Dopamine-antagonistic, anticholinergic, and GABAergic effects on declarative and procedural memory functions

Iron deficiency negatively affects behavioral measures of learning, indirect neural measures of dopamine, and neural efficiency

Iron deficiency (ID) is the most prevalent nutrient deficiency in the world, with a growing literature documenting the negative effects of ID on perception, attention, and memory. Animal models of ID suggest that dysregulation of dopamine is responsible for the deficits in memory. However, evidence that ID affects dopamine in humans is extremely limited. We report the results of a study involving college-aged women with and without ID learning two different category structures - a rule-based and an information-integration structure - selected based on the putative differential role of dopamine in learning these two structures. ID non-anemic (IDNA) and iron-sufficient (IS) women completed 1200 learning trials for each structure. EEG was collected to assess the effects of ID on features affected by dopaminergic state: error-related negativity (ERN) and positivity (Pe), feedback-related negativity (FRN), and task-related blink rate. In addition, we examined the EEG data for dynamics distinguishing IDNA from IS women, including a measure of neural efficiency. Both groups of women were able to learn both structures. However, IDNA women were initially slower and less accurate than IS women, specifically for the rule-based structure. There were large and persistent group differences in brain dynamics and neural efficiency measures. The results are discussed with respect to the selective impact of ID on initial rule-based learning and the persistent effect of ID on dopamine signaling and energetic efficiency.

Differential effects of clonazepam on declarative memory formation and face recognition

Benzodiazepines are commonly used drugs to treat anxiety in crime witnesses. These increase GABA inhibitory effects, which impairs aversive memory encoding and consolidation. Eyewitness memory is essential in justice. However, memory is malleable leading to false memories that could cause a selection of an innocent in a lineup. Here, we studied whether a low dose of Clonazepam impairs memory encoding as well as consolidation of faces and narrative of the event. We performed two experiments using a double-blind and between subject design (N = 216). Day 1: subjects watched a crime video and received Clonazepam 0.25 mg (CLZ group) or placebo (PLC group) before (Exp. 1) or after the video (Exp. 2) to assess the effect on encoding and consolidation. One week later, the memory was assessed using a present and absent target lineup and asking for a free recall. Regarding encoding, we found that in the CLZ group memory was impaired in the free recall task, while no differences were found for recognition memory. Regarding consolidation, we did not observe memory measures that were affected by this dose of benzodiazepines. The results suggest that while some aspects of eyewitness memory could be modulated even with low doses of benzodiazepine, others could not be affected. More studies should be performed with higher doses of CLZ similar to those administered in real life. These results are relevant in the judicial field to assess the reliability of the eyewitness elections under the effects of this drug.

Effects of Ketamine and Midazolam on Simultaneous EEG/fMRI Data During Working Memory Processes

Reliable measures of cognitive brain activity from functional neuroimaging techniques may provide early indications of efficacy in clinical trials. Functional magnetic resonance imaging and electroencephalography provide complementary spatiotemporal information and simultaneous recording of these two modalities can remove inter-session drug response and environment variability. We sought to assess the effects of ketamine and midazolam on simultaneous electrophysiological and hemodynamic recordings during working memory (WM) processes. Thirty participants were included in a placebo-controlled, three-way crossover design with ketamine and midazolam. Compared to placebo, ketamine administration attenuated theta power increases and alpha power decreases and midazolam attenuated low beta band decreases to increasing WM load. Additionally, ketamine caused larger blood-oxygen-dependent (BOLD) signal increases in the supplementary motor area and angular gyrus, and weaker deactivations of the default mode network (DMN), whereas no difference was found between midazolam and placebo. Ketamine administration caused positive temporal correlations between frontal-midline theta (fm-theta) power and the BOLD signal to disappear and attenuated negative correlations. However, the relationship between fm-theta and the BOLD signal from DMN areas was maintained in some participants during ketamine administration, as increasing theta strength was associated with stronger BOLD signal reductions in these areas. The presence of, and ability to manipulate, both positive and negative associations between the BOLD signal and fm-theta suggest the presence of multiple fm-theta components involved in WM processes, with ketamine administration disrupting one or more of these theta-linked WM strategies.

