Hippocampal activations during encoding and retrieval in a verbal working memory paradigm

Though the hippocampus has been associated with encoding and retrieval processes in episodic memory, the precise nature of its involvement in working memory has yet to be determined. This functional magnetic resonance imaging (fMRI) study employed a verbal working memory paradigm that allows for the within-subject comparison of functional activations during encoding, maintenance, and retrieval. In each trial, participants were shown 5 target words and, after an 8 s delay, a series of probe words. Probe words consisted of target matches, phonetically or semantically related foils, or foils unrelated to the target words. Both the left and right hippocampi showed higher mean activation amplitudes during encoding than maintenance. In contrast, the right dorsolateral prefrontal cortex (DLPFC) showed greater activation during maintenance than encoding. Both hippocampal and DLPFC regions were more active during retrieval than maintenance. Furthermore, an analysis of retrieval activation separated by probe type showed a trend toward greater bilateral hippocampal activation for probes related (both semantically and phonetically) to the target than for unrelated probes and still greater activation for target matches. This pattern suggests that there may be roles for the hippocampus and DLPFC in working memory that change as function of information processing stage. Additionally, the trend towards increased involvement of the hippocampus with the increase in relatedness of the probe stimuli to the information maintained is interpreted to be consistent with the role of the hippocampus in recollection-based retrieval in long-term memory and may indicate that this role extends to working memory processes.     

fMRI观察情绪记忆编码中的持续效应和瞬时效应

目的 通过fMRI检测情绪记忆相关脑区激活情况,探讨情绪记忆编码中持续效应与瞬时效应脑机制,为进一步探讨情绪记忆障碍相关疾病的神经机制提供依据。方法 22名健康成人参加试验。试验材料为60幅负性情景(情绪记忆)和60幅中性情景图片。采用组块-事件相关混合设计模式。受试者在完成编码任务的同时接受fMRI扫描。利用SPM 2和SPSS 13.0分别对fMRI数据及行为学数据进行统计分析。结果 情绪记忆(3.15±0.14)和中性(2.25±0.08)图片记忆成绩(d')差异有统计学意义(t=2.79,P＝0.010)。fMRI结果显示,情绪记忆增强与内侧颞叶和前额叶不同亚区相关;右侧杏仁核(r=0.50,P=0.019)和眶额皮层(r=0.64,P=0.001)与持续效应显著相关,左侧杏仁核(r=0.65,P=0.001)和眶额皮层(r=0.65,P=0.001)与瞬时效应显著相关。结论 情绪记忆编码中持续效应和瞬时效应具有不同的神经机制,分别与右侧和左侧杏仁核及眶额皮层相关。     

A dual-subsystem model of the brain's default network: self-referential processing, memory retrieval processes, and autobiographical memory retrieval

Most internally oriented mental activities are known to strongly activate the default network, which includes remembering the past, future thinking and social cognition, and are heavily self-referential, and demanding of memory retrieval processes. Based on these observations and building on related findings from the literature, the present article proposed a simple, dual-subsystem model of the default network. The ability of the model to estimate brain activity during autobiographical memory (AM) retrieval and related reference conditions was then tested by performing a quantitative meta-analysis of relevant literature. The model divided the default network into two subsystems. The first, called the 'cortical midline subsystem (CMS)', was comprised of the anteromedial prefrontal cortex and posterior cingulate cortex, and primarily mediates self-referential processing. The other, termed the 'parieto-temporal subsystem (PTS)', included the inferior parietal lobule, medial temporal lobe and lateral temporal cortex, and mainly supports memory retrieval processes. The meta-analysis of AM retrieval contrasts yielded a double dissociation that was consistent with this model. First, CMS regions associated more with an AM>laboratory-based memory (LM) contrast than with an AM>rest contrast, confirming that these regions play more critical roles in self-referential processing than memory retrieval processes. Second, all three PTS regions showed a greater association with an AM>rest contrast than with an AM>LM contrast, confirming that their role in memory retrieval processes is greater than in self-referential processing. Although the present model is limited in scope, both in terms of anatomical and functional specifications, it integrates diverse processes such as self-referential processing, episodic and semantic memory and subsystem interface, and provides useful heuristics that can guide further research on fractionation of the default network.     

