Auditory recognition memory in 2-month-old infants as assessed by event-related potentials

Previous studies of auditory recognition memory in sleeping newborns reported 2 event-related potential (ERP) components, P2 and negative slow wave (NSW), reflecting voice discrimination and detection of novelty, respectively. In the present study, using high-density recording arrays, ERPs were acquired from 26 2-month-old awake infants as they were presented with a familiar and unfamiliar voice (i.e., mother and stranger) with equal probability. In addition to P2 and NSW, we observed a positive slow wave (PSW) over the right temporo-parietal scalp, indicating memory updating. Our study suggests that infants appear to have the capacity to encode novel stimuli as early as 2 months of age.     

Neural measures of working memory in a bilateral change detection task

The change detection task is a widely used paradigm to examine visual working memory processes. Participants memorize a set of items and then, try to detect changes in the set after a retention period. The negative slow wave (NSW) and contralateral delay activity (CDA) are event‐related potentials in the EEG signal that are commonly used in change detection tasks to track working memory load, as both increase with the number of items maintained in working memory (set size). While the CDA was argued to more purely reflect the memory‐specific neural activity than the NSW, it also requires a lateralized design and attention shifts prior to memoranda onset, imposing more restrictions on the task than the NSW. The present study proposes a novel change detection task in which both CDA and NSW can be measured at the same time. Memory items were presented bilaterally, but their distribution in the left and right hemifield varied, inducing a target imbalance or “net load.” NSW increased with set size, whereas CDA increased with net load. In addition, a multivariate linear classifier was able to decode the set size and net load from the EEG signal. CDA, NSW, and decoding accuracy predicted an individual's working memory capacity. In line with the notion of a bilateral advantage in working memory, accuracy, and CDA data suggest that participants tended to encode items relatively balanced. In sum, this novel change detection task offers a basis to make use of converging neural measures of working memory in a comprehensive paradigm.     

The effect of early attention allocation on location-based attention toward a later threat: An ERP study

The current study investigated the effect of earlier attention processing on later spatial attention allocation using a prime stimulus followed by a dot-probe task. Here we recorded event-related potentials (ERPs) respectively when picture primes and face pairs were displayed at the two successive stages. For negative primes, participants showed smaller amplitudes of negative slow wave (NSW) to initial negative picture primes and greater N1 and smaller P2 amplitudes to subsequent face pairs compared with neutral primes. In addition, participants showed greater amplitudes of NSW to initial neutral picture primes and smaller N1 and greater P2 amplitudes to face pairs in neutral compared with negative prime condition. These results suggest that attention allocation toward an earlier threat influences the attention allocation toward the location of a later threat; and the initial neutral detection does not affect spatial attention allocation toward later face pairs. These findings are interpreted in terms of the theory of limited cognitive resources.     

Development of face-sensitive event-related potentials during infancy: a review.

Event-related potential (ERP) studies in adults have identified a number of components related to encoding and recognition memory of faces. Although behavioural studies indicate that even very young infants are able to detect faces and recognise familiar individuals, very few ERP studies document the neural correlates of these early abilities. In this article, we review four components (P1, N290, P400, Nc) and slow wave activity that are elicited while infants view faces. Where possible we draw links between these components and their possible equivalents to those observed in children and adults, and we highlight areas where further investigation is required. The theoretical importance of ERP studies of face processing in infants for debates about the origins and domain specificity of the adult cortical face processing system are discussed.     

Differences in mental task performance and slow potential shifts in subjects differing in cortisol level.

Hormones of the pituitary-adrenocortical axis (e.g., cortisol) are involved in the regulation of brain function. This study was aimed to clarify whether individual differences in baselines of cortisol are related to differences in heart rate (HR), slow brain potential shifts (SPS), performance data and personality. 17 males were instructed to solve 120 arithmetical tasks under time stress conditions. They could obtain monetary bonuses according to the accuracy of their task performance. This test condition was compared to a control condition. To determine the plasma level of cortisol by radioimmunoassays four blood samples were collected during the session. Baselines were estimated twice. A clustering procedure with respect to all cortisol levels resulted in a group of high responders (HC, n = 9) and a group of low responders (LC, n = 8). The HR was significantly higher in the HC group. The SPS of the LC group were characterized by a larger P300 elicited by the task followed by a steep negative slow wave (NSW) as compared to the HC group. LC subjects also showed a higher NSW before feedback presentation. The LC group solved the tasks faster and obtained more than twice the reward than the other group. They scored higher in achievement motivation and also reported increased 'Social Acceptance' and decreased 'Tiredness'. In sum, the results suggest a more efficient regulation of the arousal level of the LC group in contrast to the HC group as far as reflected in the parameters analysed.     

