Propofol and memory: a study using a process dissociation procedure and functional magnetic resonance imaging

Thirty volunteers randomly received either mild or deep propofol sedation, to assess its effect on explicit and implicit memory. Blood oxygen level‐dependent functional magnetic resonance during sedation examined brain activation by auditory word stimulus and a process dissociation procedure was performed 4 h after scanning. Explicit memory formation did not occur in either group. Implicit memories were formed during mild but not deep sedation (p = 0.04). Mild propofol sedation inhibited superior temporal gyrus activation (Z value 4.37, voxel 167). Deep propofol sedation inhibited superior temporal gyrus (Z value 4.25, voxel 351), middle temporal gyrus (Z value 4.39, voxel 351) and inferior parietal lobule (Z value 5.06, voxel 239) activation. Propofol only abolishes implicit memory during deep sedation. The superior temporal gyrus is associated with explicit memory processing, while the formation of both implicit and explicit memories is associated with superior and middle temporal gyri and inferior parietal lobule activation.     

不同镇静程度下健康志愿者事件相关电位与意识和记忆的关系

目的探讨不同镇静程度下事件相关电位(ERPs)与意识和记忆的关系。方法 10名志愿者加入本研究。采用异丙酚静脉靶控输注,记录不同镇静清醒(OAA/S)评分、ERPs各波(N1、P3) 波幅及潜伏期、无创血压、心电图、脉搏血氧饱和度。于OAA/S评分3分、2分时给志愿者听学习表内容。志愿者清醒后4 h进行记忆测试。采用加工分离程序(PDP)分离内隐记忆和外显记忆。计算学习表、干扰表包含测验和排除测验的测试成绩,计算外显记忆、内隐记忆成绩。结果与基础值比较, OAA/S评分3分时,N1潜伏期延长,波幅降低;P3波幅降低,潜伏期延长(P<0．05或0．01);OAA/S评分为2分时,N1潜伏期延长,波幅降低,P3消失;OAA/S评分3分时存在外显记忆和内隐记忆;评分2 分时,意识和外显记忆一同消失,内隐记忆存在。与OAA/S评分3分比较,2分时内隐记忆成绩下降 (P<0．01)。P3波幅与外显记忆成绩呈正相关(n=10,P<0．05或0．01)。结论 P3可作为判断镇静状态下意识和外显记忆存在或消失的指标,但不能反映内隐记忆的存在与否。     

A comparison of the effects of propofol and midazolam on memory during two levels of sedation by using target-controlled infusion

We examined memory during sedation with target-controlled infusions of propofol and midazolam in a double-blinded five-way, cross-over study in 10 volunteers. Each active drug infusion was targeted to sedation level 1 (asleep) and level 4 (lethargic) as determined with the Observer Assessment of Alertness/Sedation scale. At the target level of sedation, drug concentration was clamped for 30 min, during which time neutral words were presented. After 2 h, explicit memory was assessed by recall, and implicit memory by using a wordstem completion test. Venous drug concentrations (mean +/- SD) were 1350 ng/mL (+/-332 ng/mL) for propofol and 208 ng/mL (+/-112 ng/mL) for midazolam during Observer Assessment of Alertness/Sedation scale level 4; and 1620 ng/mL (+/-357 ng/mL) and 249 ng/mL (+/-82 ng/mL) respectively during level 1. The wordstem completion test frequencies at low level sedation were significantly higher than spontaneous frequencies (8.7% + 2.4%; P: < 0.05 in all cases), and lower than during placebo (33.6% + 23%) (P: < 0.05 in all cases, except P: = 0.076 for propofol at level 4). Clinically distinct levels of sedation were accompanied by small differences in venous propofol or midazolam concentrations. This indicates steep concentration-effect relationships. Neutral information is still memorized during low-level sedation with both drugs. The memory effect of propofol and midazolam did not differ significantly. Implications: Implicit memory can occur during different states of consciousness and might lead to psychological damage. In 10 volunteers, implicit memory was investigated during sedation with propofol and midazolam in a double-blinded, placebo-controlled study. To compare the effects of both drugs, they were titrated using a computer-controlled infusion system to produce similar high and low levels of sedation.     

