Determining working memory from ERP topography

Neural correlates of processing active and passive sentences: proficiency-dependent event-related potential evidence in Chinese English foreign language learners

We explored whether and to what extent the neural mechanisms of second language sentence processing resemble those of native speakers by investigating the temporal dynamics of syntactic processing in terms of active or passive voice in reading English sentences by Chinese English Foreign Language (EFL) learners with high or low English proficiency. Participants were divided into two groups based on their proficiency levels in English. Three types of sentences (active, passive and ungrammatical) were presented to participants when their event-related potential responses were recorded at the verbs and the final words. The results showed that high-proficiency participants exhibited a greater anterior negativity at the verb position for ungrammatical sentences compared to active sentences. Furthermore, passive sentences elicited a larger frontal positivity than active sentences at the final word position. Additionally, greater P600 effects were observed for both passive and ungrammatical sentences than active sentences at the final word. The low-proficiency group exhibited a greater anterior negativity at the verb (but not the final word) position. In conclusion, these findings emphasize the role of proficiency as a modulating factor in the processing of English active and passive sentences among Chinese EFL learners. Furthermore, the processing of English active and passive sentences by these learners can be conceptualized as a three-stage process: prediction, correction and integration, representing the underlying cognitive mechanisms. This study provides novel insights into the understanding of the cognitive mechanism involved in second language sentence processing.

Manual action re-planning interferes with the maintenance process of working memory: an ERP investigation

The current study investigated the re-planning of the grasping movements, its functional interactions with working memory (WM), and underlying neurophysiological activity. Mainly, the current study investigated the movement re-planning interference with WM domains (verbal, visuospatial) and processes (maintenance, retrieval). We combined a cognitive-motor dual-task paradigm with an EEG setting. Thirty-six participants completed the verbal and visuospatial versions of a WM task concurrently with a manual task which required performing a grasp-and-place movement by keeping the initial movement plan (prepared movement condition) or changing it for reversing the movement direction (re-planned movement condition). ERPs were extracted for the prepared and re-planned conditions in the verbal and visuospatial tasks separately during the maintenance and retrieval processes. ERP analyses showed that during the maintenance process of both the verbal and visuospatial tasks, the re-planned movements compared to the prepared movements generated a larger positive slow wave with a centroparietal maximum between 200 and 700. We interpreted this ERP effect as a P300 component for the re-planned movements. There was no ERP difference between the planned and re-planned movements during the retrieval process. Accordingly, we suggest that re-planning the grasp-and-place movement interfered at least with the maintenance of the verbal and visuospatial domains, resulting in the re-planning costs. More generally, the current study provides the initial neurophysiological investigations of the movement re-planning–WM interactions during grasping movements, and contributes to a better understanding of the neurocognitive mechanisms underlying manual action flexibility.

Electrophysiological Signatures of Conceptual and Lexical Retrieval from Semantic Memory

Retrieval from semantic memory of conceptual and lexical information is essential for producing speech. It is unclear whether there are differences in the neural mechanisms of conceptual and lexical retrieval when spreading activation through semantic memory is initiated by verbal or nonverbal settings. The same twenty participants took part in two EEG experiments. The first experiment examined conceptual and lexical retrieval following nonverbal settings, whereas the second experiment was a replication of previous studies examining conceptual and lexical retrieval following verbal settings. Target pictures were presented after constraining and nonconstraining contexts. In the nonverbal settings, contexts were provided as two priming pictures (e.g., constraining: nest, feather; nonconstraining: anchor, lipstick; target picture: BIRD). In the verbal settings, contexts were provided as sentences (e.g., constraining: "The farmer milked a..."; nonconstraining: "The child drew a..."; target picture: COW). Target pictures were named faster following constraining contexts in both experiments, indicating that conceptual preparation starts before target picture onset in constraining conditions. In the verbal experiment, we replicated the alpha-beta power decreases in constraining relative to nonconstraining conditions before target picture onset. No such power decreases were found in the nonverbal experiment. Power decreases in constraining relative to nonconstraining conditions were significantly different between experiments. Our findings suggest that participants engage in conceptual preparation following verbal and nonverbal settings, albeit differently. The retrieval of a target word, initiated by verbal settings, is associated with alpha-beta power decreases. By contrast, broad conceptual preparation alone, prompted by nonverbal settings, does not seem enough to elicit alpha-beta power decreases. These findings have implications for theories of oscillations and semantic memory.