The effect of sleep medications on prospective and retrospective memory: a population-based study

Sleep medications, especially benzodiazepines, are known to cause motor and cognitive impairments as side-effects from their use. However, an evaluation of the effects of sleep medications in general on prospective and retrospective memory remains to be seen. Thus, the effects of the different types of sleep medicines were assessed using the total score and the 8 subscales of the Prospective and Retrospective Memory Questionnaire (PRMQ) in a representative sample from the Municipality of São Paulo. The effects of each type of medication on these same parameters were evaluated afterwards. Each analysis was performed controlling for different covariates to observe their degree of interference on the observed results. Impairment due to use of sleep aid medication was observed in 6 of the 8 subscales, as well in the overall score of the PRMQ when compared to non-users. Prospective subscales were particularly affected, even when controlling for highly interfering covariates such as depression and anxiety, and objective sleep variables related to sleep architecture and wakefulness in the night. Few effects were detected between the various types of medication even when controlling for covariates, suggesting that a sample with higher power is necessary to conduct a more detailed analysis. Using pharmacological aids to improve sleep may impair prospective and (to some extent) retrospective memory. Therefore, the relationship between sleep impairment, memory deficits and medication use must be considered by physicians.

The Relationship Between Polygenic Risk Scores and Cognition in Schizophrenia

BACKGROUND

Cognitive impairment is a clinically important feature of schizophrenia. Polygenic risk score (PRS) methods have demonstrated genetic overlap between schizophrenia, bipolar disorder (BD), major depressive disorder (MDD), educational attainment (EA), and IQ, but very few studies have examined associations between these PRS and cognitive phenotypes within schizophrenia cases.

METHODS

We combined genetic and cognitive data in 3034 schizophrenia cases from 11 samples using the general intelligence factor g as the primary measure of cognition. We used linear regression to examine the association between cognition and PRS for EA, IQ, schizophrenia, BD, and MDD. The results were then meta-analyzed across all samples. A genome-wide association studies (GWAS) of cognition was conducted in schizophrenia cases.

RESULTS

PRS for both population IQ (P = 4.39 × 10-28) and EA (P = 1.27 × 10-26) were positively correlated with cognition in those with schizophrenia. In contrast, there was no association between cognition in schizophrenia cases and PRS for schizophrenia (P = .39), BD (P = .51), or MDD (P = .49). No individual variant approached genome-wide significance in the GWAS.

CONCLUSIONS

Cognition in schizophrenia cases is more strongly associated with PRS that index cognitive traits in the general population than PRS for neuropsychiatric disorders. This suggests the mechanisms of cognitive variation within schizophrenia are at least partly independent from those that predispose to schizophrenia diagnosis itself. Our findings indicate that this cognitive variation arises at least in part due to genetic factors shared with cognitive performance in populations and is not solely due to illness or treatment-related factors, although our findings are consistent with important contributions from these factors.

Dopamine is a double-edged sword: dopaminergic modulation enhances memory retrieval performance but impairs metacognition

While memory encoding and consolidation processes have been linked with dopaminergic signaling for a long time, the role of dopamine in episodic memory retrieval remained mostly unexplored. Based on previous observations of striatal activity during memory retrieval, we used pharmacological functional magnetic resonance imaging to investigate the effects of dopamine on retrieval performance and metacognitive memory confidence in healthy humans. Dopaminergic modulation by the D2 antagonist haloperidol administered acutely during the retrieval phase improved recognition accuracy of previously learned pictures significantly and was associated with increased activity in the substantia nigra/ventral tegmental area, locus coeruleus, hippocampus, and amygdala during retrieval. In contrast, confidence for new decisions was impaired by unsystematically increased activity of the striatum across confidence levels and restricted range of responsiveness in frontostriatal networks under haloperidol. These findings offer new insights into the mechanisms underlying memory retrieval and metacognition and provide a broader perspective on the presence of memory problems in dopamine-related diseases and the treatment of memory disorders.

Short-term and long-term effects of diazepam on the memory for discrimination and generalization of scopolamine

Benzodiazepines are among the most widely prescribed and misused psychopharmaceutical drugs. Although they are well-tolerated, they are also capable of producing amnestic effects similar to those observed after pharmacological or organic cholinergic dysfunction. To date, the effect of benzodiazepine diazepam on the memory for discrimination of anticholinergic drugs has not been reported. The aim of the present study was to analyze the immediate and long-term effects of diazepam on a drug discrimination task with scopolamine. Male Wistar rats were trained to discriminate between scopolamine and saline administration using a two-lever discrimination task. Once discrimination was acquired, the subjects were divided into three independent groups, (1) control, (2) diazepam, and (3) diazepam chronic administration (10 days). Subsequently, generalization curves for scopolamine were obtained. Additionally, the diazepam and control groups were revaluated after 90 days without having been given any other treatment. The results showed that diazepam produced a significant reduction in the generalization gradient for scopolamine, indicating an impairment of discrimination. The negative effect of diazepam persisted even 90 days after drug had been administered. Meanwhile, the previous administration of diazepam for 10 days totally abated the generalization curve and the general performance of the subjects. The results suggest that diazepam affects memory for the stimulus discrimination of anticholinergic drugs and does so persistently, which could be an important consideration during the treatment of amnesic patients with benzodiazepines.

