Neural correlates of prospective memory across the lifespan

OVERVIEW: Behavioural data reveal an inverted U-shaped function in the efficiency of prospective memory from childhood to young adulthood to later adulthood. However, prior research has not directly compared processes contributing to age-related variation in prospective memory across the lifespan, hence it is unclear whether the same factors explain the 'rise and fall' of prospective remembering from childhood to later adulthood. The present study examined this question using a paradigm that allowed us to consider the behavioural and neural correlates of processes associated with the prospective and retrospective components of prospective memory. METHODS: We compared 14 adolescents, 14 young adults, and 14 old adults in a paradigm where the prospective memory task was embedded in a semantic categorization task. RESULTS: The behavioural data revealed an inverted U-shaped function with adolescents and old adults performing poorly relative to young adults. Analyses of the error data revealed that different processes may have contributed to failures of prospective memory in adolescents and older adults. This finding was supported by age differences in ERP-components for cue detection and post-retrieval processes. Additionally, source localization using LORETA revealed different patterns of neural recruitment for adolescents and older adults relative to younger adults. CONCLUSION: Our findings demonstrate that adolescents and older adults show different patterns of behavioural errors and neural recruitment for successful prospective remembering indicating that different processes may contribute to the 'rise and fall' of prospective memory across the lifespan.     

Symptomatic and functional correlates of regional brain physiology during working memory processing in patients with recent onset schizophrenia

Patients with schizophrenia show altered patterns of functional activation during working memory processing; specifically, high-performing patients appear to hyper-activate and low-performing patients appear to hypo-activate when compared with controls. It remains unclear how these individual differences in neurophysiological activation relate to the clinical presentation of the syndrome. In this functional magnetic resonance imaging (fMRI) study, the relationship is examined using partial least squares (PLS), a multivariate statistical technique that selects underlying latent variables based on the covariance between two sets of variables, in this case, clinical variables and regional fMRI activations during a verbal working memory task. The PLS analysis extracted two latent variables, and the significance of these associations was confirmed through permutation. Lower levels of activation during task performance across frontal and parietal regions of interest in the left hemisphere were found to covary with poorer role functioning and greater severity of negative and disorganized symptoms, while lower activation in right frontal and subcortical regions of interest was found to covary with better social functioning and fewer positive symptoms. These results suggest that appropriately lateralized patterns of functional activation during working memory processing are related to the severity of negative and disorganized symptoms and to the level of role and social functioning in schizophrenia.     

The effects of working memory demands on the neural correlates of prospective memory

Event-related brain potentials (ERPs) were used to examine the reciprocal costs of working and prospective memory loads on the neural correlates of the realization of delayed intentions and the detection of target stimuli. The electrophysiological data revealed several interesting results: (1) distinct modulations of the ERPs were elicited by working memory targets and prospective memory cues, (2) working memory load modulated the amplitude of the N300 elicited by prospective memory cues, (3) prospective memory load was associated with a broadly distributed sustained modulation that began shortly after stimulus onset, and (4) brain-behavior correlations between the neural correlates of prospective memory and working memory varied with the working memory demands of the ongoing activity. These findings appear to indicate that attentional processes associated with the detection of prospective memory cues are sensitive to the working memory demands of the ongoing activity and that different processes may support prospective memory depending on the working memory demands of the ongoing activity.     

Remembering what could have happened: Neural correlates of episodic counterfactual thinking

Recent evidence suggests that our capacities to remember the past and to imagine what might happen in the future largely depend on the same core brain network that includes the middle temporal lobe, the posterior cingulate/retrosplenial cortex, the inferior parietal lobe, the medial prefrontal cortex, and the lateral temporal cortex. However, the extent to which regions of this core brain network are also responsible for our capacity to think about what could have happened in our past, yet did not occur (i.e., episodic counterfactual thinking), is still unknown. The present study examined this issue. Using a variation of the experimental recombination paradigm (Addis, Pan, Vu, Laiser, & Schacter, 2009. Neuropsychologia. 47: 2222–2238), participants were asked both to remember personal past events and to envision alternative outcomes to such events while undergoing functional magnetic resonance imaging. Three sets of analyses were performed on the imaging data in order to investigate two related issues. First, a mean-centered spatiotemporal partial least square (PLS) analysis identified a pattern of brain activity across regions of the core network that was common to episodic memory and episodic counterfactual thinking. Second, a non-rotated PLS analysis identified two different patterns of brain activity for likely and unlikely episodic counterfactual thoughts, with the former showing significant overlap with the set of regions engaged during episodic recollection. Finally, a parametric modulation was conducted to explore the differential engagement of brain regions during counterfactual thinking, revealing that areas such as the parahippocampal gyrus and the right hippocampus were modulated by the subjective likelihood of counterfactual simulations. These results suggest that episodic counterfactual thinking engages regions that form the core brain network, and also that the subjective likelihood of our counterfactual thoughts modulates the engagement of different areas within this set of regions.     

