不同阶段血管性认知功能障碍患者事件相关电位P300的特点

目的:探讨不同阶段血管性认知功能障碍(VCI)患者的听觉ERP-P300特点,以为其早期诊断提供客观依据。方法:根据VCI诊断标准选取血管性痴呆(VaD)、无痴呆的血管认知功能障碍(VCIND)患者各50例,并以认知功能正常的脑血管病患者50例为对照组,分别对其进行听觉ERP-P300检测。结果:(1)与对照组相比VCIND组P300潜伏期、N200-P300波间期延长,P300波幅减低;VaD组N200、P300潜伏期,P200-N200、N200-P300波间期明显延长,P300波幅减低,差异有统计学意义。(2)所有患者N200、P300潜伏期与性别无关,与MMSE分数呈负相关,P300潜伏期与年龄正相关。结论:VCIND组患者的ERP-P300特点为P300潜伏期、N200-P300波间期延长,P300波幅减低;VaD组除上述特点外,N200潜伏期、P200-N200波间期延长。ERP-P300对VCI有一定的早期诊断价值。     

Objective markers of drug effects on brain function from recordings of scalp potential in healthy volunteers

In order to stress the importance of P300 responses in drug development, we describe the spatiotemporal characteristics of this objective, evoked event-related potential. These brain activations reflect mnemonic function, in which limbic structures play a role. It is demonstrated that a pharmacological challenge concerning, for example, the cholinergic system in young healthy volunteers induces modifications in P300 reminiscent of the aging brain. We use this type of observation to build a model in which it can be verified whether the deterioration can be counteracted by treatment with "cognition-enhancing" drugs. If we accept the extrapolation of the pharmacological effects to symptomatology, scalp potential analysis offers an appropriate tool for the study of drug interactions in early proof-of-concept models.     

运动准备和执行的事件相关功能磁共振研究

目的:应用事件相关功能磁共振成像技术研究参与运动准备和执行的脑区的激活特点.方法:应用事件相关功能磁共振成像技术记录12名右利手健康受试者在序列手指运动过程中运动准备与运动执行大脑皮层的功能活动.采用美国威斯康辛医学院AFNI软件包进行每个像素的血氧变化分析,作出与运动准备和运动执行有关的脑激活图.结果:与运动准备有关的激活主要集中在双侧运动前区(PMC)前部,双侧后顶叶(PPC)后部;与执行有关的激活区主要集中在对侧初级运动区(M1),双侧辅助运动区(SMA)本部;而双侧辅助运动区前部、双侧运动前区后部在运动准备与执行过程中均有激活.结论:人脑内与运动相关的脑区功能并非单一.     

听觉事件相关电位同侧与对侧记录的比较

目的 比较同侧与对侧听觉事件相关电位（auditory event-related potential,AWRP）的反应特性，探讨AERP在二侧听皮层发源上的神经电生理特点和机制及其临床意义。方法 选择正常青年人，采用同侧与对侧导联同时记录的方法记录AERP，分析二种记录条件下AERP各波潜伏期，幅值和波形的特性。结果 同侧与对侧记录的AERP在潜伏期和幅值上无显著性差异，但同侧记录的AERP波形明显优于对侧记录的曲线，表现为波形曲线光滑，波峰明显易辨，杂波成份少。结论 AERP在二侧听皮层的神经发源基本上是对称的，但同侧的反应怀明显优于对侧，可能与AERP的发源有部分皮层下成份的参与，听觉神经通路的双侧传导以及内侧橄榄耳蜗系统的对侧抑制效应有关，临床应用时应考虑到AERP发源部位和成份多元化的影响因素。     

Decay time of the auditory sensory memory trace during wakefulness and REM sleep

In a repetitive auditory stimulus sequence, deviant infrequent tones typically elicit a component of auditory event-related potentials termed mismatch negativity (MMN). The elicitation of MMN is assumed to reflect the existence of a memory trace of the standard stimulus that has a decay time of about 10 s and is strengthened by repetition of the standards. The main aim of the present study was to test the decay time of the sensory memory trace during rapid-eye movement (REM) sleep vs. wakefulness, as indexed by the MMN. Subjects were presented 10 tone trains, separated by 3, 6, or 9 s of silence, during waking and REM sleep. Each train consisted of 9 standards of 1000 Hz and 1 deviant of 2000 Hz that occurred at position 1, 2, 4, or 6. The waking deviants elicited a frontocentral negativity with a scalp topography equivalent to the MMN component. During REM sleep, the negative component showed the same scalp distribution only for the 3-s intertrain interval (ITI). In this brain state, the MMN amplitude was smaller and decreased with prolongation of the ITI. These results suggest a weaker sensory memory trace formation and a premature decay time of such a memory trace during REM sleep as compared with wakefulness.     