Haloperidol increases false recognition memory of thematically related pictures in healthy volunteers

Dopamine can modulate long-term episodic memory. Its potential role on the generation of false memories, however, is less well known. In a randomized, double-blind, placebo-controlled experiment, 24 young healthy volunteers ingested a 4-mg oral dose of haloperidol, a dopamine D₂ -receptor antagonist, or placebo, before taking part in a recognition memory task. Haloperidol was active during both study and test phases of the experiment. Participants in the haloperidol group produced more false recognition responses than those in the placebo group, despite similar levels of correct recognition. These findings show that dopamine blockade in healthy volunteers can specifically increase false recognition memory.

Effects of Sulpiride on True and False Memories of Thematically Related Pictures and Associated Words in Healthy Volunteers

Episodic memory, working memory, emotional memory, and attention are subject to dopaminergic modulation. However, the potential role of dopamine on the generation of false memories is unknown. This study defined the role of the dopamine D2 receptor on true and false recognition memories. Twenty-four young, healthy volunteers ingested a single dose of placebo or 400 mg oral sulpiride, a dopamine D2-receptor antagonist, just before starting the recognition memory task in a randomized, double-blind, and placebo-controlled trial. The sulpiride group presented more false recognitions during visual and verbal processing than the placebo group, although both groups had the same indices of true memory. These findings demonstrate that dopamine D2 receptors blockade in healthy volunteers can specifically increase the rate of false recognitions. The findings fit well the two-process view of causes of false memories, the activation/monitoring failures model.

Memory for reward location is enhanced even though acetylcholine efflux within the amygdala is impaired in rats with damage to the diencephalon produced by thiamine deficiency

A rodent model of diencephalic amnesia produced by thiamine deficiency (pyrithiamine-induced thiamine deficiency [PTD]) was implemented to assess both changes in behavior and acetylcholine (ACh) efflux in the amygdala across four training sessions of a delayed alternation task. Two versions of the delayed alternation task were used. In one version, when a correct alternation was made a unique reward was paired with each spatial location ([left arm-chocolate milk] or [right arm-rat chow]). This paradigm is called the differential outcomes procedure (DOP). In the second version of the task, correct delayed alternation resulted in the same rewards but randomized across location (Nondifferential Outcomes Procedure [NOP]). The PTD rats were impaired on the first session of delayed alternation testing. However, both control and PTD rats using the DOP performed significantly better on delayed alternation than rats trained with the NOP.This effect was driven primarily by the PTD rats in the DOP condition outperforming all other groups on sessions 2-4. Although ACh efflux in the amygdala increased during delayed alternation testing in all groups, the NOP-trained rats had a greater rise in training-related ACh release in the post-training period. This suggests that increased amygdalar cholinergic activation is more critical for processing spatial information than episodic reward information. These data correspond with the idea that cholinergic activation of the amygdala promotes processing in other neural systems.

Memory in humans is unaffected by central H1-antagonism, while objectively and subjectively measured sedation is increased

Animal literature suggests an important role for histamine in memory. In humans, this hypothesis has been scarcely tested and results from studies that have addressed this are conflicting. Second, impaired memory performance may be secondary to sedation. This study aimed to determine whether a centrally active antihistamine impairs memory performance and to dissociate such effects from sedation. Eighteen healthy volunteers received single oral doses of dexchlorpheniramine 4 mg, lorazepam 1mg and placebo in a 3-way, double blind, crossover designed study. The active control lorazepam impaired episodic- and working memory performance and increased sedation, while dexchlorpheniramine only increased sedation.

