Effects of lorazepam and diazepam on conscious and automatic memory processes

Anti-intrusion effect of Lorazepam: an experimental study

OBJECTIVE

Easy triggering of trauma-related episodic memory fragments caused by perceptual cues is tied to strong perceptual priming in the implicit memory system. And among benzodiazepines, only lorazepam has been consistently reported to have an atypical suppression effect on perceptual priming processes. The aim of this study was to investigate the effects of single doses of lorazepam, diazepam, and a placebo on intrusive memories after exposure to a distressing videotape and to explore whether the anti-intrusive effect of lorazepam is acquired as a result of the suppression of perceptual but not conceptual priming processes.

METHODS

Under prospective, randomized, and double-blind conditions, we compared the anti-intrusion effect of a single dose of lorazepam (n=22) with that of diazepam (n=22) and a placebo (n=21) in young healthy Korean college students following exposure to a traumatic videotape.

RESULTS

We present the first finding for an anti-intrusion effect of lorazepam. One day after the medication, lorazepam, rather than diazepam or the placebo, significantly reduced the extent of intrusion and data-driven processing of the traumatic information. There were no differences among the three conditions in state anxiety, depression, and an arousal scale throughout the experiment.

CONCLUSION

Results from this study suggest the possibility of lorazepam as a candidate anti-intrusion drug, as well as the cautious use of diazepam in the treatment of PTSD patients. The anti-intrusive effect of lorazepam is directly related to its atypical inhibitory effect on implicit perceptual priming processes. The present study provides support for the enhanced perceptual priming hypothesis of PTSD.

The neuropharmacology of implicit learning

Two decades of pharmacologic research on the human capacity to implicitly acquire knowledge as well as cognitive skills and procedures have yielded surprisingly few conclusive insights. We review the empirical literature of the neuropharmacology of implicit learning. We evaluate the findings in the context of relevant computational models related to neurotransmittors such as dopamine, serotonin, acetylcholine and noradrenalin. These include models for reinforcement learning, sequence production, and categorization. We conclude, based on the reviewed literature, that one can predict improved implicit acquisition by moderately elevated dopamine levels and impaired implicit acquisition by moderately decreased dopamine levels. These effects are most prominent in the dorsal striatum. This is supported by a range of behavioral tasks in the empirical literature. Similar predictions can be made for serotonin, although there is yet a lack of support in the literature for serotonin involvement in classical implicit learning tasks. There is currently a lack of evidence for a role of the noradrenergic and cholinergic systems in implicit and related forms of learning. GABA modulators, including benzodiazepines, seem to affect implicit learning in a complex manner and further research is needed. Finally, we identify allosteric AMPA receptors modulators as a potentially interesting target for future investigation of the neuropharmacology of procedural and implicit learning.

Benzodiazepines in epilepsy: pharmacology and pharmacokinetics

Benzodiazepines (BZDs) remain important agents in the management of epilepsy. They are drugs of first choice for status epilepticus and seizures associated with post-anoxic insult and are also frequently used in the treatment of febrile, acute repetitive and alcohol withdrawal seizures. Clinical advantages of these drugs include rapid onset of action, high efficacy rates and minimal toxicity. Benzodiazepines are used in a variety of clinical situations because they have a broad spectrum of clinical activity and can be administered via several routes. Potential shortcomings of BZDs include tolerance, withdrawal symptoms, adverse events, such as cognitive impairment and sedation, and drug interactions. Benzodiazepines differ in their pharmacologic effects and pharmacokinetic profiles, which dictate how the drugs are used. Among the approximately 35 BZDs available, a select few are used for the management of seizures and epilepsy: clobazam, clonazepam, clorazepate, diazepam, lorazepam and midazolam. Among these BZDs, clorazepate has a unique profile that includes a long half-life of its active metabolite and slow onset of tolerance. Additionally, the pharmacokinetic characteristics of clorazepate (particularly the sustained-release formulation) could theoretically help minimize adverse events. However, larger, controlled studies of clorazepate are needed to further examine its role in the treatment of patients with epilepsy.

