality, and at the level of motor subprocesses by increasing response complexity. A total of 18 healthy volunteers (9 female) aged between 18 and 45 years participated in a three-way, double-blind, crossover design. Treatments were single oral doses of 4 mg dexchlorpheniramine, 1 mg lorazepam and placebo. Behavioural effects were assessed by measuring reaction times and effects on brain activity by event-related potentials.

KEY RESULTS

Dexchlorpheniramine significantly slowed reaction times, but did not significantly interact with task manipulations. However, it did significantly interact with stimulus quality, as measured by event-related potentials. Lorazepam slowed reaction times and interacted with perceptual manipulations, as shown by effects on reaction times.

CONCLUSIONS AND IMPLICATIONS

The results confirm that the histamine system is involved in sensory information processing and show that H1 blockade does not affect motoric information processing. Histamine hypofunction in clinical disorders may cause impaired sensory processing, which may be a drug target.

Effects of L-histidine depletion and L-tyrosine/L-phenylalanine depletion on sensory and motor processes in healthy volunteers

BACKGROUND AND PURPOSE

Animal studies show that histamine plays a role in cognitive functioning and that histamine H3-receptor antagonists, which increase histaminergic function through presynaptic receptors, improve cognitive performance in models of clinical cognitive deficits. In order to test such new drugs in humans, a model for cognitive impairments induced by low histaminergic functions would be useful. Studies with histamine H1-receptor antagonists have shown limitations as a model. Here we evaluated whether depletion of L-histidine, the precursor of histamine, was effective in altering measures associated with histamine in humans and the behavioural and electrophysiological (event-related-potentials) effects.

EXPERIMENTAL APPROACH

Seventeen healthy volunteers completed a three-way, double-blind, crossover study with L-histidine depletion, L-tyrosine/L-phenylalanine depletion (active control) and placebo as treatments. Interactions with task manipulations in a choice reaction time task were studied. Task demands were increased using visual stimulus degradation and increased response complexity. In addition, subjective and objective measures of sedation and critical tracking task performance were assessed.

KEY RESULTS

Measures of sedation and critical tracking task performance were not affected by treatment. L-histidine depletion was effective and enlarged the effect of response complexity as measured with the response-locked lateralized readiness potential onset latency.

CONCLUSIONS AND IMPLICATIONS

L-histidine depletion affected response- but not stimulus-related processes, in contrast to the effects of H1-receptor antagonists which were previously found to affect primarily stimulus-related processes. L-histidine depletion is promising as a model for histamine-based cognitive impairment. However, these effects need to be confirmed by further studies.

40-Hz steady state response in Alzheimer's disease and mild cognitive impairment

The 40-Hz steady state response (SSR) reflects early sensory processing and can be measured with electroencephalography (EEG). The current study compared the 40-Hz SSR in groups consisting of mild Alzheimer's disease patients (AD) (n=15), subjects with mild cognitive impairment (MCI) (n=20) and healthy elderly control subjects (n=20). All participants were naïve for psychoactive drugs. Auditory click trains at a frequency of 40-Hz evoked the 40-Hz SSR. To evaluate test-retest reliability (TRR), subjects underwent a similar assessment 1 week after the first. The results showed a high TRR and a significant increase of 40-Hz SSR power in the AD group compared to MCI and controls. Furthermore a moderate correlation between 40-Hz SSR power and cognitive performance as measured by ADAS-cog was shown. The results suggest that 40-Hz SSR might be an interesting candidate marker of disease progression.

Memory impairments in humans after acute tryptophan depletion using a novel gelatin-based protein drink

Acute tryptophan depletion (ATD) can be used to decrease serotonin levels in the brain. Traditionally, ATD has been established by administering amino acid (AA) mixtures and studies using this method showed that serotonin is involved in learning and memory processes. This study used a recently developed gelatin-based protein drink to examine whether it 1) is superior to the traditional AA method in controlling the tryptophan levels in the placebo condition, 2) impairs long-term memory and 3) differentially affects episodic and spatial memory. Sixteen healthy subjects participated in a double-blind, placebo-controlled study. Memory was assessed using a visual verbal learning test and an object relocation task (spatial memory). Tryptophan ratio significantly decreased after ATD and did not significantly increase in the placebo condition. Delayed recall in the verbal learning test and delayed relocation of objects to positions in the spatial task were impaired after ATD. Spatial short-term memory, however, improved. The current results indicate that the tryptophan levels were essentially neutral in the placebo condition compared with those in the traditional AA mixture. Our study provides further evidence that impairment in long-term episodic and elementary spatial memory after ATD is related to lowered tryptophan levels in plasma.

Serotonergic vulnerability and depression: assumptions, experimental evidence and implications

In recent years, the term serotonergic vulnerability (SV) has been used in scientific literature, but so far it has not been explicitly defined. This review article attempts to elucidate the SV concept. SV can be defined as increased sensitivity to natural or experimental alterations of the serotonergic (5-HTergic) system. Several factors that may disrupt the 5-HTergic system and hence contribute to SV are discussed, including genetic factors, female gender, personality characteristics, several types of stress and drug use. It is explained that SV can be demonstrated by means of manipulations of the 5-HTergic system, such as 5-HT challenges or acute tryptophan depletion (ATD). Results of 5-HT challenge studies and ATD studies are discussed in terms of their implications for the concept of SV. A model is proposed in which a combination of various factors that may compromise 5-HT functioning in one person can result in depression or other 5-HT-related pathology. By manipulating 5-HT levels, in particular with ATD, vulnerable subjects may be identified before pathology initiates, providing the opportunity to take preventive action. Although it is not likely that this model applies to all cases of depression, or is able to identify all vulnerable subjects, the strength of the model is that it may enable identification of vulnerable subjects before the 5-HT related pathology occurs.

