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

Bilingual Brains Learn to Use L2 Alliterations Covertly like Poets: Brain ERP Evidence

Bilinguals were documented to access their native or first language (L1) during comprehension of their second languages (L2). However, it is uncertain whether they can access L2 when reading their first language. This study used the event-related potential (ERP) technique to demonstrate the implicit and unconscious access to English words when Chinese–English bilinguals read words in Chinese, their native language. The participants were asked to judge whether the Chinese words presented in pairs were semantically related or not, meanwhile unconscious of the occasional alliteration (repetition of the first phoneme) if the Chinese words were translated into English. While the concealed prime in English translations failed to affect the reaction time, the alliteration significantly modulated N400 among advanced English learners, especially for semantically unrelated word pairs. Critically, this modulation effect was discrepant between bilinguals with high-level and normal-level English proficiency. These results indicate that L2 activation is an unconscious correlate of native-language processing depending on L2 proficiency.

Larger Volume and Different Activation of the Brain in Response to Threat in Military Officers

Introduction:

Military missions involve stressful and life-threatening situations; however, soldiers should have a healthy cognition on the battlefield despite their high-stress levels. This is an ability that should be gained during prior military training. Successful and influential training is suggested to be associated with structural and functional improvements of the brain.

Methods:

This study investigated the pattern of brain activation while observing videos relevant to life-threatening situations, in addition to brain structure. Accordingly, the obtained data were compared between 20 military members and 26 healthy controls. The study participants were all male, aged between 19 to 24 years, right-handed, studying BSc, and from the same socioeconomic status.

Results:

The obtained data presented a larger volume in a total number of 1103 voxels of the brain (in 5 brain areas) in the military group. Furthermore, the military group suggested higher brain activation in the visual processing areas of the brain when observing real combat videos; however, this increment was mostly in the areas associated with motor processing and executive functions in the controls.

Conclusion:

This study indicated that military training is associated with positive structural changes in the brain. Besides, it provided a different brain activation in response to stressful situations. These findings highlighted the importance of qualified military training.

Facilitation of Fast Backward Priming After Left Cerebellar Continuous Theta-Burst Stimulation

Traditional theories of backward priming account only for the priming effects found at long stimulus onset asynchronies (SOAs). Here, we suggest that the presence of backward priming at short SOAs may be related to the integrative role of the cerebellum. Previous research has shown that the right cerebellum is involved in forward associative priming. Functional magnetic resonance imaging reveals some activation of the left cerebellar hemisphere during backward priming; but what this activation represents is unclear. Here we explore this issue using continuous theta-burst transcranial magnetic stimulation (cTBS) and associative priming in a lexical decision task. We tested the hypothesis that the left cerebellum plays a role in backward priming and that this is dissociated from the role of the right cerebellum in forward priming. Before and after cTBS was applied to their left and right cerebellar hemispheres, participants completed a lexical decision task. Although we did not replicate the forward priming effect reported in the literature, we did find a significant increase in backward priming after left relative to right cerebellar cTBS. We consider how theories of cerebellar function in the motor domain can be extended to language and cognitive models of backward priming.

Lexical-semantic processing in the semantic priming paradigm in aphasic patients

There is evidence that the explicit lexical-semantic processing deficits which characterize aphasia may be observed in the absence of implicit semantic impairment. The aim of this article was to critically review the international literature on lexical-semantic processing in aphasia, as tested through the semantic priming paradigm. Specifically, this review focused on aphasia and lexical-semantic processing, the methodological strengths and weaknesses of the semantic paradigms used, and recent evidence from neuroimaging studies on lexical-semantic processing. Furthermore, evidence on dissociations between implicit and explicit lexical-semantic processing reported in the literature will be discussed and interpreted by referring to functional neuroimaging evidence from healthy populations. There is evidence that semantic priming effects can be found both in fluent and in non-fluent aphasias, and that these effects are related to an extensive network which includes the temporal lobe, the pre-frontal cortex, the left frontal gyrus, the left temporal gyrus and the cingulated cortex.

Conscious intention to speak proactively facilitates lexical access during overt object naming

The present study explored when and how the top-down intention to speak influences the language production process. We did so by comparing the brain's electrical response for a variable known to affect lexical access, namely word frequency, during overt object naming and non-verbal object categorization. We found that during naming, the event-related brain potentials elicited for objects with low frequency names started to diverge from those with high frequency names as early as 152 ms after stimulus onset, while during non-verbal categorization the same frequency comparison appeared 200 ms later eliciting a qualitatively different brain response. Thus, only when participants had the conscious intention to name an object the brain rapidly engaged in lexical access. The data offer evidence that top-down intention to speak proactively facilitates the activation of words related to perceived objects.