Effects of lorazepam on visual perceptual abilities

OBJECTIVE

To evaluate the effects of an acute dose of the benzodiazepine (BZ) lorazepam in young healthy volunteers on five distinguishable visual perception abilities determined by previous factor-analytic studies.

METHODS

This was a double-blind, cross-over design study of acute oral doses of lorazepam (2 mg) and placebo in young healthy volunteers. We focused on a set of paper-and-pencil tests of visual perceptual abilities that load on five correlated but distinguishable factors (Spatial Visualization, Spatial Relations, Perceptual Speed, Closure Speed, and Closure Flexibility). Some other tests (DSST, immediate and delayed recall of prose; measures of subjective mood alterations) were used to control for the classic BZ-induced effects.

RESULTS

Lorazepam impaired performance in the DSST and delayed recall of prose, increased subjective sedation and impaired tasks of all abilities except Spatial Visualization and Closure Speed. Only impairment in Perceptual Speed (Identical Pictures task) and delayed recall of prose were not explained by sedation.

CONCLUSION

Acute administration of lorazepam, in a dose that impaired episodic memory, selectively affected different visual perceptual abilities before and after controlling for sedation. Central executive demands and sedation did not account for results, so impairment in the Identical Pictures task may be attributed to lorazepam's visual processing alterations.

MNESIS: towards the integration of current multisystem models of memory

After a brief description of the "diseases of memory" which have made the greatest contribution to theoretical developments in the past years, we turn our attention to the most important concepts to have arisen from the dissociations brought to light in different neuropsychological syndromes. This is followed by a critical review of the tasks currently used to assess each memory system. We then describe the monohierarchical model proposed by E. Tulving (Philos Trans R Soc Lond, B, Biol, Sci, 356:1505-1515, 2001), together with other recent concepts, notably Baddeley's model of working memory with its latest component, the episodic buffer. Lastly, we attempt to reconcile these models with several other theoretical propositions, which we have linked together in a macromodel--the Memory NEo-Structural Inter-Systemic model (MNESIS).

Lorazepam induces multiple disturbances in selective attention: attentional overload, decrement in target processing efficiency, and shifts in perceptual discrimination and response bias

There is a general consensus that benzodiazepines affect attentional processes, yet only few studies have tried to investigate these impairments in detail. The purpose of the present study was to investigate the effects of a single dose of Lorazepam on performance in a target cancellation task with important time constraints. We measured correct target detections and correct distractor rejections, misses and false positives. The results show that Lorazepam produces multiple kinds of shifts in performance, which suggests that it impairs multipLe processes: (a) the evolution of performance over time was not the same between the placebo and the Lorazepam groups, with the Lorazepam affecting performance quite early after the beginning of the test. This is suggestive of a depletion of attentional resources during sequential attentional processing; (b) Lorazepam affected differently target and distractor processing, with target detection being the most impaired; (c) misses were more frequent under Lorazepam than under placebo, but no such difference was observed as far as false positives were concerned. Signal detection analyses showed that Lorazepam (d) decreased perceptual discrimination, and (e) reliably increased response bias. Our results bring new insights on the multiple effects of Lorazepam on selective attention which, when combined, may have deleterious effects on human performance.

Segregating two inhibitory circuits in human motor cortex at the level of GABAA receptor subtypes: a TMS study

OBJECTIVE

To investigate if different interneuronal circuits in human motor cortex mediate inhibition through different subtypes of the gamma-aminobutyric acid A receptor (GABAAR).

METHODS

Two distinct forms of motor cortical inhibition were measured in 10 healthy subjects by established transcranial magnetic stimulation (TMS) protocols: short interval intracortical inhibition (SICI) and short latency afferent inhibition (SAI). Their modification by a single oral dose of three different positive GABAAR modulators (20 mg of diazepam, 2.5 mg of lorazepam and 10 mg of zolpidem) with different affinity profiles at the various alpha-subunit bearing subtypes of the GABAAR (diazepam: non-selective, lorazepam: unknown, zolpidem: 10-fold higher affinity to alpha1- than alpha2- or alpha3-subunit bearing GABAARs, no affinity to alpha5-subunits) was tested in a randomized crossover design. In addition, the sedative drug effects were recorded by a visual analogue scale.

