Frontal and posterior sources of event-related potentials in semantic comprehension

Neural patterns elicited by lexical processing in adolescents with specific language impairment: support for the procedural deficit hypothesis?

Background

Deficits in procedural memory have been proposed to account for the language deficits in specific language impairment (SLI). A key aspect of the procedural deficit hypothesis (PDH) account of SLI is that declarative memory is intact and functions as a compensatory mechanism in the acquisition of language in individuals with SLI. The current study examined the neural correlates of lexical-phonological and lexical-semantic processing with respect to these predictions in a group of adolescents with SLI with procedural memory impairment and a group of chronologically age-matched (CA) normal controls.

Methods

Participants completed tasks designed to measure procedural and declarative memory and two ERP tasks designed to assess lexical-semantic and lexical-phonological processing in the auditory modality. Procedural memory was assessed using a statistical learning task. Lexical-semantic processing was assessed using a sentence judgment task modulating semantic congruency and lexical-phonological processing was assessed using a word/nonword decision task modulating word frequency. Behavioral performance on the tasks, mean amplitude of the cortical response, and animated topographs were examined.

Results

Performance on the statistical word-learning task was at chance for the adolescents with SLI, whereas declarative memory was no different from the CA controls. Behavioral accuracy on the lexical-semantic task was the same for the adolescents with SLI and CA controls but accuracy on the lexical-phonological task was significantly poorer for the adolescents with SLI as compared to the CA controls. An N400 component was elicited in response to semantic congruency on the lexical-semantic task for both groups but differences were noted in both the location and time course of the cortical response for the SLI and CA groups. An N400 component was elicited by word frequency on the lexical-phonological task for the CA controls not for the adolescents with SLI. In contrast, post hoc analysis revealed a cortical response based on imageability for the adolescents with SLI, but not CA controls. Statistical word learning was significantly correlated with speed of processing on the lexical decision task for the CA controls but not for the adolescents with SLI. In contrast, statistical word learning ability was not correlated with the modulation of the N400 on either task for either group.

Conclusion

The behavioral data suggests intact semantic conceptual knowledge, but impaired lexical phonological processing for the adolescents with SLI, consistent with the PDH. The pattern of cortical activation in response to semantic congruency and word frequency suggests, however, that the processing of lexical-semantic and lexical-phonological information by adolescents with a history of SLI may be supported by both overlapping and nonoverlapping neural generators to those of CA controls, and a greater reliance on declarative memory strategies. Taken together, the findings from this study suggest that the underlying representations of words in the lexicons of adolescents with a history of SLI may differ qualitatively from those of their typical peers, but these differences may only be evident when behavioral data and neural cortical patterns of activation are examined together.

Does the character-based dimension of stories impact narrative processing? An event-related potentials (ERPs) study

This event-related potentials (ERPs) study investigated online processes of integration of information relating to characters in narrative comprehension. The final sample included twenty-nine participants who read short third-person stories in which the plausibility of the characters' actions was manipulated. Stories were administered in three conditions: a character-based congruent condition including a target word that was consistent with the character's job; a character-based incongruent condition with a target word inconsistent with the character's job; a character-based neutral condition, narrating the action of a character presented by his/her proper name without information about his/her job. Results comparing the ERPs elicited by the experimental conditions revealed a greater negative amplitude of the N400 in the right temporal regions in response to the character-based incongruent compared to the character-based congruent narratives. This finding shows that implicit background character-based information affects the N400, with readers rapidly using this information to comprehend narratives.

Complex Time-Dependent ERP Hemispheric Asymmetries during Word Matching in Phonological, Semantic and Orthographical Matching Judgment Tasks

Language-induced asymmetry to single word reading has been well investigated in past research. Less known are the complex processes and related asymmetries occurring when a word is compared with the previous one, according to specific tasks. To this end, we used a paradigm based on 80 sequential word pair comparisons and three blocked tasks: phonological, semantic and orthographical matching judgment. Participants had to decide whether the target word (W2) did or did not match the prime word (W1), presented 2 sec before, according to the task. The event-related potentials (ERPs) evoked by W2 in 20 participants have been analyzed. The first negative wave, the Recognition Potential (RP), peaking at about 120 ms over parietal sites, showed greater amplitude at left sites in all tasks, thus revealing the typical left-lateralization. At frontal sites, only the phonological task showed left lateralization. The following N400 (300–450 ms) showed an interesting interaction: Match trials elicited greater left asymmetry on frontal regions to phonological than to semantic than to visual-perceptual tasks, whereas mismatch trials induced an inverted asymmetry, marked by greater amplitude over right frontal sites, regardless of the task. Concerning the late N400 (450–600 ms), phonological and semantic tasks showed an overlapping pattern, with left lateralization in match and right lateralization in mismatch conditions. Results point to complex task- and time-dependent hemispheric asymmetries in word matching.

A N400 ERP Study in letter recognition after passive tactile stimulation training in blind children and sighted controls

BACKGROUND

We previously demonstrated that using a sensory substitution device (SSD) for one week, tactile stimulation results in faster activation of lateral occipital complex in blind children than in seeing controls.

OBJECTIVE

We used long-term haptic tactile stimulation training with an SSD to test if it results in stable cross-modal reassignment of visual pathways after six months, to provide high level processing of tactile semantic content.

