Aging and working memory: early deficits in EEG activation of posterior cortical areas

Voluntary self-initiation of the stimuli onset improves working memory and accelerates visual and attentional processing

The ability of an organism to voluntarily control the stimuli onset modulates perceptual and attentional functions. Since stimulus encoding is an essential component of working memory (WM), we conjectured that controlling the initiation of the perceptual process would positively modulate WM. To corroborate this proposition, we tested twenty-five healthy subjects in a modified-Sternberg WM task under three stimuli presentation conditions: an automatic presentation of the stimuli, a self-initiated presentation of the stimuli (through a button press), and a self-initiated presentation with random-delay stimuli onset. Concurrently, we recorded the subjects' electroencephalographic signals during WM encoding. We found that the self-initiated condition was associated with better WM accuracy, and earlier latencies of N1, P2 and P3 evoked potential components representing visual, attentional and mental review of the stimuli processes, respectively. Our work demonstrates that self-initiated stimuli enhance WM performance and accelerate early visual and attentional processes deployed during WM encoding. We also found that self-initiated stimuli correlate with an increased attentional state compared to the other two conditions, suggesting a role for temporal stimuli predictability. Our study remarks on the relevance of self-control of the stimuli onset in sensory, attentional and memory updating processing for WM.

Neural and Retinal Characteristics in Relation to Working Memory in Older Adults with Mild Cognitive Impairment

OBJECTIVE

This study investigated the relationship between neural activities and retinal structures associated with working memory (WM) in older adults with mild cognitive impairment (MCI).

METHODS

Eleven older adults with MCI and 29 healthy controls (60 to 73 years old) were tested. All participants underwent an event-related potential (ERP) recording while performing the two-back memory task. The Optical coherence tomography angiography (OCT-A) was administered to examine the perfusion and vessel density in the retina.

RESULTS

Results showed that WM performance in the MCI group was negatively associated with ERP latencies in central parietal regions (CP6 and CP8) (ps< 0.05). The left nasal vessel and perfusion densities were negatively correlated with the latencies in these two central parietal regions and positively related to WM performance only in the MCI group (ps< 0.05).

CONCLUSION

The findings on WM, central parietal brain activity, and left nasal vessel and perfusion densities in the retina help us gain a better understanding of the neural and retinal underpinnings of WM in relation to MCI.

When the time is right: Temporal dynamics of brain activity in healthy aging and dementia

Brain activity and communications are complex phenomena that dynamically unfold over time. However, in contrast with the large number of studies reporting neuroanatomical differences in activation relative to young adults, changes of temporal dynamics of neural activity during normal and pathological aging have been grossly understudied and are still poorly known. Here, we synthesize the current state of knowledge from MEG and EEG studies that aimed at specifying the effects of healthy and pathological aging on local and network dynamics, and discuss the clinical and theoretical implications of these findings. We argue that considering the temporal dynamics of brain activations and networks could provide a better understanding of changes associated with healthy aging, and the progression of neurodegenerative disease. Recent research has also begun to shed light on the association of these dynamics with other imaging modalities and with individual differences in cognitive performance. These insights hold great potential for driving new theoretical frameworks and development of biomarkers to aid in identifying and treating age-related cognitive changes.

Compromised Behavior and Gamma Power During Working Memory in Cognitively Healthy Individuals With Abnormal CSF Amyloid/Tau

Research shows that gamma activity changes in Alzheimer’s disease (AD), revealing synaptic pathology and potential therapeutic applications. We aim to explore whether cognitive challenge combined with quantitative EEG (qEEG) can unmask abnormal gamma frequency power in healthy individuals at high risk of developing AD. We analyzed low (30–50 Hz) and high gamma (50–80 Hz) power over six brain regions at EEG sensor level (frontal/central/parietal/left temporal/right temporal/occipital) in a dataset collected from an aging cohort during N-back working memory (WM) testing at two different load conditions (N = 0 or 2). Cognitively healthy (CH) study participants (≥60 years old) of both sexes were divided into two subgroups: normal amyloid/tau ratios (CH-NAT, n = 10) or pathological amyloid/tau (CH-PAT, n = 14) in cerebrospinal fluid (CSF). During low load (0-back) challenge, low gamma is higher in CH-PATs than CH-NATs over frontal and central regions (p = 0.014∼0.032, effect size (Cohen’s d) = 0.95∼1.11). However, during high load (2-back) challenge, low gamma is lower in CH-PATs compared to CH-NATs over the left temporal region (p = 0.045, Cohen’s d = −0.96), and high gamma is lower over the parietal region (p = 0.035, Cohen’s d = −1.02). Overall, our studies show a medium to large negative effect size across the scalp (Cohen’s d = −0.51∼−1.02). In addition, low gamma during 2-back is positively correlated with 0-back accuracy over all regions except the occipital region only in CH-NATs (r = 0.69∼0.77, p = 0.0098∼0.027); high gamma during 2-back correlated positively with 0-back accuracy over all regions in CH-NATs (r = 0.68∼0.78, p = 0.007∼0.030); high gamma during 2-back negatively correlated with 0-back response time over parietal, right temporal, and occipital regions in CH-NATs (r = −0.70∼−0.66, p = 0.025∼0.037). We interpret these preliminary results to show: (1) gamma power is compromised in AD-biomarker positive individuals, who are otherwise cognitively healthy (CH-PATs); (2) gamma is associated with WM performance in normal aging (CH-NATs) (most significantly in the frontoparietal region). Our pilot findings encourage further investigations in combining cognitive challenges and qEEG in developing neurophysiology-based markers for identifying individuals in the prodromal stage, to help improving our understanding of AD pathophysiology and the contributions of low- and high-frequency gamma oscillations in cognitive functions.