RESULTS

Diazepam and lorazepam increased SICI, whereas zolpidem did not change SICI. In contrast, diazepam had no effect on SAI, whereas lorazepam and zolpidem decreased SAI. The sedative effects were not different between drugs.

CONCLUSIONS

The dissociating patterns of drug modification of SICI versus SAI strongly suggest that different GABAAR subtypes are involved in SICI and SAI.

SIGNIFICANCE

We provide evidence, for the first time, for a dissociation of effects of diazepam and zolpidem on SAI and confirm the previously reported differential effect of zolpidem and of diazepam and lorazepam on SICI. The differential effects of the three benzodiazepines on SAI and SICI suggest that neuronal circuits in human motor cortex that mediate inhibition through different GABAAR subtypes can be segregated by TMS.

Automatic and Controlled Uses of Memory in Alzheimer's Disease

This study used the process-dissociation procedure (Jacoby, 1991) to examine the contribution of automatic and controlled uses of memory to a stem completion task in 16 patients with Alzheimer's disease (AD) and a matched group of healthy elderly subjects (EC). In an inclusion task subjects attempted to use a studied word to complete three-letter word stems, in an exclusion task they were instructed to complete stems with unstudied words. Relative to patients with AD, EC subjects produced more target word completions under inclusion conditions, and less target word completions under exclusion conditions. The probability of the AD group using studied words to complete stems was invariant across inclusion and exclusion conditions. Estimates derived from the process-dissociation calculations, showed that the performance of the AD patients was mediated entirely by automatic uses of memory, whereas for EC subjects controlled and automatic processes codetermined task performance. Both estimates of controlled and to a lesser extent automatic uses of memory were greater for the EC than the AD subjects, indicating that the stem completion impairment in AD may not be entirely attributable to a deficiency in controlled memory processes but also due to reduced automatic processing.

Effects of the amnesic drug lorazepam on complete and partial information retrieval and monitoring accuracy

RATIONALE

In Koriat's accessibility model (Koriat, Psychol Rev, 100:609-639, 1993; Koriat, J Exp Psychol Gen, 124:311-333, 1995), when a person fails to recall a required target, he or she can nevertheless provide some partial information about the target. Moreover, individuals are able to provide feeling-of-knowing (FOK) judgments about the availability of the target in memory. The cues for the FOK evaluations reside in the products of the retrieval process itself. It was shown that the benzodiazepine lorazepam drug induces some impairment of memory.

OBJECTIVES

The effects of the amnesic benzodiazepine lorazepam on the total and partial recall of recently learned material and on FOK ratings were investigated in healthy volunteers.

METHODS

Twenty-eight healthy volunteers participated in the study: 14 of these received a capsule containing lorazepam (0.038 mg/kg) and 14 a placebo capsule. The material to be learned consisted of four-letter nonsense tetragrams with each letter providing partial information with regard to the four-letter target (Koriat, Psychol Rev, 100:609-639, 1993).

RESULTS

The number of incorrect letters reported was higher for the lorazepam than for the placebo condition. The FOK magnitude was higher for the placebo participants than for the lorazepam participants. The predictive value of FOK for recognition was preserved by the drug.

CONCLUSION

When studying four-letter nonsense letter strings, lorazepam participants present an impairment of episodic short-term memory and the drug has an effect on FOK estimates but not on the predictive accuracy of the FOK. The accessibility hypothesis of FOK was confirmed in this study and seems to retain some validity even under the effect of an amnesic drug.

Drugs, sweat, and fears: a comparison of the effects of diazepam and methylphenidate on fear conditioning

RATIONALE

Classical conditioning of a fear response involves the formation of an association between a stimulus and an emotional response and can be seen as a basic form of emotional memory. While both benzodiazepines and stimulant drugs may influence the formation of episodic memories for emotional events, their effects on fear conditioning are less clear.

OBJECTIVES

This study compared the effects of diazepam with methylphenidate on fear conditioning.

MATERIALS AND METHODS

In a single-session between groups design with three conditions [placebo, diazepam (10 mg), and methylphenidate (40 mg)], classical conditioning of a skin conductance response to a visual stimulus previously paired with a 100-db white noise was tested in 45 healthy volunteers.