Neural signatures of face-voice synchrony in 5-month-old human infants

Infants' unitary perception of their multisensory world, including learning from people (faces and speech), hinges on temporal synchrony. Despite its importance, relatively little work has investigated the brain processes involved in infants' perception of temporal synchrony. In two experiments, we examined event-related brain potentials (ERPs) to asynchronous and synchronous audio-visual speech in infants. Both experiments showed the early auditory P2 was greater for the synchronously presented pairings and later attentional processing (Nc) was greater for asynchronous pairings. In addition, dynamic stimuli used in Experiment 2 produced a greater early visual response (N1) to the asynchronous condition and an enhanced memory-related slow wave (PSW) later for the synchronous condition. These results suggest that, like adults, auditory-visual integration for young infants begins early during sensory processing rather than later during higher-level cognitive processing. However, unlike adults, infants' brain responses may be biased towards synchrony. Furthermore, effects of attentional and memory processing confirm interpretations of behavioral looking patterns suggesting infants find synchrony more familiar.     

Low-Level Prenatal Lead Exposure Alters Auditory Recognition Memory in 2-Month-Old Infants: An Event-Related Potentials (ERPs) Study

This study used event-related potentials (ERPs) to assess effects of low-level prenatal lead exposure on auditory recognition memory in 2-month-old infants. Infants were divided into four groups according to cord-blood lead concentration: (1) <2.00 μg/dL, (2) 2.00–2.99 μg/dL, (3) 3.0–3.7 μg/dL, and (4) ≥3.7 μg/dL. The first group showed the normally expected differences in P2, P750, and late slow wave (LSW) amplitudes elicited by mothers’ and strangers’ voices. These differences were not observed for one or more ERP components in the other groups. Thus, there was electrophysiological evidence of poorer auditory recognition memory at 2 months with cord-blood lead ≥2.00 μg/dL.     

Influences of postconceptional age and postnatal experience on the development of auditory recognition memory in the newborn infant

We evaluated the effects of postconceptional age and postnatal experience on the development of neonatal auditory recognition memory. Three groups were tested: a premature newborn group (tested at 35-38 weeks postconceptional age, < or = 1 week old), a full-term newborn group (tested at 39-42 weeks postconceptional age, < or = 1 week old), and a full-term experienced group (tested at 39-42 weeks postconceptional age, > 1 week old; range 8-30 days). Event-related potentials were collected while infants listened to the maternal voice alternating with a stranger's voice. Postconceptional age was correlated with the development of recognition memory for the maternal voice while there were qualitative effects of postnatal experience on latency measurements. Maturity of auditory cortical responses was not correlated with recognition memory abilities. We conclude that maturation of the recognition memory pathways is primarily a function of postconceptional age with qualitative effects of postnatal experience. Maturation of the auditory recognition memory pathway is not contingent upon maturation of the "P2" peak thought to arise from primary auditory cortex.     

What does the brain do while playing scrabble?: ERPs associated with a short-long-term memory task.

Event-related brain potentials (ERPs) were recorded while subjects performed the scrabble paradigm, a cued recall task that demands retrieving semantic memory information from long-term memory since subjects are not exposed to a previous study phase. The task combines short- and long-term memory processes and consists of forming words from a set of letters presented in random order. Short-term memory was manipulated by varying the number of letters (three, four and five) presented to the subject, while semantic memory was examined by comparing correct trials with no response trials. Behavioral results reveal that the subjects performed the task serially, as denoted by a linear reaction time increment as the number of random letters in the set increased. Short-term memory procedures were reflected by an amplitude increase of the N200 and by an amplitude decrease of the P300 increasing the number of letters. Successfully retrieving semantic information from long-term memory was indexed by a negative slow wave recorded at left frontal and left central sites, and by a positive slow wave predominant over right hemisphere sites. These findings provide evidence that semantic retrieval memory involves activity from both left and right hemispheres.     