Episodic-like and procedural memory impairments in histamine H1 Receptor knockout mice coincide with changes in acetylcholine esterase activity in the hippocampus and dopamine turnover in the cerebellum

We investigated episodic-like (ELM) and procedural memory (PM) in histamine H1 receptor knockout (H1R-KO) mice. In order to relate possible behavioral deficits to neurobiological changes, we examined H1R-KO and wild-type (WT) mice in terms of acetylcholine esterase (AChE) activity in subregions of the hippocampus and AChE and tyrosine hydroxylase (TH) expression in the striatum. Furthermore, we analyzed acetylcholine (ACh), 5-HT and dopamine (DA) levels, including metabolites, in the cerebellum of H1R-KO and WT mice. The homozygous H1R-KO mice showed impaired ELM as compared with the heterozygous H1R-KO and WT mice. The performance of homozygous H1R-KO mice in the ELM task was primarily driven by familiarity-based memory processes. While the homozygous H1R-KO mice performed similar to the heterozygous H1R-KO and WT mice during the acquisition of a PM, as measured with an accelerating rotarod, after a retention interval of 7 days their performance was impaired relative to the heterozygous H1R-KO and WT mice. These findings suggest that, both, ELM and long-term PM are impaired in the homozygous H1R-KO mice. Neurochemical assays revealed that the H1R-KO mice had significantly lower levels of AChE activity in the dentate gyrus (DG) and CA1 subregions of the hippocampus as compared with the WT mice. The homozygous H1R-KO mice also displayed significantly reduced dihydroxyphenylacetic acid (DOPAC) levels and a reduced DOPAC/DA ratio in the cerebellum, suggesting that the DA turnover in the cerebellum is decelerated in homozygous H1R-KO mice. In conclusion, homozygous H1R-KO mice display severe long-term memory deficits in, both, ELM and PM, which coincide with changes in AChE activity in the hippocampus as well as DA turnover in the cerebellum. The importance of these findings for Alzheimer's (AD) and Parkinson's disease (PD) is discussed.

Age-related slowing of movement as basal ganglia dysfunction

Attributions of age-related deficits in motor function to structural changes are compromised once the elderly exhibit lower error rates. This is because performance decrements observed in older adults are attributed to inferred strategic preferences for accuracy over speed. To understand genuine age differences in performance, we argue in the following theoretical paper that research needs to resolve methodological shortcomings and account for them within theoretical models of aging. Accounts of aging need to directly manipulate or control strategic differences in performance while assessing structural deficits. When this is done, age-related changes in motor control resemble the intermittencies of control seen in basal ganglia disorders. Given homologous circuitry in the basal ganglia, such observations could generalize to age-related changes in cognitive and emotional processes.

Histamine H1-receptor blockade in humans affects psychomotor performance but not memory

Results from recent animal studies suggest an important role for histamine in memory functioning. Histaminergic drugs might prove beneficial for people suffering from memory impairment. To determine if histamine is involved in memory functioning this study evaluates the effects of histaminergic dysfunction on memory performance by administrating a H1-antagonist to humans. The study was conducted according to a 4-way, double-blind, crossover design in 20 healthy female volunteers, aged 18-45 years. On each test day subjects completed three test sessions: before and around 2 and 4 h after administration of single oral doses of dexchlorpheniramine 2 mg or 4 mg, scopolamine 1 mg or placebo. Drug effects were assessed using tests of memory, psychomotor and attention performance, and subjective alertness. Results showed that dexchlorpheniramine impaired performance in tests of spatial learning, reaction time, tracking and divided attention but showed no effects on working memory, visual memory, word learning or memory scanning. Scopolamine induced a similar pattern of effects. In addition, both drugs decreased subjective alertness. In conclusion results show that dexchlorpheniramine and scopolamine clearly impaired performance on psychomotor and attention tasks but do not suggest a specific role of the histaminergic system in learning and memory in humans.

Apomorphine effects on episodic memory in young healthy volunteers

RATIONALE

Dopamine (DA) modulates working memory. However, the relation between DA systems and episodic (declarative) memory is less established. Frontal lobe DA function may be involved. We were interested in assessing whether apomorphine (Apo), a drug used extensively in clinical research as a probe of DA function, has an effect on episodic memory test performance in healthy volunteers.

OBJECTIVE

To investigate the effect of a presynaptic dose of Apo on episodic memory tests and on other tests thought to be sensitive to frontal lobe functions.

METHODS

Twenty healthy subjects were treated with Apo HCl (5 microg/kg sc) or placebo (10 subjects/group) in a randomized, double blind parallel group design and performance on a battery of cognitive tests was assessed.

RESULTS

Apomorphine significantly impaired performance on tests of source recognition (d.f.=19, p=0.05) and item recognition memory (d.f.=19, p<0.05), and memory interference (d.f.=19, p<0.010). No significant change was found on other tests (Go/no-Go Test, Categorized Words, Stroop, Trail Making Test, and verbal fluency).

CONCLUSION

Findings in this small sample of subjects suggest that dopaminergic transmission affects episodic memory functions.