Attenuated brain response to auditory word stimulation with sevoflurane: a functional magnetic resonance imaging study in humans

BACKGROUND: Functional magnetic resonance imaging offers a compelling, new perspective on altered brain function but is sparsely used in studies of anesthetic effect. To examine effects on verbal memory encoding, the authors imaged human brain response to auditory word stimulation using functional magnetic resonance imaging at different concentrations of an agent not previously studied, and tested memory after recovery. METHODS: Six male volunteers were studied breathing 0.0, 2.0, and 1.0% end-tidal sevoflurane (awake, deep, and light states, respectively) via laryngeal mask. In each condition, they heard 15 two-syllable English nouns via closed headphones. Each word was repeated 15 times (1/s), followed by 15 s of rest. Blood oxygenation level-dependent brain activations during blocks of stimulation versus rest were assessed with a 3-T Siemens Trio scanner and a 20-voxel spatial extent threshold. Memory was tested approximately 1.5 h after recovery with an auditory recognition task (chance performance = 33% correct). RESULTS: Scans showed widespread activations (P < 0.005, uncorrected) in the awake state, including bilateral superior temporal, frontal, and parietal cortex, right occipital cortex, bilateral thalamus, striatum, hippocampus, and cerebellum; more limited activations in the light state (bilateral superior temporal gyrus, right thalamus, bilateral parietal cortex, left frontal cortex, and right occipital cortex); and no significant auditory-related activation in the deep state. During recognition testing, subjects correctly selected 77 +/- 12% of words presented while they were awake as "old," versus 32 +/- 15 and 42 +/- 8% (P < 0.01) correct for the light and deep stages, respectively. CONCLUSIONS: Sevoflurane induces dose-dependent suppression of auditory blood oxygenation level-dependent signals, which likely limits the ability of words to be processed during anesthesia and compromises memory.     

Postoperative reading speed does not indicate implicit memory in elderly cardiac patients after propofol and remifentanyl anaesthesia

BACKGROUND: A recent study in young patients undergoing propofol-alfentanil-nitrous oxide anaesthesia demonstrated implicit memory for stories presented during operation using a postoperative reading speed task. In this study we investigated whether patients who tolerate only small amounts of anaesthetics are prone to develop implicit and explicit memories about intraoperative events. METHODS: Thirty patients with poor physical status (ASA III-IV) undergoing cardioverter defibrillator implantation were included in the study. Patients were premedicated with intravenous midazolam and anaesthesia was maintained using propofol and remifentanil infusions. During surgery one of two audio-tapes containing two short stories was played to the patients. Reading speed for the stories played during surgery and two similar stories from the other tape was tested 4 h later. Explicit memory was tested at 4 h and 24 h after audiotape presentation using a structured interview and a forced-choice recognition test pertaining to the story content. Thirty additional awake subjects served as controls. RESULTS: Although half of the patients seemed to be awake one or more times during the operation, no explicit memories of intraoperative events were reported. The forced-choice recognition of the stories was at chance level. No effect on reading speed was found in either the patients or the control subjects. CONCLUSIONS: The possible reasons for reduced explicit and implicit memory performance in elderly patients are age and poor physical status of the patients and the modality change between study and test phases. A non-anaesthetised control group of the same age and physical status should therefore be included in all studies of implicit memory.     