Serotonin and Human Cognitive Performance

In the past decade, experimental studies involving healthy human volunteers have revealed that manipulations of the central serotonin (5-HT) system can produce quite specific changes in cognitive functioning, independent of overt mood changes. Reduced 5-HT turnover is consistently associated with impaired long-term memory functioning. Low 5-HT function may also impair cognitive flexibility and improve focused attention. On the other hand, stimulation of central 5-HT has repeatedly been found to impair performance in a true vigilance task. Currently, there is little evidence for mirrored cognitive changes due to opposite 5-HT manipulations in healthy volunteers. Given the mounting evidence for a role of 5-HT in human cognition, reduced 5-HT function could be directly linked to cognitive disturbances in certain conditions, such as in depression and Alzheimer's Disease (AD). There is evidence that stimulating (i.e. normalizing) 5-HT activity in depression may have specific beneficial effects on cognition, independent of a general relief of depressive symptoms, but this premise needs to be confirmed by larger-scale clinical studies. Recently, a potential role of 5-HT in the cognitive symptoms in AD has been identified, but there is insufficient data to evaluate the effects of 5-HT stimulation on cognitive symptoms in AD. It is concluded that serotonin is a potential target for pharmacological cognition enhancement, particularly for restoration of impaired cognitive performance due to 5-HT dysfunction. Further differentiation of the role of 5-HT in normal and disturbed cognition and evaluation of the effects of 5-HT manipulations in various populations is required to establish the full potential of 5-HT drugs as cognition enhancers.

Acute tryptophan depletion affects brain-gut responses in irritable bowel syndrome patients and controls

BACKGROUND

Serotonin, a key denominator of the brain-gut axis, is involved in the regulation of gastrointestinal motility, secretion, and perception as well as cognition and mood.

AIM

To assess the effects of an acutely lowered serotonin synthesis, using the acute tryptophan depletion (ATD) method, on visceral perception, affective memory performance, and mood in diarrhoea predominant irritable bowel syndrome patients (d-IBS) and controls.

METHODS

In a randomised, double blind, crossover design, 14 d-IBS patients and fourteen matched controls were studied under ATD and placebo conditions, respectively. Perception of urge and pain was scored during rectal distensions. Affective memory performance, mood, and biochemical parameters of serotonergic metabolism were simultaneously assessed.

RESULTS

ATD significantly decreased plasma tryptophan (67.0 (2.0) v 24.9 (2.0) mumol/l) and 5-hydroxyindole acetic acid concentrations (29.9 (1.0) v 15.8 (0.6) nmol/l). ATD was associated with significantly increased urge scores specifically in the lower pressure range and overall increased pain scores. ATD significantly lowered the perceptual threshold for first perception compared with placebo (patients 10.6 (1.2) v 13.6 (0.8) mm Hg, controls 12.6 (1.3) v 15.7 (1.2) mm Hg) but not for maximal tolerable discomfort (patients 50.5 (3.6) v 51.6 (3.3) mm Hg, controls 50.9 (3.3) v 48.8 (2.9) mm Hg). ATD induced a significant shift in affective memory bias towards preferential loss of positive material but no significant changes in mood. ATD did not differentially affect the patient or control group.

CONCLUSIONS

We have provided evidence that serotonergic modulation by ATD affects both visceral perception as well as cognition in d-IBS and controls. Simultaneous measurement of brain and gut function and the application of ATD contribute to the elucidation of the complex pathophysiology of IBS.

Lower high-density lipoprotein cholesterol and increased omega-6 polyunsaturated fatty acids in first-degree relatives of bipolar patients

BACKGROUND

Lower serum high-density lipoprotein cholesterol and increased ratio of omega-6/omega-3 fatty acids have been reported in unipolar and bipolar depressed patients. Changes in cholesterol and fatty acids have been suggested to affect membrane viscosity and consequently serotonergic neurotransmitter expression. The goal of this study was to investigate whether lower baseline cholesterol and increased omega-6 and lower omega-3 fatty acids are present in healthy first-degree relatives of bipolar patients compared with controls and whether these changes were associated with neuroendocrine responses to an i.v. tryptophan challenge or mood.

METHOD

Baseline cholesterol, fatty acids and mood were determined in healthy first-degree relatives of patients with bipolar disorders (N = 30) and healthy matched controls (N = 15) (parallel-group design). Prolactin and cortisol were measured following tryptophan infusion.

RESULTS

First-degree relatives showed significantly lower plasma high-density lipoprotein cholesterol and increased total omega-6 fatty acids in phospholipids. Lower total omega-3 and higher total omega-6 fatty acids in phospholipids were positively correlated with peak prolactin response to tryptophan. Lower total omega-3 fatty acids in phospholipids and cholesteryl esters were associated with lower mood.