Visual short-term memory: Activity supporting encoding and maintenance in retinotopic visual cortex

Recent studies have demonstrated that retinotopic cortex maintains information about visual stimuli during retention intervals. However, the process by which transient stimulus-evoked sensory responses are transformed into enduring memory representations is unknown. Here, using fMRI and short-term visual memory tasks optimized for univariate and multivariate analysis approaches, we report differential involvement of human retinotopic areas during memory encoding of the low-level visual feature orientation. All visual areas show weaker responses when memory encoding processes are interrupted, possibly due to effects in orientation-sensitive primary visual cortex (V1) propagating across extrastriate areas. Furthermore, intermediate areas in both dorsal (V3a/b) and ventral (LO1/2) streams are significantly more active during memory encoding compared with non-memory (active and passive) processing of the same stimulus material. These effects in intermediate visual cortex are also observed during memory encoding of a different stimulus feature (spatial frequency), suggesting that these areas are involved in encoding processes on a higher level of representation. Using pattern-classification techniques to probe the representational content in visual cortex during delay periods, we further demonstrate that simply initiating memory encoding is not sufficient to produce long-lasting memory traces. Rather, active maintenance appears to underlie the observed memory-specific patterns of information in retinotopic cortex.     

Reactivation of visual cortex during memory retrieval: content specificity and emotional modulation

Studies on memory retrieval suggest a reactivation of cortical regions engaged during encoding, such that visual or auditory areas reactivate for visual or auditory memories. The content specificity and any emotion dependency of such reactivations are still unclear. Because distinct visual areas are specialized in processing distinct stimulus categories, we tested for face and word specific reactivations during a memory task using functional magnetic resonance imaging (fMRI). Furthermore, because visual processing and memory are both modulated by emotion, we compared reactivation for stimuli encoded in a neutral or emotionally significant context. In the learning phase, participants studied pairs of stimuli that consisted of either a scene and a face, or a scene and a word. Scenes were either neutral or negative, but did not contain faces or words. In the test phase scenes were presented alone (one in turn), and participants indicated whether it was previously paired with a face, a word, or was new. Results from the test phase showed activation in a functionally defined face-responsive region in the right fusiform gyrus, as well as in a word-responsive region in the left inferior temporal gyrus, for scenes previously paired with faces and words, respectively. Reactivation tended to be larger in both the face- and word-responsive regions when the associated scene was negative as compared to neutral. However, relative to neutral context, the recall of faces and words paired with a negative context produced smaller activations in brain regions associated with social and semantic processing, respectively, as well as poorer memory performance overall. Taken together, these results support the idea of cortical memory reactivations, even at a content-specific level, and further suggest that emotional context may produce opposite effects on reactivations in early sensory areas and more elaborate processing in higher-level cortical areas.     

Top-down processes during auditory phoneme categorization in dyslexia: a PET study

While persistence of subtle phonological deficits in dyslexic adults is well documented, deficit of categorical perception of phonemes has received little attention so far. We studied learning of phoneme categorization during an activation H(2)O(15) PET experiment in 14 dyslexic adults and 16 normal readers with similar age, handedness and performance IQ. Dyslexic subjects exhibited typical, marked impairments in reading and phoneme awareness tasks. During the PET experiment, subjects performed a discrimination task involving sine wave analogues of speech first presented as pairs of electronic sounds and, after debriefing, as syllables /ba/ and /da/. Discrimination performance and brain activation were compared between the acoustic mode and the speech mode of the task which involved physically identical stimuli; signal changes in the speech mode relative to the acoustic mode revealed the neural counterparts of phonological top-down processes that are engaged after debriefing. Although dyslexic subjects showed good abilities to learn discriminating speech sounds, their performance remained lower than those of normal readers on the discrimination task over the whole experiment. Activation observed in the speech mode in normal readers showed a strongly left-lateralized pattern involving the superior temporal, inferior parietal and inferior lateral frontal cortex. Frontal and parietal subparts of these left-sided regions were significantly more activated in the control group than in the dyslexic group. Activations in the right frontal cortex were larger in the dyslexic group than in the control group for both speech and acoustic modes relative to rest. Dyslexic subjects showed an unexpected large deactivation in the medial occipital cortex for the acoustic mode that may reflect increased effortful attention to auditory stimuli.     

