Beyond prospective memory retrieval: Encoding and remembering of intentions across the lifespan.

Combining behavioral and electrophysiological measures, we investigated the role of memory processes for prospective memory development in three different age groups over the lifespan. We focused on age differences during intention encoding, retention and retrieval in order to assess if potential age-associated performance differences in adolescence and older age can be explained by associated neurophysiological differences. Our research aim was to understand the impact of memory-related factors such as intention load and encoding time on prospective remembering, focusing especially on encoding and retention, which are two so far scarcely investigated phases. Adolescents, younger and older adults worked on a semantic judgment task with an embedded prospective memory task. Participants had to encode either one or two intentions; the encoding time was either four or eight seconds long. Younger and older adults outperformed adolescents behaviorally. Furthermore, performance was better for remembering one intention compared to remembering two intentions. On the neural level, we found age-specific modulations for the fronto-polar slow wave (FPSW) and the temporal-parietal slow wave (TPSW) that were sensitive to the number of intentions. Adolescents showed differences between encoding one or two intentions in the FPSW, while older adults showed these differences for the TPSW. Maintaining an intention increased fronto-central sustained activity compared to no intention. Furthermore, the activity during intention maintenance was sensitive to the number of intentions. Prospective positivity amplitudes during retrieval were smallest in adolescents and largest in older adults, but were not influenced by the memory manipulations. Parietal slow wave activity increased with increasing number of intentions, reflecting post-retrieval coordination between the ongoing and prospective memory task. In sum, only activity of the FPSW and the TPSW showed that age-related differences were influenced by memory-related factors during encoding, whereas these interactions were not observed for retention or retrieval. Our findings suggest that intention encoding and its efficiency play an important role in explaining age differences in prospective memory.

The role of cue detection for prospective memory development across the lifespan.

Behavioral findings suggest an inverted U-shaped pattern of prospective memory development across the lifespan. A key mechanism underlying this development is the ability to detect cues. We examined the influence of cue detection on prospective memory, combining behavioral and electrophysiological measures, in three age groups: adolescents (12-14 years), young (19-28 years), and old adults (66-77 years). Cue detection was manipulated by varying the distinctiveness (i.e., how easy it was to detect the cue based on color) of the prospective memory cue in a semantic judgment ongoing task. Behavioral results supported the pattern of an inverted U-shape with a pronounced prospective memory decrease in old adults. Adolescents and young adults showed a prospective memory specific modulation (larger amplitudes for the cues compared to other trials) already for the N1 component. No such specific modulation was evident in old adults for the early N1 component but only at the later P3b component. Adolescents showed differential modulations of the amplitude also for irrelevant information at the P3b, suggesting less efficient processing. In terms of conceptual implications, present findings underline the importance of cue detection for prospective remembering and reveal different developmental trajectories for cue detection. Our findings suggest that cue detection is not a unitary process but consists of multiple stages corresponding to several ERP components that differentially contribute to prospective memory performance across the lifespan. In adolescents resource allocation for detecting cues seemed successful initially but less efficient at later stages; whereas we found the opposite pattern for old adults.

Neural correlates of changes in a visual search task due to cognitive training in seniors.

This study aimed to elucidate the underlying neural sources of near transfer after a multidomain cognitive training in older participants in a visual search task. Participants were randomly assigned to a social control, a no-contact control and a training group, receiving a 4-month paper-pencil and PC-based trainer guided cognitive intervention. All participants were tested in a before and after session with a conjunction visual search task. Performance and event-related potentials (ERPs) suggest that the cognitive training improved feature processing of the stimuli which was expressed in an increased rate of target detection compared to the control groups. This was paralleled by enhanced amplitudes of the frontal P2 in the ERP and by higher activation in lingual and parahippocampal brain areas which are discussed to support visual feature processing. Enhanced N1 and N2 potentials in the ERP for nontarget stimuli after cognitive training additionally suggest improved attention and subsequent processing of arrays which were not immediately recognized as targets. Possible test repetition effects were confined to processes of stimulus categorisation as suggested by the P3b potential. The results show neurocognitive plasticity in aging after a broad cognitive training and allow pinpointing the functional loci of effects induced by cognitive training.

Effects of working memory load on performance and cardiovascular activity in younger and older workers.