The neurophysiology of working memory development: from childhood to adolescence and young adulthood

Working memory (WM) is an important cognitive function that is necessary to perform our daily activities. The present review briefly describes the most accepted models underlying WM and the neural networks involved in its processing. The review focuses on how the neurophysiological mechanisms develop with age in the periods from childhood to adolescence and young adulthood. Studies using behavioral, neuroimaging, and electrophysiological techniques showed the progress of WM throughout the development. The present review focuses on the neurophysiology of the basic processes underlying WM operations, as indicated by electroencephalogram-derived signals, in order to take advantage of the excellent time resolution of this technique. Children and adults use similar cerebral mechanisms and areas to encode, recognize, and keep the stimuli in memory and update the WM contents, although adults rely more on anterior sites. The possibility that a functional reorganization of WM brain processing occurs around the adolescent period is suggested, and would partly justify the high prevalence of the emergence of mental pathology in the adolescent period.

Movement Interferes with Visuospatial Working Memory during the Encoding: An ERP Study

The present study focuses on the functional interactions of cognition and manual action control. Particularly, we investigated the neurophysiological correlates of the dual-task costs of a manual-motor task (requiring grasping an object, holding it, and subsequently placing it on a target) for working memory (WM) domains (verbal and visuospatial) and processes (encoding and retrieval). Thirty participants were tested in a cognitive-motor dual-task paradigm, in which a single block (a verbal or visuospatial WM task) was compared with a dual block (concurrent performance of a WM task and a motor task). Event-related potentials (ERPs) were analyzed separately for the encoding and retrieval processes of verbal and visuospatial WM domains both in single and dual blocks. The behavioral analyses show that the motor task interfered with WM and decreased the memory performance. The performance decrease was larger for the visuospatial task compared with the verbal task, i.e., domain-specific memory costs were obtained. The ERP analyses show the domain-specific interference also at the neurophysiological level, which is further process-specific to encoding. That is, comparing the patterns of WM-related ERPs in the single block and dual block, we showed that visuospatial ERPs changed only for the encoding process when a motor task was performed at the same time. Generally, the present study provides evidence for domain- and process-specific interactions of a prepared manual-motor movement with WM (visuospatial domain during the encoding process). This study, therefore, provides an initial neurophysiological characterization of functional interactions of WM and manual actions in a cognitive-motor dual-task setting, and contributes to a better understanding of the neuro-cognitive mechanisms of motor action control.

Multidisciplinary investigation links backward-speech trait and working memory through genetic mutation

Case studies of unusual traits can provide unique snapshots of the effects of modified systems. In this study, we report on an individual from a Serbian family with the ability to rapidly, accurately and voluntarily speak backwards. We consider psychological, neural and genetic correlates of this trait to identify specific relevant neural mechanisms and new molecular pathways for working memory and speech-related tasks. EEG data suggest that the effect of word reversal precedes semantic integration of visually presented backward-words, and that event-related potentials above the frontal lobe are affected by both word reversal and the maintenance of backward-words in working memory. fMRI revealed that the left fusiform gyrus may facilitate the production of backward-speech. Exome sequencing identified three novel coding variants of potential significance in the RIC3, RIPK1 and ZBED5 genes. Taken together, our data suggest that, in this individual, the ability to speak backwards is afforded by an extraordinary working memory capacity. We hypothesise that this is served by cholinergic projections from the basal forebrain to the frontal cortex and supported by visual semantic loops within the left fusiform gyrus and that these neural processes may be mediated by a genetic mutation in RIC3; a chaperone for nicotinic acetylcholine receptors.

Processing classifier-noun agreement in a long distance: an ERP study on Mandarin Chinese

The classifier system categorizes nouns on a semantic basis. By inserting an object-gap relative clause (RC) between a classifier and its associate noun, we examined how temporary classifier-noun semantic incongruity and long-distance classifier-noun dependency are processed. Instead of a typical N400 effect, a midline anterior negativity was elicited by the temporary semantic incongruity, suggesting that the anticipation of coming words influences semantic processing and that metacognitive processes are involved in resolving the conflict. The lack of reduced P600 effects at the RC marker suggests that classifier-noun mismatch may not be effective in RC prediction. The N400 observed at the head noun suggests that the parser retains the temporary incongruity in the memory and computes the classifier-noun semantic agreement over a long distance. In addition, both successful and unsuccessful long-distance integration elicited P600 effects, supporting the view that P600 indexes more than just syntactic processing. Detailed discussion and implications are provided.

Error probability of intracranial brain computer interfaces under non-task elicited brain states

OBJECTIVE

Intracranial brain computer interfaces (BCIs) can be connected to the user's cortex permanently. The interfaces response when fed with non-task elicited brain activity becomes important as design criterion: ideally intracranial BCIs should remain silent. We study their error probability in the form of false alarms.