Re-experiencing old memories via hippocampus: a PET study of autobiographical memory

The time-scale of medial temporal lobe (MTL) involvement in storage and retrieval of episodic memory is keenly debated. To test competitive theories of long-term memory consolidation, the present work aimed at characterizing which cerebral regions are involved during retrieval of recent and remote strictly episodic autobiographical memory. Using positron emission tomography (PET), we examined mental retrieval of recent (0-1 year) and remote (5-10 years) autobiographical memories, controlling for the nature of the autobiographical memories (i.e., specificity, state of consciousness, vividness of mental visual imagery, emotion) retrieved during scanning by behavioral measures assessed at debriefing for each event recalled. Cognitive results showed that specificity and emotion did not change with time interval although both autonoetic consciousness and mental image quality were significantly higher for recent memories, suggesting an underlying shift in the phenomenal experience of remembering with the passage of time. The SPM analysis revealed common activations during the recollection of recent and remote memories that involved a widespread but mainly left-sided cerebral network, consistent with previous studies. Subtraction analysis demonstrated that the retrieval of recent (relative to remote) autobiographical memories principally activated the left dorsolateral prefrontal cortex whereas the retrieval of remote (relative to recent) autobiographical memories activated the inferior parietal cortex bilaterally. ROIs analysis revealed more hippocampal activity for remote memories than for recent ones and a preferentially right-sided involvement of the hippocampal responses whatever the remoteness of autobiographical memories. New insights based on higher hippocampal response to the remoteness of episodic autobiographical memories challenge the standard model and are less discrepant with the multiple trace theory.     

Brain networks involved in haptic and visual identification of facial expressions of emotion: An fMRI study

Previous neurophysiological and neuroimaging studies have shown that a cortical network involving the inferior frontal gyrus (IFG), inferior parietal lobe (IPL) and cortical areas in and around the posterior superior temporal sulcus (pSTS) region is employed in action understanding by vision and audition. However, the brain regions that are involved in action understanding by touch are unknown. Lederman et al. (2007) recently demonstrated that humans can haptically recognize facial expressions of emotion (FEE) surprisingly well. Here, we report a functional magnetic resonance imaging (fMRI) study in which we test the hypothesis that the IFG, IPL and pSTS regions are involved in haptic, as well as visual, FEE identification. Twenty subjects haptically or visually identified facemasks with three different FEEs (disgust, neutral and happiness) and casts of shoes (shoes) of three different types. The left posterior middle temporal gyrus, IPL, IFG and bilateral precentral gyrus were activated by FEE identification relative to that of shoes, regardless of sensory modality. By contrast, an inferomedial part of the left superior parietal lobule was activated by haptic, but not visual, FEE identification. Other brain regions, including the lingual gyrus and superior frontal gyrus, were activated by visual identification of FEEs, relative to haptic identification of FEEs. These results suggest that haptic and visual FEE identification rely on distinct but overlapping neural substrates including the IFG, IPL and pSTS region.     

Association of the distinct visual representations of faces and names: a PET activation study

A PET study of seven normal individuals was carried out to investigate the neural populations involved in the retrieval of the visual representation of a face when presented with an associated name, and conversely. Face-name associations were studied by means of four experimental matching conditions, including the retrieval of previously learned (1) name-name (NN), (2) face-face (FF), (3) name-face (NF), and (4) face-name (FN) associations, as well as a resting scan with eyes closed. Before PET images acquisition, subjects were presented with 24 unknown face-name associations to encode in 12 male/female couples. During PET scanning, their task was to decide whether the presented pair was a previously learned association. The right fusiform gyrus was strongly activated in FF condition as compared to NN and Rest conditions. However, no specific activations were found for NN condition relative to FF condition. A network of three areas distributed in the left hemisphere, both active in (NF-FF) and (FN-NN) comparisons, was interpreted as the locus of the integration of visual faces and names representations. These three regions were localized in the inferior frontal gyrus (BA 45), the medial frontal gyrus (BA 6) and the supramarginal gyrus of the inferior parietal lobe (BA 40). An interactive model accounting for these results, with BA 40 seen as an amodal binding region, is proposed.     