GABA alpha6 receptors mediate midazolam-induced anxiolysis

STUDY OBJECTIVE: To compare the ability of midazolam to produce sedation and anxiolysis and attenuate memory in 100 patients aged 20 to 70 years. The effect of a point mutation (Pro385Ser) for the gamma amino-butyric acid (GABA) alpha6 receptor on the sedative, anxiolytic, and memory effects of midazolam was determined. SETTING: University hospital. DESIGN: Prospective, randomized, double-blind study. PATIENTS: 100 ASA physical status I and II patients scheduled for surgery. INTERVENTIONS: Two midazolam dose groups, 20 microg/kg and 40 microg/kg, with 40 patients per group and 20 control patients receiving saline as a sham control. Treatments were randomly assigned. Blood was collected at the beginning of each study. MEASUREMENTS: Patient sedation and anxiolysis were measured using a visual analog scale and explicit and implicit memory of a word task determined before and six minutes after midazolam or saline. A 365-base pair fragment of the GABA alpha6 receptor gene was amplified by polymerase chain reaction (PCR) from patient blood DNA and digested with the restrictase Fok I. Restriction fragments were visualized by ethidium bromide staining after electrophoresis to evaluate the GABA alpha6 receptor subunit mutation. MAIN RESULTS: Midazolam produced dose-related sedation and anxiolysis. Explicit (recall) memory was attenuated with high-dose midazolam but implicit (recognition) memory remained intact. The GABA alpha6 receptor mutation did not affect baseline sedation, anxiety, or memory but significantly attenuated the anxiolytic effect of low-dose midazolam. Sedation and explicit memory were not affected by the mutation. CONCLUSIONS: A Pro385Ser mutation of the GABA alpha6 receptor subunit decreased the anxiolytic effect of low-dose midazolam.     

Comparison of a new composite index based on midlatency auditory evoked potentials and electroencephalographic parameters with bispectral index (BIS) during moderate propofol sedation

BACKGROUND AND OBJECTIVE: Derived parameters of the electroencephalogram and auditory evoked potentials can be used to determine depth of anaesthesia and sedation. However, it is not known whether any parameter can identify the occurrence of awareness in individual patients. We have compared the performance of bispectral index and a new composite index derived from auditory evoked potentials and the electroencephalogram (AAI 1.61) in predicting consciousness, explicit and implicit memory during moderate sedation with propofol. METHODS: Twenty-one patients with spinal anaesthesia received intraoperatively propofol at the age-corrected C(50) for loss of consciousness and were presented test words via headphones. Bispectral index and AAI 1.61 (auditory evoked potentials, AEP-Monitor2) were recorded in parallel as well as the Observer's Assessment of Alertness/Sedation-score. Postoperatively, testing for explicit and implicit memory formation was performed. RESULTS: Bispectral index and AAI 1.61 correlated well with loss of consciousness defined by an Observer's Assessment of Alertness/Sedation-score of 2 (identical P(K) of 0.87), but did not allow a prediction of postoperative explicit or implicit recall. CONCLUSIONS: Both bispectral index and AAI may be indices of depth of sedation rather than indicators of memory formation, which persists during propofol sedation even after loss of consciousness.     

Drug-induced Amnesia Is a Separate Phenomenon from Sedation: Electrophysiologic Evidence

Background: Sedative-hypnotic drugs not only increase sedation, but also impair memory as serum concentration increases. These drugs also produce profound changes in the auditory event-related potential (ERP). The ability of various ERP components to predict changes in sedation and memory produced by various drugs was tested.

Methods: Sixty-five healthy volunteers randomly received intravenous placebo, midazolam, propofol, thiopental, fentanyl with ondansetron, or ondansetron alone at five different stable target concentrations (three increasing, two decreasing) using a computer-controlled infusion pump to produce varying degrees of sedation without loss of consciousness. ERPs were recorded while volunteer participants detected a deviant auditory stimulus and made a button-press response to a target tone (standard oddball paradigm, 80:20 ratio, to elicit a P3 response). At each target concentration, volunteers learned a list of 16 words. The predictive probabilities (Pk) of various ERP components were determined for word recognition at the end of the day (memory) and log reaction time to the deviant stimulus (sedation).

Results: The N2 latency of the ERP consistently predicted log reaction time in all groups (Pk +/- SE from 0.58 +/- 0.04 to 0.71 +/- 0.04). The N2P3 amplitude of the ERP was the best predictor of memory performance for midazolam (Pk, 0.63 +/- 0.04), propofol (Pk, 0.62 +/- 0.05), and thiopental (Pk, 0.66 +/- 0.04). There was a differential ability to predict memory performance from sedation for midazolam and propofol.     