METHODS

Using electrocorticograms recorded during task and non-task brain states, we compute false alarms, investigate their origin and introduce strategies to reduce them, using signal detection theory, classifier cascading and adaptation concepts.

RESULTS

We show that the incessant dynamics of the brain is prone to spontaneously produce signals, the spectral and topographical characteristics of which can resemble those associated with common control tasks, generating brain state classification errors.

CONCLUSIONS

In addition to hit and bit rates, response of BCIs to non-task brain states constitutes an important measure of BCI performance. Static classification cascading reduces considerably false positives during no-task brain states.

SIGNIFICANCE

False alarms in intracranial BCIs are undesirable and could have dangerous consequences for the users. Designs which effectively incorporate the error correction strategies discussed in this paper, could be more successful when taken from the laboratory or acute care setting and used in the real world.

Gain of the human dura in vivo and its effects on invasive brain signal feature detection

Invasive brain signal recordings generally rely on bioelectrodes implanted on the cortex underneath the dura. Subdural recordings have strong advantages in terms of bandwidth, spatial resolution and signal quality. However, subdural electrodes also have the drawback of compromising the long-term stability of such implants and heighten the risk of infection. Epidurally implanted electrodes might provide a viable alternative to subdural electrodes, offering a compromise between signal quality and invasiveness. Determining the feasibility of epidural electrode implantation for e.g., clinical research, brain-computer interfacing (BCI) and cognitive experiments, requires the characterization of the electrical properties of the dura, and its effect on signal feature detection. In this paper we report measurements of brain signal attenuation by the human dura in vivo. In addition, we use signal detection theory to study how the presence of the dura between the sources and the recording electrodes affects signal power features in motor BCI experiments. For noise levels typical of clinical brain signal recording equipment, we observed no detrimental effects on signal feature detection due to the dura. Subdural recordings were found to be more robust with respect to increased instrumentation noise level as compared to their epidural counterpart nonetheless. Our findings suggest that epidural electrode implantation is a viable alternative to subdural implants from the feature detection viewpoint.

Neural generators of sustained activity differ for stimulus-encoding and delay maintenance

The ability to maintain information online beyond sensory stimulation is regarded as a key contribution of working memory to goal-directed behaviour. It is widely accepted that sustained neural activity is a key mechanism of stimulus maintenance, but it is unclear to what extent the neural generators of sustained activity change from stimulus-encoding to maintenance. Using event-related potentials in humans, we show that, in a delayed match-to-sample task, slow shifts over parieto-occipital electrode sites had a different topography and polarity during encoding and delay maintenance of images depicting scenes. This clearly demonstrates that neural generators of sustained activity associated with stimulus-encoding and delay maintenance differed, and that the change between these generators occurred time-locked to the onset of the delay period. We also investigated how monetary reward incentives modulated the amplitude and topography of sustained delay activity and the ability to suppress irrelevant distracting information during the delay. Reward incentives improved maintenance performance and this was correlated with an expansion of the parieto-occipital electrode sites that were entrained into sustained delay activity (rather than improved distractor suppression), suggesting that under the influence of reward, the parieto-occipital regions that contributed to delay maintenance expanded in size.

Stage and load effects on ERP topography during verbal and spatial working memory

Frontal-parietal neural networks play a significant role in the functional organization of visual working memory (WM). The relative contribution of material-specific information (e.g., verbal or spatial) on activation of WM circuitry is not fully understood. Process-specific models of WM propose that the activation of WM circuitry is more dependent on the stage of WM than on the type of information being processes. This study investigated the effects of WM information type (verbal, spatial), stage (encoding, maintenance), and load on both the anterior-posterior topography and lateralized scalp distributions of the event-related potential (ERP) P3 amplitude. Seventeen young adults performed verbal and spatial tasks that were equated for stimulus properties and response requirements. Both tasks were presented under 1- and 3-load conditions. The anterior-posterior topography of P3 amplitude at left hemisphere, midline, and right hemisphere scalp locations was affected by the stage of WM and the memory load, but not by the type of information. The encoding stage showed minimal load effects and was associated with a posterior-maximum P3 amplitude distribution. During the maintenance stage, probe letters were presented that were irrelevant to the previously encoded stimuli. Here, higher WM load produced relatively greater frontal and reduced parietal P3 amplitude compared to lower WM load. These anterior-posterior P3 amplitude patterns for encoding and maintenance were similar at left, midline, and right locations. Within the limitations of the study, our results tend to support a process-dependent activation of WM circuits in that P3 amplitude topography only differed as a result of WM stage and load, and not as a result of the type of information (verbal or spatial) presented.