The role of the basal forebrain in episodic memory retrieval: a positron emission tomography study

Human lesion data indicate that the basal forebrain or orbitofrontal cortex, or both, as well as medial temporal and diencephalic structures, is important for normal memory and that its disruption causes the pure amnesic syndrome, in which episodic memory is grossly impaired while other kinds of memory remain preserved. Among these critical areas, functional imaging studies have so far failed to detect activation of the basal forebrain, although activation in the nearby orbitofrontal cortex has been reported during episodic memory retrieval. We employed positron emission tomography to elucidate the neural basis of episodic memory recall utilizing two types of time cues and successfully detected activity in the basal forebrain for the first time. Specifically, recall of previously memorized words from temporal cues was associated with activity in the basal forebrain, right middle frontal gyrus, right superior temporal gyrus, and posterior cingulate gyrus, whereas their recall from person cues was associated with activity in the left insula, right middle frontal gyrus, and posterior cingulate gyrus. Furthermore, percentage increases of regional blood flow in the basal forebrain were correlated with behavioral data of successful recall. Our results provide clear evidence that the human basal forebrain has a specific role in episodic memory recall, especially that from time-contextual information.     

Neurocognitive correlates of incidental verbal memory encoding: a magnetoencephalographic (MEG) study

In our current study, we applied whole head magnetoencephalography (MEG) in a subsequent memory paradigm. Magnetic fields were recorded while 20 healthy subjects (10 females, 10 males) incidentally encoded words during semantic and structural verbal processing tasks. Physiological data were then sorted according to the performance in subsequent memory tests and according to levels of processing, respectively, and analyzed for gender effects. Behavioral results show a clear advantage of semantic processing over structural processing with respect to retrieval success for both females and males. Despite alikeness of behavioral data, MEG results show considerable differences between males and females concerning both subsequent memory effects and levels of processing effects. For male subjects, we identified more distinct magnetic fields in anterior regions for subsequently remembered than for subsequently forgotten words (latency range from 300-650 ms after word onset) and for semantic processing than for structural processing, respectively. For female subjects, corresponding magnetic field differences pointed to posterior regions (subsequent memory effects from 450 ms to 750 ms after word onset). No qualitative differences were observed between subsequent memory effects during semantic processing compared to subsequent memory effects during structural processing. We try to reconcile results from male data with previous findings concerning subsequent memory effects by proposing the concept of width of processing, which holds that incidental memory formation is mediated by frontal activity on a physiological level and brought forward on a cognitive level by enhanced associating imposed by the task demands of semantic processing. Female data cannot be fully incorporated in this framework, but all the more prompt further gender-specific analyses of subsequent memory effects.     