Model-Predicted Balance Between Neural Excitation and Inhibition Was Maintained Despite of Age-Related Decline in Sensory Evoked Local Field Potential in Rat Barrel Cortex

The balance between neural excitation and inhibition has been shown to be crucial for normal brain function. However, it is unclear whether this balance is maintained through healthy aging. This study investigated the effect of aging on the temporal dynamics of the somatosensory evoked local field potential (LFP) in rats and tested the hypothesis that excitatory and inhibitory post-synaptic activities remain balanced during the aging process. The LFP signal was obtained from the barrel cortex of three different age groups of anesthetized rats (pre-adolescence: 4–6 weeks, young adult: 2–3 months, middle-aged adult: 10–20 months) under whisker pad stimulation. To confirm our previous finding that the initial segment of the evoked LFP was solely associated with excitatory post-synaptic activity, we micro-injected gabazine into the barrel cortex to block inhibition while LFP was collected continuously under the same stimulus condition. As expected, the initial slope of the evoked LFP in the granular layer was unaffected by gabazine injection. We subsequently estimated the excitatory and inhibitory post-synaptic activities through a balanced model of the LFP with delayed inhibition as an explicit constraint, and calculated the amplitude ratio of inhibition to excitation. We found an age-dependent slowing of the temporal dynamics in the somatosensory-evoked post-synaptic activity, as well as a significant age-related decrease in the amplitude of the excitatory component and a decreasing trend in the amplitude of the inhibitory component. Furthermore, the delay of inhibition with respect to excitation was significantly increased with age, but the amplitude ratio was maintained. Our findings suggest that aging reduces the amplitude of neural responses, but the balance between sensory evoked excitatory and inhibitory post-synaptic activities is maintained to support normal brain function during healthy aging. Further whole cell patch clamp experiments will be needed to confirm or refute these findings by measuring sensory evoked synaptic excitatory and inhibitory activities in vivo during the normal aging process.

The effect of age, educational level, gender and cognitive reserve on visuospatial working memory performance across adult life span

Working memory (WM) is a limited capacity cognitive system that temporarily holds information for processing. In the present study, we tested the effect of age, gender and cognitive reserve in terms of educational level, working and leisure time activities on an active visuospatial WM task. One-hundred thirty-four participants between 20 and 80 years old performed an n-back task with different degree of WM demanding. Reaction times (RTs) became slower and accuracy decreased with age; the former started to decline in participants that were 35 years old, the latter in participants that were 57 years old. Males were faster than females. Educational level (10 years in accuracy and 15 years in RTs) showed a positive effect on accuracy and RTs. Cognitive reserve had a positive effect on accuracy but no effect on RTs. In conclusion, age-related decline influenced earlier the speed and later the accuracy in a task that required active processes. While male was faster independently of WM demanding and age, middle school degree and an average cognitive reserve prevent errors during performance. Coherently, high school degree prevents slowing down but only in low demanding condition.

Age-Related Alterations in Electroencephalography Connectivity and Network Topology During n-Back Working Memory Task

The study of the healthy brain in elders, especially age-associated alterations in cognition, is important to understand the deficits created by Alzheimer's disease (AD), which imposes a tremendous burden on individuals, families, and society. Although, the changes in synaptic connectivity and reorganization of brain networks that accompany aging are gradually becoming understood, little is known about how normal aging affects brain inter-regional synchronization and functional networks when items are held in working memory (WM). According to the classic Sternberg WM paradigm, we recorded multichannel electroencephalography (EEG) from healthy adults (young and senior) in three different conditions, i.e., the resting state, 0-back (control) task, and 2-back task. The phase lag index (PLI) between EEG channels was computed and then weighted and undirected network was constructed based on the PLI matrix. The effects of aging on network topology were examined using a brain connectivity toolbox. The results showed that age-related alteration was more prominent when the 2-back task was engaged, especially in the theta band. For the younger adults, the WM task evoked a significant increase in the clustering coefficient of the beta-band functional connectivity network, which was absent in the older adults. Furthermore, significant correlations were observed between the behavioral performance of WM and EEG metrics in the theta and gamma bands, suggesting the potential use of those measures as biomarkers for the evaluation of cognitive training, for instance. Taken together, our findings shed further light on the underlying mechanism of WM in physiological aging and suggest that different EEG frequencies appear to have distinct functional correlates in cognitive aging. Analysis of inter-regional synchronization and topological characteristics based on graph theory is thus an appropriate way to explore natural age-related changes in the human brain.