RESULTS

Diazepam blocked fear conditioning, despite responses to the unconditioned aversive stimulus and neutral control stimulus being unimpaired. Conditioning remained intact after methylphenidate. Conditioned responses were not extinguished completely by the end of the experiment, and it was not possible to draw conclusions about the effects of the drugs on extinction.

CONCLUSIONS

Although diazepam has well-documented amnesic effects, it has not been found to affect implicit forms of memory like perceptual and conceptual priming. As the present study found impaired fear conditioning after diazepam, it adds weight to recent findings that emotional memories are disproportionately impaired by the benzodiazepines.

Dissociated effects of diazepam and lorazepam on short-latency afferent inhibition

Peripheral nerve inputs have an inhibitory effect on motor cortex excitability at short intervals (short-latency afferent inhibition, SAI). This can be tested by coupling electrical stimulation of peripheral nerve with transcranial magnetic stimulation (TMS) of the motor cortex. SAI is reduced by the anticholinergic drug scopolamine, and in patients with Alzheimer's disease. Therefore, it is possible that SAI is a marker of central cholinergic activity important for memory function. The benzodiazepine lorazepam also reduces SAI. Since benzodiazepines impair memory formation, but do not do so uniformly, with a maximum amnesic effect after lorazepam but less or no effect after diazepam, we were interested in testing in this non-behavioural study to what extent the effects of lorazepam and diazepam on circuits involved in SAI could be dissociated. In addition, and for control, we tested the effects of lorazepam and diazepam on short-interval intracortical inhibition (SICI), a motor cortical inhibition mediated through the GABA(A) receptor. Lorazepam markedly reduced SAI, whereas diazepam slightly increased it. In contrast, both benzodiazepines uniformly increased SICI. Our findings demonstrate opposite effects of lorazepam and diazepam on SAI, an inhibition modulated by central cholinergic activity, but the same effects on SICI, a marker of neurotransmission through the GABA(A) receptor. This dissociation suggests, for the first time, that TMS measures of cortical inhibition provide the opportunity to segregate differences of benzodiazepine action in human central nervous system circuits.

Specific effects of an amnesic drug: effect of lorazepam on study time allocation and on judgment of learning

We investigated the effects of lorazepam, a benzodiazepine, on the allocation of study time, memory, and judgment of learning, in a cognitive task where the repetition of word presentation was manipulated. The aim was to assess whether lorazepam would affect the learning processes and/or whether the participants would be aware of the amnesic difficulty. A total of 30 healthy volunteers participated in the study, 15 of whom received a capsule containing the lorazepam drug (0.038 mg/kg) and 15 a placebo capsule. First, the accuracy of delayed judgments of learning (JOL) was measured in both groups. For the JOL ratings, results showed that all the participants benefited from word repetition. Although the overall performance was lower in the lorazepam than in the placebo group, the accuracy of the JOL ratings was preserved by the drug. Second, all the participants benefited from the repetition of learning, although the performances of the lorazepam-treated subjects remained lower than those of the placebo participants. The repetition of learning had an effect on JOL in both groups. Finally, the time spent learning each (allocation study time) pair of words was measured. For the placebo group, results revealed that study time decreased significantly with the frequency of presentation. For the lorazepam group, no effect of presentation frequency was found. Overall, our findings suggest that the lorazepam drug has a differential effect on the monitoring and the control processes involved in a learning task. The implications of these findings are discussed within the theoretical framework of metacognition.

Comparative pharmacokinetics and pharmacodynamics of short-acting hypnosedatives: zaleplon, zolpidem and zopiclone