氟哌啶醇对小鼠在避暗实验中学习记忆获得、巩固和再现过程的影响

目的:考察抗精神病药氟哌啶醇对小鼠在避暗实验中学习记忆的获得、巩固和再现过程的影响。方法:实验于2003-09/2004-01在沈阳药科大学药学院神经药理实验室完成。选择健康雄性昆明种小鼠200只。①氟哌啶醇对小鼠运动能力的影响:首先将50只小鼠随机均分5组,氟哌啶醇0.01mg/kg组、0.03mg/kg组、0.1mg/kg组、0.3mg/kg组、空白对照组。应用自主活动测定仪记录10min内小鼠自主活动次数。②避暗实验:训练前将小鼠头背着洞口放入明室,先适应环境3min,然后给暗室铜栅通以36V电流,小鼠一进入暗室即受电击,其正确反应是回到明室,铜栅通电持续5min,此为训练过程。24h后对小鼠进行记忆测验,记录小鼠第一次进入暗室的时间,此为避暗潜伏期,并记录5min内小鼠进入暗室的次数(即避暗错误次数),5min内未进入暗室的小鼠其潜伏期按300s计算。③应用避暗法考察氟哌啶醇对小鼠学习记忆的获得、巩固和再现过程的各实验中,每50只小鼠随机均分5组,空白对照组,氟哌啶醇0.01mg/kg组、0.03mg/kg组、0.1mg/kg组、阳性药物对照组。训练前50min各组皮下注射氟哌啶醇或溶媒,阳性药对照组在训练前10min腹腔注射东莨菪碱3mg/kg,此种给药方案测定小鼠记忆的获得过程;训练后各组立即给予受试药物或溶媒的给药方案为测定记忆的巩固过程,阳性对照组皮下注射亚硝酸钠125mg/kg;测验前50min各组给予受试药物或溶媒的给药方案为测定小鼠记忆的再现过程,阳性对照组在测验前30min灌胃300mL/L乙醇10mL/kg。结果:200只小鼠均进入结果分析。①氟哌啶醇在0.01～0.1mg/kg剂量范围内,与空白对照组比较小鼠自主活动无明显变化;而在0.3mg/kg剂量下,小鼠自主活动明显减少(P<0.001)。因此,在以下避暗实验中,氟哌啶醇采用0.01～0.1mg/kg剂量范围。②与空白对照组比较,训练前给予氟哌啶醇0.01～0.1mg/kg对小鼠错误潜伏期和错误次数无明显影响。阳性药东莨菪碱能明显增加小鼠避暗错误次数并缩短错误潜伏期。③训练后给予氟哌啶醇0.01mg/kg或0.1mg/kg,能明显缩短小鼠错误潜伏期(P<0.05),对小鼠错误次数无明显影响。阳性药亚硝酸钠能明显增加小鼠避暗错误次数(P<0.01),并缩短错误潜伏期(P<0.01)。④与空白对照组比较,测试前给予氟哌啶醇0.01～0.1mg/kg对小鼠错误潜伏期和错误次数无明显影响。阳性药乙醇能明显增加小鼠避暗错误次数(P<0.001),并缩短错误潜伏期(P<0.01)。结论:氟哌啶醇(0.01mg/kg,0.1mg/kg)损伤了避暗实验过程中小鼠记忆的巩固过程,而对记忆获得和再现过程没有明显影响。     