CONCLUSIONS

Abnormalities of lower plasma high-density lipoprotein cholesterol and increased total omega-6 fatty acids in phospholipids in these subjects are in agreement with findings in bipolar and major depressed patients. Changes in fatty acids show an association with central serotonergic parameters. It is suggested that these abnormalities in cholesterol and fatty acids may constitute a trait marker for bipolar disorders.

Memory functions and focussed attention in middle-aged and elderly subjects are unaffected by a low, acute dose of caffeine

The putative beneficial effects of caffeine on cognitive performance may vary between ages. The acute cognitive effects of 100 g caffeine on memory functions and focussed attention were investigated in sixteen middle-aged (45-60 years) and fourteen elderly (60-75 years) healthy men and women according to a cross-over design. Caffeine did not affect short-term memory span or speed, long-term memory retrieval functions or focussed attention. It is proposed that in middle-aged and elderly subjects cognitive effects may occur predominantly at higher caffeine dosages.

Dissociable effects of a single dose of ecstasy (MDMA) on psychomotor skills and attentional performance

Ecstasy (3,4-methylenedioxymethamphetamine, MDMA) is a psychoactive recreational drug widely used by young people visiting dance parties, and has been associated with poor cognitive function. The current study assessed the influence of a single dose of MDMA 75 mg and alcohol 0.5 g/kg on cognition, psychomotor performance and driving-related task performance. Twelve healthy recreational ecstasy users participated in an experimental study conducted according to a double-blind, double-dummy, placebo-controlled three-way cross-over design. MDMA improved psychomotor performance, such as movement speed and tracking performance in a single task, as well as in a divided attention task. MDMA impaired the ability to predict object movement under divided attention. However, the inability to accurately predict object movement after MDMA may indicate impairment of particular performance skills relevant to driving. There was no effect of MDMA on visual search, planning or retrieval from semantic memory.

Monoamine depletion in psychiatric and healthy populations: review

A number of techniques temporarily lower the functioning of monoamines: acute tryptophan depletion (ATD), alpha-methyl-para-tyrosine (AMPT) and acute phenylalanine/tyrosine depletion (APTD). This paper reviews the results of monoamine depletion studies in humans for the period 1966 until December 2002. The evidence suggests that all three interventions are specific, in terms of their short-term effects on one or two neurotransmitter systems, rather than on brain protein metabolism in general. The AMPT procedure is somewhat less specific, affecting both the dopamine and norepinephrine systems. The behavioral effects of ATD and AMPT are remarkably similar. Neither procedure has an immediate effect on the symptoms of depressed patients; however, both induce transient depressive symptoms in some remitted depressed patients. The magnitude of the effects, response rate and quality of response are also comparable. APTD has not been studied in recovered major depressive patients. Despite the similarities, the effects are distinctive in that ATD affects a subgroup of recently remitted patients treated with serotonergic medications, whereas AMPT affects recently remitted patients treated with noradrenergic medications. The evidence also suggests that ATD and APTD affect different cognitive functions, in particular different memory systems. Few studies investigated cognitive effects of the procedures in patients. Patients who are in remission for longer may also be vulnerable to ATD and AMPT, but the relationship with prior treatment is much weaker. For these patients, individual vulnerability markers are the more important determinants of depressive response, making these techniques potentially useful models of vulnerability to depression.

Pronounced cognitive deficits following an intravenous L-tryptophan challenge in first-degree relatives of bipolar patients compared to healthy controls

Cognitive impairment has repeatedly been described in bipolar disorders (BD). Serotonin (5-hydroxytryptophan; 5-HT) is possibly involved in these cognitive processes, more particularly in executive functions, learning, memory, and attention. The aim of this study was to investigate serotonergic vulnerability and its relation to cognitive functioning in healthy first-degree relatives of BD patients. We investigated the effects of an intravenous (i.v.) tryptophan (Trp) challenge and placebo on cognitive performance in 30 healthy first-degree relatives of bipolar patients (FH) and 15 matched controls in a double-blind crossover design. A distinction was made between relatives of type I BD patients (FH I) and type II BD patients (FH II). Performances on planning, memory, attention, and psychomotor tasks were assessed 3 h after Trp infusion. After Trp, planning and attention were impaired in FH subjects but not in controls. Independent of Trp, FH subjects showed cognitive deficits on memory, focused and divided attention, and psychomotor performance. FH I subjects showed more pronounced cognitive impairments then FH II and controls. In all groups, Trp impaired memory and psychomotor performance significantly. In conclusions, cognitive deficits in FH following Trp may reflect a central 5-HT vulnerability in frontal brain areas. Independent of Trp, cognitive deficits in FH provide evidence for a trait marker for BD.

Nutritional manipulation and psychiatric conditions: focus on mood and cognition

In this paper, several experimental models of human depression and cognitive dysfunction, which are designed specifically to mimic the proposed mechanisms of action of many nutritional supplements, are illustrated. These mechanisms of interest are antioxidant effects, glucose utilization, neuronal membrane function and neurotransmitter effects, with particular reference to nutrient-based amino acid manipulations of neurotransmission, such as tryptophan depletion. It is concluded that the application of experimental human models of altered mood and cognitive function may illuminate substantially the quest for nutritional enhancement of human mood and cognitive function.