ERPs during continuous recognition memory for words

Event-related brain potentials (ERPs) were recorded from 10 young adults during a version of the continuous recognition memory paradigm. Words were presented after lags of either 2, 8 or 32 intervening items (equiprobable) following their first presentation, and subjects were required on each trial to make a choice: new (never presented previously) or old (previously presented) response. To assess the effect of probability of new to old items, words were presented in separate blocks with ratios of new to old of 2:1 and 1:1. Reaction time increased and successful recognition decreased systematically as the lag between first and second presentations of an item increased, supporting the distinction between primary (immediate memory) and secondary memory for verbal material. However, there were no systematic effects of item lag on the ERP components. ERPs to new items were characterized by larger N300 and smaller P300 amplitudes (from about 250 to 700 ms) than those to old items. These amplitude differences between old and new ERPs were interpreted as primarily reflecting repetition as opposed to semantic priming effects. These old/new effects did not interact with probability, suggesting that frequency of occurrence is not a major determinant the ERP old/new difference. Old items elicited a late negativity following the behavioral response that was interpreted as due to the presence of a "positive slow wave," with a frontally oriented distribution to new words that was absent in the ERPs to old words. Similarly, subtraction of ERPs elicited by new items that were subsequently unrecognized from those subsequently recognized, showed that underlying the ERP subsequent "memory effect" was a "frontal positive slow wave," dissociable from P300 on the basis of differences in scalp distribution. Since positive slow wave has been interpreted as reflecting "further processing," the data suggest that such processing, possibly similar to elaboration (Graf & Mandler, 1984), enhanced the probability of subsequent recognition.     

Capnography in spontaneously breathing preterm and term infants.

OBJECTIVE: To investigate sidestream EtCO2 wave patterns as related to prematurity. DESIGN: The EtCO2 wave pattern was analyzed longitudinally in 20 sequential preterm, 32-37 weeks of gestation and 39 fullterm controls. Infants with a cardiorespiratory disease, neurological deficit or a metabolic disorder were not included in the study. Sidestream EtCO2 was employed. Wave patterns were identified and baseline expiratory/inspiratory length and wave amplitude were measured. RESULTS: Two predominant (about 75%) wave patterns were identified: (i) (with plateau) significantly more prevalent among infants born at term as compared with preterm infants across their postconceptional ages (PCA) (P=0.005-0.04), (ii) (plateau free) significantly more prevalent among the youngest preterm infants as compared with the fullterm controls. Expiratory length was significantly correlated with respiratory rate (RR) across ages (P=0.01-0.001) whereas inspiratory length was correlated with RR among the two youngest groups of infants only (P=0.002 and 0.004). Wave patterns were not found to be affected by environmental temperatures, blood pressure, body weight, haemoglobin level, aminophylline or O2 supplementation. CONCLUSION: These findings suggest that EtCO2 wave pattern distribution among preterm infants is distinctly different from that of term controls, regardless of PCA, while inspiration is related to the degree of maturity. Alveolar pathology could probably be missed by sidestream capnography.     

Sleep spindles and rapid eye movement sleep as predictors of next morning cognitive performance in healthy middle‐aged and older participants

Spindles and slow waves are hallmarks of non‐rapid eye movement sleep. Both these oscillations are markers of neuronal plasticity, and play a role in memory and cognition. Normal ageing is associated with spindle and slow wave decline and cognitive changes. The present study aimed to assess whether spindle and slow wave characteristics during a baseline night predict cognitive performance in healthy older adults the next morning. Specifically, we examined performance on tasks measuring selective and sustained visual attention, declarative verbal memory, working memory and verbal fluency. Fifty‐eight healthy middle‐aged and older adults (aged 50–91 years) without sleep disorders underwent baseline polysomnographic sleep recording followed by neuropsychological assessment the next morning. Spindles and slow waves were detected automatically on artefact‐free non‐rapid eye movement sleep electroencephalogram. All‐night stage N2 spindle density (no./min) and mean frequency (Hz) and all‐night non‐rapid eye movement sleep slow wave density (no./min) and mean slope (μV/s) were analysed. Pearson's correlations were performed between spindles, slow waves, polysomnography and cognitive performance. Higher spindle density predicted better performance on verbal learning, visual attention and verbal fluency, whereas spindle frequency and slow wave density or slope predicted fewer cognitive performance variables. In addition, rapid eye movement sleep duration was associated with better verbal learning potential. These results suggest that spindle density is a marker of cognitive functioning in older adults and may reflect neuroanatomic integrity. Rapid eye movement sleep may be a marker of age‐related changes in acetylcholine transmission, which plays a role in new information encoding.     