Acute effects of the ampakine farampator on memory and information processing in healthy elderly volunteers

Ampakines act as positive allosteric modulators of AMPA-type glutamate receptors and facilitate hippocampal long-term potentiation (LTP), a mechanism associated with memory storage and consolidation. The present study investigated the acute effects of farampator, 1-(benzofurazan-5-ylcarbonyl) piperidine, on memory and information processes in healthy elderly volunteers. A double-blind, placebo-controlled, randomized, cross-over study was performed in 16 healthy, elderly volunteers (eight male, eight female; mean age 66.1, SD 4.5 years). All subjects received farampator (500 mg) and placebo. Testing took place 1 h after drug intake, which was around Tmax for farampator. Subjects performed tasks assessing episodic memory (wordlist learning and picture memory), working and short-term memory (N-back, symbol recall) and motor learning (maze task, pursuit rotor). Information processing was assessed with a tangled lines task, the symbol digit substitution test (SDST) and the continuous trail making test (CTMT). Farampator (500 mg) unequivocally improved short-term memory but appeared to impair episodic memory. Furthermore, it tended to decrease the number of switching errors in the CTMT. Drug-induced side effects (SEs) included headache, somnolence and nausea. Subjects with SEs had significantly higher plasma levels of farampator than subjects without SEs. Additional analyses revealed that in the farampator condition the group without SEs showed a significantly superior memory performance relative to the group with SEs. The positive results on short-term memory and the favorable trends in the trail making test (CTMT) are interesting in view of the development of ampakines in the treatment of Alzheimer's disease and schizophrenia.

Dissociation of cholinergic function in spatial and procedural learning in rats

The cholinergic system has long been known for its role in acquisition and retention of new information. Scopolamine, a muscarinic acetylcholine receptor antagonist impairs multiple memory systems, and this has promoted the notion that drug-induced side effects are responsible for diminished task execution rather than selective impairments on learning and memory per se. Here, we revisit this issue with the aim to dissociate the effects of scopolamine (0.2-1.0 mg/kg) on spatial learning in the water maze. Experiments 1 and 2 showed that acquisition of a reference memory paradigm with constant platform location is compromised by scopolamine independent of whether the animals are pre-trained or not. Deficits were paralleled by drug induced side-effects on sensorimotor parameters. Experiment 3 explored the role of muscarinic receptors in acquisition of an episodic-like spatial delayed matching to position (DMTP) protocol, and scopolamine still caused a learning deficit and side-effects on sensorimotor performance. Rats extensively pre-trained in the DMTP protocol with 30 s and 1 h delays over several months in experiment 4 and tested in a within-subject design under saline and scopolamine had no sensorimotor deficits, but spatial working memory remained compromised. Experiment 5 used the rising Atlantis platform in the DMTP paradigm. Intricate analysis of the amount of dwelling and its location revealed a clear deficit in spatial working memory induced by scopolamine, but there was no effect on sensorimotor or procedural task demands. Apart from the well-known contribution to sensorimotor and procedural learning, our findings provide compelling evidence for an important role of muscarinic acetylcholine receptor signaling in spatial episodic-like memory.

Psychomotor and memory effects of haloperidol, olanzapine, and paroxetine in healthy subjects after short-term administration

RATIONALE

Impaired psychomotor function has been shown to be associated with clinical and functional outcome in schizophrenia. However, few studies have investigated the short-term effects of antipsychotics on the cognitive and psychomotor functions of this patient group. Because many confounding factors tend to influence the test results in patient research, this study investigates the drugs' effects in healthy volunteers.

OBJECTIVES

The short-term effects of haloperidol (2.5 mg), olanzapine (10 mg), and paroxetine (20 mg) on psychomotor function in 15 healthy volunteers are compared with placebo and each other.

METHODS

In a crossover design, the subjects completed a battery of psychomotor tasks assessing psychomotor speed, sensorimotor accuracy, visuospatial monitoring, and speed of information processing. In addition, peak velocity of saccadic eye movements and subscales of the visual analog scales were analyzed as the objective and subjective measures for sedation, respectively. Finally, the verbal memory test was used to assess the drugs' effects on memory.

RESULTS

Apart from affecting the pursuit task where visuospatial monitoring, sensorimotor speed, and sensorimotor accuracy are measured simultaneously, haloperidol has been proven to be not associated with sedative nor with impairing effects on psychomotor function or verbal memory. In contrast, olanzapine had significant sedative effects. Moreover, the subjects displayed a significant impairment on all measures of psychomotor function and verbal memory, which was not attributable to the drug's sedative effects. After administration of paroxetine, no effects were found, with the exception of a single improvement in eye movement velocity.