氟哌啶醇对小鼠在避暗实验中学习记忆获得、巩固和再现过程的影响

目的：考察抗精神病药氟哌啶醇对小鼠在避暗实验中学习记忆的获得、巩固和再现过程的影响。方法：实验于2003—09／2004-01在沈阳药科大学药学院神经药理实验室完成。选择健康雄性昆明种小鼠200只。①氟哌啶醇对小鼠运动能力的影响：首先将50只小鼠随机均分5组，氟哌啶醇0．01mg／kg组、0．03mg／kg组、0．1mg／kg组、0．3mg／kg组、空白对照组。应用自主活动测定仪记录10min内小鼠自主活动次数。②避暗实验：训练前将小鼠头背着洞口放入明室，先适应环境3min，然后给暗室铜栅通以36V电流，小鼠一进入暗室即受电击，其正确反应是回到明室，铜栅通电持续5min．此为训练过程。24h后对小鼠进行记忆测验，记录小鼠第一次进入暗室的时间，此为避暗潜伏期，并记录5min内小鼠进入暗室的次数（即避暗错误次数）．5min内未进入暗室的小鼠其潜伏期按300s计算。③应用避暗法考察氟哌啶醇对小鼠学习记忆的获得、巩固和再现过程的各实验中，每50只小鼠随机均分5组，空白对照组，氟哌啶醇0．01mg／kg组、0．03mg／kg组、0．1mg／kg组，阳性药物对照组。训练前50min各组皮下注射氟哌啶醇或溶媒，阳性药对照组在训练前10min腹腔注射东莨菪碱3mg／kg，此种给药方案测定小鼠记忆的获得过程；训练后各组立即给予受试药物或溶媒的给药方案为测定记忆的巩固过程，阳性对照组皮下注射亚硝酸钠125mg／kg；测验前50min各组给予受试药物或溶媒的给药方案为测定小鼠记忆的再现过程，阳性对照组在测验前30min灌胃300mL/L乙醇10mL/Mkg。结果：200只小鼠均进入结果分析。①氟哌啶醇在0．01～0．1mg／kg剂量范围内，与空白对照组比较小鼠自主活动无明显变化；而在0．3mg／kg剂量下．小鼠自主活动明显减少（P〈0．001）。因此，在以下避暗实验中，氟哌啶醇采用0．01～0．1mg／kg剂量范围。②与空白对照组比较，训练前给予氟哌啶醇0．01～0．1mg／kg对小鼠错误潜伏期和错误次数无明显影响。阳性药东莨菪碱能明显增加小鼠避暗错误次数并缩短错误潜伏期。③训练后给予氟哌啶醇0．01mg／kg或0．1mg／kg，能明显缩短小鼠错误潜伏期（P〈0．05），对小鼠错误次数无明显影响。阳性药亚硝酸钠能明显增加小鼠避暗错误次数（P〈0．01），并缩短错误潜伏期（P〈0．01）。④与空白对照组比较，测试前给予氟哌啶醇0．01～0．1mg／kg对小鼠错误潜伏期和错误次数无明显影响。阳性药乙醇能明显增加小鼠避暗错误次数（P〈0．001），并缩短错误潜伏期（P〈0．01）。结论：氟哌啶醇（0．01mg／kg，0．1mg／kg）损伤了避暗实验过程中小鼠记忆的巩固过程，而对记忆获得和再现过程没有明显影响。     

Ecphory of autobiographical memories: an fMRI study of recent and remote memory retrieval

Ecphory occurs when one recollects a past event cued by a trigger, such as a picture, odor, or name. It is a central component of autobiographical memory, which allows us to "travel mentally back in time" and re-experience specific events from our personal past. Using fMRI and focusing on the role of medial temporal lobe (MTL) structures, we investigated the brain bases of autobiographical memory and whether they change with the age of memories. Importantly, we used an ecphory task in which the remote character of the memories was ensured. The results showed that a large bilateral network supports autobiographical memory: temporal lobe, temporo-parieto-occipital junction, dorsal prefrontal cortex, medial frontal cortex, retrosplenial cortex and surrounding areas, and MTL structures. This network, including MTL structures, changed little with the age of the memories.     

The effect of adult-acquired hippocampal damage on memory retrieval: an fMRI study

Bilateral hippocampal pathology typically results in significant memory problems. Despite apparently similar structural damage, patients with such lesions can differ in the pattern of impairment and preservation of memory functions. Previously, an fMRI study of a developmental amnesic patient whose anoxic hippocampal damage was incurred perinatally revealed his residual hippocampal tissue to be active during memory retrieval. This hippocampal activity was apparent during the retrieval of personal and general facts relative to a control task. In this study, we used a similar fMRI paradigm to investigate whether residual hippocampal activation was present also in patient VC with adult-acquired anoxic hippocampal pathology. VC's performance and reaction times on the experimental personal and general fact tasks were comparable to age-matched control subjects. However, in contrast to the elderly control sample and the previous developmental amnesic patient, his residual hippocampal tissue did not show activation changes during the experimental tasks. This finding indicates that patient VC's successful retrieval of personal and general facts was achieved without a significant hippocampal contribution. It further suggests that the hippocampal activation observed in the elderly controls and previous developmental amnesic patient was not necessary for successful task performance. The reason for this difference in hippocampal responsivity between VC and the developmental amnesic patient remains to be determined. We speculate that it may relate to the age at which hippocampal damage occurred reflecting plasticity within the developing brain, or to cognitive differences between VC, the developmental amnesic patient, and the control subjects.     

Selective visual and auditory attention toward utterances-a PET study.