The role of dual-task and task-switch in prospective memory: Behavioural data and neural correlates

Event-based prospective memory (PM) requires remembering the delayed execution of an intended action in response to a pre-specified PM cue while being actively engaged in an ongoing task in which the cue is embedded. To date, experimental paradigms vary as to whether or not they require participants immediately to stop working on the ongoing task whenever they encounter a PM event (cue) and directly switch to the prospective action (task-switch approach). Alternatively, several other paradigms used in the literature encourage participants to continue working on the ongoing task item after the cue, and only then, perform the prospective action (dual-task approach). The present study explores the possible behavioural and electrophysiological effects that both approaches may have on PM performance. Seventeen young adults performed both versions of a standard PM task in a counterbalanced order during which behavioural data and electroencephalogram (EEG) were recorded. Behavioural data showed a decrement in PM performance in the task-switch compared to the dual-task condition. In addition, EEG data revealed differences between the dual-task and task-switch approach in event-related potential (ERP) components associated with response inhibition and with post-retrieval monitoring (i.e. late positive complex). No differences between the two tasks were found with regard to the PM event detection processes (i.e. N300) and the retrieval of the intended action from long-term memory. In sum, findings demonstrate that it does make a difference which task approach is applied and suggest that dual-task and task-switch paradigms may result in different processing and neurophysiological dynamics particularly concerning attentional resources and cognitive control.     

Hippocampal-neocortical networks differ during encoding and retrieval of relational memory: Functional and effective connectivity analyses

Encoding and retrieval of relational information requires interaction between the hippocampus and various neocortical regions, but it is unknown whether the connectivity of hippocampal-neocortical networks is different at input and output stages. To examine this, we conducted a network analysis of event-related fMRI data collected during a face-recognition, remember/know paradigm. Directed analyses in the medial temporal lobe identified a small region in the left hippocampus that showed differential activation for encoding and retrieval of recollected versus familiar items. Multivariate seed partial least squares (PLS) analysis was used to identify brain regions that were functionally connected to this hippocampal region at encoding and retrieval of ‘remembered’ items. Anatomically based structural equation modeling (SEM) was then used to test for differences in effective connectivity of network nodes between these two memory stages. The SEM analysis revealed a reversal of directionality between the left hippocampus (LHC) and left inferior parietal cortex (LIPC) at encoding and retrieval. During encoding, activation of the LHC had a positive influence on the LIPC, whereas during retrieval the reverse pattern was found, i.e., the LIPC activation positively influenced LHC activation. These findings emphasize the importance of hippocampal-parietal connections and underscore the complexity of their interactions in initial binding and retrieval/reintegration of relational memory. We also found that, during encoding, the right hippocampus had a positive influence on the right retrospenial cortex, whereas during retrieval this influence was significantly weaker. We submit that examining patterns of connectivity can be important both to elaborate and constrain models of memory involving hippocampal-neocortical interactions.     

The temporal dynamics of prospective memory: a review of the ERP and prospective memory literature

This review article examines the literature using event-related brain potentials (ERPs) to study the temporal dynamics of the neurocognitive processes underpinning event-based prospective memory (PM). The successful encoding of delayed intentions is associated with slow wave activity over the frontal region in younger adults and this activity is attenuated in older adults. The realization of delayed intentions is associated with distinct components of the ERPs that are associated with the detection of a PM cue in the environment (N300), the retrieval of an intention from memory (recognition old-new effect), signaling the need to switch from the ongoing activity (frontal positivity), and configuration of the PM task set (parietal positivity). The development of prospective memory across the lifespan appears to reflect development of processes associated with retrieval of the cue-intention association from memory, and executive processes related to cue detection. The final section of the review examines the nature of executive processes that support PM within the context of a theory of the supervisory attentional system.     