What Does the n-Back Task Measure as We Get Older? Relations Between Working-Memory Measures and Other Cognitive Functions Across the Lifespan

Working memory (WM) declines with increasing age. The WM capacity is often measured by means of the computerized version of the n-back task. Although the n-back task is widely used in aging research, little is known about its construct validity and specific cognitive functions involved in this task. Moreover, to date, no studies analyzed the construct validity as a function of age. To this end, we conducted a study in a sample of N = 533 individuals aged between 20 and 80 years. The sample was divided into three age groups: young (20-40), middle-aged (41-60), and old (61-80 years). A number of psychometric tests was selected that measure attention, memory, and executive control to elucidate the impact of these constructs on n-back performance. A series of correlation analyses was conducted to assess the relationship between n-back performance and specific cognitive functions in each age group separately. The results show a progressive increase in reaction times and a decrease in the proportion of detected targets from young to old subjects. Age-related impairments were also found in all psychometric tests except for the vocabulary choice test measuring crystallized intelligence. Most importantly, correlations yielded different age-related patterns of functions contributing to performance in the n-back task: whereas performance was most related to executive functions in young age, a combination of attentional and executive processes was associated with performance in middle-aged subjects. In contrast, in older age, mainly attentional, verbal memory, and updating and to a lesser extent executive processes seem to play a crucial role in the n-back task, suggesting a shift of processing strategies across the lifespan.

ERP and Behavioral Effects of Physical and Cognitive Training on Working Memory in Aging: A Randomized Controlled Study

Working memory (WM) performance decreases with age. A promising method to improve WM is physical or cognitive training. The present randomized controlled study is aimed at evaluating the effects of different training methods on WM. A sample of 141 healthy older adults (mean age 70 years) was assigned to one of four groups: physical training, cognitive training, a social control group, and a no-contact control group. The participants trained for four months. Before and after the training, n-back task during an EEG recording was applied. The results show that cognitive training enhanced the target detection rate in the 2-back task. This was corroborated by an increased number of repeated digits in the backward digit-span test but not in other memory tests. The improvement of WM was supported by an increased P3a prior to a correct target and an increased P3b both in nontarget and target trials. No ERP effects in the physical and no-contact control groups were found, while a reduction of P3a and P3b was found in the social control group. Thus, cognitive training enhances frontal and parietal processing related to the maintenance of a stored stimulus for subsequent matching with an upcoming stimulus and increases allocation of cognitive resources. These results indicate that multidomain cognitive training may increase WM capacity and neuronal activity in older age.

Generalization of Context-Specific Training in Individuals with Mild Cognitive Impairment: An Event-Related Potential Study

Background

This study examined the neural processes associated with the generalization of the effect of context-specific (CS) training to noncontextual situations among individuals with mild cognitive impairment (MCI).

Methods

Fourteen and 16 participants with MCI were randomly allocated to a Chinese calligraphy writing (CW) training or a control group, respectively. The CW participants learned how to write Chinese strokes in a semicursive style to construct characters, tapping on working memory functions. The control group, on the other hand, learned how to use a tablet computer without emphasis on working memory functions. They then performed two 2-back tasks with CS semicursive strokes and non-context-specific (NCS) digits. Event-related electroencephalogram signals were concurrently recorded.

Results

The CW participants had a significantly shorter reaction time in the CS than in the NCS task (p < 0.05). They showed significantly longer latency in working memory updating (N200; t<Sub>11</Sub> = 4.70, p = 0.05) and shorter latency in the evaluation of visual representation (P300; t<Sub>12</Sub> = 4.67; p = 0.05) than the control group when performing the 2-back CS task. Shorter P300 latency was also revealed in the 2-back NCS task (t<Sub>12</Sub> = 5.15, p = 0.041), suggesting a possible generalization of the training effect among the CW participants.

Conclusion

The results suggest that CS working memory is likely to be generalized to NCS domains among individuals with MCI. Future research should extend the scope of the generalization and apply it beyond experimental conditions.

Object individuation and compensation in healthy aging

Theories on neural compensation suggest that aged participants overactivate the brain areas involved in a task to compensate for the age-related decline. In this electrophysiological study, we investigated the temporal locus of neural overactivation in aging during multiple target processing. We measured performance and three event-related brain potential responses (N1, N2pc, and contralateral delay activity) in young and old adults, while they enumerated a variable number (1-4) of targets presented in an easy (distractor absent) or difficult (distractor present) condition. The main results indicated that although N2pc (∼200 ms) increased in amplitude in the distractor-present condition in the young group, no modulation occurred for the old group. Old participants were associated with larger N2pc amplitudes than young participants in the distractor-absent condition, where both groups had comparable levels of accuracy. These effects were not present for N1 and contralateral delay activity. Overall, the data suggest that in enumeration, aging is associated with compensatory effects that rely on the selection mechanism responsible for target individuation.