Serotonergic dysregulation in bipolar disorders: a literature review of serotonergic challenge studies

OBJECTIVES

Serotonin (5-hydroxytryptamine; 5-HT) and endocrine abnormalities have been repeatedly reported in bipolar disorders (BD). Useful methods to investigate 5-HT responsivity, and the interaction with neuroendocrine functioning, are provided by acute 5-HT challenge and depletion paradigms. In this review 5-HT challenges are limited to paradigms that stimulate 5-HT activity in BD.

METHODS

Literature was searched for in electronic libraries: MEDLINE and PSYCHLIT, period 1966-2001. Papers describing effects of an acute 5-HT challenge on neuroendocrine functioning in BD patients were selected.

RESULTS

Review of the literature revealed 15 studies: five papers described the effects of 5-HT challenges in manic BD patients, four papers in euthymic BD and seven in depressed BD patients. The reviewed 5-HT challenge paradigms are acute administration of oral and intravenous (i.v.) dosage of d,l-fenfluramine, tryptophan, 5-hydroxytryptophan, ipsapirone and buspirone. There were no papers which investigated neuroendocrine effects of m-chlorophenylpiperazine, clomipramine and citalopram in BD patients and were therefore not reviewed.

CONCLUSIONS

The literature on 5-HT challenge procedures in BD shows evidence for a blunted prolactin (PRL) in mania and depression as well as a blunted cortisol in euthymic BD patients. This suggests that in both mania and depression similar changes in the 5-HT system are involved. It is speculated that blunting of cortisol responses in euthymic BD patients may be a result of chronically altered 5-HT functioning, whereas changes in PRL release following 5-HT challenges reflect more state-dependent changes in 5-HT activity. The 5-HT responsivity in BD patients has also been associated with pharmacological treatment, suicidal behaviour, weight loss and age. Recommendations for future research are given.

Effects of acute tryptophan depletion on mood and cortisol release in first-degree relatives of type I and type II bipolar patients and healthy matched controls

Biological vulnerability for bipolar disorders (BD) in relatives of BD patients has not as yet been established. Serotonergic vulnerability was studied, using acute tryptophan depletion (ATD), in healthy first-degree relatives of BD patients and healthy controls. The effects of ATD on mood and cortisol release in 30 healthy adult, lifetime symptom free, unaffected first-degree relatives of BD patients (Family History; FH) were compared with effects in 15 healthy matched controls in a placebo-controlled, double-blind, crossover design. During ATD and placebo, salivary cortisol response was also assessed during a stress-inducing speech task (SIST). First-degree relatives of type II BD patients (FH II) showed an elevation of mood, whereas control subjects and relatives of type I BD patients (FH I) showed a lowering of mood after ATD. ATD was followed by a decrease in cortisol level in both FH subgroups, but not in the controls. The results suggest serotonergic vulnerability that affected mood in FH II subjects and cortisol release in both FH I and FH II subjects.

Safety of soy-derived phosphatidylserine in elderly people

Phosphatidylserine (PS) is a phospholipid which has been claimed to enhance neuronal membrane function, and can be derived from several sources. Earlier studies used brain cortex derived PS, of which the human tolerability of 300mg daily in 130 patients has been shown. The human tolerability of PS derived from soybean has not been reported, although it is widely sold as a nutritional supplement which may improve cognitive function in the elderly. We report the results of a study of the safety of two dosages of soy-phosphatidylserine (S-PS) in elderly. Subjects were 120 elderly of both sexes who fulfilled the more stringent criteria for age-associated memory impairment; some also fulfilled the criteria for age-associated cognitive decline. Subjects were allocated at random to one of the three treatment groups: placebo, 300 or 600 mg S-PS daily. Standard biochemical and hematological safety parameters, blood pressure, heart rate and adverse events were assessed at baseline, after 6 and 12 weeks of treatment. No significant differences were found in any of the outcome variables between the treatment groups after Bonferonni-Holme correction. In conclusion, soy derived PS is a safe nutritional supplement for older persons if taken up to a dosage of 200 mg three times daily.

Cognition following acute tryptophan depletion: difference between first-degree relatives of bipolar disorder patients and matched healthy control volunteers

BACKGROUND

Serotonergic circuits have been proposed to mediate cognitive processes, particularly learning and memory. Cognitive impairment is often seen in bipolar disorders in relation to a possible lowered serotonergic turnover.

METHODS

We investigated the effects of acute tryptophan depletion (ATD) on cognitive performance in healthy first-degree relatives of bipolar patients (FH) (N= 30) and matched controls (N= 15) in a placebo-controlled, double-blind cross-over design. Performance on planning, memory and attention tasks were assessed at baseline and 5 h after ATD.

RESULTS

Following ATD, speed of information processing on the planning task was impaired in the FH group but not in the control group. FH subjects with a bipolar disorder type I relative (FH I) showed impairments in planning and memory, independent of ATD. In all subjects, ATD impaired long-term memory performance and speed of information processing. ATD did not affect short-term memory and focused and divided attention.

