Development of active controlled retrieval during middle childhood

The aim of this study was to examine the development of active controlled memory retrieval in children. Active retrieval is an effortful retrieval required to disambiguate information stored in memory. Brain imaging studies and monkey experiments have shown that the ventrolateral prefrontal cortex (VLPFC) is specifically engaged in this retrieval in both adult humans and monkeys. Three groups of 6‐, 8‐, and 11‐year‐old children and adults were tested on an active retrieval task. Results showed a marked difference in performance between 6‐year olds, who made more errors and had longer response time, and 8‐ and 11‐year olds, who had performance similar to adults. These results provide evidence that the VLPFC and the network supporting its top–down modulation undergo substantial maturational changes between 6 and 8 years old, giving children better active control of visual memory. © 2012 Wiley Periodicals, Inc. Dev Psychobiol 55: 443–449, 2013     

Effects of mnemonic load on cortical activity during visual working memory: Linking ongoing brain activity with evoked responses

The mechanisms generating task-locked changes in cortical potentials remain poorly understood, despite a wealth of research. It has recently been proposed that ongoing brain oscillations are not symmetric, so that task-related amplitude modulations generate a baseline shift that does not average out, leading to slow event-related potentials. We test this hypothesis using multivariate methods to formally assess the co-variation between task-related evoked potentials and spectral changes in scalp EEG during a visual working memory task, which is known to elicit both evoked and sustained cortical activities across broadly distributed cortical regions. 64-channel EEG data were acquired from eight healthy human subjects who completed a visuo-spatial associative working memory task as memory load was parametrically increased from easy to hard. As anticipated, evoked activity showed a complex but robust spatio-temporal waveform maximally expressed bilaterally in the parieto-occipital and anterior midline regions, showing robust effects of memory load that were specific to the stage of the working memory trial. Similarly, memory load was associated with robust spectral changes in the theta and alpha range, throughout encoding in posterior regions and through maintenance and retrieval in anterior regions, consistent with the additional resources required for decision making in prefrontal cortex. Analysis of the relationship between event-related changes in slow potentials and cortical rhythms, using partial least squares, is indeed consistent with the notion that the former make a causal contribution to the latter.     

Working memory performance of older adults with insomnia

Older individuals suffering insomnia typically report declines in their cognitive performance beyond what they consider to be normal changes due to the aging process. Recent neuro‐imaging studies have demonstrated frontal lobe hypo‐activation among insomniac populations when compared with healthy, good sleepers. However, research is yet to confirm whether frontal lobe hypo‐activation translates into objective declines when performing tasks hypothesized to draw upon this brain region. This study aimed to investigate whether older insomnia sufferers demonstrate significantly impaired performance on a challenging working memory task when compared with age‐matched good sleepers. Forty‐nine older individuals (mean age = 69.43 years, SD = 4.83) suffering from sleep maintenance insomnia were compared with 49 age‐matched good sleepers. Cognitive performance was assessed using the Double Span Memory Task, a computer‐based working memory task that requires participants to indicate the names and/or spatial locations of increasingly longer sequences of visually presented objects. After controlling for general intelligence, the individuals suffering from insomnia did not perform differently when compared with the good sleepers on either the simpler or more cognitively demanding components of the task. Older individuals with insomnia did not display an observable impairment of working memory in this study relative to good sleepers. Despite the mixed results from previous research, this study adds weight to the absence of objective impairment in insomniacs, at least while performing short‐term demanding cognitive tasks.     

Visual encoding differentially affects auditory event-related potentials during working memory retrieval

Previous working memory studies using auditory stimuli at both encoding and retrieval show amplitude decreases in event-related potentials (N100 and late positive wave, LPW) at retrieval as a function of memory load. This study tested if these effects are associated with phonological or semantic coding by presenting visual stimuli at encoding and auditory stimuli at retrieval. We hypothesized that event-related potentials associated with phonological but not semantic coding would be affected by modality differences at encoding and retrieval. Memory sets having one, three, or five visual digits were followed by auditory probes that subjects classified as present or absent from the set. Reaction time increased and LPW amplitudes decreased with increases in memory load, but there were no significant effects of memory load on N100 amplitude. Results suggest that with respect to brain activity that covaries with memory load, probe N100 amplitude is associated with phonological coding and LPW amplitude is associated with semantic coding.     