Benzodiazepines have historically been the mainstay of treatment for sleeping disorders, yet they have many shortcomings. A new group of sedative hypnotic agents has been developed for this purpose. Similar to the benzodiazepines, zaleplon, zolpidem and zopiclone have activity at the GABA receptor complex, yet they appear to have more selectivity for certain subunits of the GABA receptor. This produces a clinical profile that is more efficacious with fewer side effects. Zaleplon, zolpidem and zopiclone are structurally distinct. Due to variation in binding to the GABA receptor subunits, these three compounds show subtle differences in their effect on sleep stages, and as antiepileptics, anxiolytics and amnestics. The duration of action of zaleplon, zolpidem and zopiclone can be related to their individual pharmacokinetic profile, which subsequently determines the time course of drug effect. Each of these compounds has a unique pharmacokinetic profile with different bioavailability, volume of distribution and elimination half-lives. Zaleplon has a rapid elimination so there are fewer residual side effects after taking a single dose at bedtime. By comparison, zolpidem and zopiclone have a more delayed elimination so there may be a prolonged drug effect. This can result in residual sedation and side effects but may be useful for sustained treatment of insomnia with less waking during the night. There are also differences in potency based on plasma concentrations suggesting that there are differences in binding to the GABA receptor complex. Although zaleplon has a much lower bioavailability (30%), the treatment dose is similar to zolpidem and zopiclone (bioavilaibility of 70%) because of the increased potency of zaleplon. The pharmacokinetics and pharmacodynamics of zaleplon, zolpidem and zopiclone are significantly different from benzodiazepines. The new drugs are sufficiently unique from each other to allow customisation of treatment for various types of insomnia. While zaleplon may be best indicated for the delayed onset of sleep, zolpidem and zopiclone may be better indicated for maintaining a complete night's sleep. Only the patient's symptoms and response to treatment will dictate the best course of treatment.

Ordinal Process Dissociation and the Measurement of Automatic and Controlled Processes

The process-dissociation equations (L. Jacoby, 1991) have been applied to results from inclusion and exclusion tasks to derive quantitative estimates of the influence of controlled and automatic processes on memory. This research has provoked controversies (e.g., T. Curran & D. Hintzman, 1995) regarding the validity of specific assumptions underlying the process-dissociation equations. In this article, the author explores the conclusions one can draw about the ordinal relations between automatic and controlled processes across experimental conditions from results in the inclusion and exclusion tasks. Given relatively neutral assumptions, this article presents and proves 6 theorems that allow investigators to draw conclusions about the ordinal relations between automatic and/or controlled processes across experimental conditions. An illustrative example is presented, and the current approach is compared with the original process-dissociation framework.

Stem-completion tasks (indirect, direct inclusion and exclusion) are differently affected by equipotent doses of lorazepam and flunitrazepam

This study was designed to explore the effects on performance in stem-completion tasks of two benzodiazepines (BZ) in equipotent doses: lorazepam, a drug that atypically disrupts perceptual priming, and flunitrazepam, a compound with standard BZ effects. The study followed a placebo-controlled, double-blind, parallel-group design. Thirty-six young and healthy subjects carried out three completion tasks at theoretical peak-plasma concentrations of drugs: (a) indirect tasks, in which the subjects were instructed to complete stems with the first word that came to mind; (b) direct inclusion tasks/cued recall, in which the participants had to try to use words seen at study as completions; and (c) direct exclusion tasks, in which words seen at study were to be avoided. The PDP was applied to the results in the inclusion and exclusion tasks, to obtain indices of explicit/controlled (C) and implicit/automatic (A) memory. The C index was lowered by both BZs and A was equivalent in all treatments, confirming the general amnestic action of BZs. However, lorazepam led to decreases in completions in the indirect and inclusion tasks, while flunitrazepam impaired performance in the exclusion task. The qualitative differences between the drugs in their effects on performance suggest that these BZs may lead to differences in response bias.

Effects of alcohol on controlled and automatic memory processes

The authors used the process-dissociation procedure (L. L. Jacoby, 1998) to examine the effects of alcohol on controlled and automatic influences on memory performance. Participants studied 1 of 2 word lists and subsequently were cued with word stems to recall the words from both lists. Fifty-four men were administered either a moderate dose of alcohol (0.82 g/kg) or placebo prior to studying the word list. Results indicated that alcohol decreased estimates of controlled contributions to performance on the task. In contrast, alcohol did not appear to affect automatic influences on this task. Integrated with recent findings using a different cognitive task, these data suggest that alcohol impairs performance on implicit, conceptually driven tasks but not on implicit, perceptually driven tasks.