CONCLUSIONS

The results suggest serotonergic vulnerability affecting frontal lobe areas in FH subjects, indicated by impaired planning. Biological vulnerability in FH I subjects is reflected in impaired planning and memory performance. In conclusion, the cognitive dysfunctions in FH subjects indicate an endophenotype constituting a possible biological marker in bipolar psychopathology. Serotonin appears to be involved in speed of information processing, verbal and visual memory and learning processes.

Dissociable hormonal, cognitive and mood responses to neuroendocrine challenge: evidence for receptor-specific serotonergic dysregulation in depressed mood

Fifteen patients with major depression, dysthymia, or anxiety disorder with depressed mood (DSM-IV diagnoses) and 16 controls received single oral doses of 0.5mg/kg metachlorophenylpiperazine (m-CPP), a 5-HT(2C) agonist, and 10 mg ipsapirone, a 5-HT(1A) agonist, according to double-blind, placebo-controlled, cross-over design. The groups' levels of cortisol, adrenocorticotrophic hormone (ACTH) and prolactin did not differ at baseline. Both 5-HT agonists significantly elevated cortisol, ACTH, and prolactin. The cortisol response to ipsapirone was significantly blunted in major depression and dysthymia patients. Neuroendocrine responses to m-CPP did not differ between groups, but m-CPP selectively increased profile of mood states (POMS) depression and tenseness scores in patients. No effects of ipsapirone on mood were found. However, ipsapirone impaired memory performance in controls, but tended to improve memory performance in patients. The results support the evidence for both hypothalamic and possibly hippocampal 5-HT(1A) receptor desensitisation and non-hypothalamic, 5-HT(2C) receptor sensitisation, probably fronto-cortical, in patients with major depression and dysthymia.

Nutrients, age and cognition

Our knowledge about the influence of nutritional supplements on human cognition, especially in the elderly, rests largely on animal behavioural research and neurochemical experiments in vitro, while only a few epidemiological studies and even fewer controlled experiments in humans are reported. This is an inherent problem, due partly to the difficulty of conducting controlled nutritional experiments in humans, but may also partly be due to the gap between the research disciplines of nutritional and neurobehavioral experimental science.

LEARNING OBJECTIVES

The aim of this paper is to discuss some new findings in this line of research, and to stress the importance of the need to start bridging the gap between disciplines by identifying possible human experimental models of altered cognitive function, which can elucidate the specific mechanisms of action through which nutritional supplements may enhance cognitive performance in humans in vivo. These experimental models are important because the research in this field is mostly based on epidemiological studies, which describe associations between nutrients and cognitive functions. Contrary to epidemiological studies, experimental models mimic associations between nutrients and cognition by manipulating their presumed mechanisms of action and can eventually explain the causal nature of found associations.

Mood congruent memory bias induced by tryptophan depletion

BACKGROUND

Mood congruent memory bias predicts a more superior recall memory of learnt material congruent with the mood state at the time of learning. The present study is the first report of an experimental study in which a biological mood induction was used to test this hypothesis. The influence of acute tryptophan (TRP) depletion, inducing low serotonin neurotransmission and a depression of mood, on memory bias was evaluated in healthy volunteers (16 with and 11 without a family history of major affective disorder).

METHODS

Twenty-seven subjects received 100 g of an amino acid mixture with and without TRP according to a placebo-controlled, double-blind, balanced, cross-over design. An affective memory test consisting of a 30-word list with words of positive, neutral, and negative affective valence and a mood questionnaire were assessed at 6 and 24 h following treatment administration.

RESULTS

TRP depletion impaired delayed recall of neutral and positive words, but not of negative words. There was no interaction of family history and treatment and there was no post hoc association between the influence of TRP-depletion on mood and on affective memory bias.

CONCLUSION

Experimentally induced serotonergic depletion in normal individuals shifts affective memory bias towards negative affective valent verbal stimuli.

Non-serotonergic pharmacological profiles and associated cognitive effects of serotonin reuptake inhibitors

The current study was carried out to investigate the cognitive effects of two serotonin reuptake inhibitors (SSRIs), sertraline and paroxetine, with special reference to differences in their affinity for other neurotransmitter systems, i.e. anticholinergic activity of paroxetine and putative dopamine reuptake activity of sertraline. The study was conducted according to a double-blind, three-way cross-over design. During three treatment periods of 2 weeks, 24 healthy middle-aged (aged 30-50 years) subjects of both sexes received sertraline (50 mg on days 1-7, 100 mg on days 8-14), paroxetine (20 mg on days 1-7, 40 mg on days 8-14) and placebo. Paroxetine specifically impaired delayed recall in a word learning test at a dose of 20 and 40 mg. Sertraline did not affect word learning but improved performance on a verbal fluency task at a dose of 50 and 100 mg. Neither drug affected performance on a short-term memory scanning task. These subtle but significant changes in cognitive performance can be explained by subtle differences in pharmacological profiles of these SSRIs. The additional anticholinergic effects of paroxetine could account for its induction of long-term memory impairment. Similarly, the additional dopaminergic effects of sertraline could account for its induction of slightly improved verbal fluency. The impairing and facilitating cognitive effects of paroxetine and sertraline, respectively, may be more pronounced in the elderly depressed patient.