CONCLUSIONS

Short-term administration of olanzapine, and not of haloperidol, impedes several aspects of psychomotor function and verbal memory in healthy volunteers.

Long-term cognitive impact of anticholinergic medications in older adults

OBJECTIVE

The objective of this study was to determine whether chronic use of medications with anticholinergic (AC) properties impact older adults' cognitive functioning.

METHODS

Six years of cognitive test data from two groups of older adults (AC and control) were examined retrospectively (N = 592).

RESULTS

Declines over time were found for the AC group on parts A and B of the Trail Making Test.

CONCLUSION

Physicians prescribing ACs to older adult patients should be aware of their potential effects on psychomotor speed and executive functioning. These cognitive effects may lead to impairments in daily functioning resulting in the need to reevaluate patient medications.

Midazolam amnesia and short-term/working memory processes

We examined whether midazolam impairs short-term/working memory processes. We hypothesize that prior dissociations in midazolam's effects on short-term/working memory tasks and episodic memory tasks arise because midazolam has a larger effect on episodic memory processes than on short-term/working memory processes. To examine these issues, .03 mg/kg of participant's bodyweight of midazolam was administered in a double-blind placebo-controlled within-participant design. Performance on the digit span and category generation/recall tasks was examined. The results of Experiment 1 demonstrated that: (1) midazolam impaired performance on the digit span task; (2) midazolam did not impair performance on the category generation task; (3) midazolam impaired performance on the category recall task; and (4) midazolam's effect on category recall was four times as large as its effect on digit span. The results of Experiment 2 demonstrated that midazolam did not impair digit span performance when the digit span task was administered at a later time. These results suggest that midazolam can impair short-term/working memory processes, but these effects are substantially smaller than midazolam's effect on episodic memory processes. Moreover, they demonstrate that conscious awareness of materials during study is not sufficient to produce episodic memory.

The cognitive-affective neuroscience of the unconscious

There is an ongoing debate about how best to conceptualize the unconscious. Early psychodynamic views employed theories influenced by physics to explain clinical material, while subsequent cognitivist views relied on computational models of the mind to explain laboratory data. More recently, advances in cognitive-affective neuroscience have provided new insights into the workings of unconscious cognition and affect. We briefly review some of this recent work and its clinical implications.

Sedation and memory: studies with a histamine H-1 receptor antagonist

The influence of sedation on the effect of an H-1 receptor antagonist on various cognitive functions, including memory, were evaluated. Diphenhydramine (50, 75 and 100 mg) and lorazepam (0.5 and 1.5 mg) were given on single occasions to 12 healthy volunteers (six males, six females) aged 20-33 (mean 23.4) years. Subjective assessments of sedation, sleep latencies, digit symbol substitution, choice reaction time, sustained attention and memory recall were studied 1.0 h before and 0.5, 2.0 and 3.5 h after drug ingestion. The study was double blind, placebo controlled and with a crossover design. With all doses of diphenhydramine there was subjective sedation, reduced sleep latencies and impairments in performance on the digit symbol substitution, choice reaction time and sustained attention tasks. No effects were observed with 0.5 mg lorazepam. With 1.5 mg lorazepam there was subjective sedation, fewer digit symbol substitutions, slowed choice reaction time, impaired attention and memory, but no effect on sleep latencies. Contrast analysis of data measured at all time points showed that although there was no difference in the effect of diphenhydramine (100 mg) and lorazepam (1.5 mg) on those tasks without a memory component, response times were slower with lorazepam on those tasks with a memory component. However, both 100 mg diphenhydramine and 1.5 mg lorazepam impaired prompted recall measured at 2 h post-ingestion only. It is considered that impaired memory is not necessarily associated with sedation, and that impairment of memory with drugs that lead to sedation may be effected through neuronal systems independent of those that affect arousal.

Modulation of memory and visuospatial processes by biperiden and rivastigmine in elderly healthy subjects

RATIONALE

The central cholinergic system is implicated in cognitive functioning. The dysfunction of this system is expressed in many diseases like Alzheimer's disease, dementia of Lewy body, Parkinson's disease and vascular dementia. In recent animal studies, it was found that selective cholinergic modulation affects visuospatial processes even more than memory function.

OBJECTIVE

In the current study, we tried to replicate those findings. In order to investigate the acute effects of cholinergic drugs on memory and visuospatial functions, a selective anticholinergic drug, biperiden, was compared to a selective acetylcholinesterase-inhibiting drug, rivastigmine, in healthy elderly subjects.