Biomarkers for the effects of benzodiazepines in healthy volunteers

Studies of novel centrally acting drugs in healthy volunteers are traditionally concerned with kinetics and tolerability, but useful information may also be obtained from biomarkers of clinical endpoints. A useful biomarker should meet the following requirements: a consistent response across studies and drugs; a clear response of the biomarker to a therapeutic dose; a dose-response relationship; a plausible relationship between biomarker, pharmacology and pathogenesis. In the current review, all individual tests found in studies of benzodiazepine agonists registered for anxiety in healthy volunteers since 1966 were progressively evaluated for compliance with these requirements. A MedLine search yielded 56 different studies, investigating the effects of 16 different benzodiazepines on 73 different (variants of ) neuropsychological tests, which could be clustered into seven neuropsychological domains. Subjective and objective measures of alertness were most sensitive to benzodiazepines. The most consistent effects were observed on saccadic peak velocity (SPV) and visual analogue scores ( VAS) of alertness, where 100% and 79% of all studies respectively showed statistically significant effects. A dose-response relationship could be constructed for temazepam and SPV, which was used to determine dose equivalencies relative to temazepam, for seven different benzodiazepines. These dose equivalencies correlated with the lowest recommended daily maintenance dose (r2 = 0.737, P < 0.05). This relationship between SPV reduction and clinical efficacy could reflect the clinical practice of aiming for maximum tolerated levels, or it could represent a common basis behind SPV reduction and anxiolytic activity for benzodiazepines (probably sedation). The number of tests used in human psychopharmacology appears to be excessive and their sensitivity and reproducibility low.

Effects of the benzodiazepine lorazepam on monitoring and control processes in semantic memory

Lorazepam has been repeatedly shown to induce memory impairments. The effects of this benzodiazepine on the processes involved in the strategic regulation of memory accuracy have not as yet been explored. An experimental procedure that delineates the role of monitoring and control processes was used. Fifteen lorazepam and 15 placebo subjects were examined using a semantic memory task that combined both a forced- and a free-report option and a no-incentive and an incentive condition. Memory accuracy was lower in the lorazepam than in the placebo group. Lorazepam impaired control sensitivity (the extent to which volunteering of answers is affected by the confidence judgments). While the absolute aspect of monitoring was impaired (calibration scores), both the discriminative aspect (the ability to distinguish between correct and incorrect answers) and the response criterion setting (the confidence threshold set for volunteering a report) were spared. The pharmacological dissociation between monitoring effectiveness and control sensitivity indicates that these two components involve distinct processes.

Conscious and automatic uses of memory in chronic pain patients

Memory deficits in chronic pain patients are frequently observed. The objective of this study was to explore memory performances of chronic pain patients by using the Process Dissociation Procedure developed by Jacoby (J. Mem. Lang. 30 (1991) 513). This procedure permits to separate the contribution of controlled processes from automatic processes operating within a memory task. The results show a significant decrease of controlled processes in chronic pain patients. Furthermore for both groups, automatic processes contribute in a similar extent to the memory performance. The estimates of controlled processes in the chronic pain patients are significantly related to the fear of pain and catastrophic beliefs. This is interpreted as a sign of interference between the attention consumed by pain experience (namely fear related to pain) and the attention to be allocated to the memory task.

Different effects of lorazepam and diazepam on perceptual integration

Recent research has established the detrimental effect of lorazepam, a benzodiazepine, on both implicit and explicit memory. Furthermore, lorazepam is known to affect perceptual integration. Diazepam, on the other hand, though being a benzodiazepine too, only impairs explicit memory, leaving implicit memory fairly intact. Little is known about the effect of diazepam on perceptual integration. The present study aimed at filling in this gap, by comparing the effects of lorazepam and diazepam on the detection of discontinuities in random-shaped outlines. In line with previous findings, the results in a lorazepam-treated group were quite different from the results in a placebo-treated group. The results in a diazepam-treated group were analogous to the results in the placebo-treated group and different from the results in the lorazepam-treated group. This shows that lorazepam and diazepam differ, not only with respect to their effect on implicit memory, but also with respect to their effect on perceptual integration. It is argued that this bears important consequences for memory research that makes use of a pharmacological dissociation rationale.