Structural correlates of prospective memory

Prospective memory (PM) includes the encoding and maintenance of an intention, and the retrieval and execution of this intention at the proper moment in the future. The present study expands upon previous behavioral, electrophysiological, and functional work by examining the association between grey matter volume and PM. Estimates of grey matter volume in theoretically relevant regions of interest (prefrontal, parietal, and medial temporal) were obtained in conjunction with performance on two PM tasks in a sample of 39 cognitively normal and very mildly demented older adults. The first PM task, termed focal in the literature, is supported by spontaneous retrieval of the PM intention whereas the second, termed non-focal, relies on strategic monitoring processes for successful intention retrieval. A positive relationship was observed between medial temporal volume and accuracy on the focal PM task. An examination of medial temporal lobe subregions revealed that this relationship was strongest for the hippocampus, which is considered to support spontaneous memory retrieval. There were no significant structure–behavior associations for the non-focal PM task. These novel results confirm a relationship between behavior and underlying brain structure proposed by the multiprocess theory of PM, and extend findings on cognitive correlates of medial temporal lobe integrity.     

ERP correlates of retrieval orientation: direct versus indirect memory tasks

The neural correlates of the processes involved in cueing memory retrieval were investigated using ERPs to unstudied (new) items in a yes/no recognition test (direct memory task) and a semantic judgement task (indirect memory task). Subjects encoded either pictures or auditory words and were tested on visual words. We replicated previous findings that ERPs to correct rejections of new items in a yes/no recognition test differ according to the study material, with ERPs to words encoded as pictures being more negative (relative to a average mastoid reference) than words encoded auditorily [Hornberger, M., Morcom, A.M., et al., 2004. Neural correlates of retrieval orientation: effects of study-test similarity. J. Cogn. Neurosci. 16 (7), 1196-1210]. This difference was sustained from approximately 450-1,200 ms. An effect of study material on the ERP to new items was found in the indirect memory task but was both earlier onsetting and shorter lived, ca. 250-600 ms. These findings add weight to the concept of 'retrieval orientation' [Rugg, M.D., Wilding, E.L., 2000. Retrieval processing and episodic memory. Trends Cogn. Sci. 4 (3) 108-115] - differential processing of retrieval cues according to the form of the sought-for information - by showing that a putative ERP correlate of retrieval orientation is restricted to direct memory tasks.     

Neural correlates of cognitive control and conflict detection in the Stroop and digit-location tasks

In two experiments, event-related brain potentials were used to examine the neural correlates of cognitive control and conflict processing in the Stroop and digit-location tasks. The relevant dimension was cued on a trial-by-trial basis before stimulus onset. This method allows one to dissociate modulations of the event-related brain potentials (ERPs) associated with cognitive control from modulations of the ERPs associated with conflict processing that are temporally confounded in the standard Stroop task. Cognitive control was associated with a slow wave over the occipital-parietal region that differentiated goal-compatible from goal-incompatible responses in both the Stroop and digit-location tasks. Conflict processing was associated with a N450, in the Stroop task, and a conflict sustained potential (SP) in both tasks. The amplitude of the N450 was similar for color naming and word reading trials. The character of the conflict SP varied over the frontal and central-parietal regions. Over the left lateral frontal region the conflict SP was similar in amplitude across type of response in the Stroop and digit-location tasks. Over the right lateral frontal region the conflict SP was greater in amplitude for the less dominant stimulus dimension (i.e. color or digit). The findings of these experiments clearly demonstrate that different neural systems support cognitive control and conflict processing, with some degree of hemispheric specialization observed for conflict processing.     

Neural correlates of memory retrieval and evaluation

Results from recent neuroimaging studies have led to a controversy as to whether right or left prefrontal regions are relatively more important for episodic retrieval. To address this issue, we recorded event-related brain potentials during two recognition tests with identical stimuli but differing retrieval demands. In both tests, participants viewed a sequence of object drawings, half of which were identical to ones viewed earlier except for a change in size and half of which were new. Instructions were to discriminate between old and new objects (general test) or to additionally decide whether old objects were larger or smaller at study (specific test). Frontal brain potentials that were more positive during the specific than during the general test for both old and new objects were interpreted as neural correlates of the process by which specific attributes of test cues are compared with information retrieved from memory. Another ERP difference between the specific and general tests, which was observed for old objects only, had a left posterior scalp topography and was interpreted to reflect the reactivation of memories for studied objects. Frontal and posterior potentials thus reflected two memory processes important for accurate episodic retrieval. Furthermore, our findings suggest that both left and right prefrontal regions were engaged when demands to retrieve and evaluate perceptual information increased.     