METHODS

A double-blind, placebo-controlled, randomised, cross-over study was performed in 16 healthy, elderly volunteers (eight men, eight women; mean age 66.1, SD 4.46 years). All subjects received biperiden (2 mg), rivastigmine (3 mg) and placebo with an interval of 7 days between them. Testing took place 1 h after drug intake (which was around Tmax for both drugs). Subjects were presented with tests for episodic memory (wordlist and picture memory), working memory tasks (N-back, symbol recall) and motor learning (maze task, pursuit rotor). Visuospatial abilities were assessed by tests with high visual scanning components (tangled lines and Symbol Digit Substitution Test).

RESULTS

Episodic memory was impaired by biperiden. Rivastigmine impaired recognition parts of the episodic memory performance. Working memory was non-significantly impaired by biperiden and not affected by rivastigmine. Motor learning as well as visuospatial processes were impaired by biperiden and improved by rivastigmine.

CONCLUSIONS

These results implicate acetylcholine as a modulator not only of memory but also of visuospatial abilities.

Modifications in avoidance reactions of mice, on a second exposure to the hot plate, resist to various amnesia-inducing treatments

The avoidance responses of mice exposed to the hot plate (55 degrees C) were found to be modified when tested a second time. In fact, when forepaws licking was no longer observed, the rearing was clearly anticipated (7 s instead of 15 s) as well as jumping (24 s instead of 55 s). These modifications of avoidance strategies as well as their latencies were still observed even 24 days after the first exposure. Avoidance responses were prevented by morphine or haloperidol injected prior to the first exposure, but not with scopolamine or diazepam. These modifications were not affected in mice injected with morphine or submitted to either a supramaximal electroshock or to ether anesthesia delivered immediately after the first hot plate exposure. Among the various known types of memory, these modifications could be linked to procedural memory.

Effects of repeated administration of Uncaria hooks on the acquisition and central neuronal activities in ethanol-treated mice

The effects of the repeated administration of Uncaria hooks were examined on the impaired memory acquisition and the level of neurotransmitters in the cortex, hippocampus and striatum in ethanol-treated mice, in comparison with those with L-deprenyl and N-methyl-D-glucamine as positive controls. Ethanol-induced amnesia was significantly ameliorated by repeated administration of methanol extract and alkaloid fraction of Uncaria hooks, similar to in the positive controls. Treatment with methanol extract and alkaloid fraction of Uncaria hooks significantly reduced the ethanol-induced increase of dopamine in the hippocampus. The 5-hydroxytryptamine and glutamic acid neuronal activities were significantly changed by Uncaria hooks, but not by L-deprenyl, in all examined brain tissues of ethanol-treated mice. On the other hand, the GABAergic and cholinergic neuronal activities did not show any significant changes by Uncaria hooks in any of the examined brain tissues of the ethanol-treated animals. The results suggest that the extracts of Uncaria hooks exert a beneficial effect on ethanol-induced memory impairment, and that the central 5-hydroxytryptaminergic and glutaminergic neuronal systems play an important role in the memory acquisition of Uncaria hooks.

Contributions of memory circuits to language: the declarative/procedural model

The structure of the brain and the nature of evolution suggest that, despite its uniqueness, language likely depends on brain systems that also subserve other functions. The declarative/procedural (DP) model claims that the mental lexicon of memorized word-specific knowledge depends on the largely temporal-lobe substrates of declarative memory, which underlies the storage and use of knowledge of facts and events. The mental grammar, which subserves the rule-governed combination of lexical items into complex representations, depends on a distinct neural system. This system, which is composed of a network of specific frontal, basal-ganglia, parietal and cerebellar structures, underlies procedural memory, which supports the learning and execution of motor and cognitive skills, especially those involving sequences. The functions of the two brain systems, together with their anatomical, physiological and biochemical substrates, lead to specific claims and predictions regarding their roles in language. These predictions are compared with those of other neurocognitive models of language. Empirical evidence is presented from neuroimaging studies of normal language processing, and from developmental and adult-onset disorders. It is argued that this evidence supports the DP model. It is additionally proposed that "language" disorders, such as specific language impairment and non-fluent and fluent aphasia, may be profitably viewed as impairments primarily affecting one or the other brain system. Overall, the data suggest a new neurocognitive framework for the study of lexicon and grammar.