The purpose of this study was to reveal functional areas of the brain modulating processing of selective auditory or visual attention toward utterances. Regional cerebral blood flow was measured in six normal volunteers using positron emission tomography during two selective attention tasks and a control condition. The auditory task activated the auditory, inferior parietal, prefrontal, and anterior cingulate cortices. The visual task activated the visual association, inferior parietal, and prefrontal cortices. Both conditions activated the same area in the superior temporal sulcus. During the visual task, deactivation was observed in the auditory cortex. These results indicate that there exists a modality-dependent selective attention mechanism which activates or deactivates cortical areas in different ways.     

EEG oscillations and recognition memory: theta correlates of memory retrieval and decision making

Studies of memory retrieval have identified electroencephalographic (EEG) correlates of a test item's old-new status, reaction time, and memory load. In the current study, we used a multivariate analysis to disentangle the effects of these correlated variables. During retrieval, power of left-parietal theta (4-8 Hz) oscillations increased in proportion to how well a test item was remembered, and theta in central regions correlated with decision making. We also studied how these oscillatory dynamics complemented event-related potentials. These findings are the first to demonstrate that distinct patterns of theta oscillations can simultaneously relate to different aspects of behavior.     

Learning to perform a new movement with robotic assistance: comparison of haptic guidance and visual demonstration

Background  

Mechanical guidance with a robotic device is a candidate technique for teaching people desired movement patterns during motor rehabilitation, surgery, and sports training, but it is unclear how effective this approach is as compared to visual demonstration alone. Further, little is known about motor learning and retention involved with either robot-mediated mechanical guidance or visual demonstration alone.     

Cognitive reserve modulates functional brain responses during memory tasks: a PET study in healthy young and elderly subjects

Cognitive reserve (CR) is the ability of an individual to cope with advancing brain pathology so that he remains free of symptomatology. Epidemiological evidence and in vivo neurometabolic data suggest that CR may be mediated through education or IQ. The goal of this study was to investigate CR-mediated differential brain activation in 17 healthy young adults and 19 healthy elders. Using nonquantitative H(2)(15)O PET scanning, we assessed relative regional cerebral blood flow while subjects performed a serial recognition memory task under two conditions: nonmemory control (NMC), in which one shape was presented in each study trial; and titrated demand (TD), in which study list length was adjusted so that each subject recognized shapes at approximately 75% accuracy. A factor score that summarized years of education and scores on two IQ indices was used as an index of CR. Voxel-wise, multiple regression analyses were performed with TD minus NMC difference PET counts as the dependent variable and the CR variable as the independent variable of interest. We identified brain regions where regression slopes were different from zero in each separate group, and also those where regression slopes differed between the two age groups. The slopes were significantly more positive in the young in the right inferior temporal gyrus, right postcentral gyrus, and cingulate, while the elderly had a significantly more positive slope in left cuneus. Brain regions where systematic relationships between CR and brain activation differ as a function of aging are loci where compensation for aging has occurred. They may mediate differential ability to cope with brain changes in aging.     

Interactions between working memory and visual perception: an ERP/EEG study

How do working memory and perception interact with each other? Recent theories of working memory suggest that they are closely linked, and in fact share certain brain mechanisms. We used a sequential motion imitation task in combination with EEG and ERP techniques for a direct, online examination of memory load's influence on the processing of visual stimuli. Using a paradigm in which subjects tried to reproduce random motion sequences from memory, we found a systematic decrease in ERP amplitude with each additional motion segment that was viewed and memorized for later imitation. High-frequency (>20 Hz) oscillatory activity exhibited a similar position-dependent decrease. When trials were sorted according to the accuracy of subsequent imitation, the amplitude of the ERPs during stimulus presentation correlated with behavioral performance: the larger the amplitude, the more accurate the subsequent imitation. These findings imply that visual processing of sequential stimuli is not uniform. Rather, earlier information elicits stronger neural activity. We discuss possible explanations for this observation, among them competition for attention between memory and perception and encoding of serial order by means of differential activation strengths.