The Pattern of Memory Loss Resulting From Intravenously Administered Diazepam Elisabeth O. Clark, MA; Murray Glanzer, PhD; Herman Turndorf, MD
\s=b\ A
word recognition task was deto determine the stage in memory affected by a single 10-mg intravenous injection of diazepam and the duration of the effect. Injection in three experimental
signed
subjects produced
an
anterograde
amne-
sia for the 14 to 24-minute period immediately after injection. Memory loss resulted from impaired storage, the stage during which information is entered into memory. Retention and retrieval stages of memory were unaffected. This temporary amnesia may result from increased inhibition in the hippocampal system produced by diazepam, which shares many properties with the inhibitory neurotransmitter \g=g\-aminobutyric acid. (Arch Neurol 36:296-300, 1979)
l\/Temory consists of three successive
stages: (1) storage, the encoding registration of information; (2) retention, the maintenance of stored information; and (3) retrieval, the and
recovery of that information. (The term "storage" will be used here to cover the entire process of entering an item into long-term store or secondary memory. The distinction between long- and short-term store will not be used in the text since all the recogni¬ tion testing was directed at items in long-term store. Details concerning the distinction between long- and Accepted
for publication April 18, 1978. From the Department of Psychology, New York University (Ms Clark and Dr Glanzer), and the Departments of Psychiatry (Ms Clark) and Anesthesiology (Dr Turndorf), New York University Medical Center. Reprint requests to Department of Psychology, New York University, 6 Washington Pl, Rm 550, New York, NY 10003 (Dr Glanzer).
short-term store appear elsewhere.1 Moreover, there has been some dis¬ agreement in the literature in label¬ ing the various components of memo¬ ry. The first stage, here called "stor¬ age," has also been labeled "encod¬ ing." The second stage, which we label "retention," has been referred to as "storage" by other writers.) The present study examines the effect of a single, fixed dose of diaze¬ pam on the stages of memory and the duration of that effect. We will relate
findings to possible physiological structures involved and to current
our
theories of
anterograde amnesia. Diazepam (Valium) is a widely used benzodiazepine tranquilizer. Clinical
studies have demonstrated that intra¬ venously administered diazepam pro¬ duces rapid onset of a temporary memory impairment and physiologi¬ cal and behavioral changes, the major¬ ity of which last from 15 to 30 minutes.2-7 This amnesic interval pro¬ vides an opportunity to study the stage or stages of memory affected by the drug. Memory for information may be tested by two methods, recall and recognition. In a recall test, the subject must produce items presented earlier. In a recognition test, the subject must choose the items pre¬ sented earlier from among distractor items. Several studies have tested the ability of subjects to recall events or information presented after diazepam injection. Clarke et al1 found impair¬ ment two hours after injection for recall of short word lists read to subjects within minutes after injec¬ tion. Korttila and Linnoila7 pinched
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15 minutes after injection and found that response to the pinch was normal but that subjects did not recall the pinch when asked later. Fox et al" used a questionnaire to assess surgical patients' recall of events following premedication with diaze¬ pam. Seventy-five percent of the patients had amnesia for events occurring in the first 30 minutes after injection. These studies indicate that, regardless of the type of information presented during the first 15 to 30 minutes after intravenous (IV) injec¬ tion, the subject will show impaired recall of this information later. Studies of the effect of diazepam on recognition memory give results in line with studies of recall. Dundee and Pandit4 found that patients tested 24 hours after a 5- or 10-mg injection of diazepam showed impaired recogni¬ tion for pictures. This impairment was greatest when pictures had been presented two to three minutes after injection and continued at less severe levels for 20 to 30 minutes. Clarke et al·' also found that their subjects were impaired in recognition in the study just mentioned. However, these stud¬ ies have not determined clearly whether the drug is affecting storage, retention, retrieval, or some combina¬ tion of these stages.
subjects
A
recent
recognition study by
Frumin and colleagues indicated that the amnesic effect of diazepam
involves the storage stage of memory. In their study, patients saw ten pictures of common objects 15 min¬ utes after intravenous injection of diazepam and prior to administration of a general anesthetic and surgery.
Twenty-four hours later, the patients were impaired in discrimination of old and new pictures. Two recent studies by Ghoneim and Mewaldt""1 added further support to this interpreta¬
1,800 1,600
tion.