Temporal dynamics of adaptation to natural sounds in the human auditory cortex

We aimed at testing the cortical representation of complex natural sounds within auditory cortex by conducting 2 human magnetoencephalography experiments. To this end, we employed an adaptation paradigm and presented subjects with pairs of complex stimuli, namely, animal vocalizations and spectrally matched noise. In Experiment 1, we presented stimulus pairs of same or different animal vocalizations and same or different noise. Our results suggest a 2-step process of adaptation effects: first, we observed a general item-unspecific reduction of the N1m peak amplitude at 100 ms, followed by an item-specific amplitude reduction of the P2m component at 200 ms after stimulus onset for both animal vocalizations and noise. Multiple dipole source modeling revealed the right lateral Heschl's gyrus and the bilateral superior temporal gyrus as sites of adaptation. In Experiment 2, we tested for cross-adaptation between animal vocalizations and spectrally matched noise sounds, by presenting pairs of an animal vocalization and its corresponding or a different noise sound. We observed cross-adaptation effects for the P2m component within bilateral superior temporal gyrus. Thus, our results suggest selectivity of the evoked magnetic field at 200 ms after stimulus onset in nonprimary auditory cortex for the spectral fine structure of complex sounds rather than their temporal dynamics.     

Attenuated Brain Response to Auditory Word Stimulation with Sevoflurane: A Functional Magnetic Resonance Imaging Study in Humans

Background: Functional magnetic resonance imaging offers a compelling, new perspective on altered brain function but is sparsely used in studies of anesthetic effect. To examine effects on verbal memory encoding, the authors imaged human brain response to auditory word stimulation using functional magnetic resonance imaging at different concentrations of an agent not previously studied, and tested memory after recovery.

Methods: Six male volunteers were studied breathing 0.0, 2.0, and 1.0% end-tidal sevoflurane (awake, deep, and light states, respectively) via laryngeal mask. In each condition, they heard 15 two-syllable English nouns via closed headphones. Each word was repeated 15 times (1/s), followed by 15 s of rest. Blood oxygenation level-dependent brain activations during blocks of stimulation versus rest were assessed with a 3-T Siemens Trio scanner and a 20-voxel spatial extent threshold. Memory was tested approximately 1.5 h after recovery with an auditory recognition task (chance performance = 33% correct).

Results: Scans showed widespread activations (P < 0.005, uncorrected) in the awake state, including bilateral superior temporal, frontal, and parietal cortex, right occipital cortex, bilateral thalamus, striatum, hippocampus, and cerebellum; more limited activations in the light state (bilateral superior temporal gyrus, right thalamus, bilateral parietal cortex, left frontal cortex, and right occipital cortex); and no significant auditory-related activation in the deep state. During recognition testing, subjects correctly selected 77 +/- 12% of words presented while they were awake as "old," versus 32 +/- 15 and 42 +/- 8% (P < 0.01) correct for the light and deep stages, respectively.     

Cortical processing of complex auditory stimuli during alterations of consciousness with the general anesthetic propofol

BACKGROUND: The extent to which complex auditory stimuli are processed and differentiated during general anesthesia is unknown. The authors used blood oxygenation level-dependent functional magnetic resonance imaging to examine the processing words (10 per period; compared with scrambled words) and nonspeech human vocal sounds (10 per period; compared with environmental sounds) during propofol anesthesia. METHODS: Seven healthy subjects were tested. Propofol was given by a computer-controlled pump to obtain stable plasma concentrations. Data were acquired during awake baseline, sedation (propofol concentration in arterial plasma: 0.64 +/- 0.13 microg/ml; mean +/- SD), general anesthesia (4.62 +/- 0.57 microg/ml), and recovery. Subjects were asked to memorize the words. RESULTS: During all periods including anesthesia, the sounds conditions combined elicited significantly greater activations than silence bilaterally in primary auditory cortices (Heschl gyrus) and adjacent regions within the planum temporale. During sedation and anesthesia, however, the magnitude of the activations was reduced by 40-50% (P < 0.05). Furthermore, anesthesia abolished voice-specific activations seen bilaterally in the superior temporal sulcus during the other periods as well as word-specific activations bilaterally in the Heschl gyrus, planum temporale, and superior temporal gyrus. However, scrambled words paradoxically elicited significantly more activation than normal words bilaterally in planum temporale during anesthesia. Recognition the next day occurred only for words presented during baseline plus recovery and was correlated (P < 0.01) with activity in right and left planum temporale. CONCLUSIONS: The authors conclude that during anesthesia, the primary and association auditory cortices remain responsive to complex auditory stimuli, but in a nonspecific way such that the ability for higher-level analysis is lost.     