Training and testing ERP-BCIs under different mental workload conditions

OBJECTIVE

As one of the most popular and extensively studied paradigms of brain-computer interfaces (BCIs), event-related potential-based BCIs (ERP-BCIs) are usually built and tested in ideal laboratory settings in most existing studies, with subjects concentrating on stimuli and intentionally avoiding possible distractors. This study is aimed at examining the effect of simultaneous mental activities on ERP-BCIs by manipulating various levels of mental workload during the training and/or testing of an ERP-BCI.

APPROACH

Mental workload was manipulated during the training or testing of a row-column P300-speller to investigate how and to what extent the spelling performance and the ERPs evoked by the oddball stimuli are affected by simultaneous mental workload.

MAIN RESULTS

Responses of certain ERP components, temporal-occipital N200 and the late reorienting negativity evoked by the oddball stimuli and the classifiability of ERP features between targets and non-targets decreased with the increase of mental workload encountered by the subject. However, the effect of mental workload on the performance of ERP-BCI was not always negative but depended on the conditions where the ERP-BCI was built and applied. The performance of ERP-BCI built under an ideal lab setting without any irrelevant mental activities declined with the increasing mental workload of the testing data. However, the performance was significantly improved when an ERP-BCI was built under an appropriate mental workload level, compared to that built under speller-only conditions.

SIGNIFICANCE

The adverse effect of concurrent mental activities may present a challenge for ERP-BCIs trained in ideal lab settings but which are to be used in daily work, especially when users are performing demanding mental processing. On the other hand, the positive effects of the mental workload of the training data suggest that introducing appropriate mental workload during training ERP-BCIs is of potential benefit to the performance in practical applications.

Age-related changes in brain activity are specific for high order cognitive processes during successful encoding of information in working memory

Memory capacity suffers an age-related decline, which is supposed to be due to a generalized slowing of processing speed and to a reduced availability of processing resources. Information encoding in memory has been demonstrated to be very sensitive to age-related changes, especially when carried out through self-initiated strategies or under high cognitive demands. However, most event-related potentials (ERP) research on age-related changes in working memory (WM) has used tasks that preclude distinction between age-related changes in encoding and retrieval processes. Here, we used ERP recording and a delayed match to sample (DMS) task with two levels of memory load to assess age-related changes in electrical brain activity in young and old adults during successful information encoding in WM. Age-related decline was reflected in lower accuracy rates and longer reaction times in the DMS task. Beside, only old adults presented lower accuracy rates under high than low memory load conditions. However, effects of memory load on brain activity were independent of age and may indicate an increased need of processing after stimulus classification as reflected in larger mean voltages in high than low load conditions between 550 and 1000 ms post-stimulus for young and old adults. Regarding age-related effects on brain activity, results also revealed smaller P2 and P300 amplitudes that may signal the existence of an age dependent reduction in the processing resources available for stimulus evaluation and categorization. Additionally, P2 and N2 latencies were longer in old than in young participants. Furthermore, longer N2 latencies were related to greater accuracy rates on the DMS task, especially in old adults. These results suggest that age-related slowing of processing speed may be specific for target stimulus analysis and evaluation processes. Thus, old adults seem to improve their performance the longer they take to evaluate the stimulus they encode in visual WM.

Memory timeline: Brain ERP C250 (not P300) is an early biomarker of short-term storage

Brain event-related potentials (ERPs) offer a quantitative link between neurophysiological activity and cognitive performance. ERPs were measured while young adults performed a task that required storing a relevant stimulus in short-term memory. Using principal components analysis, ERP component C250 (maximum at 250 ms post-stimulus) was extracted from a set of ERPs that were separately averaged for various task conditions, including stimulus relevancy and stimulus sequence within a trial. C250 was more positive in response to task-specific stimuli that were successfully stored in short-term memory. This relationship between C250 and short-term memory storage of a stimulus was confirmed by a memory probe recall test where the behavioral recall of a stimulus was highly correlated with its C250 amplitude. ERP component P300 (and its subcomponents of P3a and P3b, which are commonly thought to represent memory operations) did not show a pattern of activation reflective of storing task-relevant stimuli. C250 precedes the P300, indicating that initial short-term memory storage may occur earlier than previously believed. Additionally, because C250 is so strongly predictive of a stimulus being stored in short-term memory, C250 may provide a strong index of early memory operations.