METHODS

We enrolled 12 blind and 12 sighted children. The SSD transforms images to a stimulation matrix in contact with the dominant hand. Subjects underwent twice-daily training sessions, 5 days/week for six months. Children were asked to describe line orientation, name letters, and read words. ERP sessions were performed at baseline and 6 months to analyze the N400 ERP component and reaction times (RT). N400 sources were estimated with Low Resolution Electromagnetic Tomography (LORETA). SPM8 was used to make population-level inferences.

RESULTS

We found no group differences in RTs, accuracy of identifications, N400 latencies or distributions with the line task at 1 week or at 6 months. RTs on the letter recognition task were also similar. After 6 months, behavioral training increased accurate letter identification in both seeing and blind children (Chi 2 = 11906.934, p = 0.000), but the increase was larger in blind children (Chi 2 = 8.272, p = 0.004). Behavioral training shifted peak N400 amplitude to left occipital and bilateral parietal cortices in blind children, but to left precentral and postcentral and bilateral occipital cortices in sighted controls.

CONCLUSIONS

Blind children learn to recognize SSD-delivered letters better than seeing controls and had greater N400 amplitude in the occipital region. To the best of our knowledge, our results provide the first published example of standard letter recognition (not Braille) by children with blindness using a tactile delivery system.

The temporal course of vicarious embarrassment: An electrophysiological study

Vicarious embarrassment as a social pain emotion has been studied from cognitive and neuroimaging perspectives. However, the dynamic time course of vicarious embarrassment remains unclear. We conducted an event-related potential (ERP) study to investigate the temporal dynamics of vicarious embarrassment and examine the role of perspective-taking in an emotional judgment task. The ERP results showed that vicarious embarrassment evoked more negative MFN (250-310 ms) and N400 (400-520 ms) components than the neutral condition over the frontal region. The time-frequency analysis results showed that, in the 200-1,600 ms time window, greater alpha power was elicited when participants imagined themselves rather than others in an awkward situation; in the 500-1,900 ms time window, for both groups, vicarious embarrassment involved greater theta oscillations than the neutral condition over the frontal region. These results extend previous findings that vicarious emotion involves mentalizing processes, and demonstrate that people first detect and evaluate the target's misconduct and negative outcomes and then experience the vicarious embarrassment.

The engagement of cortical areas preceding exogenous vergence eye movements

Source analyses on event related potentials (ERPs) derived from the electroencephalogram (EEG) were performed to examine the respective roles of cortical areas preceding exogenously triggered saccades, combined convergences, and combined divergences. All eye movements were triggered by the offset of a central fixation light emitting diode (LED) and the onset of a lateral LED at various depths in an otherwise fully darkened room. Our analyses revealed that three source pairs, two located in the frontal lobe–the frontal eye fields (FEF) and an anterior frontal area–, and one located within the occipital cortex, can account for 99.2% of the observed ERPs. Overall, the comparison between source activities revealed the largest activity in the occipital cortex, while no difference in activity between FEF and the anterior frontal area was obtained. For all sources, increased activity was observed for combined vergences, especially combined convergences, relative to saccades. Behavioral results revealed that onset latencies were longest for combined convergences, intermediate for combined divergences, and the shortest for saccades. Together, these findings fit within a perspective in which both occipital and frontal areas play an important role in retinal disparity detection. In the case of saccades and combined divergences stimulus-locked activity was larger than response-locked activity, while no difference between stimulus- and response-locked activity was observed for combined convergences. These findings seem to imply that the electrophysiological activity preceding exogenous eye movements consists of a sensory-related part that is under cortical control, while subcortical structures may be held responsible for final execution.

Effect of word association on linguistic event-related potentials in moderately to mildly constraining sentences

The processing of word associations in sentence context depends on several factors. EEG studies have shown that when the expectation of the upcoming word is high (high semantic constraint), the within-sentence word association plays a negligible role, whereas in the opposite case, when there is no expectation (as in pseudo-sentences), the role of word association becomes more pronounced. However, what happens when the expectations are not high (mild to moderate semantic constraint) is not yet clear. By adopting a cross-factorial design, crossing sentence congruity with within-sentence word association, our EEG recordings show that association comes into play during semantic processing of the word only when the sentence is meaningless. We also performed an exploratory source localization analysis of our EEG recordings to chart the brain regions putatively implicated in processing the said factors and showed its complementarity to EEG temporal analysis. This study furthers our knowledge on sentence processing and the brain networks involved in it.

FN400 and LPC memory effects for concrete and abstract words

According to dual-process models, recognition memory depends on two neurocognitive mechanisms: familiarity, which has been linked to the frontal N400 (FN400) effect in studies using ERPs, and recollection, which is reflected by changes in the late positive complex (LPC). Recently, there has been some debate over the relationship between FN400 familiarity effects and N400 semantic effects. According to one view, these effects are one and the same. Proponents of this view have suggested that the frontal distribution of the FN400 could be due to stimulus concreteness: recognition memory experiments commonly use highly imageable or concrete words (or pictures), which elicit semantic ERPs with a frontal distribution. In the present study, we tested this claim using a recognition memory paradigm in which subjects memorized concrete and abstract nouns; half of the words changed font color between study and test. FN400 and LPC old/new effects were observed for abstract as well as concrete words, and were stronger over right hemisphere electrodes for concrete words. However, there was no difference in anteriority of the FN400 effect for the two word types. These findings challenge the notion that the frontal distribution of the FN400 old/new effect is fully explained by stimulus concreteness.