Grabbing your ear: rapid auditory-somatosensory multisensory interactions in low-level sensory cortices are not constrained by stimulus alignment

Multisensory interactions are observed in species from single-cell organisms to humans. Important early work was primarily carried out in the cat superior colliculus and a set of critical parameters for their occurrence were defined. Primary among these were temporal synchrony and spatial alignment of bisensory inputs. Here, we assessed whether spatial alignment was also a critical parameter for the temporally earliest multisensory interactions that are observed in lower-level sensory cortices of the human. While multisensory interactions in humans have been shown behaviorally for spatially disparate stimuli (e.g. the ventriloquist effect), it is not clear if such effects are due to early sensory level integration or later perceptual level processing. In the present study, we used psychophysical and electrophysiological indices to show that auditory-somatosensory interactions in humans occur via the same early sensory mechanism both when stimuli are in and out of spatial register. Subjects more rapidly detected multisensory than unisensory events. At just 50 ms post-stimulus, neural responses to the multisensory 'whole' were greater than the summed responses from the constituent unisensory 'parts'. For all spatial configurations, this effect followed from a modulation of the strength of brain responses, rather than the activation of regions specifically responsive to multisensory pairs. Using the local auto-regressive average source estimation, we localized the initial auditory-somatosensory interactions to auditory association areas contralateral to the side of somatosensory stimulation. Thus, multisensory interactions can occur across wide peripersonal spatial separations remarkably early in sensory processing and in cortical regions traditionally considered unisensory.     

Is the failure to detect stimulus deviance during sleep due to a rapid fading of sensory memory or a degradation of stimulus encoding?

The mismatch negativity (MMN) is thought to reflect the outcome of a system responsible for the detection of change in an otherwise repetitive, homogenous acoustic environment. This process depends on the storage and maintenance of a sensory representation of the frequently presented stimulus to which the deviant stimulus is compared. Few studies have been able to record the MMN in non-rapid eye movement (NREM) sleep. This pattern of results might be explained by either a rapid fading of sensory memory or an inhibition of stimulus input prior to entry into the cortical MMN generator site. The present study used a very rapid rate of presentation in an attempt to capture mismatch-related negativity prior to the fading of sensory memory. Auditory event-related potentials were recorded from 12 subjects during a single sleep period. A 1000 Hz standard stimulus was presented every 150 ms. At random, on 6.6% of the trials, the standard was changed to either a large 2000 Hz or a small 1100 Hz deviant. In wakefulness, the large deviant elicited an extended negativity that was reduced in amplitude following the presentation of the small deviant. This negativity was also apparent during REM sleep following the presentation of the large deviant. These deviant-related negativities (DRNs) were probably a composite of N1 and MMN activity. During NREM sleep (stage 2 and slow-wave sleep), only the large deviant continued to elicit a DRN. However this DRN might be overlapped by the initial activity of a component that is unique to sleep, the N350. There was little evidence of the DRN or the MMN during sleep following the presentation of the small deviant. A rapid rate of presentation, therefore, does not preserve the MMN following small deviance within sleep. It is possible that inhibition of sensory input occurs before entry into the MMN generating system in the temporal cortex.     

A shift of visual spatial attention is selectively associated with human EEG alpha activity

Event-related potentials and ongoing oscillatory electroencephalogram (EEG) activity were measured while subjects performed a cued visual spatial attention task. They were instructed to shift their attention to either the left or right visual hemifield according to a cue, which could be valid or invalid. Thereafter, a peripheral target had to be evaluated. At posterior parietal brain areas early components of the event-related potential (P1 and N1) were higher when the cue had been valid compared with invalid. An anticipatory attention effect was found in EEG alpha magnitude at parieto-occipital electrode sites. Starting 200 ms before target onset alpha amplitudes were significantly stronger suppressed at sites contralateral to the attended visual hemifield than ipsilateral to it. In addition, phase coupling between prefrontal and posterior parietal electrode sites was calculated. It was found that prefrontal cortex shows stronger phase coupling with posterior sites that are contralateral to the attended hemifield than ipsilateral sites. The results suggest that a shift of attention selectively modulates excitability of the contralateral posterior parietal cortex and that this posterior modulation of alpha activity is controlled by prefrontal regions.     

Can electrophysiological assessments of brain function be useful to the intensive care physician in daily clinical practice?

Changes in electroencephalogram parameters and auditory event-related potentials, induced by interruption to propofol sedation in intensive care patients, provide a number of electrophysiological measures that can be used to assess neurological function accurately. Studies of electroencephalogram parameters suggest that power spectral estimation, as root mean square power, is more useful and precise than spectral edge frequency 95% in evaluating the functional integrity of the brain. When such parameters are used to evaluate neurological function, in particular the N100 and mismatch negativity components, a precise assessment of a patient's readiness to awaken from a pharmacologically induced coma (such as sedation) can be obtained. In terms of ease of use, however, it is more difficult to establish whether N100 or mismatch negativity is superior.     

P50 and acoustic startle gating are not related in healthy participants

Although P50 event-related potential (ERP) suppression and acoustic startle prepulse inhibition are conceptualized as measures of sensory and sensorimotor gating, respectively, the relationship between these measures is unclear. In the present study, P50 and prepulse inhibition trials were interleaved in a single testing session to determine their relationship. Thirty-one healthy participants were presented with startle- and P50-eliciting stimuli across six trial blocks. Lead stimuli (i.e., the prepulse to the acoustic startle and the first click in the dual click ERP paradigm) resulted in significant gating, or amplitude attenuation, of responses to the startle probe and second paired click. There were no meaningful correlations between the P50 and prepulse inhibition variables, indicating that P50 suppression and acoustic startle prepulse inhibition measure distinct neural mechanisms. The implications of these findings for operationally defining the psychological construct of gating with these psychophysiological measures are discussed.