Combining and comparing EEG, peripheral physiology and eye-related measures for the assessment of mental workload

While studies exist that compare different physiological variables with respect to their association with mental workload, it is still largely unclear which variables supply the best information about momentary workload of an individual and what is the benefit of combining them. We investigated workload using the n-back task, controlling for body movements and visual input. We recorded EEG, skin conductance, respiration, ECG, pupil size and eye blinks of 14 subjects. Various variables were extracted from these recordings and used as features in individually tuned classification models. Online classification was simulated by using the first part of the data as training set and the last part of the data for testing the models. The results indicate that EEG performs best, followed by eye related measures and peripheral physiology. Combining variables from different sensors did not significantly improve workload assessment over the best performing sensor alone. Best classification accuracy, a little over 90%, was reached for distinguishing between high and low workload on the basis of 2 min segments of EEG and eye related variables. A similar and not significantly different performance of 86% was reached using only EEG from single electrode location Pz.

Age-Related Effects on ERP and Oscillatory EEG-Dynamics in a 2-Back Task

It is well known that working memory is one of the most vulnerable cognitive functions in elderly. However, little is known about the neuronal underpinnings and temporal dynamics of working memory mechanisms in healthy aging which are necessary to understand the age-related changes. To this end, 36 young and 36 old healthy individuals performed a 2-back task and a 0-back control task, while the electroencephalogram (EEG) was recorded. Participants were instructed to press a response key whenever a target appeared and not to respond in case of nontargets. Expectedly, older participants showed considerably slower RTs and significantly higher rates of omitted targets and false alarms than young participants in the 2-back task, whereas no age-group difference in detection rate was found in the 0-back task. From the EEG event-related potentials as well as time-frequency plots were computed. The ERPs showed a general delay of the frontocentral N2, and an attenuation and delay of both the P3a and P3b in older versus younger adults. Importantly, the frontal P3a was reduced in older adults in the 2-back task. Time-frequency decomposition revealed consistently lower power in frontal theta (6 Hz) and parietal alpha (9–11 Hz) frequency range in older versus younger adults whereas no age-related differences were found in the delta frequency range. Task unspecific reduction of posterior alpha in elderly was paralleled by a reduction of the P3b. In contrast, the older adults had a strongly reduced frontal theta power in the 2-back task, which parallels the P3a reduction in the ERPs. The widespread reduction of alpha may indicate that older adults needed to recruit more attentional resources for successful task performance, whereas reduced frontal theta may indicate that older adults are less able to recruit frontal resources related to top-down control with increasing task demands. This suggests a less efficient fronto-parietal network synchronicity in older individuals that leads to deficits in identification and maintenance of task relevant stimuli.

Toxoplasma gondii impairs memory in infected seniors

Almost 30% of humans present a Toxoplasma gondii positive antibody status and its prevalence increases with age. The central nervous system is the main target. However, little is known about the influence of asymptomatic i.e. latent Toxoplasmosis on cognitive functions in humans. To investigate neurocognitive dysfunctions in asymptomatic older adults with T. gondii positive antibody status a double-blinded neuropsychological study was conducted. The participants were classified from a population-based sample (N=131) of healthy participants with an age of 65 years and older into two groups with 42 individuals each: Toxoplasmosis positive (T-pos; IgG>50 IU/ml) and Toxoplasmosis negative (T-neg; IgG=0 IU/ml). The outcome measures were a computer-based working-memory test (2-back) and several standardized psychometric tests of memory and executive cognitive functions. T-pos seniors showed an impairment of different aspects of memory. The rate of correctly detected target symbols in a 2-back task was decreased by nearly 9% (P=0.020), corresponding to a performance reduction of about 35% in working memory relative to the T-neg group. Moreover, T-pos seniors had a lower performance in a verbal memory test, both regarding immediate recall (10% reduction; P=0.022), delayed recognition (6%; P=0.037) and recall from long-term memory assessed by the word fluency tests (12%; P=0.029). In contrast, executive functions were not affected. The effects remained mostly unchanged after controlling for medication. The impairment of memory functions in T-pos seniors was accompanied by a decreased self-reported quality of life. Because of the high prevalence of asymptomatic Toxoplasmosis and an increasing population of older adults this finding is of high relevance for public health.

The decline of verbal and visuospatial working memory across the adult life span

It has been well established that working memory abilities decrease with advancing age; however, the specific time point in the adult life span at which this deficit begins and the rate at which it advances are still controversial. There is no agreement on whether working memory declines equally for visuospatial and verbal information, and the literature disagrees on how task difficulty may influence this decay. We addressed these questions in a lifespan sample of 1,500 participants between 21 and 80 years old. The n-back task was used, with letters and circles presented at different positions around an imaginary circle, to evaluate working memory in the verbal and visuospatial domains, respectively. The participants' task was to judge whether the current stimulus matched a stimulus that was shown n trials prior. Both domains were evaluated in two levels of difficulty: 1-back and 2-back. The comparison across decades showed that discrimination in the visuospatial and 1-back tasks started to decline earlier in women than in men; however, discrimination was equal between the sexes in the verbal and 2-back tasks. Performance on tasks in the visuospatial domain exhibited more pronounced decline than in those in the verbal domain. The rate of decline in working memory accuracy was superior in 2-back tasks than in 1-back tasks, independent of the domain. These results revealed that the effects of aging on working memory are less dependent on the type of information and more reliant on the resources demanded by the task.