The relationship between brain reaction and English reading tests for non-native English speakers

This research analyzed the brain activity of non-native English speakers while engaged in English reading tests. The brain wave event-related potentials (ERPs) of participants were used to analyze the difference between making correct and incorrect choices on English reading test items. Three English reading tests of differing levels were designed and 20 participants, 10 males and 10 females whose ages ranged from 20 to 24, voluntarily participated in the experiment. Experimental results were analyzed by performing independent t-tests on the ERPs of participants for gender, difficulty level, and correct versus wrong options. Participants who chose incorrect options elicited a larger N600, verifying results found in the literature. Another interesting result was found: For incorrectly answered items, different areas of brain showing a significant difference in ERPs between the chosen and non-chosen options corresponded to gender differences; for males, this area was located in the right hemisphere whereas for females, it was located in the left. Experimental results imply that non-native English speaking males and females employ different areas of the brain to comprehend the meaning of difficult items.

Electrophysiological evidence for a specific neural correlate of musical violation expectation in primary-school children

The majority of studies on music processing in children used simple musical stimuli. Here, primary schoolchildren judged the appropriateness of musical closure in expressive polyphone music, while high-density electroencephalography was recorded. Stimuli ended either regularly or contained refined in-key harmonic transgressions at closure. The children discriminated the transgressions well above chance. Regular and transgressed endings evoked opposite scalp voltage configurations peaking around 400ms after stimulus onset with bilateral frontal negativity for regular and centro-posterior negativity (CPN) for transgressed endings. A positive correlation could be established between strength of the CPN response and rater sensitivity (d-prime). We also investigated whether the capacity to discriminate the transgressions was supported by auditory domain specific or general cognitive mechanisms, and found that working memory capacity predicted transgression discrimination. Latency and distribution of the CPN are reminiscent of the N400, typically observed in response to semantic incongruities in language. Therefore our observation is intriguing, as the CPN occurred here within an intra-musical context, without any symbols referring to the external world. Moreover, the harmonic in-key transgressions that we implemented may be considered syntactical as they transgress structural rules. Such structural incongruities in music are typically followed by an early right anterior negativity (ERAN) and an N5, but not so here. Putative contributive sources of the CPN were localized in left pre-motor, mid-posterior cingulate and superior parietal regions of the brain that can be linked to integration processing. These results suggest that, at least in children, processing of syntax and meaning may coincide in complex intra-musical contexts.

Feasibility of event-related potential methodology to evaluate changes in cortical processing after rehabilitation in children with cerebral palsy: a pilot study

This study examined the feasibility of using event-related potentials (ERPs) to measure changes in cortical processing following an established rehabilitative intervention (constraint-induced movement therapy, CIMT) for children with cerebral palsy (CP). Sixteen participants with a diagnosis of hemiparetic CP, with a median age of 6 years, were assessed pre and immediately post CIMT and at 6-month follow-up, using a picture-word match/mismatch discrimination task and standard neurobehavioral measures. Intervention effects were evident in improved performance on behavioral tests of sensory and motor function and the increased mean ERP amplitude of the N400 match/mismatch response on the side ipsilateral to the lesion. These effects were maintained 6 months after the intervention. No such changes were observed on the side contralateral to the lesion. This research suggests that ERPs can measure rehabilitation-induced changes in neural function in children with CP.

Neurobiological bases of reading comprehension: Insights from neuroimaging studies of word level and text level processing in skilled and impaired readers

For accurate reading comprehension, readers must first learn to map letters to their corresponding speech sounds and meaning and then they must string the meanings of many words together to form a representation of the text. Furthermore, readers must master the complexities involved in parsing the relevant syntactic and pragmatic information necessary for accurate interpretation. Failure in this process can occur at multiple levels and cognitive neuroscience has been helpful in identifying the underlying causes of success and failure in reading single words and in reading comprehension. In general, neurobiological studies of skilled reading comprehension indicate a highly overlapping language circuit for single word reading, reading comprehension and listening comprehension with largely quantitative differences in a number of reading and language related areas. This paper reviews relevant research from studies employing neuroimaging techniques to study reading with a focus on the relationship between reading skill, single word reading, and text comprehension.

The influence of transient spatial attention on the processing of intracutaneous electrical stimuli examined with ERPs

OBJECTIVE

Determine the influence of transient spatial attention on the processing of intracutaneous electrical stimuli.

METHODS

Electrical stimuli, a single pulse or five pulses, were presented at the index fingers of the left or right hand. The to-be-attended hand and stimulated finger varied randomly from trial to trial. Participants had to press a foot pedal only when the relevant stimulus, varied between participants, occurred at the attended hand. EEG was measured to extract relevant ERP components.