Medial temporal lobe involvement in an implicit memory task: evidence of collaborating implicit and explicit memory systems from FMRI and Alzheimer's disease

We used a prototype extraction task to assess implicit learning of a meaningful novel visual category. Cortical activation was monitored in young adults with functional magnetic resonance imaging. We observed occipital deactivation at test consistent with perceptually based implicit learning, and lateral temporal cortex deactivation reflecting implicit acquisition of the category's semantic nature. Medial temporal lobe (MTL) activation during exposure and test suggested involvement of explicit memory as well. Behavioral performance of Alzheimer's disease (AD) patients and healthy seniors was also assessed, and AD performance was correlated with gray matter volume using voxel-based morphometry. AD patients showed learning, consistent with preserved implicit memory, and confirming that AD patients' implicit memory is not limited to abstract patterns. However, patients were somewhat impaired relative to healthy seniors. Occipital and lateral temporal cortical volume correlated with successful AD patient performance, and thus overlapped with young adults' areas of deactivation. Patients' severe MTL atrophy precluded involvement of this region. AD patients thus appear to engage a cortically based implicit memory mechanism, whereas their relative deficit on this task may reflect their MTL disease. These findings suggest that implicit and explicit memory systems collaborate in neurologically intact individuals performing an ostensibly implicit memory task.     

Drug-induced amnesia is a separate phenomenon from sedation: electrophysiologic evidence

BACKGROUND: Sedative-hypnotic drugs not only increase sedation, but also impair memory as serum concentration increases. These drugs also produce profound changes in the auditory event-related potential (ERP). The ability of various ERP components to predict changes in sedation and memory produced by various drugs was tested. METHODS: Sixty-five healthy volunteers randomly received intravenous placebo, midazolam, propofol, thiopental, fentanyl with ondansetron, or ondansetron alone at five different stable target concentrations (three increasing, two decreasing) using a computer-controlled infusion pump to produce varying degrees of sedation without loss of consciousness. ERPs were recorded while volunteer participants detected a deviant auditory stimulus and made a button-press response to a target tone (standard oddball paradigm, 80:20 ratio, to elicit a P3 response). At each target concentration, volunteers learned a list of 16 words. The predictive probabilities (Pk) of various ERP components were determined for word recognition at the end of the day (memory) and log reaction time to the deviant stimulus (sedation). RESULTS: The N2 latency of the ERP consistently predicted log reaction time in all groups (Pk +/- SE from 0.58 +/- 0.04 to 0.71 +/- 0.04). The N2P3 amplitude of the ERP was the best predictor of memory performance for midazolam (Pk, 0.63 +/- 0.04), propofol (Pk, 0.62 +/- 0.05), and thiopental (Pk, 0.66 +/- 0.04). There was a differential ability to predict memory performance from sedation for midazolam and propofol. CONCLUSIONS: Midazolam and propofol affect memory differentially from their sedative effects, and these are indexed by specific components of the auditory ERP. These components of the ERP are associated with specific, but not necessarily unique, neuroanatomic structures. Thus, these drugs act by additional mechanisms beyond general central nervous system depression to produce the effects of sedation and memory impairment.     

Cortical Processing of Complex Auditory Stimuli during Alterations of Consciousness with the General Anesthetic Propofol

Background: The extent to which complex auditory stimuli are processed and differentiated during general anesthesia is unknown. The authors used blood oxygenation level-dependent functional magnetic resonance imaging to examine the processing words (10 per period; compared with scrambled words) and nonspeech human vocal sounds (10 per period; compared with environmental sounds) during propofol anesthesia.