The relationship between P3 amplitude and working memory performance differs in young and older adults

While some elderly show deteriorations in cognitive performance, others achieve performance levels comparable to young adults. To examine whether age-related changes in brain activity varied with working memory performance efficiency, we recorded electroencephalography (EEG) from young and older healthy adults during performance on an n-back task with two loads (0- and 1-back) and two versions (identity and integrated). Young adults showed a typical P3 amplitude pattern with a parietal-maximum. Compared to young adults, the P3 amplitude of older adults was characterized by frontal hyperactivity coupled with posterior hypoactivity. Moreover, P3 amplitude in young and older adults varied with working memory performance efficiency. Among young adults, more efficient performance correlated with a larger P3 amplitude at parietal sites. In contrast, a higher P3 amplitude at midline electrode sites in older adults correlated with less efficient performance. Particularly, the enhanced frontal midline EEG activity in older adults during working memory performance seems to reflect inefficient use of neural resources due to frontal lobe dysfunction.

Cardiovascular costs of working memory performance: effects of age and performance feedback

Ageing is associated with impaired working memory (WM) performance that may increase cardiovascular costs in older workers. Performance feedback (FB) was assumed to compensate for performance decline and reduce cardiovascular costs. Forty-eight younger (29 ± 3 yr) and 45 older (55 ± 4 yr) healthy workers had to perform a 0-back task (low WM load), 2-back task (high WM load) and 2-back task with FB (high WM load & FB). Age-related performance decline and enhanced blood pressure (BP) reactivity to WM load were found. The baroreflex sensitivity (BRS) decreased under high WM load in older workers compared to younger workers. The FB abolished age differences in omission rate and increased low frequency heart rate variability (HRV) in both age groups. Moreover, FB reduced heart rate in older workers and increased BRS as well as high frequency HRV in younger workers. The results suggest that older workers compensate for WM performance decline at cost of heightened BP due to age-related reductions of vagal tone and impairments of the baroreflex mechanism. The performance FB helps older workers to partly compensate for performance deficits and reduce cardiovascular costs by moderate decreases in sympathetic tone.

Learning and memory

Learning and memory functions are crucial in the interaction of an individual with the environment and involve the interplay of large, distributed brain networks. Recent advances in technologies to explore neurobiological correlates of neuropsychological paradigms have increased our knowledge about human learning and memory. In this chapter we first review and define memory and learning processes from a neuropsychological perspective. Then we provide some illustrations of how noninvasive brain stimulation can play a major role in the investigation of memory functions, as it can be used to identify cause-effect relationships and chronometric properties of neural processes underlying cognitive steps. In clinical medicine, transcranial magnetic stimulation may be used as a diagnostic tool to understand memory and learning deficits in various patient populations. Furthermore, noninvasive brain stimulation is also being applied to enhance cognitive functions, offering exciting translational therapeutic opportunities in neurology and psychiatry.

Aging ebbs the flow of thought: adult age differences in mind wandering, executive control, and self-evaluation

Two experiments examined the relations among adult aging, mind wandering, and executive-task performance, following from surprising laboratory findings that older adults report fewer task-unrelated thoughts (TUTs) than do younger adults (e.g., Giambra, 1989; Jackson & Balota, 2012). Because older adults may experience more ability- and performance-related worry during cognitive tasks in the laboratory, and because these evaluative thoughts (known as task-related interference, "TRI") might be sometimes misclassified by subjects as task-related, we asked subjects to distinguish task-related thoughts from TRI and TUTs when probed during ongoing tasks. In Experiment 1, younger and older adults completed either a go/no-go or a vigilance version of a sustained attention to response task (SART). Older adults reported more TRI and fewer TUTs than did younger adults while also performing more accurately. In Experiment 2, subjects completed either a 1- or a 2-back version of the n-back task. Older adults again reported more TRI and fewer TUTs than younger adults in both versions, while performing better than younger adults in the 1-back and worse in the 2-back. Across experiments, older adults' reduced TUT rates were independent of performance relative to younger adults. And, although older adults consistently reported more TRI and less mind wandering than did younger adults, overall they reported more on-task thoughts. TRI cannot, therefore, account completely for prior reports of decreasing TUTs with aging. We discuss the implications of these results for various theoretical approaches to mind-wandering.

Event-related potentials and changes of brain rhythm oscillations during working memory activation in patients with first-episode psychosis

BACKGROUND

Earlier contributions have documented significant changes in sensory, attention-related endogenous event-related potential (ERP) components and θ band oscillatory responses during working memory activation in patients with schizophrenia. In patients with first-episode psychosis, such studies are still scarce and mostly focused on auditory sensory processing. The present study aimed to explore whether subtle deficits of cortical activation are present in these patients before the decline of working memory performance.

METHODS

We assessed exogenous and endogenous ERPs and frontal θ event-related synchronization (ERS) in patients with first-episode psychosis and healthy controls who successfully performed an adapted 2-back working memory task, including 2 visual n-backworking memory tasks as well as oddball detection and passive fixation tasks.