Interactions between working memory and visual perception: an ERP/EEG study

How do working memory and perception interact with each other? Recent theories of working memory suggest that they are closely linked, and in fact share certain brain mechanisms. We used a sequential motion imitation task in combination with EEG and ERP techniques for a direct, online examination of memory load's influence on the processing of visual stimuli. Using a paradigm in which subjects tried to reproduce random motion sequences from memory, we found a systematic decrease in ERP amplitude with each additional motion segment that was viewed and memorized for later imitation. High-frequency (>20 Hz) oscillatory activity exhibited a similar position-dependent decrease. When trials were sorted according to the accuracy of subsequent imitation, the amplitude of the ERPs during stimulus presentation correlated with behavioral performance: the larger the amplitude, the more accurate the subsequent imitation. These findings imply that visual processing of sequential stimuli is not uniform. Rather, earlier information elicits stronger neural activity. We discuss possible explanations for this observation, among them competition for attention between memory and perception and encoding of serial order by means of differential activation strengths.

Event-related potential correlates of the word length effect in working memory

It has been proposed that a frontally distributed ERP negativity reflects rehearsal within the phonological loop component of working memory. This study investigated the relationship between phonological rehearsal and frontal negativity, by examining the effects of word length and articulatory suppression (continuously uttering an irrelevant word) on memory for auditorily presented words while ERPs were recorded. P2 amplitude, thought to reflect word identification, was increased for long compared to short words. However, this difference did not remain under conditions of suppression. A centrally maximum early negativity was larger in the short than long word silent conditions and this word length effect was reduced under suppression. The early negativity was interpreted as reflecting the transfer of the information from input to output buffers in the silent conditions that was prevented by the suppression. There was only a word length effect for the late frontally distributed negativity in the suppression conditions, suggesting that this component was not associated with phonological loop rehearsal but rather other working memory processes that operate under high load conditions.

ERP/CSD indices of impaired verbal working memory subprocesses in schizophrenia

To disentangle subprocesses of verbal working memory deficits in schizophrenia, long EEG epochs (>10 s) were recorded from 13 patients and 17 healthy adults during a visual word serial position test. ERP generator patterns were summarized by temporal PCA from reference-free current source density (CSD) waveforms to sharpen 31-channel topographies. Patients showed poorer performance and reduced left inferior parietotemporal P3 source. Build-up of mid-frontal negative slow wave (SW) in controls during item encoding, integration, and active maintenance was absent in patients, whereas a sustained mid-frontal SW sink during the retention interval was comparable across groups. Mid-frontal SW sinks (encoding and retention periods) and posterior SW sinks and sources (encoding only) were related to performance in controls only. Data suggest disturbed processes in a frontal-parietotemporal network in schizophrenia, affecting encoding and early item storage.

The Wisconsin Card Sort Test and P300 responses to novel auditory stimuli in schizophrenic patients

The authors studied the relationship between performance on the Wisconsin Card Sort Test (WCST) and P300 activity in schizophrenics and normal controls. Fourteen male predominantly medicated schizophrenics and matched non-ill controls were administered the WCST and tests of temporal lobe (delayed verbal and spatial memory) and general intellectual functioning (Shipley). Patients were rated with negative and positive symptom scales extracted from the Brief Psychiatric Rating Scale. Subjects performed a tone discrimination task requiring identification of rare targets in both a standard oddball paradigm and a three-stimulus paradigm that included rare novel sounds. Reference independent data from 16 scalp electrodes yielded Global Field Power (GFP), from which P300 latency was determined. P300 amplitude measures included amplitude at this identified latency as well as amplitude integrated over a 100 ms time window centered over it. These amplitude measures were examined at six selected electrode locations. Schizophrenics produced smaller P300 responses that tended to be slower, but there were no group differences in the relationships between neuropsychological performance and P300 responses. Across diagnostic groups percent perseverative errors predicted lower integrated and peak P300 amplitude during the novel but not the standard oddball paradigm. The effect on integrated P300 amplitude was localized to anterior leads after novel stimuli. Negative symptoms predicted lower WCST performance, lower integrated P300 amplitude, and smaller GFP after novel stimuli. Positive symptoms predicted reduced overall GFP and specific but inconsistent reductions in parietal P300 amplitude. The results suggest relationships between dorsolateral prefrontal competence, P300 activity in response to stimulus novelty, and negative symptoms in schizophrenic patients, paralleling findings obtained from blood flow and other measures of brain activity.