Methods: Seven healthy subjects were tested. Propofol was given by a computer-controlled pump to obtain stable plasma concentrations. Data were acquired during awake baseline, sedation (propofol concentration in arterial plasma: 0.64 +/- 0.13 [mu]g/ml; mean +/- SD), general anesthesia (4.62 +/- 0.57 [mu]g/ml), and recovery. Subjects were asked to memorize the words.

Results: During all periods including anesthesia, the sounds conditions combined elicited significantly greater activations than silence bilaterally in primary auditory cortices (Heschl gyrus) and adjacent regions within the planum temporale. During sedation and anesthesia, however, the magnitude of the activations was reduced by 40-50% (P < 0.05). Furthermore, anesthesia abolished voice-specific activations seen bilaterally in the superior temporal sulcus during the other periods as well as word-specific activations bilaterally in the Heschl gyrus, planum temporale, and superior temporal gyrus. However, scrambled words paradoxically elicited significantly more activation than normal words bilaterally in planum temporale during anesthesia. Recognition the next day occurred only for words presented during baseline plus recovery and was correlated (P < 0.01) with activity in right and left planum temporale.     

Hemispheric specialization for processing auditory nonspeech stimuli

The left hemisphere specialization for speech perception might arise from asymmetries at more basic levels of auditory processing. In particular, it has been suggested that differences in "temporal" and "spectral" processing exist between the hemispheres. Here we used functional magnetic resonance imaging to test this hypothesis further. Fourteen healthy volunteers listened to sequences of alternating pure tones that varied in the temporal and spectral domains. Increased temporal variation was associated with activation in Heschl's gyrus (HG) bilaterally, whereas increased spectral variation activated the superior temporal gyrus (STG) bilaterally and right posterior superior temporal sulcus (STS). Responses to increased temporal variation were lateralized to the left hemisphere; this left lateralization was greater in posteromedial HG, which is presumed to correspond to the primary auditory cortex. Responses to increased spectral variation were lateralized to the right hemisphere specifically in the anterior STG and posterior STS. These findings are consistent with the notion that the hemispheres are differentially specialized for processing auditory stimuli even in the absence of linguistic information.     

Separating intra-modal and across-modal training effects in visual working memory: an fMRI investigation

Working memory training is a useful tool to examine dissociations between specific working memory processes. Although current models propose a distinction between modality-specific working memory processes, to our knowledge no study has directly examined the effects of visual versus auditory working memory training. Functional magnetic resonance imaging was used to investigate whether visual working memory processes can be trained specifically and whether those effects can be separated from across-modal training effects. We found decidedly larger training gains after visual working memory training compared with auditory or no training on a visual 2-back task. These effects were accompanied by specific training-related decreases in the right middle frontal gyrus arising from visual training only. Likewise, visual and auditory training led to decreased activations in the superior portion of the right middle frontal gyrus and the right posterior parietal lobule. We infer that the combination of effects resulted from increased neural efficiency of intra-modal (visual) processes on the one hand and of across-modal (general control) processes on the other hand. Therefore, visual processes of working memory can be trained specifically, and these effects can be functionally dissociated from alterations in general control processes common to both working memory trainings.     

A comparison of oral midazolam solution with temazepam as a day case premedicant.

Seventy-five women undergoing elective day case gynaecological surgery were randomised into one of three groups to receive an oral formulation of midazolam IV solution 10 mg, temazepam 20 mg or placebo for premedication. The two treatment groups showed a significant reduction in anxiety score compared with placebo (P less than 0.002 and P less than 0.04 for placebo compared with temazepam and midazolam respectively). Similarly the treatment groups showed a significantly greater sedation score compared with placebo. Recovery as assessed by letter deletion and memory tests was no worse for the treatment groups than for placebo. Patient acceptance of the two treatment groups was significantly greater than that of placebo. There was no significant difference between treatment groups with respect to anxiolysis, sedation or recovery. As a day case premedicant, midazolam IV solution 10 mg orally was found to be as effective as temazepam 20 mg and superior to placebo, in terms of anxiolysis and sedation, but did not offer any clinical advantage over temazepam in this setting.     

