Electrophysiological correlates of the retention of tones differing in timbre in auditory short-term memory

We examined the electrophysiological correlates of retention in auditory short-term memory (ASTM) for sequences of one, two, or three tones differing in timbre but having the same pitch. We focused on event-related potentials (ERPs) during the retention interval and revealed a sustained fronto-central ERP component (most likely a sustained anterior negativity; SAN) that became more negative as memory load increased. Our results are consistent with recent ERP studies on the retention of pitch and suggest that the SAN reflects brain activity mediating the low-level retention of basic acoustic features in ASTM. The present work shows that the retention of timbre shares common features with the retention of pitch, hence supporting the notion that the retention of basic sensory features is an active process that recruits modality-specific brain areas.     

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.     

Memory specificity is linked to repetition effects in event-related potentials across the lifespan

The specificity with which past experiences can be remembered varies across the lifespan, possibly due to differences in how precisely information is encoded. Memory formation can be investigated through repetition effects, the common finding that neural activity is altered when stimuli are repeated. However, whether differences in this indirect measure of memory formation relate to lifespan differences in memory specificity has not yet been established. In the present study, we examined repetition effects in event-related potentials and their relation to recognition. During incidental encoding, children (aged 7–9 years), young adults (18–30 years), and older adults (65–76 years) viewed repeated object images from different categories. During subsequent recognition, we distinguished memory for the specific items versus the general categories. We identified repetition suppression in all age groups, and repetition enhancement for adults. Furthermore, individual item recognition performance comprising lure discrimination was positively associated with the magnitude of the neural repetition effects, which did not differ between groups, indicating common neural mechanisms of memory formation. Our findings demonstrate that neural repetition effects reflect the formation of highly specific memory representations and highlight their significance as a neural indicator of individual differences in episodic memory encoding across the lifespan.     

Memory retrieval processing: neural indices of processes supporting episodic retrieval

Event-related potentials (ERPs) were acquired during separate test phases of a verbal recognition memory exclusion task in order to contribute to current understanding of the functional significance of differences between ERPs elicited by new (unstudied) test words, which are assumed to index processes engaged in pursuit of task-relevant information. Participants were asked to endorse old words from one study task (targets), and to reject new test words as well as those from a second study task (non-targets). The study task designated as the target category varied across test phases. The left-parietal ERP old/new effect - the electrophysiological signature of recollection - was reliable for targets and for non-targets in all test phases, consistent with the view that participants recollected information about both of these classes of test word. The contrast between the ERPs evoked by new test words separated according to target designation revealed no reliable differences. These findings contrast with those in a recent study in which the same tasks were used, but in which the accuracy of task judgments was markedly higher (Dzulkifli, M.A., & Wilding, E. L. (2005). Electrophysiological indices of strategic episodic retrieval processing. Neuropsychologia, 43, 1152-1162). In that study, there were reliable differences between the ERPs evoked by the two classes of new words, but reliable left-parietal ERP old/new effects for targets only. In combination, the findings suggest that differences between ERPs evoked by new test words can reflect processes that are important for controlling what kinds of information will and will not be recollected.     

Age-related changes in neural activity during source memory encoding in young, middle-aged and elderly adults

Source memory, the ability to remember contextual information present at the moment an event occurs, declines gradually during normal aging. The present study addressed whether source memory decline is related to changes in neural activity during encoding across age. Event-related potentials (ERPs) were recorded in three groups of 14 subjects each: young (21-26 years), middle-aged (50-55 years) and older adults (70-77 years). ERPs were recorded while the subjects performed a natural/artificial judgment on images of common objects that were presented randomly in one of the quadrants of the screen (encoding phase). At retrieval, old images mixed with new ones were presented at the center of the screen and the subjects judged whether each image was new or old and, if old, were asked to indicate at which position of the screen the image was presented in the encoding session. The neurophysiological activity recorded during encoding was segregated for the study items according to whether their context was correctly retrieved or not, so as to search for subsequent memory effects (SME). These effects, which consisted of larger amplitude for items subsequently attracting a correct source judgment than an incorrect one, were observed in the three groups, but their onset was delayed across the age groups. The amplitude of the SME was similar across age groups at the frontal and central electrode sites, but was manifested more at the posterior sites in middle-aged and older adults, suggesting that source memory decline may be related to less efficient encoding mechanisms.     