RESULTS

The N100 and N150 were enhanced for attended as compared to unattended stimuli. The N100, N150, P260, and the P500 were enlarged for five pulse as compared to single pulse stimuli. The P260, which is thought to reflect a call for attention, was enhanced for unattended as compared to attended stimuli. Source analyses indicate that attentional effects on the N100, N150, and P260 may be related to changes in activity in secondary somatosensory areas and the anterior cingulate cortex.

CONCLUSIONS

A transient manipulation of spatial attention increases cortical activity induced by attended relative to unattended intracutaneous electrical stimuli, but initially unattended stimuli appear to induce an enhanced orienting effect.

SIGNIFICANCE

Initially unattended intracutaneous electrical stimuli seem to induce a call for attention.

An fMRI investigation of detection of semantic incongruities in autistic spectrum conditions

The aim of this study was to investigate differences in the brain's haemodynamic response to semantically incongruent and congruent sentences in adults with an autistic spectrum condition (ASC) and a typically developing Control group. We used functional magnetic resonance imaging to measure regional variations in neural activity during detection of semantic incongruities within written sentences. Whilst the 12 controls showed a pattern of activity extending from posterior cingulate cortices bilaterally and the left occipitotemporal region to the left superior and inferior temporal lobes, right anterior cingulate and right inferior frontal gyrus, the 12 participants with an ASC presented a more spatially restricted activation pattern, including the left inferior frontal gyrus, left anterior cingulate cortex and right middle frontal gyrus. These results are coherent with the hypothesis that impaired integration of multiple neural networks in people with an ASC is related to previous observations that this group have difficulties in the use of context to predict the final word of sentences.

The Involvement of Occipital Cortex in the Early Blind in Auditory and Tactile Duration Discrimination Tasks

Early blind participants outperform controls on several spatially oriented perceptual tasks such as sound localization and tactile orientation discrimination. Previous studies have suggested that the recruitment of occipital cortex in the blind is responsible for this improvement. For example, electroencephalographic studies showed an enlarged posterior negativity for the blind in these tasks compared to controls. In our study, the question was raised whether the early blind are also better at tasks in which the duration of auditory and tactile stimuli must be discriminated. The answer was affirmative. Our electroencephalographic data revealed an enlarged posterior negativity for the blind relative to controls. Source analyses showed comparable solutions in the case of auditory and tactile targets for the blind. These findings support the interpretation of these negativities in terms of a supramodal rather than a modality-specific process, although confirmation with more spatially sensitive methods seems necessary. We additionally examined whether the early blind are less affected by irrelevant tactile or auditory exogenous cues preceding auditory or tactile targets than controls. No differences in alerting and orienting effects of these cues were found between the blind and the controls. Together, our results support the view that major differences between early blind participants and sighted controls on auditory and tactile duration discrimination tasks relate to a late and likely supramodal process that takes place in occipital areas.

Clinical studies on event-related potentials (ERPs) N400 and the related factors in patients with poststroke depression (PSD)

OBJECTIVE

To evaluate event-related potentials (ERPs), N400, and the related factors in patients with poststroke depression (PSD).

METHODS

Eighty-five stroke patients with depression, conforming to the diagnoses standard of Chinese Classification of Mental Diseases (3rd edition) (CCMD-3), were treated with fluoxetine hydrochloride for 3 months and another 85 stroke patients without depression were selected as the control group. The traits about N400 and blood platelet 5-HT concentrations of all patients were measured.

RESULTS

There were significant differences between the incubation periods and average amplitudes of N400 in patients with PSD and those in patients without PSD (p < 0.01), while the blood platelet 5-HT concentrations of PSD patients were much lower than those of the patients without PSD (p < 0.01). For PSD patients, the N400 incubation periods were significantly shortened, averaged amplitudes were significantly increased (p < 0.01), and the blood platelet 5-HT concentrations were significantly raised after 3 months' treatment.

CONCLUSIONS

For ERPs N400 in PSD patients, the incubation period is significantly prolonged and the average amplitude is reduced. Blood platelet 5-HT concentration may influence ERPs N400 in PSD patients.

SIGNIFICANCE

N400 detections are helpful to the early diagnostic of PSD, and provide objective electrophysiology indexes for follow-up visits.

Lexical quality in the brain: ERP evidence for robust word learning from context

We examined event-related potentials (ERPs) before and after word learning, using training contexts that differed in their level of contextual support for meaning acquisition. Novel words appeared either in contexts that were semantically constraining, providing strong cues to meaning, or in contexts that were weakly constraining, that is, uninformative. After each sentence, participants were shown the word in isolation and were asked to generate a close synonym. Immediately after training, words trained in high-constraint contexts elicited a smaller left temporal negativity (N300(FT7)) compared with words trained in low-constraint contexts, and both types of trained words elicited a stronger medial frontal negativity (N350(Fz)) relative to familiar words. Two days after training the N300(FT7) disappeared and was replaced by a later, left parietal (P600(Pz)) effect. To examine robust learning, we administered a semantic priming test two days after training. Familiar words and words trained in high-constraint contexts elicited strong N400 effects. By contrast, words trained in low-constraint contexts elicited a weak N400 effect, and novel (untrained rare) words elicited no semantic priming. These findings suggest that supportive contexts and the use of an active meaning-generation task may lead to robust word learning. The effects of this training can be observed as changes in an early left frontal component, as well as the classical N400 effect. We discuss implications for theories of "partial" semantic knowledge and for robust word learning and instruction.