1,400
Physiological and clinical changes following IV administration of diaze¬ pam correlate with the reported time course
1,200
of amnesic effects. In human
Experimental
subjects, 10 to 20 mg of intravenously given diazepam produces relaxation and drowsiness starting 30 to 90 seconds after injection and continuing for 15 to 30 minutes." Kelly et al" correlated reduction in anxiety with changes in physiological measures following IV injection of 10 mg of diazepam. Anxiety was rated both by patients and observers, and forearm blood flow and heart rate were measured. The authors stated that the peak effects for all measures occurred within 20 to 30 minutes after injec¬ tion. Hillestad et al" plotted the time course for physiological and behav¬ ioral effects of intravenously given diazepam. The measures of serum blood levels over time are shown in Fig 1. Serum concentration of diaze¬ pam peaks within 15 minutes after injection and decreases substantially by 30 minutes. Hilletad et al" also mentioned a memory disturbance that reached a peak 15 minutes after injec¬ tion, was still present at 30 minutes, and was gone by 60 minutes. They did not, however, report the nature of the memory testing. In the present study, the timing of the tests and the administration of
the drug were phased so as to permit the following: (1) isolation of the stage or stages in memory affected by the drug, and (2) delineation of the extent of the amnesic effect produced and its correlation with the behavioral and physiological effects of the drug. SUBJECTS AND METHODS Method A word recognition task was used in which the subject was required to distin¬ guish between words presented auditorially earlier in the session, "old" words, and words heard for the first time, "new" words. The lag between the initial and second presentation of each word was approximately 28 minutes. This enabled us to present a new word prior to IV adminis¬ tration of 10 mg of diazepam and to test recognition for that word during the 15 to 30-minute period when the drug concentra¬ tion was greatest. It also enabled us to present words during peak diazepam concentration and to test for word recogni¬ tion after the drug concentration had subsided. Thus, it was possible to deter-
Ss
Serum Level
1
_
c
1,000 TS> 800 600
-1
E
g
co
400 200 1_I_Il_I_1_I_I_I_I_I_I_1_I_I_I—J/—Í #-
0
0
10 20 30 40 50 60 70 80 90 100110120 24 hr Minutes After Injection
1.—Mean recognition scores for experimental and control groups over time. Also plotted is serum level concentration resulting from intravenous administration of 20-mg of diazepam (from Hillestad et al'3).
Fig
mine the stage of memory affected by the If retrieval were affected, there would be a drop in recognition memory for words presented before the peak concen¬ tration of diazepam and tested during the peak concentration, in the first 15 to 30 minutes after injection. If storage were
Study Design
drug.
impaired,
a
drop
in
recognition
Block Preload 1
memory
would occur only for words first presented in the interval when diazepam had its peak concentration and tested later. There would be no decrease in recognition memo¬ ry for words presented prior to injection and tested while diazepam was active. If retention were affected, there would be a drop in recognition memory for words first presented either before or during the peak drug concentration.
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new
Drug injection 50 new words + 50 old words (block 2 new words) 50 new words + 50 old words (block 3 new words) 10
Experimental Design The structure of the experimental ses¬ sion is outlined in the Table. All materials were prerecorded. Eleven blocks of words were presented, separated by five-minute intervals. All words had a normative count of >40 occurrences per million." First, a preload block of 150 words was read to the subject at a rate of one word every three seconds. The subject repeated each word aloud. Ten successive blocks of 100 words, 50 old and 50 new, were then presented, one word every five seconds. Diazepam was administered to the experimental subjects after the third block of 100 words. Control subjects went through the same procedure except that they received no injection. Subjects were required to repeat each word and identify it as old or new. Fifty words from the preload list appeared as old words in block 1. Another 50 words from the preload list appeared as old items in block 2. Except for the old words in block 1, all old words first appeared two blocks earlier as new words, giving an average lag of 200 words or 28 minutes between the two occurrences. Old words in block 3 were
Procedure words 50 new words + 50 old (re¬ peated) words from pre¬ load list 50 new words + 50 old words from preload list 50 new words + 50 old words (block 1 new words) 150
50
new words + 50 old words (block 8 new words)
words in block 1, old words in block the new words from block 2, etc. Each block required approximately nine minutes for presentation and testing. In the five-minute interval separating succes¬ sive blocks, the first two minutes were filled with a digit vigilance task. In this task, the subject was given a target digit before hearing a two-minute string of random digits read at a rate of one per second. The subject's task was to repeat the target digit immediately whenever the target was heard in the string of digits. A different target digit was assigned for each list. After the vigilance task, subjects rested for three minutes. The vigilance task was used to prevent rehearsal of words at the end of each block and to assess alertness of experimental subjects. It also varied the task for the subject, making the experiment less monotonous.