Electrophysiological correlates of familiarity in recognition memory and exclusion tasks

ERPs were acquired in the test phases of three memory experiments, where three classes of word were presented. These were: (i) words encountered in a prior study phase (studied words), (ii) words presented at test for the first time (new words), and (iii) new words repeated after a lag of 7-9 intervening words (repeated test words). In experiments 1 and 2, participants were asked to respond on one key to studied words and on another to new as well as to repeated test words. In experiment 3, a binary response was again required, but in this case repeated test and studied words were assigned to the same key. In each experiment, the principal focus for analysis was on the differences between the ERPs at mid-frontal electrode locations from 300 to 500 ms post-stimulus that were associated with incorrect responses to studied words (misses) and correct responses to new words. It has been proposed that relatively greater positivity for studied than for new words at this locus reflects the greater familiarity of studied than of unstudied words. ERPs elicited by misses were reliably more positive-going than those elicited by correct rejections in experiments 1 and 2 only. These findings support the link between this modulation of the electrical record and familiarity in so far as the designs of the experiments lead to the prediction that the average level of familiarity associated with misses should be higher in the first two experiments than in the third. In combination with findings in other studies, these data support dual-process accounts of recognition memory.     

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.     

The neural correlates of insight in Chinese verbal problems: an event related-potential study

The electrophysiological correlates of “Chinese anagrams” solving were studied using high-density event-related potentials (ERPs). Results showed that Insight solutions elicited a more positive ERP deflection (P400-600) than did Search solutions in the time window of 400-600 ms. Dipole source analysis showed that the generator of P400-600 was localized in the fusiform gyrus, which might be involved in breaking mental sets during reconstruction of the Chinese anagrams. Then, Insight solutions elicited a more positive ERP deflection (LPC) than did Search solutions between 640 and 780 ms. Dipole source analysis showed that the generator of LPC was localized in the right superior temporal gyrus, which might reflect forming novel associations when subjects regrouped the decompositions of the characters.     

Examining the development of memory for temporal context and its underlying neural processes using event-related potentials

Time is a critical feature of episodic memory—memory for events from a specific time and place (Tulving, 1972). Previous research indicates that temporal memory (memory for ‘when’) is slower to develop than memory for other details (e.g., ‘what’ and ‘where’), with improvements observed across middle and late childhood. The factors that drive these changes are not yet clear. We used an event-related potential (ERP) recognition memory paradigm to investigate the underlying processes of memory for temporal context in middle to late childhood (7−9-year-olds; 10−12-year-olds) and young adulthood. Behaviorally, we observed age-related improvements in the ability to place events in temporal context. ERP analyses showed old/new effects for children and adults. We also found brain-behavior relations for 1) episodic memory (ERP mean amplitude difference between source hits and correctly identified new trials was correlated to behavioral accuracy), and 2) temporal memory (ERP mean amplitude difference between source hits and source error trials was correlated to accuracy of temporal memory judgments). This work furthers our understanding of the cognitive processes and neural signatures supporting temporal memory development in middle to late childhood, and has implications for episodic memory development more broadly.     

Electrophysiological indices of strategic episodic retrieval processing

Event-related potentials (ERPs) were acquired during test phases of a recognition memory exclusion task, in order to contribute to current understanding of the processes responsible for the ways in which memory retrieval can be controlled strategically. Participants were asked to endorse old words from one study task (targets) and to reject new test words as well as those from a second study task (non-targets). The study task designated as the target category varied across test phases. The left-parietal ERP old/new effect--the electrophysiological signature of recollection--was reliable for targets only in all test phases, consistent with the view that participants control recollection strategically in service of task demands. The contrast between the ERPs evoked by new test words separated according to target designation revealed reliable differences at midline, anterior and right-hemisphere locations. These differences likely reflect processes that form part of a retrieval attempt and are interpreted here as indices of processes that are important for the strategic regulation of episodic retrieval.     

Experience-dependent neural specialization during infancy

The ability to recognize the difference among faces of another race or species declines from 6 to 9 months of age. During this time, perceptual biases are formed, leading to lasting deficits in recognizing individuals of other races and species. However, little is known about how early infant experience shapes the neural structures underlying face processing. Here we found neural specialization, in infants who received 3 months of training with six individually labeled monkey faces. However, neural specialization was not found after an equal amount of training with the same six faces labeled at the category-level (i.e., all faces labeled “monkey”) or when infants were exposed to faces without labels. These results suggest that neural specialization for faces requires learning at the individual level during infancy.     

P300 latency jitter and its correlates in people with amyotrophic lateral sclerosis

ObjectivePeople with amyotrophic lateral sclerosis (ALS) can benefit from brain-computer interfaces (BCIs). However, users with ALS may experience significant variations in BCI performance and event-related potential (ERP) characteristics. This study investigated latency jitter and its correlates in ALS.MethodsElectroencephalographic (EEG) responses were recorded from six people with ALS and nine neurotypical controls. ERP amplitudes and latencies were extracted. Classifier-based latency estimation was used to calculate latency jitter. ERP components and latency jitter were compared between groups using Wilcoxon rank-sum tests. Correlations between latency jitter and each of the clinical measures, ERP features, and performance measures were investigated using Spearman and repeated measures correlations.ResultsLatency jitter was significantly increased in participants with ALS and significantly negatively correlated with BCI performance in both ALS and control participants. ERP amplitudes were significantly attenuated in ALS, and significant correlations between ERP features and latency jitter were observed. There was no significant correlation between latency jitter and clinical measures.ConclusionsLatency jitter is increased in ALS and correlates with both BCI performance and ERP features.SignificanceThese results highlight the associations of latency jitter with BCI performance and ERP characteristics and could inform future BCI designs for people with ALS.     