Interdependence modulates the brain response to word-voice incongruity

Social orientation (interdependence as opposed to independence) has been suggested as a major cultural dimension. In the present work, we used a specific stimulus-locked component of electroencephalogram and found, for the first time, that the perceiver's social orientation modulates the brain response to incongruity of word meaning to attendant vocal tone. Participants judged the verbal meaning of emotionally spoken emotional words while ignoring the vocal tone. As predicted, there was a greater negative event-related potential between 450 and 900 ms after the stimulus onset when the verbal content was incongruous with the background vocal tone, relative to when the two were congruous. Of importance, this incongruity-based late negativity was larger when participants were unobtrusively exposed to schematic human faces while listening to the stimulus words and for females than for males. Moreover, this late negativity was reliably predicted by chronic social orientation for females, but not for males and in the face condition, but not in the no-face control condition. Implications for future work on culture are discussed.

Frontolimbic activity and cognitive bias in major depression

In order to explore neural activity that accompanies cognitive bias in mood disorders, the authors had clinically depressed and nondepressed controls complete a self-evaluation procedure in which they indicated whether trait words were self-descriptive. Dense-array (256-channel) electroencephalography was recorded. Greater depression and low Positive Affect were associated with decreased endorsement of favorable (Good) traits, and greater anxiety and high Negative Affect were associated with increased endorsement of unfavorable (Bad) traits. For controls, the event-related potential (ERP) showed an enhanced visual N1 for trials in which Bad traits were endorsed. For depressed participants, this N1 was attenuated, specifically for these endorsed Bad trials. A similar pattern was observed in the P2-medial frontal negativity (P2-MFN) complex, with controls showing an enhanced MFN to the endorsed Bad words, while depressed participants showed an attenuated or absent medial frontal response on these items specifically. Distributed linear-inverse source analysis of the ERP localized the N1 effect to the inferotemporal-occipital cortex and the medial frontal effect to the dorsal anterior cingulate cortex. The altered ERP responses in depressed participants may provide clues to the neurophysiological processes associated with negatively biased cognition and self-evaluation in clinical depression.

Age-related differences in brain activity during extended continuous word recognition in children

To examine the development of verbal recognition memory in primary-school children, 36 healthy younger children (8-9 years old) and 36 healthy older children (11-12 years old) participated in an ERP study with an extended continuous recognition task. Each word of a series of 30 words was shown randomly for six times interspersed with distracter words. The children were required to make old versus new decisions. The data analyses focused on old/new effects (repetition 1 vs. new word) and multiple repetition effects (repetitions 1 through 5) for the N1, P2, N400, and the late positive complex (LPC, 500-800 ms after stimulus onset). Younger children exhibited a strong P2 multiple repetition effect across left lateral regions, with P2 amplitudes increasing linearly with the number of word repetitions. Compared to younger children, older children exhibited a much stronger N400 old/new effect across parietal regions. Old/new and repetition effects for N1 and LPC were similar in both age groups. Correlational analysis showed that in older children, larger N400 old/new effects on the continuous recognition task were moderately associated with better verbal learning on an auditory verbal learning task. In both age groups, the gain in recognition accuracy over multiple repetitions correlated with the LPC repetition effect. The age differences in P2 repetition effects and N400 old/new effects suggest that in younger children whole-word orthographic representations are dependent on the strength of the memory trace and that lexical-semantic representations develop with age. The LPC results suggest that recollection plays a substantial role in recognition memory of both younger and older children.

A cortical network for semantics: (de)constructing the N400

Measuring event-related potentials (ERPs) has been fundamental to our understanding of how language is encoded in the brain. One particular ERP response, the N400 response, has been especially influential as an index of lexical and semantic processing. However, there remains a lack of consensus on the interpretation of this component. Resolving this issue has important consequences for neural models of language comprehension. Here we show that evidence bearing on where the N400 response is generated provides key insights into what it reflects. A neuroanatomical model of semantic processing is used as a guide to interpret the pattern of activated regions in functional MRI, magnetoencephalography and intracranial recordings that are associated with contextual semantic manipulations that lead to N400 effects.

Cortical dynamics of word recognition

While functional neuroimaging studies have helped elucidate major regions implicated in word recognition, much less is known about the dynamics of the associated activations or the actual neural processes of their functional network. We used intracerebral electroencephalography recordings in 10 patients with epilepsy to directly measure neural activity in the temporal and frontal lobes during written words' recognition, predominantly in the left hemisphere. The patients were presented visually with consonant strings, pseudo-words, and words and performed a hierarchical paradigm contrasting semantic processes (living vs. nonliving word categorization task), phonological processes (rhyme decision task on pseudo-words), and visual processes (visual analysis of consonant strings). Stimuli triggered a cascade of modulations in the gamma-band (>40 Hz) with reproducible timing and task-sensitivity throughout the functional reading network: the earliest gamma-band activations were observed for all stimuli in the mesial basal temporal lobe at 150 ms, reaching the word form area in the mid fusiform gyrus at 200 ms, evidencing a superiority effect for word-like stimuli. Peaks of gamma-band activations were then observed for word-like stimuli after 400 ms in the anterior and middle portion of the superior temporal gyrus (BA 38 and BA 22 respectively), in the pars triangularis of Broca's area for the semantic task (BAs 45 and 47), and in the pars opercularis for the phonological task (BA 44). Concurrently, we observed a two-pronged effect in the prefrontal cortex (BAs 9 and 46), with nonspecific sustained dorsal activation related to sustained attention and, more ventrally, a strong reflex deactivation around 500 ms, possibly due to semantic working memory reset.