Neural correlates of memory for faces

When we encounter someone in our dairy lives, we have some impressions of that person. Previous psychological studies have reported that the impressions for ather people affect memory for faces of other people. However, little is known about the neural mechanisms underlying the effects of face-based impressions on memory for faces. The goal of this review article is to review functional neuroimaging findings which investigate neural activations related to the effects of facial expressions, attractiveness, and trustworthiness on memory for faces, and to propose a functional model regarding the memory processing of faces. Three major findings emerged from this review. First, face-based positive signals, including the smiling expression and facial attractiveness, enhanced memory for faces, and the memory enhancement was involved in an interaction between activities in the reward-related orbitofrontal cortex and the memory-related hippocampus. Second, the information of untrustworthiness conveyed from faces enhanced the remembering of faces, and an interaction between activities in the punishment-related insula and the memory-related hippocampus contributed to this memory enhancement. Third, the processing of facial attractiveness highly correlated with the processing of trustworthiness, and the orbitofrontal and insular cortices, in which activities were negatively correlated, showed significant activations in each process of face-based positive and negative signals. Memory for faces could be organized by the "core" system, which is involved in the basic memory process of faces, and the "sub" system, which is important in the modulation of memory for faces.     

Prospective memory in adults with high-functioning autism spectrum disorders: Exploring effects of implementation intentions and retrospective memory load

This study examined, for the first time, the impact of implementation intentions on prospective memory (PM) performance in adults with autism spectrum disorders (ASD) and further explored the role of retrospective memory for PM in ASD. PM was assessed with Virtual Week, a computerized game simulating upcoming everyday-life tasks. Twenty-seven adults with ASD and 27 age- and ability-matched controls were included. Half of the participants were instructed to form implementation intentions (i.e., encoding PM tasks in form of if-then statements), while the rest received simple PM instructions. Results provide first tentative evidence for beneficial effects of implementation intentions and PM tasks with low demands on retrospective memory for adults with ASD's PM. Overall, results point to the importance of planning and retrospective memory for successful prospective remembering in ASD.     

Neural correlates of consolidation in working memory

Many of our daily activities rely on a brain system called working memory, which implements our ability to encode information for short-term maintenance, possible manipulation, and retrieval. A recent intracranial study of patients performing a paradigmatic working memory task revealed that the maintenance of information involves a distributed network of oscillations in the gamma band (>40 Hz). Using a similar task, we focused on the encoding stage and targeted a process referred to as short-term consolidation, which corresponds to the encoding of novel items in working memory. The paradigm was designed to manipulate the subjects' intention to encode: series of 10 letters were presented, among which only five had to be remembered, as indicated by visual cues preceding or following each letter. During this task we recorded the intracerebral EEG of nine epileptic patients implanted in mesiotemporal structures, perisylvian regions, and prefrontal areas and used time-frequency analysis to search for neural activities simultaneous with the encoding of the letters into working memory. We found such activities in the form of increases of gamma band activity in a set of regions associated with the phonological loop, including the Broca area and the auditory cortex, and in the prefrontal cortex, the pre- and postcentral gyri, the hippocampus, and the fusiform gyrus.     

Impairments in prospective and retrospective memory following stroke

Prospective memory (PM) is the ability to carry out a planned intention at a future time. We studied PM deficits in a group of community-dwelling stroke survivors compared with normal controls. Twelve stroke patients and 12 matched controls performed a series of tests assessing executive function, prospective (PM) and retrospective memory (RM). Patients performed less well than controls on laboratory measures of PM and associative RM; they also showed deficits on standard tests of RM and executive control. The groups did not differ on more structured clinical measures of executive function, RM, PM or self-rated PM and RM. The results are discussed in terms of an impairment in the ability to ‘self-initiate’ effortful cognitive processes.     