Dynamics of parietofrontal networks underlying visuospatial short-term memory encoding

Brain imaging studies in TEP, functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) have shown that visuospatial short-term memory tasks depend on dorsal parietofrontal networks. Knowing the spatiotemporal dynamics of this network would provide further understanding of the neural bases of the encoding process. We combined magnetoencephalography (MEG) with EEG and fMRI techniques to study this network in a task, in which participants had to judge the symmetry in position of two dots, presented either simultaneously ("immediate comparison") or successively ("memorization" of a first dot and "delayed comparison", after 3 s, with a second dot). With EEG, larger amplitude was observed in the parietocentral P3b component (350-500 ms) in the immediate and "delayed comparisons" than in "memorization" condition, where topography at this time was more anterior and right lateralized. MEG provided a more accurate localization and temporal variations of sources, revealing a strong M4 component at 450 ms in the "memorization" condition, with two sources localized in parietal and right premotor regions. These localizations are consistent with both fMRI foci and EEG cortical current source densities (CSD), but only MEG revealed the strong increase in premotor region at 450 ms related to "memorization". These combined results suggest that EEG P3B and MEG M4 components reflect two different dynamics in parietofrontal networks: the parietocentral P3b indexes a decision mechanism during the immediate and "delayed comparisons", whereas the MEG M4 component, with a larger right premotor source, reflects the encoding process in visuospatial short-term memory.

An event-related potential investigation of the relationship between semantic and perceptual levels of representation

The present study was conducted to investigate relationships between semantic and perceptual levels of representation. A picture-word repetition paradigm was used in which we manipulated the semantic relationship between pictures and words. Experiment 1 involved two types of trials, one with words that had the same meaning as pictures and one with words that were unrelated to pictures. In Experiment 2 we replaced words that were identical in meaning with words that were semantically associated to pictures. In both experiments, visually presented probe stimuli were used to determine the presence of perceptual effects within the visual system, originating from the semantic interaction between words and pictures. In both experiments, conditions with unrelated picture-word pairs generated a search process following the N400 which included activity overlying the visual cortex. Probe stimuli were found to attenuate the amplitude of the search related negativity. The latency of the interaction, which was significant at the time of the N1 response to the probe, suggested that the attempt to find a relationship between the picture and the word involved processing within extrastriate visual areas. UVF probes provided stronger attenuation, possibly because the UVF has direct transmission to the ventral processing stream which is believed to be involved in visual semantic processing. Semantic interactions between matching picture-word pairs in Experiment 1 were found to have an effect on the ERPs to probes presented at the same location as pictures. Probes presented under these conditions showed a stronger P2 over frontal areas followed by a more negative P3 over occipital areas. Although we had expected beforehand to find earlier effects in the latency of the probes' P1 and N1 responses, this result is consistent with the idea that retinotopic levels of object representation are linked with the semantic level of object description. Unlike Experiment 1, same location probes presented in associated picture-word conditions of Experiment 2 did not result in any specific ERP effects on the P2 and P3 components. This suggest that semantic interactions between pictures and words do not automatically propagate to the perceptual level, unless there is direct reference from the word to the visual representation of the object.

Event-related potentials in a working-memory task in schizophrenics and controls

Event-related potentials (ERPs) were recorded from 65 channels in 12 schizophrenics and 12 age- and sex-matched controls during a delayed matching-to-sample design with variation of working-memory (WM) challenge: following a 500 ms visual sample stimulus (called S1, two diamonds varying in size, rotation angle and vertical position), the same pattern was either presented throughout a 6s retention interval (no challenge) or a diamond pattern differing from the first one in at least one dimension was presented during this interval (WM challenge). The 500 ms matching stimulus (called S2) comprised one diamond, which had to be matched for identity to either the left or the right diamond of the sample stimulus. The topographical distribution of ERPs during an interval of 500 ms after S1-onset, 5s of the retention interval, a 500 ms-interval preceding the S2, and a 1s postimperative interval were evaluated. No WM challenge during the retention interval induced a right-posterior accentuation of the slow negative potentials in either group, while WM challenge evoked a tendency for left-hemispheric negativity in controls, but not in patients. Patients exhibited a postimperative negative variation (PINV) with left-anterior focus irrespective of the preceding WM challenge, while in controls, the left-anterior PINV was found only following WM challenge. In schizophrenic patients the lack of a left-anterior accentuation of negative ERPs under WM challenge might be related to WM dysfunction, and the condition-independent PINV might be considered either the consequence of this dysfunction or indication of processes related more to the diagnoses than to WM-challenge and -dysfunction.