An ERP investigation of the Stroop task: the role of the cingulate in attentional allocation and conflict resolution

The majority of studies support a role of the anterior cingulate cortex (ACC) in the attentional control necessary for conflict resolution in the Stroop task; however, the time course of activation and the neural substrates underlying the Stroop task remain contentious. We used high-density EEG to record visual-evoked potentials from 16 healthy subjects while performing a manual version of the traditional Stroop colour-word task. Difference waveforms for congruent-control and incongruent-control conditions were similar in amplitude and had a similar spatial distribution in the time window of 260-430 ms post stimulus onset. Source estimation indicated particularly middle cingulate involvement in congruent-control and incongruent-control difference waveforms. In contrast, the difference waveform for the incongruent-congruent contrast was observed later (in the time window of 370-480 ms), had a different spatial distribution, and source estimation indicated that the anterior cingulate underlies this difference waveform. As congruent-control and incongruent-control differences have a similar timeframe and cingulate source, we propose that this indicates early attentional allocation processes. That is, the identification of two sources of information (the word and the colour it is printed in) and the selective attention to one. The later peak in the incongruent-congruent difference wave, originating in anterior cingulate, likely reflects identification (and subsequent resolution) of conflict in the two sources of information.

Semantic memory in schizophrenia: association with cell membrane essential fatty acids

INTRODUCTION

Semantic memory and language deficits are associated with schizophrenia. Understanding how these systems operate in this disorder will likely require a multi-factorial model that explains their linkages with cognition and modulation by dopamine. A biological factor that may provide causal convergence for these connections is cell membrane composition and dynamics.

METHODS

N400 is an electrophysiological measure of semantic memory and language that is sensitive to deficits in schizophrenia. Relationships among N400, cognition, dopamine, and cell membrane polyunsaturated fatty acids (PUFAs) were examined for patients tested under medicated (haloperidol only) and unmedicated (placebo) conditions. Relationships between these factors and clinical symptoms were also evaluated. The sample included 37 male schizophrenia inpatients and 34 male normal controls. The N400 priming effect was measured from visual event-related potentials recorded during a semantic priming-lexical decision task, in which semantic association (related versus unrelated words) and presentation rate (Stimulus Onset Asynchrony/SOAs: 350 and 950 ms) were varied.

RESULTS

N400 was associated with cognition (speed, visuoperception, attention) in patients and controls. These relationships were influenced by SOA in both groups, and by pharmacological condition in patients. Levels of total PUFAs and arachidonic acid were associated with N400 in unmedicated patients. Clinical symptoms (paranoia, thought disturbance) were associated with N400, but not with cognition or PUFAs.

CONCLUSIONS

Results suggest cell membrane fatty acids are associated with semantic memory and language in schizophrenia. Findings also suggest a series of linkages that are modulated by dopamine: cell membrane fatty acids are associated with N400 semantic priming; N400 semantic priming is associated with clinical symptoms.

ERP measures of partial semantic knowledge: left temporal indices of skill differences and lexical quality

This study examines the sensitivity of early event-related potentials (ERPs) to degrees of word semantic knowledge. Participants with strong, average, or weak vocabulary skills made speeded lexical decisions to letter strings. To represent the full spectrum of word knowledge among adult native-English speakers, we used rare words that were orthographically matched with more familiar words and with pseudowords. Since the lexical decision could not reliably be made on the basis of word form, subjects were obliged to use semantic knowledge to perform the task. A d' analysis suggested that high-skilled subjects adopted a more conservative strategy in response to rare versus more familiar words. Moreover, the high-skilled participants showed a trend towards an enhanced "N2c" to rare words, and a similar posterior temporal effect reached significance approximately 650 ms. Generators for these effects were localized to left temporal cortex. We discuss implications of these results for word learning and for theories of lexical semantic access.

Activation of the posterior cingulate by semantic priming: a co-registered ERP/fMRI study

Although the N400 is the best understood semantically sensitive component of the event-related potential (ERP), others have been observed as well. In an earlier lexical decision study, an N300 ERP was found to be enhanced to unprimed targets, although the effect could also be characterized as a prolonged P2 to primed targets as described in other reports. Because its scalp topography suggested its neural source might be of interest, a source localization was conducted that suggested that this component emanated from the dorsal posterior cingulate cortex (dPCC). In order to confirm this word N300 localization, a functional magnetic resonance imaging (fMRI) study was conducted to replicate the ERP study with a separate sample of 17 participants in an event-related design, using a 3-T scanner. A significant activation in the right dPCC was found corresponding to the N300 localization. The activation was greater on the related prime trials, supporting the characterization of the ERP component as being a P2 rather than an N300. A review is provided which suggests that a number of separate lines of ERP research regarding the word N300, the picture N300, the word P2, the phonological mismatch negativity, and the word midline frontal negativity may be most parsimoniously regarded as dealing with the same ERP component and that they all therefore emanate from the dPCC. It is suggested that this region plays a role in stimulus-response mapping in polymodal fashion. It is also suggested that the ERP component be termed a P2-dPCC.