Mechanisms influencing stimulus-response properties of the human corticospinal system

BACKGROUND

Stimulus-response (S-R) properties of the corticospinal system in humans depend on the interactions that take place at different sites along the corticospinal pathway. The mechanisms influencing stimulus-response curves elicited by transcranial magnetic stimulation (TMS) and their operation site along the human neuraxis are poorly understood. In this study, we investigated the effects of CNS-active drugs with distinct mechanisms of action on S-R curves. Effects of each of these drugs on S-R curves would point to the involvement of specific mechanisms. Additionally, relative sensitivity of S-R curves compared with other measures of corticospinal excitability was studied.

METHODS

We studied the effects of lorazepam, which is a positive allosteric modulator of GABA(A) receptors; lamotrigine, an inhibitor of voltage-gated Na(+) and Ca(2+) channels; and D-amphetamine, an indirect agonist of the dopaminergic-adrenergic system on S-R curves, motor thresholds (MT), and intracortical inhibition (ICI) and facilitation (ICF) with a double-pulse technique. Maximum peripheral M responses and F waves were investigated as measures of the total alpha-motoneuron pool and its excitability.

RESULTS

F and M waves were unaffected by either the drugs or placebo. S-R curves were significantly depressed by lorazepam and lamotrigine without changes in ICI and ICF. Both S-R curves and ICF were enhanced by D-amphetamine. MT increased only with lamotrigine.

CONCLUSIONS

S-R curves were influenced by changes in the GABAergic and monoaminergic system and Na(+) and Ca(2+) channel properties. Our results indicate that, out of different parameters of motor system excitability, S-R curves were the most sensitive.

A double-dissociation of behavioural and event-related potential effects of two benzodiazepines with similar potencies

This study was designed to explore the role of benzodiazepine affinity to benzodiazepine binding site on acute psychomotor, subjective and memory effects, as well as auditory Event Related Potential (ERP) latencies, in healthy volunteers. Two benzodiazepines with similar affinity to benzodiazepine binding sites, or potency, were compared: the atypical compound lorazepam (2.0 mg), which has been reported to impair priming, and a standard benzodiazepine, flunitrazepam (0.6 mg, 0.8 mg, 1.0 mg). The study followed a placebo-controlled, double-blind, parallel-group design. Sixty subjects completed a test battery before treatment and at theoretical peak plasma concentration of drugs. Lorazepam and 1.0 mg of flunitrazepam led to comparable alterations on psychomotor, subjective and auditory episodic memory measures. A double-dissociation was found for lorazepam and the equipotent dose of flunitrazepam (1.0 mg): lorazepam was more deleterious than flunitrazepam in time taken to identify fragmented shapes. Lorazepam also impaired direct and indirect stem-completion in comparison to placebo, but this effect was abolished when time to identify shapes was used as a covariate. By contrast, 1.0 mg of flunitrazepam prolonged auditory ERP latencies to a greater extent than lorazepam. High affinity to the benzodiazepine binding sites does not seem to explain the consistent lorazepam-induced impairment of indirect stem-completion. Differences in impairment profile between the benzodiazepines employed may relate to the modality (visual or not) of the tasks used.

Are lorazepam-induced deficits in attention similar to those resulting from aging?

The purpose of this experiment was to compare, in three tasks of attention, the impairment caused by lorazepam (1 and 2.5 mg) administered to young volunteers with the impairment that results from aging. Performance on digit cancellation (DC), digit-symbol substitution (DSS), and Paced Auditory Serial Addition Task (PASAT) was significantly impaired by lorazepam (2.5 mg) and was significantly worse in the middle-aged group (mean +/- SEM, aged 58.9+/-0.8 years) compared with the younger, IQ-matched group (20.7+/-0.2 years). However, there were interesting differences in the extent of impairments among the three tests. In the DC test, lorazepam (2.5 mg) produced a significantly greater impairment than was seen in either the middle-aged men or middle-aged women. However, in the DSS test, the middle-aged women were significantly more impaired than either the middle-aged men or the young volunteers tested after lorazepam (2.5 mg). In the PASAT, both the lorazepam (2.5 mg) group and the middle-aged women were more impaired than the middle-aged men. These results raise the important possibility of gender differences in age-related decline of attentional processes.