Effects of advanced aging on the neural correlates of successful recognition memory

Functional neuroimaging studies have reported that the neural correlates of retrieval success (old > new effects) are larger and more widespread in older than in young adults. In the present study we investigated whether this pattern of age-related ‘over-recruitment’ continues into advanced age. Using functional magnetic resonance imaging (fMRI), retrieval-related activity from two groups (N = 18 per group) of older adults aged 84-96 years (‘old-old’) and 64-77 years (‘young-old’) was contrasted. Subjects studied a series of pictures, half of which were presented once, and half twice. At test, subjects indicated whether each presented picture was old or new. Recognition performance of the old-old subjects for twice-studied items was equivalent to that of the young-old subjects for once-studied items. Old > new effects common to the two groups were identified in several cortical regions, including medial and lateral parietal and prefrontal cortex. There were no regions where these effects were of greater magnitude in the old-old group, and thus no evidence of over-recruitment in this group relative to the young-old individuals. In one region of medial parietal cortex, effects were greater (and only significant) in the young-old group. The failure to find evidence of over-recruitment in the old-old subjects relative to the young-old group, despite their markedly poorer cognitive performance, suggests that age-related over-recruitment effects plateau in advanced age. The findings for the medial parietal cortex underscore the sensitivity of this cortical region to increasing age.     

The relation between race-related implicit associations and scalp-recorded neural activity evoked by faces from different races

Abstract

The neural correlates of the perception of faces from different races were investigated. White participants performed a gender identification task in which Asian, Black, and White faces were presented while event-related potentials (ERPs) were recorded. Participants also completed an implicit association task for Black (IAT-Black) and Asian (IAT-Asian) faces. ERPs evoked by Black and White faces differed, with Black faces evoking a larger positive ERP that peaked at 168 ms over the frontal scalp, and White faces evoking a larger negative ERP that peaked at 244 ms. These Black/White ERP differences significantly correlated with participants’ scores on the IAT-Black. ERPs also differentiated White from Asian faces and a significant correlation was obtained between the White-Asian ERP difference waves at ~500 ms and the IAT-Asian. A positive ERP at 116 ms over occipital scalp differentiated all three races, but was not correlated with either IAT. In addition, a late positive component (around 592 ms) was greater for the same race compared to either other race faces, suggesting potentially more extended or deeper processing of the same race faces. Taken together, the ERP/IAT correlations observed for both other races indicate the influence of a race-sensitive evaluative process that may include early more automatic and/or implicit processes and relatively later more controlled processes.     

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

Summary. Using the n-back task, we recently identified, in young subjects, a positive-negative event related potential component (PN_wm) in a time-range window between 140 and 280ms after stimulus onset representing an electrophysiological correlate of working memory load. To evaluate age-related electrophysiological changes in working memory processing, we applied the same neuropsychological paradigm and compared densities of the PN_wm component in 17 young (mean age: 26) and 17 healthy elderly individuals (mean age: 75). Both age groups displayed a PN_wm component during the two working memory tasks. For the 1-back task, densities were similar in both young and elderly individuals. In contrast, PN_wm densities increased with higher memory load (2-back>1-back) in the younger but not in the older group. This difference was mainly observed over parietal electrodes suggesting an impaired activation of neural generators within this brain region. The present results are consistent with the hypothesis of decreased brain reserve in the elderly and provide evidence for age-related deficits in the recruitment of posterior cortical neurons with increasing working memory load.Both authors have contributed equally to this work     

Evidence for a differential contribution of early perceptual and late cognitive processes during encoding to episodic memory impairment in schizophrenia

Objectives: Schizophrenia is characterised by significant episodic memory impairment that is thought to be related to problems with encoding, however the neuro-functional mechanisms underlying these deficits are not well understood. The present study used a subsequent recognition memory paradigm and event-related potentials (ERPs) to investigate temporal aspects of episodic memory encoding deficits in schizophrenia.

Methods: Electroencephalographic data was recorded in 24 patients and 19 healthy controls whilst participants categorised single words as pleasant/unpleasant. ERPs were generated to subsequently recognised versus unrecognised words on the basis of a forced-choice recognition memory task. Subsequent memory effects were examined with the late positive component (LPP). Group differences in N1, P2, N400 and LPP were examined for words correctly recognised.