Localization of Syntactic and Semantic Brain Responses using Magnetoencephalography

Electrophysiological methods have been used to study the temporal sequence of syntactic and semantic processing during sentence comprehension. Two responses associated with syntactic violations are the left anterior negativity (LAN) and the P600. A response to semantic violation is the N400. Although the sources of the N400 response have been identified in the left (and right) temporal lobe, the neural signatures of the LAN and P600 have not been revealed. The present study used magnetoencephalography to localize sources of syntactic and semantic activation in Finnish sentence reading. Participants were presented with sentences that ended in normally inf lected nouns, nouns in an unacceptable case, verbs instead of nouns, or nouns that were correctly inflected but made no sense in the context. Around 400 msec, semantically anomalous last words evoked strong activation in the left superior temporal lobe with significant activation also for word class errors (N400). Weaker activation was seen for the semantic errors in the right hemisphere. Later, 600-800 msec after word onset, the strongest activation was seen to word class and morphosyntactic errors (P600). Activation was significantly weaker to semantically anomalous and correct words. The P600 syntactic activation was localized to bilateral sources in the temporal lobe, posterior to the N400 sources. The results suggest that the same general region of the superior temporal cortex gives rise to both LAN and N400 with bilateral reactivity to semantic manipulation and a left hemisphere effect to syntactic manipulation. The bilateral P600 response was sensitive to syntactic but not semantic factors.

Semantic priming modulates the N400, N300, and N400RP

OBJECTIVE

To determine whether ERP components can differentiate between the semantic priming mechanisms of automatic spreading activation, expectancy, and semantic matching.

METHODS

The present study manipulated two factors known to differentiate semantic priming mechanisms: associations between words (forward, backward, and symmetrical) and prime-target stimulus onset asynchrony (SOA). Twenty-six participants were tested in each SOA condition while high-density 128-channel data were collected. Principal components analysis was applied to separate the ERP components.

RESULTS

Priming was observed for all conditions. Three semantic components were present: (1) the standard N400 effect for symmetric and forward priming pairs at both short and long SOAs, (2) an N300 for the long SOA symmetric priming pairs, and (3) a right-lateralized posterior N400RP for long SOA backward priming pairs.

CONCLUSIONS

Results suggest that the N300 reflects expectancy, but only for categorical and/or semantic similarity priming. Results further suggest that the N400RP is a replicable ERP component that responds to semantic matching. There is also some evidence that the N400 indirectly responds to both ASA and expectancy, perhaps as part of a post-lexical updating process and that backward priming at short SOAs is different from that at long SOAs.

SIGNIFICANCE

Improved understanding of the semantic properties of the N400 and related ERP components may increase their utility for understanding language processes and for diagnostic purposes.

Event perception: a mind-brain perspective

People perceive and conceive of activity in terms of discrete events. Here the authors propose a theory according to which the perception of boundaries between events arises from ongoing perceptual processing and regulates attention and memory. Perceptual systems continuously make predictions about what will happen next. When transient errors in predictions arise, an event boundary is perceived. According to the theory, the perception of events depends on both sensory cues and knowledge structures that represent previously learned information about event parts and inferences about actors' goals and plans. Neurological and neurophysiological data suggest that representations of events may be implemented by structures in the lateral prefrontal cortex and that perceptual prediction error is calculated and evaluated by a processing pathway, including the anterior cingulate cortex and subcortical neuromodulatory systems.

Hemispheric differences in strong versus weak semantic priming: evidence from event-related brain potentials

GOALS

Research with lateralized word presentation has suggested that strong ("close") and weak ("remote") semantic associates are processed differently in the left and right cerebral hemispheres [e.g., Beeman, M. j., & Chiarello, C. (1998). Complementary right- and left-hemisphere language comprehension. Current Directions in Psychological Science, 7(1), 2-8]. Recently, this hypothesis has been challenged [Coney, J. (2002). The effect of associative strength on priming in the cerebral hemispheres. Brain and Cognition, 50(2), 234-241]. We predicted that foveal presentation of strong and weak associates would elicit different patterns of hemispheric activity, as indexed by high-density event-related brain potentials (ERPs), and that source localization of the scalp potentials would help clarify the nature of hemispheric contributions to semantic organization.

METHODS

128-channel ERPs were recorded in two experiments as subjects performed a lexical decision task. Word trials were equally divided into strongly related, weakly related, and unrelated word pairs. All words were foveally presented. SOA was 800 ms in Experiment 1, and 200 ms in Experiment 2.