Intentional retrieval suppression can conceal guilty knowledge in ERP memory detection tests

Brain-activity markers of guilty knowledge have been promoted as accurate and reliable measures for establishing criminal culpability. Tests based on these markers interpret the presence or absence of memory-related neural activity as diagnostic of whether or not incriminating information is stored in a suspect's brain. This conclusion critically relies on the untested assumption that reminders of a crime uncontrollably elicit memory-related brain activity. However, recent research indicates that, in some circumstances, humans can control whether they remember a previous experience by intentionally suppressing retrieval. We examined whether people could use retrieval suppression to conceal neural evidence of incriminating memories as indexed by Event-Related Potentials (ERPs). When people were motivated to suppress crime retrieval, their memory-related ERP effects were significantly decreased, allowing guilty individuals to evade detection. Our findings indicate that brain measures of guilty knowledge may be under criminals’ intentional control and place limits on their use in legal settings.     

Sensory memory during physiological aging indexed by mismatch negativity (MMN)

Physiological aging affects early sensory-perceptual processes. The aim of this experiment was to evaluate changes in auditory sensory memory in physiological aging using the Mismatch Negativity (MMN) paradigm as index. The MMN is a marker recorded through the electroencephalogram and is used to evaluate the integrity of the memory system. We adopted a new, faster paradigm to look for differences between 3 groups of subjects of different ages (young, middle age and older adults) as a function of short or long intervals between stimuli. We found that older adults did not show MMN at long interval condition and that the duration of MMN varied according to the participants' age. The current study provides electrophysiological evidence supporting the theory that the encoding of stimuli is preserved during normal aging, whereas the maintenance of sensory memory is impaired. Considering the advantage offered by the MMN paradigm used here, these data might be a useful reference point for the assessment of auditory sensory memory in pathological aging (e.g., in neurodegenerative diseases).     

Functional correlates of distractor suppression during spatial working memory encoding

Executive working memory operations are related to prefrontal regions in the healthy brain. Moreover, neuroimaging data provide evidence for a functional dissociation of ventrolateral and dorsolateral prefrontal cortex. Most authors either suggest a modality-specific or a function-specific prefrontal cortex organization. In the present study we particularly aimed at the identification of different prefrontal cerebral areas that are involved in executive inhibitory processes during spatial working memory encoding. In an fMRI study (functional magnetic resonance imaging) we examined the neural correlates of spatial working memory processing by varying the amount of executive demands of the task. Twenty healthy volunteers performed the Corsi Block-Tapping test (CBT) during fMRI. The CBT requires the storage and reproduction of spatial target sequences. In a second condition, we presented an adapted version of the Block-Suppression-Test (BST). The BST is based on the original CBT but additionally requires the active suppression of visual distraction within the target sequences. In comparison to the CBT performance, particularly the left dorsolateral prefrontal cortex (BA 9) showed more activity during the BST condition. Our results show that the left dorsolateral prefrontal cortex plays a crucial role for executive controlled inhibition of spatial distraction. Furthermore, our findings are in line with the processing model of a functional dorsolateral-ventrolateral prefrontal cortex organization.     

Sleep-dependent prospective memory consolidation is impaired with aging

Study ObjectivesExisting literature suggests that sleep-dependent memory consolidation is impaired in older adults but may be preserved for personally relevant information. Prospective memory (PM) involves remembering to execute future intentions in a timely manner and has behavioral importance. As previous work suggests that N3 sleep is important for PM in young adults, we investigated if the role of N3 sleep in PM consolidation would be maintained in older adults.MethodsForty-nine young adults (mean age ± SD: 21.8 ± 1.61 years) and 49 healthy older adults (mean age ± SD: 65.7 ± 6.30 years) were randomized into sleep and wake groups. After a semantic categorization task, participants encoded intentions comprising four related and four unrelated cue-action pairs. They were instructed to remember to perform these actions in response to cue words presented during a second semantic categorization task 12 h later that encompassed either daytime wake (09:00 am–21:00 pm) or overnight sleep with polysomnography (21:00 pm–09:00 am).ResultsThe significant condition × age group × relatedness interaction suggested that the sleep benefit on PM intentions varied according to age group and relatedness (p = 0.01). For related intentions, sleep relative to wake benefitted young adults’ performance (p < 0.001) but not older adults (p = 0.30). For unrelated intentions, sleep did not improve PM for either age group. While post-encoding N3 was significantly associated with related intentions’ execution in young adults (r = 0.43, p = 0.02), this relationship was not found for older adults (r = −0.07, p = 0.763).ConclusionsThe age-related impairment of sleep-dependent memory consolidation extends to PM. Our findings add to an existing body of work suggesting that the link between sleep and memory is functionally weakened in older adulthood.     