the
4
new
were
Subjects The experimental subjects were two residents and a nurse in the New York
University-Bellevue Department of Anes¬ thesiology. Control subjects were nine students of approximately the same age and years of education. All subjects were
Injection
Minutes After h
I
IN
volunteers who gave informed consent.
o
O * » ( m .20). The analyses reflect the marked change in experi¬ mental group performance in block 6 and steady control group perform¬ =
=
ance.
Figure 1 also includes the data of Hillestad et al" showing serum levels over time after IV injection of 20 mg of diazepam. (A 10-mg injection" gave a lower but parallel plot. The peak serum level of about 400 ng/ml occurred at 15 minutes after injection, then dropped to 350 ng/ml at 30 minutes and to 165 ng/ml at 60 minutes. We used the 20-mg plot because it is based on a larger number of subjects.) The Hillestad et al" data are supported by the general litera¬ which places the peak effect ture,of the drug 15 to 30 minutes after injection. Dundee and Pandit4 showed a peak amnesic effect for the period one to two minutes after injection. It is possible that if our testing had been resumed sooner after injection, a greater impairment might have been demonstrated. However, the Hillestad et al" data in terms of the peak serum level do not support this idea. We also obtained additional evi¬ dence that the drug had its peak effect during the 15 to 30 minutes after injection and that this effect is solely on storage. In the pilot work for this study, we experimented with a similar design in which the old words were repeated in the immediately succeeding block of trials rather than two blocks later as in the procedure just described. The interval between blocks was only four minutes rather than five. Therefore, the average lag in our pilot experiment was 100 inter;lls
words rather than 200, and 13 rather than 28 minutes. If the effect of the drug is on retrieval but some¬ what later than we assumed, then the decrement in recognition memory should occur at the same point in time with this arrangement. If the drug has its effect during the first 15 to 30 minutes after injection and has that effect only on storage, then the decre¬ ment seen in Fig 2 should be observed earlier in the blocks of trials, since the lag between presentation and test was shorter. The pilot subject was given a 10-mg injection of diazepam after block 2. Performance on block 3 was unaf¬ fected, indicating that retrieval of block 2 information was normal. Block 4 showed a steep decline in memory that continued through block 5. By block 6, this subject showed complete recovery of memory. Yet block 6 reflected recognition memory for block 5 words presented 30 to 39 minutes after injection, when amnesic effects are maximal in Fig 1. Compar¬ ison of these data with the data for the experimental subjects supports the assertion that the drug has its effect during storage, not retrieval. Recognition is poor for words pre¬ sented in a restricted time period
vening
following diazepam injection regard¬ less of when they are subsequently
tested.
COMMENT
The data reported here agree with the findings of Frumin et al." The present study also supports the assignment by previous research¬ ers*"" of the memory effects of diaze¬ pam to prevention of storage and extends the findings in two ways. First and more important, the study shows that the only stage affected is storage. The other two stages of memory, retention and retrieval, are unaffected. This point has general theoretical import, as will be pointed out below. Second, the study also matches more precisely the time course for amnesic effects to that of blood level and other physiological
changes. The encoding deficit
we have dem¬ onstrated may be the result of several physiological changes in the brain. These could be reflected in changes in the neural firing rates of hippocampal structures concerned with memory. We shall present neurophysiological evidence on limbic areas that may be responsible for diazepam-induced am¬ nesia and possible transmitter sys¬ tems involved. In animals, neural activity in the
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hippocampus and
in the
amygdala,
which has strong indirect efferent connections to the
hippocampus, is depressed following diazepam injec¬