BACKGROUND: Working memory (WM) declines with ageing, and this may cause problems in older workers who have to do complex work requiring WM. PURPOSE: We tested the assumption that an increase in WM load negatively affects performance and results in impaired cardiovascular adaptation to changing task demands in older workers relative to younger ones. METHOD: Thirty-three younger (29 ± 3 years) and 32 older (55 ± 3 years) workers had to perform a visual 0-back (low WM load) and 2-back (high WM load) task. Heart rate (HR), heart rate variability (HRV), beat-to-beat blood pressure (BP) and baroreflex were registered. RESULTS: In the high WM load condition, older adults responded more slowly and less accurately than younger adults, while no age effects in the low WM load condition were found. Older workers showed a higher systolic blood pressure (SBP) reactivity to high WM load as well as a diminished post-task recovery of SBP and HRV than younger workers. Factor analysis demonstrated a close relationship between HR, baroreflex and HRV and their modulation by a common factor ("vagal tone") in the younger group. By contrast, HR was more related to the "sympathetic" factor in the older group. CONCLUSION: The data suggest that older workers as compared with younger ones are impaired in tasks requiring WM, which is accompanied by enhanced cardiovascular "costs" in terms of increased SBP and reduced vagal control over HR.

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.

Age-related differences in performance and stimulus processing in dual task situation.

Competition for limited processing resources is most critical in dual-tasks which incorporate cognitive and motor demands. Performance is usually diminished with increasing age in such tasks. This decline is relevant for activities in real life like driving. In the present study we aim to examine if there are age-related differences in stimulus processing in a dual-task and if these differences have an impact on performance of a driving-like tracking task. Young and older participants performed a dual-task consisting of a tracking task and a visual attention task. Alongside, the EEG was recorded for calculating the P300 (P3) of the event-related potential as a reflection of controlled stimulus processing. In the visual attention task older vs. young participants showed more misses and false alarms. For young participants the P3 shows an expected pattern of higher amplitudes for relevant compared to irrelevant stimuli. This was not found for the older participants. A general age-related decline in tracking performance was relatively more pronounced if a secondary motor response was required in the visual attention task and also after irrelevant stimuli. The results suggest that older compared to young participants had greater difficulties to differentiate between relevant and irrelevant stimuli in a dual-task situation as they probably apply comparable attentional resources to all stimuli. This may also explain the higher error rates. These results have important implications for the understanding of age-related stimulus processing in dual and multi task situations in real life as for instance driving.

Preparatory processes and compensatory effort in older and younger participants in a driving-like dual task.

OBJECTIVE: The nature of increased-age-related dual-task interference was examined during a driving-like dual task in the laboratory. BACKGROUND: Previous research revealed age-related deficits in dual tasks especially when cognitive and motor demands are involved. The specific contributions of sensory input, working memory demands, and/or coordination of motor responses to dual-task interference are not clear and should be clarified in the present study. METHOD: Younger and older participants performed a driving-like tracking task and a visually cued attention task within a dual task. Behavioral and electrophysiological data were recorded during task performance. RESULTS: Overall tracking performance was lower for the older versus younger participants. This age-related decline was particularly pronounced in the time interval after the stimulus when the attention task demanded a motor response. In contrast, older participants tracked relatively better than the younger participants in the time interval preceding the stimulus. In the attention task, the older versus younger participants showed increased responses times and rates of false alarms and misses, suggesting a deficit in retaining the context in the cue-stimulus interval. The electroencephalogram data suggest that the older participants invested more resources than the younger participants in dual-task management during the cue-stimulus interval. CONCLUSION: Evidence was found for increased motor interference and a deficient context processing as well as for an increased investment of processing resources in the older compared with the younger group. APPLICATION: The results suggest that in-vehicle information systems for older drivers should be designed to support cue maintenance and that simultaneous motor demands should not be required.

Age related strategic differences in processing irrelevant information.

Deficient control of irrelevant information with greater age can be demonstrated in paradigms like inhibition of return (IOR). IOR is a mechanism to protect the organism from redirecting attention to a previously scanned irrelevant location and is assumed to be generated slower but to a comparable amount with increasing age. We investigated this putative deficit by means of event-related potentials (ERPs). As expected, IOR developed later in older subjects. In the cue-related ERPs, young subjects showed a large frontocentral N2 (reflecting control or inhibition) which was virtually absent in the old subjects. Instead, the older subjects showed a P3b, reflecting controlled processing of information. Thus, older adults process irrelevant stimuli more like relevant ones, thereby overloading their information processing system.

Effects of aging and job demands on cognitive flexibility assessed by task switching.