Mechanisms influencing acquisition and recall of motor memories

An internal model of the dynamics of a tool or an object is part of the motor memory acquired when learning to use the tool or to manipulate the object. Changes in synaptic efficacy may underlie acquisition and storage of memories. Here we studied the effect of pharmacological agents that interfere with synaptic plasticity on acquisition of new motor memories and on recall of a previously learned internal model. Forty-nine subjects, divided into six groups, made reaching movements while holding a robotic arm that applied forces to the hand. On day 1, all subjects learned to move in force field A. On day 2, each group of subjects was tested on their ability to recall field A and their ability to learn a new internal model in field B. Four groups participated in the experiments of day 2 under the effects of lorazepam (LZ; a GABA type A receptor-positive allosteric modulator), dextromethorphan [DM; an N-methyl-D-aspartate (NMDA) receptor blocker], lamotrigine (LG, a drug that blocks voltage-gated Na(+) and Ca(2+) channel), or scopolamine (SP; muscarinic receptor antagonist). Two control groups were tested in a drug-free condition: one group that was not exposed to additional experimental protocols (NP) and another group was tested under ~24 h of sleep deprivation between completion of learning on day 1 and start of testing on day 2 (SD). Recall of field A was normal in all groups. Learning of field B was reduced by LZ and DM but not by SP, LG, SD or in the NP condition. These results suggest that a 24-h sleep-deprivation period may have little or no effect on consolidation of this motor memory and that NMDA receptor activation and GABAergic inhibition are mechanisms operating in the acquisition but not recall of new motor memories in humans.

Mechanisms of action of midazolam on expression of contextual fear in rats

BACKGROUND

Midazolam may suppress conditioned fear after an aversive event by disrupting the memory trace formed during conditioning, by altering the emotional part of the aversive event, or by the combination of both effects. The purpose of the present study was to determine whether affective-related processes contribute to the amnesic-like effects of midazolam on aversive events.

METHODS

The effects of acute administration of low doses of midazolam (0.37-3 mg kg(-1)) on fear conditioning (association between a neutral context and an aversive stimulus) and on innate anxiety in fearful surroundings were examined in rats. The effect of midazolam on the deleterious consequences of pre-exposure to the context (a non-aversive event) for subsequent fear conditioning was then compared with its effect on fear conditioning. The role of midazolam as an affective context was assessed by performing the testing phase under midazolam. Possible locomotor impairment or long-term effects of midazolam were controlled in additional experiments.

RESULTS

Midazolam reduced both contextual fear conditioning and spontaneous fear. The deleterious effect of midazolam on pre-exposure to the context was of the same magnitude as its effect on the acquisition phase of fear conditioning. The effects of midazolam on both pre-exposure to the context and fear conditioning were unchanged when rats received a second injection of midazolam before the retention phase.

CONCLUSIONS

Low doses of midazolam that do not impair locomotion suppress conditioned fear to the context by acting on memory processes rather than on affective or anxiolytic processes.

An investigation into the acute nootropic effects of Hypericum perforatum L. (St. John's Wort) in healthy human volunteers

Hypericum perforatum L. (St. John's Wort) is a complex herb that has been used for centuries for its putative medicinal properties, and has current therapeutic relevance as a treatment of mild to moderate depression. Recently, two studies in rodents have suggested that hypericum may also have memory-enhancing effects. It has a complex pharmacology, in that acute administration modulates numerous neurotransmitter systems that have previously been observed to either augment or impair a variety of memory processes in humans. This study aimed to examine whether acute administration of standardized hypericum extract could exert a nootropic effect in normal human subjects. The study employed a double-blind, crossover, repeated-measures design. Twelve healthy young subjects completed the Cognitive Drug Research (CDR) memory battery, following administration of placebo, 900 mg and 1800 mg hypericum (Blackmore's Hyperiforte). The findings suggested that hypericum does not have an acute nootropic effect in healthy humans at these doses. However, there was some evidence for an impairing effect on accuracy of numeric working memory and delayed picture recognition at the higher dose. This observed impairment could be due to a sensitivity of these specific tasks to modulation by neurotransmitters that have been noted to have memory-impairing effects (e.g. y-aminobutyric acid (GABA), serotonin).

Effects of pharmacologically induced changes in NMDA-receptor activity on long-term memory in humans

In a double-blind crossover design, either 30 mg of the noncompetitive NMDA-receptor antagonist memantine or a placebo was administered to 40 healthy male volunteers. Twenty line drawings of objects and 20 photographs of unfamiliar faces were presented on a computer screen. After a retention interval of 80 min, the participants' task was to select the original objects and faces from a set of 80 items. Results were analyzed applying a signal-detection-theory approach. Recognition performance for objects was significantly impaired under memantine as compared to placebo, whereas performance on face recognition was not affected. Findings support the notion of differential effects of NMDA-receptor antagonists on memory functions in humans.