RESULTS

We included 15 patients with first-episode psychosis and 18 controls in this study. Compared with controls, patients with first-episode psychosis displayed increased latencies of early visual ERPs and phasic θ ERS culmination peak in all conditions. However, they also showed a rapid recruitment of working memory-related neural generators, even in pure attention tasks, as indicated by the decreased N200 latency and increased amplitude of sustained θ ERS in detection compared with controls.

LIMITATIONS

Owing to the limited sample size, no distinction was made between patients with first-episode psychosis with positive and negative symptoms. Although we controlled for the global load of neuroleptics, medication effect cannot be totally ruled out.

CONCLUSION

The present findings support the concept of a blunted electroencephalographic response in patients with first-episode psychosis who recruit the maximum neural generators in simple attention conditions without being able to modulate their brain activation with increased complexity of working memory tasks.

Age-related differences in working memory performance in a 2-back task

The present study aimed to elucidate the neuro-cognitive processes underlying age-related differences in working memory. Young and middle-aged participants performed a two-choice task with low and a 2-back task with high working memory load. The P300, an event-related potential reflecting controlled stimulus–response processing in working memory, and the underlying neuronal sources of expected age-related differences were analyzed using sLORETA. Response speed was generally slower for the middle-aged than the young group. Under low working memory load the middle-aged participants traded speed for accuracy. The middle-aged were less efficient in the 2-back task as they responded slower while the error rates did not differ for groups. An age-related decline of the P300 amplitude and characteristic topographical differences were especially evident in the 2-back task. A more detailed analysis of the P300 in non-target trials revealed that amplitudes in the young but not middle-aged group differentiate between correctly detected vs. missed targets in the following trial. For these trials, source analysis revealed higher activation for the young vs. middle-aged group in brain areas which support working memory processes. The relationship between P300 and overt performance was validated by significant correlations. To sum up, under high working memory load the young group showed an increased neuronal activity before a successful detected target, while the middle-aged group showed the same neuronal pattern regardless of whether a subsequent target will be detected or missed. This stable memory trace before detected targets was reflected by a specific activation enhancement in brain areas which orchestrate maintenance, update, storage, and retrieval of information in working memory.

Working memory and aging: separating the effects of content and context

In 3 experiments, we investigated the hypothesis that age-related differences in working memory might be due to the inability to bind content with context. Participants were required to find a repeating stimulus within a single series (no context memory required) or within multiple series (necessitating memory for context). Response time and accuracy were examined in 2 task domains: verbal and visuospatial. Binding content with context led to longer processing time and poorer accuracy in both age groups, even when working memory load was held constant. Although older adults were overall slower and less accurate than young adults, the need for context memory did not differentially affect their performance. It is therefore unlikely that age differences in working memory are due to specific age-related problems with content-with-context binding.

Brain ERP components predict which individuals progress to Alzheimer's disease and which do not

Predicting which individuals will progress to Alzheimer's disease (AD) is important in both clinical and research settings. We used brain Event-Related Potentials (ERPs) obtained in a perceptual/cognitive paradigm with various processing demands to predict which individual Mild Cognitive Impairment (MCI) subjects will develop AD versus which will not. ERP components, including P3, memory "storage" component, and other earlier and later components, were identified and measured by Principal Components Analysis. When measured for particular task conditions, a weighted set of eight ERP component_conditions performed well in discriminant analysis at predicting later AD progression with good accuracy, sensitivity, and specificity. The predictions for most individuals (79%) had high posterior probabilities and were accurate (88%). This method, supported by a cross-validation where the prediction accuracy was 70-78%, features the posterior probability for each individual as a method of determining the likelihood of progression to AD. Empirically obtained prediction accuracies rose to 94% when the computed posterior probabilities for individuals were 0.90 or higher (which was found for 40% of our MCI sample).

[Cognitive competence of older workers]

The article provides a short overview on cognitive strengths and weaknesses of older workers. The older people who are under the age of 65 years already exhibit changes in performance and neurophysiological measures in laboratory tasks that test fluid intelligence. Apart from deficits, the physiological data of the older people show clear evidence for compensatory strategies. Cognitive performance on the current job is usually less impaired. This can be explained by practice, learning, and selection, which are, however, often linked with higher effort. The cognitive competence of older employees varies exorbitantly, which is due to the influence of various factors like education, lifestyle, and in particular the type of work. Thus, the cognitive competence of older employees can be preserved and possibly even enhanced by changes in the work situation as well as by individual training procedures such as cognitive training.