tion. In cats, there is an initial decrease in hippocampal and amygda¬ loid firing following diazepam admin¬ istration.1" Morillo"" and Himwich et al-1 recorded responses from the hippocampus of cats during amygda¬ loid stimulation. Intravenous injection of diazepam decreased the normal response in the ipsilateral hippocam¬ pus. Other researchers have reported raised firing thresholds in the amyg¬ dala of cats'-'- and rabbits'" after diaze¬ pam injection. Thus, diazepam may be responsible for both a direct decrease in hippocampal activity and an indi¬ rect decrease produced by lowering amygdaloid input to the hippocam¬ pus. The hippocampus is of special inter¬ est in studies of human memory. In her studies of memory deficits follow¬ ing surgery, Milner-"-" interprets re¬ sults from tests with bilateral hippocampectomy patients to indicate that storage of new information is no longer possible. Patients have a gen¬ eral anterograde amnesia for infor¬ mation presented after bilateral re¬ moval of the hippocampal formation. Information stored prior to surgery is intact and can be retrieved normally. As with our experimental subjects, retention and retrieval of previously stored information is unimpaired in these hippocampal patients. Milner suggests that "the hippocampal re¬ gion acts to prime activity in cortical where storage is taking areas place."-'"'"1"11 We may assume that the way in which the hippocampus, a part of the Papez circuit,-7 has its effect on memory is by maintaining the reverberatory firing of neurons necessary to store a memory. If reverberatory firing in the hippo¬ campus is necessary for memory stor¬ age, a drug that decreases repetitive firing would impair memory. Diaze¬ pam is apparently such a drug, depressing repetitive neural firing caused by electrical stimulation or chemical irritants. It eliminates sei¬ zure discharges induced in the hippo¬ campus by amygdaloid stimulation in cats-5 as well as afterdischarges elicited by direct hippocampal stimu¬ lation."' In rabbits, diazepam also decreases the afterdischarge of hippo¬ campal neurons following stimulation without changing the firing thresh¬ old.-1 This indicates that in rabbits diazepam affects precisely the rever¬ beratory types of hippocampal firing presumed important for memory pro-
cesses.
At the transmitter level, diazepam may affect neural processes by mim¬ icking the inhibitory effects of the neurotransmitter -aminobutyric acid (GABA). Current evidence points to inhibitory effects of GABÀ on an excitatory loop originating in the hippocampus. -Ammobutyric acid eliminates seizure discharges in hip¬ pocampal cells in vitro"" as does diaze¬ Diazepam and pam in vivo."" GABA produce the same effects on cerebellar neurons and are both affected in the same way by GABA """
"s-"
antagonists."" Furthermore, diazepam
induced GABA defi¬ cit, which suggests that it is not mere¬ ly activating the GABA system but may be a GABA-ergic analogue."" Therefore, the evidence suggests that increased activity of GABA or diaze¬ pam acts to block the learning loop necessary for storage by inhibiting hippocampal pyramidal neurons which produce the reverberatory firing nec¬ essary for memory storage. The literature on the effects of can
counteract
diazepam
on
an
hippocampal activity,
on
the critical role of the hippocampus in the storage of new information, and our own data assigning the diazepam effect to impairment of storage are all congruent. The literature and data suggest that our subjects had difficul¬ ty in storing items following diaze¬ pam administration because hippo¬ campal activity had decreased. Anterograde amnesia has been re¬ ferred to above. There are several theories that have been developed concerning the character of the gener¬ al class of anterograde amnesias found in hippocampectomy, global amnesia, and Korsakoff's syndrome. One widely accepted theory is that the amnesia stems from an encoding or
storage deficit.24·*3
Another theory, supported by the correlation of retrograde and antero¬ grade amnesia in clinical cases, is that anterograde amnesia results from retrieval difficulties.""" The present results support an encoding deficit theory by demonstrating that an anterograde amnesia can be produced with no sign of a retrograde amnesia. The experimental subjects showed normal retrieval at the same time that they showed severe impairment in the ability to encode new information. Therefore, the correlation of retro¬ grade and anterograde amnesia is not evidence of a necessary relationship, and the argument that there is a necessary involvement of a retrieval deficit in anterograde amnesia is countered.
In summary, our study has deter¬ mined that the memory loss that follows injection of diazepam comes solely from disruption of the storage stage. A possible physiological system and a transmitter mechanism in¬ volved in the effect have been
proposed—the hippocampal system
inhibitory GABA neurons in the hippocampal complex that may be mimicked by diazepam. The relation of the findings to a general theory of anterograde amnesia has also been and
indicated.
Elisabeth 0. Clark held a predoctoral fellow¬ from the National Institutes of Mental Health during the course of this investigation. The work was supported in part by grant BNS 76-04923 from the National Science Foundation. Drs E. E. Coons, Samuel M. Feldman, and Richard J. Koppenaal reviewed the article. Dr Coons brought current research on GABA and the benzodiazepines to our attention.
ship
Nonproprietary Name and Trademark of Drug
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