In a cross-sectional, electrophysiological study 91 workers of a big car factory performed a series of switch tasks to assess their cognitive control functions. Four groups of workers participated in the study: 23 young and 23 middle aged assembly line employees and 22 young and 23 middle aged employees with flexible job demands like service and maintenance. Participants performed three digit categorisation tasks. In addition to single task blocks, a cue-based (externally guided) and a memory-based (internally guided) task switch block was administered. Compared to young participants, older ones showed the typical RT-decline. No differences between younger and older participants regarding the local switch costs could be detected despite the source of the current task information. In contrast, whereas the groups did not differ in mixing costs in the cued condition, clear performance decrements in the memory-based mixing block were observed in the group of older employees with repetitive work demands. These findings were corroborated by a number of electrophysiological results showing a reduced CNV suggesting an impairment of task specific preparation, an attenuated P3b suggesting reduced working memory capacity and a decreased Ne suggesting deficits in error monitoring in older participants with repetitive job demands. The results are compatible with the assumption that long lasting, unchallenging job demands may induce several neurocognitive impairments which are already evident in the early fifties. Longitudinal studies are needed to confirm this assumption.

Age-dependent impairment of auditory processing under spatially focused and divided attention: an electrophysiological study.

By using event-related potentials (ERPs) the present study examines if age-related differences in preparation and processing especially emerge during divided attention. Binaurally presented auditory cues called for focused (valid and invalid) or divided attention to one or both ears. Responses were required to subsequent monaurally presented valid targets (vowels), but had to be suppressed to non-target vowels or invalidly cued vowels. Middle-aged participants were more impaired under divided attention than young ones, likely due to an age-related decline in preparatory attention following cues as was reflected in a decreased CNV. Under divided attention, target processing was increased in the middle-aged, likely reflecting compensatory effort to fulfill task requirements in the difficult condition. Additionally, middle-aged participants processed invalidly cued stimuli more intensely as was reflected by stimulus ERPs. The results suggest an age-related impairment in attentional preparation after auditory cues especially under divided attention and latent difficulties to suppress irrelevant information.

Neural activity associated with executive functions in adolescents with attention-deficit/hyperactivity disorder (ADHD).

This study used event-related potentials (ERPs) and flanker-task performance to compare executive functions in adolescents with ADHD, their siblings and independent healthy controls. The aim was to investigate the processing of distracting stimuli, control over inappropriate responses, and the detection of errors in the presence of incompatible and No-go stimuli (arrow-heads and a circle, respectively). Performance showed no major differences between the groups, although No-go errors were numerically increased for the patients. Adolescents with ADHD were not characterised by the absence of post-error response slowing. The ADHD group showed a generally smaller N2 and a missing amplification of the frontal P3 (P3a) in No-go vs. incompatible trials most likely reflecting impaired inhibitory processing. In response-locked potentials error-related negativity (Ne) and positivity (Pe) did not clearly differentiate between the groups. This study shows that ADHD children are more impaired in controlled than automatic response processing and inhibition. This was particularly evident in reduced frontal activity in general and especially after No-go stimuli. Deficient error processing may, however, not be a cardinal feature of adolescents with ADHD. Future work must orient towards determining if there is a subgroup for whom the inhibitory impairment is characteristic.

Feedback-related processes during a time-production task in young and older adults.

OBJECTIVE: We examined whether the age-related decline in the integrity of the mid-brain dopamine system plays a role in the adaptation of precisely timed motor responses by feedback information. METHODS: Participants performed a time-production task with feedback given after each trial. They were encouraged to use the feedback for improving temporal response accuracy. Event-related potentials to the feedback were analyzed. RESULTS: Older participants performed poorer than the young. Overall, high response accuracy was more favoured following positive than negative feedback. Older participants performed even worse after negative feedback than the younger. The feedback-related negativity (FRN) was of lower amplitude for older vs. young participants. FRN amplitude correlated significantly with response accuracy only for the young group. CONCLUSIONS: The decreased response accuracy during time production of the older group may be related to a weakened fronto-striatal dopamine system and thus a reduced ability to use feedback information for improving temporal aspects of the motor response. SIGNIFICANCE: The study points to difficulties especially for older participants to process error feedback, and it underlines the importance of positive feedback in order to improve temporal response accuracy. Suggestions can be drawn for the design of feedback information especially for older adults in motor learning environments.

Time estimation in healthy ageing and neurodegenerative basal ganglia disorders.