EEG power changes reflect distinct mechanisms during long‐term memory retrieval

The roles of theta and alpha oscillations for long‐term memory (LTM) retrieval are still under debate. Both are modulated by LTM retrieval demands, but it is unclear what specific LTM functions they are related to. Here, different oscillatory correlates of LTM retrieval could be obtained for theta and alpha with a paradigm that is suited to monitor the activation of a varying number of material‐specific LTM representations. Both frequency bands responded parametrically to the number of retrieved items. However, only the alpha effect dissociated topographically for material type, indicating that the activation of material‐specific representations became systematically modulated. For theta, this effect was material‐unspecific with mid‐frontal topography. These results suggest that alpha is functionally related to the activation of stored information, whereas theta is a sign of retrieval‐related control processes.     

不同年龄精神分裂症患者的工作记忆

目的:探讨不同年龄精神分裂症患者的工作记忆差异,以及工作记忆与精神分裂症患者临床症状的关系。方法:采用横断面研究方法,用数字广度和空间广度测验分别对124例健康被试和123例符合美国精神障碍诊断与统计学手册第四版(DSM-Ⅳ)中精神分裂症诊断标准的住院患者进行工作记忆评估,采用阳性和阴性症状量表(PANSS)对患者进行临床症状评定。结果:除数字广度逆序分外,精神分裂症组数字广度和空间广度测验其余各项成绩均低于正常对照组(均P<0.05)。精神分裂症组和正常对照组的数字广度总分、正序分、逆序分均与年龄呈负相关(r=-0.21～-0.37,均P<0.05)。将两组按照年龄分为高年龄组和低年龄组进行协方差分析,数字广度和空间广度测验均表现出显著的组别和年龄效应(均P<0.05),但组别和年龄无交互作用(均P>0.05)。在精神分裂症组中,数字广度总分和数字广度逆序分与PANSS总分负相关(r=-0.22,-0.24,均P<0.05);数字广度总分、正序分、逆序分、空间广度总分、逆序分与阴性症状负相关(r=-0.22～-0.26,均P<0.05)。结论:本研究提示同正常人一样,精神分裂症患者的言语工作记忆随年龄增长逐渐下降,但这种下降并无疾病特异性,患者工作记忆水平的下降与阴性症状存在一定负相关。     

Death of memory T-cell subsets in humans: changes during aging

Aging is characterized by a progressive decline in various T-cell functions that are associated with a deficiency of naive and central memory T-cell subsets and the accumulation of oligoclonal effector memory T-cell subsets. In this article, we briefly review different pathways of death signaling and alterations in apoptotic signaling pathways in order to understand changes in various T cells in human aging.     

加工速度、工作记忆以及推理能力的年龄组和受教育程度水平差别

目的:探讨不同年龄阶段人群中,年龄与受教育程度对加工速度、工作记忆及推理能力的作用。方法:在全国6大行政区分年龄段并匹配性别进行取样,选取健康受试1754人[年龄16~86岁;男833人,女921人;受教育年限(10.4±3.2)年],将年龄分为16~24、25~34、35~44、45~54、55~64、65~69、70~86岁7个年龄段,将受教育程度分为小学及以下、初中、高中及以上3个受教育程度]。采用韦氏成人智力量表第四版(WAIS-IV)中文版的译码、背数、矩阵推理分量表分别评估加工速度、工作记忆广度及工作记忆、推理能力4项认知功能。采用多项式曲线拟合的方法对各认知成分随年龄的下降趋势进行拟合;使用单因素方差分析LSD多重比较法或Kruskal-Wallis H两两比较进行组间比较;使用通径分析的方法考察不同年龄阶段年龄、受教育程度对各认知成分的影响。结果:多项式曲线拟合结果发现,除工作记忆外,加工速度、工作记忆广度和推理能力得分随年龄的下降趋势均为非直线性趋势(R2=99.7%、98.5%、98.9%),且下降速度总体上逐渐放缓。受教育程度越高,各项认知成分的水平越高,且在加工速度和推理能力得分上随年龄下降的坡度越大。对不同年龄段各认知成分受教育程度组间的差异分析发现,在65~69岁、70~86岁上推理能力得分受教育程度组间差异无统计学意义(均P>0.05),其他年龄段受教育程度高者各认知得分均要高(均P<0.01)。通径分析表明,在不同的年龄阶段,使用不同的认知随年龄下降模型进行模型拟合时均拟合良好(χ2/df<3,各拟合优度指数均>0.9,残差均<0.05)。结论:加工速度和推理能力随年龄的下降呈非直线性下降趋势;不同的年龄阶段年龄与各认知成分的关系不同,50岁后主要通过加工速度中介;受教育程度在不同的认知成分随年龄的下降中表现不同。     