Results: Patients performed more poorly than controls on the recognition task. During encoding patients had significantly reduced N400 and LPP amplitudes than controls. LPP amplitude correlated with task performance however amplitudes did not differ between patients and controls as a function of subsequent memory. No significant differences in N1 or P2 amplitude or latency were observed.

Conclusions: The present results indicate that early sensory processes are intact and dysfunctional higher order cognitive processes during encoding are contributing to episodic memory impairments in schizophrenia.     

Examining the neural basis of episodic memory: ERP evidence that faces are recollected differently from names

Episodic memory is supported by recollection, the conscious retrieval of contextual information associated with the encoding of a stimulus. Event-Related Potential (ERP) studies of episodic memory have identified a robust neural correlate of recollection—the left parietal old/new effect—that has been widely observed during recognition memory tests. This left parietal old/new effect is believed to provide an index of generic cognitive operations related to recollection; however, it has recently been suggested that the neural correlate of recollection observed when faces are used as retrieval cues has an anterior scalp distribution, raising the possibility that faces are recollected differently from other types of information. To investigate this possibility, we directly compared neural activity associated with remember responses for correctly recognized face and name retrieval cues. Compound face–name stimuli were studied, and at test either a face or a name was presented alone. Participants discriminated studied from unstudied stimuli, and made a remember/familiar decision for stimuli judged ‘old’. Remembering faces was associated with anterior (500–700 ms) and late right frontal old/new effects (700–900 ms), whereas remembering names elicited mid frontal (300–500 ms) and left parietal (500–700 ms) effects. These findings demonstrate that when directly compared, with reference to common episodes, distinct cognitive operations are associated with remembering faces and names. We discuss whether faces can be remembered in the absence of recollection, or whether there may be more than one way of retrieving episodic context.     

Individual differences in executive functioning modulate age effects on the ERP correlates of retrieval success

The present study aimed to investigate whether the level of executive functioning modulated the effects of aging on episodic memory performance and on the electrophysiological correlates of retrieval success (‘old/new effect’). We used a differential approach in which young and older adults were divided into four groups of 14 participants according to their scores on a composite executive index: young-high, young-low, old-high and old-low. ERPs were recorded while participants performed a word-stem cued-recall task. Behavioral results demonstrated that age-related deficits in memory performance were reduced but not eliminated in individuals with a higher executive functioning level. Young participants exhibited ERP old/new effects on frontal and parietal areas. At posterior sites, the effect was entirely left-sided for young-low adults while for young-high participants it was bilateral, maximal at left sites and of greater amplitude. For the old-low group, both frontally-based and parietally-based processes appeared to be affected by the aging process. They also demonstrated a late frontal negative component, which might indicate an unsuccessful additional attempt to cope with retrieval difficulties. In the old-high group, ERP effects on frontal areas were relatively intact while the parietal effect was impaired compared to young adults. However, old-high subjects exhibited earlier, larger and more symmetrical effects than did old-low adults, which was in line with their better memory performance. These findings provide some support for the executive decline hypothesis of cognitive aging by showing that neural correlates of retrieval success in episodic memory are differentially affected by aging according to executive functioning level. They are consistent with the view that a high executive functioning level may help older adults recruit a cerebral pattern which enables them to perform a memory task more efficiently.     

The relevance of the functional 5-HT1A receptor polymorphism for attention and working memory processes during mental rotation of characters

Numerous lines of research indicate that attentional processes, working memory and saccadic processes are highly interrelated. In the current study, we examine the relation between these processes with respect to their cognitive-neurophysiological and neurobiological background by means of event-related potentials (ERPs) in a sample of N = 72 healthy probands characterized for the functional serotonin receptor 1 A (5-HT1A) C(−1019)G polymorphism.The results support a close interrelation between working memory, attentional and saccadic processes. Yet, these processes are differentially modulated by the 5-HT1A C(−1019)G polymorphism. The 5-HT1A C(−1019)G polymorphism primarily affects attentional processing, whereas processes related to the mental rotation of an object are independent of 5-HT1A genetic variation. It is shown that an increasing number of −1019 G alleles leads to a differential reduction of the N1 above the left and right hemisphere and hence bottom-up attentional processing. In the way increasing numbers of −1019 G alleles lead to a reduction of attentional processes, saccadic activity increases as a similar function of the number of −1019 G alleles. This increase in activity occurs parallel in time to the process of mental rotation. It is hypothesized that decreased attentional processes, dependent on different 5-HT1A C(−1019)G genotypes, may cause parietal networks to increase saccadic activity in order to perform mental rotation.