术前口服咪唑安定的遗忘作用与内隐记忆的关系

目的 观察咪唑安定的遗忘作用与内隐记忆的关系,同时调查术前口服咪唑安定有无逆行性遗忘作用,对短期记忆的影响及顺行性遗忘的起效时间和效果。方法 60例择期下腹部及下肢手术病人分为三组,每组20例：A组口服咪唑安定7．5mg;B组口服咪唑安定15mg;C组为对照组。入室后服药,然后行硬膜外腰麻联合麻醉。观察脑电、95％谱边界频率（SEF）和双频谱指数（BIS）;根据国际标准化进行镇静分级与评分;采用图片识记和术后测试模糊辨听率的方法进行记忆与遗忘的调查及内隐记忆调查。结果 （1）A、B两组病人从服药后20分钟开始镇静评分较服药前明显降低并与C组比较差异有显著意义。但A、B两组之间在镇静觉醒评分和镇静开始时间差异无显著意义。（2）术后6小时遗忘率调查,A组服药后30分钟,B组服药后20分钟遗忘率较服药前显著升高,并保持在70％－80％的高水平,两组间差异无显著意义。而C组遗忘率 始终为0。（3）三组间模糊辨听率差异无显著意义。（4）服药期间短期记忆10分钟遗忘率三组均为0。（5）服药后30分钟A、B两组的BIS与SEF均较服药前明显降低,但仍维持在80Hz,两组间差异也无显著意义。结论 术前口服咪唑安定7．5mg,30分钟后即可产生良好的顺行性遗忘作用,增大剂量并未明显提高其疗效。咪唑安定不产生逆行性遗忘作用。药物作用期间即刻记忆完整而长期记忆受损,对记忆的影响仅限于外显记忆而不包括内隐记忆。因此这种遗忘作用尚不能完全达到防止麻醉中知晓的目的。     

Specific brain networks during explicit and implicit decoding of emotional prosody

To better define the underlying brain network for the decoding of emotional prosody, we recorded high-resolution brain scans during an implicit and explicit decoding task of angry and neutral prosody. Several subregions in the right superior temporal gyrus (STG) and bilateral in the inferior frontal gyrus (IFG) were sensitive to emotional prosody. Implicit processing of emotional prosody engaged regions in the posterior superior temporal gyrus (pSTG) and bilateral IFG subregions, whereas explicit processing relied more on mid STG, left IFG, amygdala, and subgenual anterior cingulate cortex. Furthermore, whereas some bilateral pSTG regions and the amygdala showed general sensitivity to prosody-specific acoustical features during implicit processing, activity in inferior frontal brain regions was insensitive to these features. Together, the data suggest a differentiated STG, IFG, and subcortical network of brain regions, which varies with the levels of processing and shows a higher specificity during explicit decoding of emotional prosody.     

Absence of explicit and implicit memory in unconscious patients using a TCI of propofol

BACKGROUND: Episodes of implicit memory have been described during propofol anaesthesia. It remains unclear whether implicit memory is caused by short periods of awareness or occurs in an unconscious subject. METHODS: Sixty patients were randomized in an experimental group (EG), a control group (CG) and a reference group (RG). Loss of consciousness (LOC) was obtained by progressive stepwise increases of propofol using a target-controlled infusion device (Diprifusor, Alaris Medical Systems, San Diego, CA). A tape containing 20 words was played to the patients in the CG before the start of anaesthesia and to the patients in the EG at a constant calculated concentration of propofol associated with LOC. The tape was not played to the patients in the RG. Three memory tests were performed postoperatively. RESULTS: Explicit and implicit memories were evidenced in the CG but not in the EG. CONCLUSION: In our group of young ASA I/II patients, in the absence of any noxious stimulus, no implicit or explicit memory was found when the calculated concentration of propofol using a Diprifusor was maintained at the level associated with LOC.