Impaired memory consolidation during sleep in patients with functional memory disorder

Functional memory disorder (FMD) is characterized by mnestic and attentional deficits without symptoms of mild cognitive impairment or dementia. FMD usually develops in subjects with high psychosocial stress level and is classified to the somatoform disorders. We assessed memory performance (procedural mirror tracing task, declarative visual and verbal memory task) and other cognitive functions before and after one night of sleep in 12 FMD patients (mean age: 51.7 yrs, 7 females) and 12 healthy subjects matched for age, gender and IQ. Memory performance and other neurocognitive tasks did not differ between the groups at baseline. After one night of sleep, FMD patients showed an impairment of declarative memory consolidation compared to healthy subjects (visual task: p = 0.004; verbal task: p = 0.039). Spectral analysis of sleep-EEG indicated an increased cortical excitation in FMD. We hypothesize that a hyperarousal state in FMD might contribute to sleep disturbance implicating negative effects on declarative memory consolidation.     

Sensory suppression and increased neuromodulation during actions disrupt memory encoding of unpredictable self-initiated stimuli

Actions modulate sensory processing by attenuating responses to self- compared to externally generated inputs, which is traditionally attributed to stimulus-specific motor predictions. Yet, suppression has been also found for stimuli merely coinciding with actions, pointing to unspecific processes that may be driven by neuromodulatory systems. Meanwhile, the differential processing for self-generated stimuli raises the possibility of producing effects also on memory for these stimuli; however, evidence remains mixed as to the direction of the effects. Here, we assessed the effects of actions on sensory processing and memory encoding of concomitant, but unpredictable sounds, using a combination of self-generation and memory recognition task concurrently with EEG and pupil recordings. At encoding, subjects performed button presses that half of the time generated a sound (motor-auditory; MA) and listened to passively presented sounds (auditory-only; A). At retrieval, two sounds were presented and participants had to respond which one was present before. We measured memory bias and memory performance by having sequences where either both or only one of the test sounds were presented at encoding, respectively. Results showed worse memory performance – but no differences in memory bias –, attenuated responses, and larger pupil diameter for MA compared to A sounds. Critically, the larger the sensory attenuation and pupil diameter, the worse the memory performance for MA sounds. Nevertheless, sensory attenuation did not correlate with pupil dilation. Collectively, our findings suggest that sensory attenuation and neuromodulatory processes coexist during actions, and both relate to disrupted memory for concurrent, albeit unpredictable sounds.     

Increased fMRI responses during encoding in mild cognitive impairment

Structural and functional magnetic resonance imaging (fMRI) was performed on 21 healthy elderly controls, 14 subjects with mild cognitive impairment (MCI) and 15 patients with mild Alzheimer's disease (AD) to investigate changes in fMRI activation in relation to underlying structural atrophy. The fMRI paradigm consisted of associative encoding of novel picture-word pairs. Structural analysis of the brain was performed using voxel-based morphometry (VBM) and hippocampal volumetry. Compared to controls, the MCI subjects exhibited increased fMRI responses in the posterior hippocampal, parahippocampal and fusiform regions, while VBM revealed more atrophy in MCI in the anterior parts of the left hippocampus. Furthermore, the hippocampal volume and parahippocampal activation were negatively correlated in MCI, but not in controls or in AD. We suggest that the increased fMRI activation in MCI in the posterior medial temporal and closely connected fusiform regions is compensatory due to the incipient atrophy in the anterior medial temporal lobe.     

Age-related effects on the neural correlates of autobiographical memory retrieval

Older adults recall less episodically rich autobiographical memories (AM), however, the neural basis of this effect is not clear. Using functional MRI, we examined the effects of age during search and elaboration phases of AM retrieval. Our results suggest that the age-related attenuation in the episodic richness of AMs is associated with difficulty in the strategic retrieval processes underlying recovery of information during elaboration. First, age effects on AM activity were more pronounced during elaboration than search, with older adults showing less sustained recruitment of the hippocampus and ventrolateral prefrontal cortex (VLPFC) for less episodically rich AMs. Second, there was an age-related reduction in the modulation of top-down coupling of the VLPFC on the hippocampus for episodically rich AMs. In sum, the present study shows that changes in the sustained response and coupling of the hippocampus and prefrontal cortex (PFC) underlie age-related reductions in episodic richness of the personal past.