A decline in motor performance and timing performance is evident not only in clinical patient groups, e.g. with Parkinson's or Huntington's disease but also in normal ageing. Common to the mentioned groups is a deterioration in dopaminergic function of fronto-striatal brain circuits. These areas belong to a distributed network in the brain playing an important role in time perception and timing behaviour. Therefore, we measured time estimation performance in five groups of healthy young and healthy old participants, of patients with Parkinson's disease (PD), with presymptomatic and symptomatic Huntington's disease (HD). Participants were instructed to indicate by a precise button press when 1.2s had elapsed after stimulus onset. They received feedback after correct (within a specified time window) or incorrect responses. When compared to the young control group the performance in old participants, patients with Parkinson's, presymptomatic and symptomatic Huntington's disease was inferior, while differences were not noticed between the latter four groups. The data underline the importance of fronto-striatal circuits in the brain for time processing and time estimation. It is suggested that it is not the degree of dysfunction of the fronto-striatal dopamine system but rather the mere existence of a dysfunction, even if subtle, which is pivotal for a decline in timing performance. A time estimation task can serve as a useful tool to detect even faint changes in the integrity of the fronto-striatal dopamine system.

Flanker interference in young and older participants as reflected in event-related potentials.

The present study investigates behavioural and event-related potential (ERP) differences between young and older participants in two variants of a flanker task. Flankers preceded the target by 100 ms (Experiment 1) or were presented simultaneously with the target (Experiment 2). In both experiments the response times showed an age-related slowing and a compatibility effect, which did not differ significantly across age. The older participants committed only half as many errors as the young ones. The visual ERPs revealed that the speed of visual perception was similar between groups. In addition the processing of the targets, but not of the flankers, appeared to be enhanced in the older participants. Moreover the lateralized readiness potential (LRP) started later and was larger for old vs. young participants, which was most pronounced for the incorrect LRP activation due to the flankers. The LRP amplitude effect is due to an enhanced activation over contralateral motor areas, which appears to be a general finding unrelated to the error rate. In summary, in the present study we could not find evidence for enhanced flanker interference in the performance of older compared to young participants. The reduced error rates for older participants are likely due to enhanced processing of the targets and delayed transmission of flanker information from visual to motor areas.

Interaction of facial expressions and familiarity: ERP evidence.

There is mounting evidence that under some conditions the processing of facial identity and facial emotional expressions may not be independent; however, the nature of this interaction remains to be established. By using event-related brain potentials (ERP) we attempted to localize these interactions within the information processing system. During an expression discrimination task (Experiment 1) categorization was faster for portraits of personally familiar vs. unfamiliar persons displaying happiness. The peak latency of the P300 (trend) and the onset of the stimulus-locked LRP were shorter for familiar than unfamiliar faces. This implies a late perceptual but pre-motoric locus of the facilitating effect of familiarity on expression categorization. In Experiment 2 participants performed familiarity decisions about portraits expressing different emotions. Results revealed an advantage of happiness over disgust specifically for familiar faces. The facilitation was localized in the response selection stage as suggested by a shorter onset of the LRP. Both experiments indicate that familiarity and facial expression may not be independent processes. However, depending on the kind of decision different processing stages may be facilitated for happy familiar faces.

Effects of ageing on cognitive task preparation as reflected by event-related potentials.

OBJECTIVE: The anticipation of complex cognitive tasks involves effortful preparation being reflected in the contingent negative variation (CNV) of the event-related potential. In the literature there are contradictory results concerning the effect of age on this potential. We wanted to investigate effects of age, time-on-task, and task difficulty on the CNV. METHOD: Young and middle-aged participants performed a visual search and a non-search task during an early and a late phase of a 6-h session. RESULTS: Performance data revealed increased response times and error rates for middle-aged vs. young participants. Most importantly, an increased frontal CNV amplitude was found for the older participants, especially pronounced in the search task. A late positivity which was elicited to the offset of the preceding stimulus was increased for the middle-aged vs. young group in the visual search task only. There was no effect of time-on-task on performance, but the CNV became larger with time-on-task in the search task while it became smaller in the non-search task. CONCLUSIONS: The results suggest an enhancement of effortful task preparation for middle-aged participants especially when the task is difficult. SIGNIFICANCE: This underlines the role of the CNV as a neurophysiological indicator for effortful cognitive preparation.

Auditory change detection in schizophrenia: sources of activity, related neuropsychological function and symptoms in patients with a first episode in adolescence, and patients 14 years after an adolescent illness-onset.