Acute dietary tryptophan depletion impairs maintenance of "affective set" and delayed visual recognition in healthy volunteers

RATIONALE

Altered serotonergic transmission in affective disorders and Alzheimer's disease has prompted research aimed at defining the precise cognitive effects of depleting central serotonin in humans, using acute dietary tryptophan depletion.

OBJECTIVE

We examined the effects of tryptophan depletion on mood and cognition in healthy volunteers. Cognitive tests of memory and attentional processing were employed to test hypotheses of central 5-hydroxytryptamine (5-HT) function related to cortical processing.

METHODS

A double-blind, parallel design, placebo control study was employed with 15 subjects in each group. Mood rating scales were performed at the start and 5 h after ingestion of the drink. Cognitive tests were also performed at 5 h, after completion of the subjective rating scales.

RESULTS

A robust reduction in total tryptophan was achieved in the test group. Subjects receiving the placebo drink showed the expected effect of shift on the affective shifting task, that is, more errors in the more difficult shift versus the non-shift condition. The tryptophan-depleted group made a similar number of errors in the shift trials but failed to reduce the number of errors in the non-shift trials. The tryptophan-depleted group showed a significant impairment on the delayed pattern recognition task. No significant effects on the subjective mood measures were found.

CONCLUSIONS

Tryptophan depletion abolished the normal tendency to improve error scores on non-shift trials in response to affective cues on a go/no-go task. We suggest that this inability to "maintain set" in the non-shift condition may be due to a disruption of semantic retrieval processes concerned with affect. The novel finding of impairment on a delayed visual pattern recognition task confirms and extends previous studies where selective effects on memory and learning have been found following acute tryptophan depletion.

The influence of soy-derived phosphatidylserine on cognition in age-associated memory impairment

Phosphatidylserine (PS) is a phospholipid widely sold as a nutritional supplement. PS has been claimed to enhance neuronal membrane function and hence cognitive function, especially in the elderly. We report the results of a clinical trial of soybean-derived PS (S-PS) in aging subjects with memory complaints. Subjects were 120 elderly (> 57 years) of both sexes who fulfilled the more stringent criteria for age-associated memory impairment (AAMI); some also fulfilled the criteria for age-associated cognitive decline. Subjects were allocated at random to one of the three treatment groups: placebo, 300mg S-PS daily, or 600mg S-PS daily. Assessments were carried out at baseline, after 6 and 12 weeks of treatment, and after a wash-out period of 3 weeks. Tests of learning and memory, choice reaction time, planning and attentional functions were administered at each assessment. Delayed recall and recognition of a previously learned word list comprised the primary outcome measures. No significant differences were found in any of the outcome variables between the treatment groups. There were also no significant interactions between treatment and 'severity of memory complaints'. In conclusion, a daily supplement of S-PS does not affect memory or other cognitive functions in older individuals with memory complaints.

Tryptophan depletion impairs memory consolidation but improves focussed attention in healthy young volunteers

Animal and human studies have provided evidence for serotonergic modulation of cognitive processes. However, the exact nature of this relationship is not clear. We used the acute tryptophan depletion (ATD) method to investigate the effects of lowered serotonin synthesis on cognitive functions in 17 healthy young volunteers. The study was conducted according to a placebo-controlled, double-blind, crossover design. Cognitive performance and mood were assessed at baseline and 5 and 9 h after administration of ATD. A specific impairment of word recognition, without effects on short-term memory, occurred during ATD. No memory deficits were seen if ATD was induced after acquisition of new words. The Stroop Test and dichotic listening task demonstrated a modality independent improvement of focussed attention after ATD. Fluency was also improved after ATD. ATD did not alter speed of information processing, divided attention or planning functions. These results indicate that serotonin is essential in the process of long-term memory consolidation, primarily in the first 30 min after acquisition. Improvement of specific cognitive processes by lowered 5-HT function may be linked to the removal of inhibitory actions of 5-HT in the cortex.

MASERATI: a RocketBorne tunable diode laser absorption spectrometer

The MASERATI (middle-atmosphere spectrometric experiment on rockets for analysis of trace-gas influences) instrument is, to our knowledge, the first rocket-borne tunable diode laser absorption spectrometer that was developed for in situ measurements of trace gases in the middle atmosphere. Infrared absorption spectroscopy with lead salt diode lasers is applied to measure water vapor and carbon dioxide in the altitude range from 50 to 90 km and 120 km, respectively. The laser beams are directed into an open multiple-pass absorption setup (total path length 31.7 m) that is mounted on top of a sounding rocket and that is directly exposed to ambient air. The two species are sampled alternately with a sampling time of 7.37 ms, each corresponding to an altitude resolution of approximately 15 m. Frequency-modulation and lock-in techniques are used to achieve high sensitivity. Tests in the laboratory have shown that the instrument is capable of detecting a very small relative absorbance of 10(-4)-10(-5) when integrating spectra for 1 s. The instrument is designed and qualified to resist the mechanical stress occurring during the start of a sounding rocket and to be operational during the cruising phase of the flight when accelerations are very small. Two almost identical versions of the MASERATI instrument were built and were launched on sounding rockets from the Andøya Rocket Range (69 degrees N) in northern Norway on 12 October 1997 and on 31 January 1998. The good technical performance of the instruments during these flights has demonstrated that MASERATI is indeed a new suitable tool to perform rocket-borne in situ measurements in the upper atmosphere.