Monitoring retrieval from long-term memory by slow event-related brain potentials

Slow event-related brain potentials of nine subjects were recorded in an experimentally controlled long-term memory retrieval task (the Fan paradigm) from electrode sites F3, Fz, F4, Cz, P3, Pz, and P4. In all retrieval conditions, a very pronounced DC-like negative potential appeared over the left frontal cortex. This negativity was switched on with the presentation of the probe stimuli and prevailed in some conditions throughout the total recording epoch of 14 s. Particular retrieval conditions became manifest in distinct slow wave effects. The amplitude of a bilaterally distributed frontal negative slow wave increased when a more diversified associative structure had to be searched. The amplitude of another negative slow wave, which peaked bilaterally over parietal areas, was affected by the type of concepts that had to be retrieved. The amplitude was larger with general concepts (category labels) and smaller with specific concepts (category exemplars). These results suggest that distinct strategies are invoked when subjects are required to draw conclusions about different contents stored permanently in an associative network.     

No effect of targeted memory reactivation during slow‐wave sleep on emotional recognition memory

Recent work has suggested that the benefits of sleep for memory consolidation are enhanced for highly salient (versus non‐salient) memories. Using a technique known as targeted memory reactivation, it is possible to selectively strengthen newly learned memories by re‐exposing the sleeping brain to auditory cues. The aim of the current study was to examine whether emotionally salient memories are also more responsive to targeted memory reactivation in slow‐wave sleep than neutral memories. In an initial training phase, participants memorised emotionally negative and neutral pictures, which were each paired with a semantically related sound. Recognition for the pictures was assessed before and after a 90‐min nap opportunity, during which half the sounds were re‐presented during slow‐wave sleep (as assessed via online polysomnographic sleep monitoring). We observed no effect of targeted memory reactivation on the recognition of emotionally negative or neutral memories. Our results highlight the importance of the memory paradigm used to assess targeted memory reactivation, and suggest that the robust and durable nature of recognition memory may make it an insensitive measure of behavioural targeted memory reactivation benefits. To fully assess the impacts of targeted memory reactivation on emotional memory processing in sleep, future studies should adopt experimental paradigms that maximise the salience of emotional stimuli while also providing a sensitive index of memory accuracy.     

Event-related potentials (ERPs) in a learning and memory test

The present study outlines a new paradigm to investigate the effects of learning and memory on event-related potentials (ERPs). In the learning phase, subjects had to learn a sequence of 12 auditory consonant-vowel syllables. In the test phase, subjects had to detect and report a change in the learned sequence. Auditory ERPs were recorded from the frontal, vertex, and parietal midline positions. In the learning phase, an early negative effect (EN) and a P3 with a slow wave (SW) occurred for the learned syllables, whereas a pre-stimulus negativity (PSN) occurred prior to the syllables not yet learned. In the test phase, the PSN preceded both the replaced syllables and those presented in their old positions. The EN and an N2-P3 complex were elicited by the replaced syllables, the EN by the syllables presented in their old positions. It was concluded that the ERPs can display specific effects related to cognitive processes underlying learning and memory. The PSN was suggested to reflect the expectation of the stimuli, the EN the activation of a template and the rehearsal of the stimuli. The SW was suggested to be related to a template match process with the learned syllables. The N2, elicited by the replaced stimuli, could imply a cognitive template mismatch and the P3 with the SW the updating of working memory.     