BACKGROUND: The event-related brain response mismatch negativity (MMN) registers changes in auditory stimulation with temporal lobe sources reflecting short-term echoic memory and frontal sources a deviance-induced switch in processing. Impairment, controversially present at the onset of schizophrenia, develops rapidly and can remain independent of clinical improvement. We examined the characteristics of the scalp-recorded MMN and related these to tests of short-term memory and set-shifting. We assessed whether the equivalent dipole sources are affected already at illness-onset in adolescence and how these features differ after a 14-year course following an adolescent onset. The strength, latency, orientation and location of frontal and temporal lobe sources of MMN activity early and late in the course of adolescent-onset schizophrenia are analysed and illustrated. METHODS: MMN, a measure of auditory change-detection, was elicited by short deviant tones in a 3-tone oddball-presentation and recorded from 32 scalp electrodes. Four dipole sources were placed following hypothesis-led calculations using brain electrical source analysis on brain atlas and MR-images. A short neuropsychological test battery was administered. We compared 28 adolescent patients with a first episode of schizophrenia and 18 patients 14 years after diagnosis in adolescence with two age-matched control groups from the community (n = 22 and 18, respectively). RESULTS: MMN peaked earlier in the younger than the older subjects. The amplitude was reduced in patients, especially the younger group, and was here associated with negative symptoms and slow set-shifting. In first-episode patients the temporal lobe sources were more ventral than in controls, while the left cingular and right inferior-mid frontal sources were more caudal. In the older patients the left temporal locus remained ventral (developmental stasis), the right temporal locus extended more antero-laterally (illness progression), and the right frontal source moved antero-laterally (normalised). CONCLUSION: From the start of the illness there were differences in the dipole-model between healthy and patient groups. Separate characteristics of the sources of the activity differences showed an improvement, stasis or deterioration with illness-duration. The precise nature of the changes in the sources of MMN activity and their relationship to selective information processing and storage depend on the specific psychopathology and heterogeneous course of the illness.

Maturation processes in automatic change detection as revealed by event-related brain potentials and dipole source localization: significance for adult AD/HD.

Mismatch negativity (MMN) is an event-related potential reflecting automatic attention-related information processing marking the detection of auditory change. The bilateral scalp distribution develops by 14 years of age, and is elicited with adult latencies by 17 years. But consistent with reports of continued brain maturation after adolescence, we show here that features of the temporal and frontal lobe dipole sources also continue to develop in the third decade of life. This has consequences for studies of the developmental course of MMN anomalies, from childhood into adulthood, in attention-deficit/hyperactivity disorder. Two groups of healthy subjects with mean ages of 17 and 30 years were presented with a 3-tone auditory oddball. The duration-deviant MMN was recorded during attention to a visual discrimination (auditory-passive condition) and an active auditory discrimination. MMN amplitudes were smaller in the older subjects and the MMN lasted longer over the right hemisphere. Latencies and moments of the four dipoles in the temporal and frontal lobes did not distinguish the two subject-groups. But both temporal lobe sources were located significantly more ventrally and further left in the young adult than in the adolescent subjects. The left cingular source moved posteriorly and the right inferior frontal source moved antero-medially in the older subjects. Brain development in the third decade may cause the two frontal sources to move apart on the rostro-caudal axis but the temporal lobe sources to move left on the lateral and down on the dorsoventral axes. Thus special care is necessary in interpreting putative dysfunctional neurobiological changes in developmental attention-deficit disorders where as-yet-unspecified sub-groups may show a late developmental lag, partial lag, or no lag at all, associated with other impairments.

The functional locus of the lateralized readiness potential.

The lateralized readiness potential (LRP) is considered to reflect motor activation and has been used extensively as a tool in elucidating cognitive processes. In the present study, we attempted to more precisely determine the origins of the LRP within the cognitive system. The response selection and motor programming stages were selectively manipulated by varying symbolic stimulus response compatibility and the time to peak force of an isometric finger extension response. Stimulus response compatibility and time to peak force affected response latency, as measured in the electromyogram, in a strictly additive fashion. The effects of the experimental manipulations on stimulus- and response-synchronized LRPs indicate that the LRP starts after the completion of response-hand selection and at the beginning of motor programming. These results allow a more rigorous interpretation of LRP findings in basic and applied research.

Are fingers special? Evidence about movement preparation from event-related brain potentials.

Ulrich, Leuthold, and Sommer (1998) suggested that movement preparation at the level of the motor cortex, as indexed by the lateralized readiness potential (LRP), proceeds in a strongly hierarchical fashion, where parameters other than response hand are prepared only if all the movement parameters are known. These conclusions were based on an experiment where a precue provided information about response hand, direction of finger movement, and movement force. To assess the generality of these findings, we replaced the force parameter with response finger. LRP indicated that preparation of the required finger is possible even when preliminary information is incomplete. Therefore, movement preparation appears to follow different rules when anatomical relationships (hand and finger) are concerned as compared to functional parameters like movement direction. On the other hand, at a limb-unspecific level, as indicated by the contingent negative variation, we confirmed evidence for parallel programming of all movement parameters.