A comparison of the amnesic effects of lorazepam in alcoholics and non-alcoholics

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.

Midazolam does not inhibit association formation, just its storage and strengthening

RATIONALE

Although there have been many studies examining the effects of benzodiazepines on memory performance, their effects on working memory are equivocal and little is known about whether they affect the efficacy of practice of already learned material.

OBJECTIVES

The objectives in two experiments were to examine (a) whether midazolam impairs performance on a working memory task designed to minimize mnemonic strategies such as rehearsal or chunking of information to be recalled and (b) the effect of midazolam on repeated practice of paired associates that were learned before drug administration.

MATERIALS AND METHODS

Both experiments involved subcutaneous administration of 0.03 mg of saline or midazolam per kilogram of bodyweight in within-subject, placebo-controlled designs, involving 23 subjects in (a) and 31 in (b).

RESULTS

The drug had no effect on the ability to recall the digits in serial order even though the encoding task prevented the digits from being rehearsed or maintained in an articulatory buffer. Paired associates that were learned before the injection showed a benefit of subsequent practice under saline but not under midazolam.

CONCLUSIONS

The results suggest that (a) midazolam does not affect the formation of new associations in short-term memory provided that the presentation rate is not too fast to form these associations when sedated, despite the evidence that the drug blocks long-term memory (LTM) retention of associations; and (b) the potential for over-learning with practice of learned associations in LTM is adversely affected by midazolam such that repeated exposures do not strengthen new learning.

Interference effects on verbal memory function, following oral lorazepam

Previous studies have consistently reported deficits in verbal memory following oral lorazepam administration. The possible role of susceptibility to interference effects as a contributory mechanism in benzodiazepine amnesia has not been examined as an independent variable. In addition, most studies of benzodiazepine amnesia have not controlled for the possible confounding effects of alcohol consumption, recently reported to affect the degree of amnesia produced by lorazepam. The present study assessed the verbal memory capabilities of 24 low social drinkers (MAST score < 3) receiving either oral lorazepam (2 mg) or placebo. Interference effects on verbal memory were assessed using the Auditory herbal Learning Test, with either the interference word list (trial B) or a counting backwards task. Lorazepam significantly reduced the recall scores for list B, compared to the first presentation of list A, suggesting lorazepam may increase susceptibility to proactive interference. There was no drug effect on retroactive interference. With regard to recall per se, lorazepam impaired verbal learning for initial acquisition trials (trials 2 and 3) but not subsequent trials, where learning was comparable to the placebo. Lorazepam did not produce significant impairment in immediate and delayed recall trials. This pattern of recall does not conform to the classic profile of benzodiazepine-induced amnesia; potential explanations for this are discussed.

A comparison of age-related deficits in memory and frontal lobe function following oral lorazepam administration

Differential responses on cognitive function of young (18-45 years, n = 17) and elderly (60-75 years, n = 9) subjects were compared before and after a challenge with lorazepam (2 mg oral) or placebo. Tests of memory and frontal lobe function were administered to determine the specificity of the amnesic deficit produced and the interaction of drug and the aging brain. Anterograde amnesia, as assessed by recall of a word list, was noted in both groups and was greater in the elderly. Whereas lorazepam produced only impaired recall in the young group, the elderly group manifested a further range of cognitive impairments, including decreased verbal fluency on the controlled oral word association test and reduced performance on the Wisconsin card-sorting test. These impairments in the elderly group could not be attributed to performance deficits pre-drug. Short-term memory, as evidenced by digit span and the copy trial of the Rey figure, was not impaired by lorazepam. It is concluded that whilst lorazepam produces a relatively `pure' amnesia in young to middle aged adults, in the elderly there is an admixture of deficits in some frontal lobe functions. This is presumed to reflect age-related changes in the brain and may be analogous to the spectrum of results noted in Korsakoff's psychosis as opposed to 'pure' diencephalic amnesia.