Spatial reference and working memory across the lifespan of male Fischer 344 rats

Loss of mnemonic function is among the earliest and most disconcerting consequences of the aging process. This study was designed to provide a comprehensive profile of spatial mnemonic abilities in male Fischer 344 (F344) rats across the lifespan. Young, middle-aged, and aged F344 rats were trained in spatial reference and working memory versions of the water maze task. There was a progressive age-related decline in spatial reference memory across the lifespan. Reliable individual differences were observed among aged rats, with some aged rats performing as well as young cohorts and others performing outside this range. An age-related delay-dependent decline was observed on a working memory version of the water maze task although no relationship between performance on reference and working memory tasks was present. Notably, middle-aged rats were impaired relative to young on both tasks. Together these data demonstrate that individual differences in spatial reference memory exist among aged F344 rats and provide novel data demonstrating an unrelated decline in working memory across the lifespan, suggesting that age-related mnemonic dysfunction may occur across multiple brain systems.

Working memory load-related electroencephalographic parameters can differentiate progressive from stable mild cognitive impairment

Recent studies described several changes of endogenous event-related potentials (ERP) and brain rhythm synchronization during memory activation in patients with Alzheimer's disease (AD). To examine whether memory-related EEG parameters may predict cognitive decline in mild cognitive impairment (MCI), we assessed P200 and N200 latencies as well as beta event-related synchronization (ERS) in 16 elderly controls (EC), 29 MCI cases and 10 patients with AD during the successful performance of a pure attentional detection task as compared with a highly working memory demanding two-back task. At 1 year follow-up, 16 MCI patients showed progressive cognitive decline (PMCI) and 13 remained stable (SMCI). Both P200 and N200 latencies in the two-back task were longer in PMCI and AD cases compared with EC and SMCI cases. During the interval 1000 ms to 1700 ms after stimulus, beta ERS at parietal electrodes was of lower amplitude in PMCI and AD compared with EC and SMCI cases. Univariate models showed that P200, N200 and log% beta values were significantly related to the SMCI/PMCI distinction with areas under the receiver operating characteristic curve of 0.93, 0.78 and 0.72, respectively. The combination of all three EEG hallmarks was the stronger predictor of MCI deterioration with 90% of correctly classified MCI cases. Our data reveal that PMCI and clinically overt AD share the same pattern of working memory-related EEG activation characterized by increased P200-N200 latencies and decreased beta ERS. They also show that P200 latency during the two-back task may be a simple and promising EEG marker of rapid cognitive decline in MCI.

Health status, mood, and cognition in experimentally induced subclinical hypothyroidism

OBJECTIVE

The objective of the study was to determine whether subclinical hypothyroidism causes decrements in health status, mood, and/or cognitive function.

DESIGN

This was a double-blinded, randomized, crossover study of usual dose l-thyroxine (L-T4) (euthyroid arm) vs. lower dose L-T4 (subclinical hypothyroid arm) in hypothyroid subjects.

PATIENTS

Nineteen subjects on L-T4 therapy for primary hypothyroidism participated in the study.

MEASUREMENTS

Subjects underwent measurements of health status, mood, and cognition using validated instruments: Short Form 36, Profile of Mood States, and tests of declarative memory (paragraph recall, complex figure), working memory (N-back, subject ordered pointing, digit span backward), and motor learning (pursuit rotor). The same measures were repeated after 12 wk on each of the study arms.

RESULTS

Mean TSH levels increased to 17 mU/liter on the subclinical hypothyroid arm (P < 0.0001). Mean free T4 and free T3 levels remained within the normal range. The Profile of Mood States fatigue subscale and Short Form 36 general health subscale were slightly worse during the subclinical hypothyroid arm. Measures of working memory (N-back, subject ordered pointing) were worse during the subclinical hypothyroid arm. These differences did not depend on mood or health status but were related to changes in free T4 or free T3 levels. There were no decrements in declarative memory or motor learning.

CONCLUSIONS

We found mild decrements in health status and mood in L-T4-treated hypothyroid subjects when subclinical hypothyroidism was induced in a blinded, randomized fashion. More importantly, there were independent decrements in working memory, which suggests that subclinical hypothyroidism specifically impacts brain areas responsible for working memory.

Working memory deficits in multiple sclerosis: comparison between the n-back task and the Paced Auditory Serial Addition Test

Working memory (WM) deficits are common in multiple sclerosis (MS). The Paced Auditory Serial Addition Test (PASAT) is used frequently to measure WM in clinical settings. The n-back paradigm is used often in experimental studies of WM. One unique component of the n-back task is that it provides a measure of reaction time (RT), an additional behavioral index of processing speed and task difficulty. Despite the use of both tasks to measure WM, their common variance has not been documented. We tested 32 MS patients and 20 controls; performance measures were obtained for both tasks. Compared with controls, MS patients generally had poorer performance on both the PASAT and n-back task. MS patients also had slower RTs on the n-back than controls and showed more slowing than controls as a function of WM load. Correlational analyses showed a high correspondence between performance measures on the PASAT and n-back. Principal components analysis pointed to a common feature of the PASAT, n-back, and specific other neuropsychological measures, that is, processing speed. Although the PASAT and n-back were shown to have a significant amount of shared variance, each test has specific advantages and disadvantages for use in clinical populations.