Mood effects of 24-hour tryptophan depletion in healthy first-degree relatives of patients with affective disorders

BACKGROUND

Acute tryptophan (TRP) depletion was evaluated in healthy volunteers with or without a family history of major affective disorder (FH+ versus FH-).

METHODS

Twenty-seven subjects (16 FH+, 11 FH-) received 100 g of an amino acid mixture with and without TRP according to a placebo-controlled, double-blind cross-over design and a diet devoid of TRP for the next 24 hours.

RESULTS

The ratio TRP/large neutral amino acids declined to 22% of baseline values after 6 hours, and increased during the night reaching 85% of baseline after 24 hours. Overall, after 6 hours, TRP depletion lead to a lowering of mood, but after 24 hours, these changes were no longer detected. Mood changes and gastrointestinal side effects were significantly more evident in FH+ subjects than in FH- subjects.

CONCLUSIONS

Our data support the hypothesis that subjects with a positive family history for depression are predisposed to increased vulnerability to the adverse consequences of serotonergic imbalance.

Caffeine improves cognitive performance after strenuous physical exercise

The effects of three carbohydrate electrolyte solutions (CES) containing different amounts of caffeine on cognitive function and the combined effects of these drinks and exercise on cognitive functions were investigated in a double-blind, cross-over study. On five separate occasions, fifteen endurance trained male athletes (23.3 years) received water placebo, CES placebo (68.8 g/l), and three CES drinks containing low, medium and high dosages of caffeine (150, 225 and 320 mg/l). Each occasion, 8 ml/kg of the drink was consumed before -- and 6 ml/kg of the drink was consumed during an all-out 1 hour time trial on a bicycle ergometer. Cognitive (attentional, psychomotor, and memory) tests were carried out immediately before and immediately after exercise. Before exercise, long term memory was improved by CES plus low dose caffeine compared to both placebos. Immediately after exercise, all cognitive functions were improved by CES plus low- and medium-dose caffeine compared to placebo. These results comprise the first practical demonstration of the cognition improving effects of low amounts of caffeine in CES after strenuous physical exercise.

Lithium induced cognitive side-effects in bipolar disorder: a qualitative analysis and implications for daily practice

Qualitative analysis of the literature on cognitive side-effects of lithium in patients with a bipolar disorder identified four of 17 studies that fulfilled criteria of adequate methodological quality. Analysis of these four studies showed that lithium had a negative effect on memory and speed of information processing, often without subjective complaints or awareness of mental slowness. The consequences of these findings for daily practice are discussed, in particular with respect to driving performance. When neurocognitive complaints or deficits are present, lithium plasma level, thyroid functions and degree of mood disturbance should be assessed. In cases where all these parameters are within normal limits and neurocognitive complaints still persist, dose reduction of lithium, thyroid hormone addition, prescription of a slow release preparation or replacement of lithium by another moodstabiliser should be considered. Guidelines are suggested with respect to further neuropsychological screening.

Tryptophan depletion in normal volunteers produces selective impairment in memory consolidation

Serotonin (5-hydroxytryptamine; 5-HT) circuits may play a role in cognitive performance, particularly in learning and memory. Cognitive impairment is often seen in depressed patients, in whom 5-HT turnover in the brain is thought to be lowered. A possible human pharmacological model to study the involvement of the serotonergic system in cognitive impairment is to reduce central 5-HT synthesis through L-tryptophan depletion in healthy subjects. In this study, the cognitive effects of tryptophan depletion were assessed and whether genetically or developmentally determined vulnerability factors were predictive of the cognitive impairment induced by tryptophan depletion. Sixteen healthy volunteers with a positive family history of depression and 11 without were given 100 g of an amino acid mixture with or without tryptophan, according to a double-blind, cross-over design. Tryptophan depletion specifically impaired long-term memory performance in all subjects: delayed recall performance, recognition sensitivity, and recognition reaction times were significantly impaired after tryptophan depletion relative to placebo. Short-term memory and perceptual and psychomotor functions were unchanged. There were no differences between groups with a positive and a negative family history for depression. On the basis of these results, it is concluded that tryptophan depletion specifically impairs long-term memory formation, presumably as a result of an acute decrease in 5-HT turnover in the brain.

Specificity of the tryptophan depletion method

Thirteen healthy subjects were subjected to tryptophan (TRP) depletion, lysine (LYS) depletion, and a placebo condition in a double blind cross-over study. The aim of the study was to test the specificity of psychological effects induced by TRP depletion. Subjects ingested a 100 g amino acid mixture with or without TRP or LYS. Six hours later, plasma TRP levels had decreased by 77% in the TRP depletion test and LYS levels by 51% in the LYS depletion condition. After 6 h of TRP depletion, subjects reported significantly more tiredness and lowering of mood, compared to subjects in the placebo group, and memory performance declined. After 6 h of LYS depletion, no significant differences in mood and memory compared to placebo were found. We conclude that the effects of TRP depletion on mood and memory are specific for the depletion of TRP and are not caused by the depletion of an amino acid per se. This supports the hypothesis that TRP depletion affects brain serotonin metabolism and not only brain protein metabolism in general.