Using event-related potentials to study perinatal nutrition and brain development in infants of diabetic mothers

Proper prenatal and postnatal nutrition is essential for optimal brain development and function. The early use of event-related potentials enables neuroscientists to study the development of cognitive function from birth and to evaluate the role of specific nutrients in development. Perinatal iron deficiency occurs in severely affected infants of diabetic mothers. In animal models, severe perinatal iron deficiency targets the explicit memory system of the brain. Cross-sectional ERP studies have shown that infants of diabetic mothers have impairments in recognition memory from birth through 8 months of age. The purpose of this study was to evaluate longitudinal development of recognition memory using ERPs in infants of diabetic mothers compared with control infants. Infants of diabetic mothers were divided into high and low risk status based upon their birth weights and iron status and compared with healthy control infants. Infants were tested in the newborn period for auditory recognition memory, at 6 months for visual recognition memory and at 8 months for cross modal memory. ERPs were evaluated for developmental changes in the slow waves that are thought to reflect memory and the Nc component that is thought to reflect attention. The results of the study showed differences in development between the IDMs and control infants in the development of the slow waves over the left anterior temporal leads and age-related patterns of development in the NC component. These results are consistent with animal models showing that perinatal iron deficiency affects the development of the memory networks of the brain. This study highlights the value of using ERPs to translate basic science information obtained from animal models to the development of the human infant.     

Using Event-Related Potentials to Study Perinatal Nutrition and Brain Development in Infants of Diabetic Mothers

Proper prenatal and postnatal nutrition is essential for optimal brain development and function. The early use of event-related potentials enables neuroscientists to study the development of cognitive function from birth and to evaluate the role of specific nutrients in development. Perinatal iron deficiency occurs in severely affected infants of diabetic mothers. In animal models, severe perinatal iron deficiency targets the explicit memory system of the brain. Cross-sectional ERP studies have shown that infants of diabetic mothers have impairments in recognition memory from birth through 8 months of age. The purpose of this study was to evaluate longitudinal development of recognition memory using ERPs in infants of diabetic mothers compared with control infants. Infants of diabetic mothers were divided into high and low risk status based upon their birth weights and iron status and compared with healthy control infants. Infants were tested in the newborn period for auditory recognition memory, at 6 months for visual recognition memory and at 8 months for cross modal memory. ERPs were evaluated for developmental changes in the slow waves that are thought to reflect memory and the Nc component that is thought to reflect attention. The results of the study showed differences in development between the IDMs and control infants in the development of the slow waves over the left anterior temporal leads and age-related patterns of development in the NC component. These results are consistent with animal models showing that perinatal iron deficiency affects the development of the memory networks of the brain. This study highlights the value of using ERPs to translate basic science information obtained from animal models to the development of the human infant.     

The component structure of ERP subsequent memory effects in the Von Restorff paradigm and the word frequency effect in recall

We examined the degree to which ERP components elicited by items that are isolated from their context, either by their font size (“size isolates”) or by their frequency of usage, are correlated with subsequent immediate recall. Study lists contained (a) 15 words including a size isolate, (b) 14 high frequency (HF) words with one low frequency word (“LF isolate”), or (c) 14 LF words with one HF word. We used spatiotemporal PCA to quantify ERP components. We replicated previously reported P300 subsequent memory effects for size isolates and found additional correlations with recall in the novelty P3, a right lateralized positivity, and a left lateralized slow wave that was distinct from the slow wave correlated with recall for nonisolates. LF isolates also showed evidence of a P300 subsequent memory effect and also elicited the left lateralized subsequent memory effect, supporting a role of distinctiveness in word frequency effects in recall.     

Effects of intention load and background context on prospective remembering: an event-related brain potential study

Prospective remembering reflects the ability to realize intentions that must be delayed over some period of time. Recent evidence indicates that distinct modulations of the event-related brain potentials may be associated with the detection of a prospective memory cue (N300) and the recovery of an intention from memory (LPC, slow wave). The present experiments examined the degree to which these modulations were influenced by task manipulations that were expected to differentially influence cue detection and memory-related processes. Varying the number of intentions modulated the amplitude of a slow wave that may reflect memory-related processes. In contrast, varying the distinctiveness of the cues modulated the N300 and the early portion of the LPC indicating that this manipulation primarily influenced detection and categorization processes. These findings indicate that the N300, LPC and slow wave reflect functionally distinct processes associated with prospective memory.