RESULTS

Topographic analyses revealed medial frontal (MFN) and parietal (N400/LPC) effects for both strong and weak associates. Between approximately 450 and 550 ms, the magnitude of the N400/LPC effect indicated priming for both strong and weak associates over left parietal sites, while priming over right parietal sites was restricted to strongly related word pairs. During this interval, spatiotemporal source modeling showed that these scalp effects were best accounted for by ipsilateral sources in the medial temporal lobe. The observed pattern of asymmetries for strong versus weak associates is not consistent with certain proposals regarding the complementarity of right- and left-hemisphere contributions to semantics. It is, however, consistent with findings from visual half-field studies (Hasbrooke and Chiarello, 1998). We discuss the relevance of these results for theories of hemispheric asymmetry and meta-control in lexical semantic access.

Mood States Modulate Activity in Semantic Brain Areas during Emotional Word Encoding

It is controversially discussed whether or not mood-congruent recall (i.e., superior recall for mood-congruent material) reflects memory encoding processes or reduces to processes during retrieval. We therefore investigated the neurophysiological correlates of mood-dependent memory during emotional word encoding. Event-related potentials (ERPs) were recorded while participants in good or bad mood states encoded words of positive and negative valence. Words were either complete or had to be generated from fragments. Participants had to memorize words for subsequent recall. Mood-congruent recall tended to be largest in good mood for generated words. Starting at 200 ms, mood-congruent ERP effects of word valence were obtained in good, but not in bad mood. Only for good mood, source analysis revealed valence-related activity in ventral temporal cortex and for generated words also in prefrontal cortex. These areas are known to be involved in semantic processing. Our findings are consistent with the view that mood-congruent recall depends on the activation of mood-congruent semantic knowledge during encoding. Incoming stimuli are more readily transformed according to stored knowledge structures in good mood particularly during generative encoding tasks. The present results therefore show that mood-congruent memory originates already during encoding and cannot be reduced to strategic processes during retrieval.

ERPs of metaphoric, literal, and incongruous semantic processing in schizophrenia

The ability of schizophrenia patients to access metaphorical meaning was studied on the basis of psycholinguistic models of metaphor processing. ERPs were recorded from 20 schizophrenic and 20 control participants who were asked to read metaphorical, literal, and incongruous sentences and to judge their meaningfulness. In all participants, incongruous endings to sentences evoked the most negative N400 amplitude, whereas literal endings evoked more negative N400 amplitude than metaphorical ones, consistent with the direct model of metaphor processing. Although the patients had ERPs patterns that were similar to controls, they exhibited a more negative N400 amplitude for all sentences, LPC amplitude reduction, and latency delay in both components. The results suggest that schizophrenics have no specific anomalies in accessing the meaning of metaphors but are less efficient in integrating the semantic context of all sentences--both figurative and literal.

Response Execution in Lexical Decision Tasks Obscures Sex-specific Lateralization Effects in Language Processing: Evidence from Event-related Potential Measures during Word Reading

A common hypothesis about sex differences in language processing attributes these differences to a bilateral contribution of language-related brain areas in females and a left-hemispheric dominated activation in males. However, most imaging studies failed to find such a generalized lateralization effect and reported a left-lateralized activation in both sexes instead. In a previous semantic priming study, we found a sustained (approximately 190-640 ms) bilateral positivity in the ERP waveforms, which was larger for the female group. Word reading and lexical decision were confounded in that study. In the present study we used a delayed response to separate semantic processing from response selection and execution. The modification of the task design, together with a dense sensor array, showed that females developed a bilateral sustaining posterior positivity/frontal negativity during reading/semantic processing. In contrast, males showed an attenuated positivity at left posterior sites and an attenuated negativity at right frontal sites. This sex-specific lateralization effect disappeared during response processing, evoking a bilaterally distributed activation for both sexes (frontal negative and posterior positive), which was larger for the female subjects. We conclude that, at least under specific conditions, language processing evokes a bilateral activation in females and a lateralization effect in males. However, the processing of the response, which is dominated by a 'P300-like' component evoked by this process, evokes a larger activation in both sexes which obscures the sex-specific lateralization effect when semantic processing and response processing are not separated.

Dynamics of task sets: Evidence from dense-array event-related potentials

Prior research suggests that task sets facilitate coherent, goal-directed behavior by providing an internal, contextual frame that biases selection toward context-relevant stimulus attributes and responses. Questions about how task sets are engaged, maintained, and shifted have recently become a major focus of research on executive control processes. We employed dense-array (128-channel) event-related potential (ERP) methodology to examine the dynamics of brain systems engaged during the preparation and implementation of task switching. The EEG was recorded while participants performed letter and digit judgments to pseudorandomly-ordered, univalent (#3, A%) and bivalent (G5) stimulus trials, with the appropriate task cued by a colored rectangle presented 450 ms before target onset. Results revealed spatial and temporal variations in brain activity that could be related to preparatory processes common to both switch and repeat trials, switch-specific control processes engaged to reconfigure and maintain task set under conflict, and visual priming benefits of task repetition. Despite extensive practice and improvement, both behavioral and ERP results indicated that subjects maintained high levels of executive control processing with extended task engagement. The patterns of ERP activity obtained in the present study fit well with functional neuroanatomical models of self-regulation of action. The frontopolar and right-lateralized frontal switch effects obtained in the present study are consistent with the role of these regions in adapting to changing contextual contingencies. In contrast, the centroparietal P3b and N384 effects related to the contextual ambiguity of bivalent trials are consistent with the context monitoring and updating functions associated with the posterior cingulate learning circuit.