Nutrients, age and cognitive function

Many nutrients or indices of nutritional status are associated with cognitive functioning, although the size of the effects on cognitive performance may be small. Results from recent studies, however, seem consistently to indicate that supplementation with beta-carotene and alpha-tocopherol, substances that promote antioxidant vitamins A and E, respectively, can be beneficial to cognitive function in elderly people. Folate rather than vitamin B12 appears to be associated with cognitive functioning. Furthermore the daily intake of ginkgo biloba extract can enhance cognitive performance and has been proved to delay cognitive decline in dementia. A proper dietary composition with regard to the ratio of carbohydrates to proteins, as well as the inclusion of sufficient micronutrients, seems to be favourable in the maintenance of cognitive function in the elderly. Glucose can enhance cognitive function, but a rapid decline of glucose levels may impair cognitive function or may induce feelings of lack of energy. Low doses of caffeine may also enhance cognitive function, although most studies on caffeine and cognition, as with studies on glucose and cognition, have not been carried out in elderly individuals. The effects of nutritional supplements are modest but do not seem to be very different from those of medicinal or investigational cognition-enhancing or anti-dementia drugs.

Cognition enhancers in age-related cognitive decline

A review of recently published studies on the effect of cognition enhancers in non-demented human study participants is presented. The heterogeneity of the therapeutic target, age-associated cognitive decline, can be improved by separately treating groups in whom age-extrinsic factors may underlie cognitive pathology. Standardisation of cognitive assessments is necessary, since many different tests are applied to answer the same question. Modelling cognitive dysfunction, either by pharmacological or nonpharmacological means, in humans is highly recommended since it allows hypotheses to be tested in a clearly operationalised way. Predictive validity of the currently applied models for the clinical situation remains a problem, however. The scopolamine (hyoscine) model has, to a reasonable extent, predictive validity for the cholinergic agents. The results of 67 single-dose studies and 30 multiple-dose studies are summarised. All single-dose studies and 14 multiple-dose studies were carried out in young or elderly human volunteers. In 45 of 81 volunteer studies, models of cognitive dysfunction were employed. The scopolamine model was the most used (n = 21); the other studies induced cognitive dysfunction by means of benzodiazepines (8), hypoxia (7), alcohol (5) and sleep-deprivation (4). The remaining 16 multiple-dose studies were clinical trials of a duration varying between 2 weeks and 1 year (average duration was 14 weeks). In these trials, the effects of cognition enhancers were assessed in elderly people in whom impairment of memory, psychomotor performance or cognitive function was determined. These included age-associated memory impairment (AAMI) and age-associated cognitive decline (AACD). There were many studies in which the cognition enhancing properties of substances in humans were reliably demonstrated. The cognition enhancing properties of substances that are widely used, such as caffeine, nicotine and vitamins, may already be active against AACD. New developments such as serotonin (5-hydroxytryptamine3; 5-HT3) antagonists and N-methyl-D-aspartate (NMDA) antagonists have provided marginal and disappointing results in AAMI. There is no cognition enhancer that has reliably and repeatedly been demonstrated to be efficacious for the treatment of AACD. However, this situation may change as the selectivity, specificity and adverse effect profiles of substances that are being developed for the treatment of AD may be expected to be improved in the future.

Cognitive impairment in elderly people. Predisposing factors and implications for experimental drug studies

The consequences for cognitive functioning of normal aging, depression and dementia are well known. However, the borderline between normal and pathological cognitive aging is less well understood. Recently, it has been found that it is important to differentiate between 'successful', 'usual' and pathological cognitive aging. This article reviews existing views on this borderline. Recently, it has been found that health-related factors, or biological life events, may determine the rate of cognitive aging. Various different, but similar, diagnostic descriptions of age-related cognitive dysfunction exist simultaneously: benign senescent forgetfulness, malignant senescent forgetfulness, age-associated memory impairment, age-consistent memory impairment, late-life forgetfulness, mild cognitive changes (subthreshold) and cognitive impairment disorders are some examples of different diagnostic categories. There are also various diagnostic tools to obtain these experimental diagnoses; for example, the Global Deterioration Scale, the Clinical Dementia Rating Scale and the Cambridge Mental Disorders of the Elderly Examination. A diagnosis is considered important for the early detection of dementia. Pharmacological treatments are still in the experimental stage. Improvement of cognitive function has particularly been studied in clinical trials with groups of patients with Alzheimer's disease as well as patient groups with age-associated memory impairment. Future strategies may orient more towards treating symptoms of cognitive dysfunction, probably also on the basis of diagnosis of health-related factors, in age-related cognitive decline and depression.

Diode laser spectrometer for monitoring up to five atmospheric trace gases in unattended operation

An automated diode laser spectrometer for recording concentrations of trace gases is described. It has been tested for unattended operation in the laboratory and at an atmospheric surveillance station for several months. The sensitivities reached are, e.g., 50 ppt for NO(2) and 300 ppt for NO. In an optical path length of 100 m the lowest extinction measured in unattended operation is ~1.5 x 10(-5) for a measuring time of ~60 s. Recordings of trace gases are shown for urban and rural atmospheric conditions.