Neural correlates of music-syntactic processing in two-year old children

Music is a basic and ubiquitous socio-cognitive domain. However, our understanding of the time course of the development of music perception, particularly regarding implicit knowledge of music-syntactic regularities, remains contradictory and incomplete. Some authors assume that the acquisition of knowledge about these regularities lasts until late childhood, but there is also evidence for the presence of such knowledge in four- and five-year-olds. To explore whether such knowledge is already present in younger children, we tested whether 30-month-olds (N = 62) show neurophysiological responses to music-syntactically irregular harmonies. We observed an early right anterior negativity in response to both irregular in-key and out-of-key chords. The N5, a brain response usually present in older children and adults, was not observed, indicating that processes of harmonic integration (as reflected in the N5) are still in development in this age group. In conclusion, our results indicate that 30-month-olds already have acquired implicit knowledge of complex harmonic music-syntactic regularities and process musical information according to this knowledge.     

Neural correlates of cognitive reappraisal in children: an ERP study

Cognitive emotion regulation strategies, such as reappraising the emotional meaning of events, are linked to positive adjustment and are disrupted in individuals showing emotional distress, like anxiety. The late positive potential (LPP) is sensitive to reappraisal: LPP amplitudes are reduced when unpleasant pictures are reappraised in a positive light, suggesting regulation of negative emotion. However, only one study has examined reappraisal in children using the LPP. The present study examined whether directed reappraisals reduce the LPP in a group of 5- to 7-year-olds, and correlate with individual differences in fear and anxiety. EEG was recorded from 32 typically developing children via 64 scalp electrodes during a directed reappraisal task. Mothers reported on child anxiety. Fearful behavior was observed. As predicted, LPP amplitudes were larger to unpleasant versus neutral pictures;counter to predictions, the LPP was not sensitive to reappraisal. The degree to which unpleasant versus neutral pictures elicited larger LPPs was correlated with greater anxiety and fear. Results suggest that reappraisal in young children is still developing, but that the LPP is sensitive to individual differences related to fear and anxiety. The utility of the LPP as a measure of cognitive emotion regulation and emotional processing biases in children is discussed.     

Neural correlates of working memory for sign language

Eight, early bilingual, sign language interpreters participated in a PET study, which compared working memory for Swedish Sign Language (SSL) with working memory for audiovisual Swedish speech. The interaction between language modality and memory task was manipulated in a within-subjects design. Overall, the results show a previously undocumented, language modality-specific working memory neural architecture for SSL, which relies on a network of bilateral temporal, bilateral parietal and left premotor activation. In addition, differential activation in the right cerebellum was found for the two language modalities. Similarities across language modality are found in Broca's area for all tasks and in the anterior left inferior frontal lobe for semantic retrieval. The bilateral parietal activation pattern for sign language bears similarity to neural activity during, e.g., nonverbal visuospatial tasks, and it is argued that this may reflect generation of a virtual spatial array. Aspects of the data suggesting an age of acquisition effect are also considered. Furthermore, it is discussed why the pattern of parietal activation cannot be explained by factors relating to perception, production or recoding of signs, or to task difficulty. The results are generally compatible with Wilson's [Psychon. Bull. Rev. 8 (2001) 44] account of working memory.     

代谢组学检测法应用于肌张力障碍诊断的研究

目的 应用核磁共振代谢组学技术研究肌张力障碍患者血清中的小分子代谢物(分子量小于1 000)与正常人血清中小分子代谢物的差异,筛选肌张力障碍患者血清中的特征代谢物,建立肌张力障碍患者血清代谢图谱的诊断模型,从代谢组学角度探讨肌张力障碍发病的可能机制,为肌张力障碍的早期检测、诊断、干预提供依据.方法 采集2012年7月至12月在我院就诊的18例肌张力障碍患者的血清,并分别采集4例男性3例女性的正常血清,应用核磁共振技术检测血清中小分子的代谢谱,并对谱图的积分数据进行主成分分析(PCA)和偏最小二乘法判别分析,以辨识血清代谢产物的变化.结果 肌张力障碍患者与健康人血清中小分子代谢物的质谱磁共振图谱有明显差异,其中主成分分析模式识别法未能区分实验组和健康对照组,而用偏最小二乘法判别分析模式识别方法可明显区分两组,并能提供两组之间差别所对应的代谢物质.结论 采用代谢组学技术研究肌张力障碍患者血清代谢组与健康人存在明显差异;偏最小二乘法判别分析模式识别法明显优于主成分分析法,能够去除非实验因素的影响,提高分类效果.通过对代谢组学数据分析,可以发现肌张力障碍患者的代谢产物异常,有望发现特征性生物标志物,为进一步干预提供依据,具有较好的临床应用价值.