Electrophysiological potentials reveal cortical mechanisms for mental imagery, mental simulation, and grounded (embodied) cognition

Grounded cognition theory proposes that cognition, including meaning, is grounded in sensorimotor processing. The mechanism for grounding cognition is mental simulation, which is a type of mental imagery that re-enacts modal processing. To reveal top-down, cortical mechanisms for mental simulation of shape, event-related potentials were recorded to face and object pictures preceded by mental imagery. Mental imagery of the identical face or object picture (congruous condition) facilitated not only categorical perception (VPP/N170) but also later visual knowledge [N3(00) complex] and linguistic knowledge (N400) for faces more than objects, and strategic semantic analysis (late positive complex) between 200 and 700 ms. The later effects resembled semantic congruity effects with pictures. Mental imagery also facilitated category decisions, as a P3 peaked earlier for congruous than incongruous (other category) pictures, resembling the case when identical pictures repeat immediately. Thus mental imagery mimics semantic congruity and immediate repetition priming processes with pictures. Perception control results showed the opposite for faces and were in the same direction for objects: Perceptual repetition adapts (and so impairs) processing of perceived faces from categorical perception onward, but primes processing of objects during categorical perception, visual knowledge processes, and strategic semantic analysis. For both imagery and perception, differences between faces and objects support domain-specificity and indicate that cognition is grounded in modal processing. Altogether, this direct neural evidence reveals that top-down processes of mental imagery sustain an imagistic representation that mimics perception well enough to prime subsequent perception and cognition. Findings also suggest that automatic mental simulation of the visual shape of faces and objects operates between 200 and 400 ms, and strategic mental simulation operates between 400 and 700 ms.

Word and pseudoword superiority effects reflected in the ERP waveform

A variant of the Reicher-Wheeler task was used to determine when in the event-related potential (ERP) waveform indices of word and pseudoword superiority effects might be present, and whether ERP measures of superiority effects correlated with standardized behavioral measures of orthographic fluency and single word reading. ERPs were recorded to briefly presented, masked letter strings that included real words (DARK/PARK), pseudowords (DARL/PARL), nonwords (RDKA/RPKA), and letter-in-xs (DXXX, PXXX) stimuli. Participants decided which of two letters occurred at a given position in the string (here, forced-choice alternatives D and P). Behaviorally, both word (more accurate choices for letters in words than in baseline nonwords or letter-in-xs) and pseudoword (more accurate choices for letters in pseudowords than in baseline conditions) superiority effects were observed. Electrophysiologically, effects of orthographic regularity and familiarity were apparent as early as the P150 time window (100-160ms), an effect of lexicality was observed as early as the N200 time window (160-200ms), and peak amplitude of the N300 and N400 also differentiated word and pseudoword as compared to baseline stimuli. Further, the size of the P150 and N400 ERP word superiority effects was related to standardized behavioral measures of fluency and reading. Results suggest that orthographic fluency is reflected in both lower-level, sublexical, perceptual processing and higher-level, lexical processing in fluently reading adults.

Neural correlates of cross-domain affective priming

The affective priming effect has mostly been studied using reaction time (RT) measures; however, the neural bases of affective priming are not well established. To understand the neural correlates of cross-domain emotional stimuli presented rapidly, we obtained event-related potential (ERP) measures during an affective priming task using short SOA (stimulus onset asynchrony) conditions. Two sets of 480 picture-word pairs were presented at SOAs of either 150ms or 250ms between prime and target stimuli. Participants decided whether the valence of each target word was pleasant or unpleasant. Behavioral results from both SOA conditions were consistent with previous reports of affective priming, with longer RTs for incongruent than congruent pairs at SOAs of 150ms (771 vs. 738ms) and 250ms (765 vs. 720ms). ERP results revealed that the N400 effect (associated with incongruent pairs in affective processing) occurred at anterior scalp regions at an SOA of 150ms, and this effect was only observed for negative target words across the scalp at an SOA of 250ms. In contrast, late positive potentials (LPPs) (associated with attentional resource allocation) occurred across the scalp at an SOA of 250ms. LPPs were only observed for positive target words at posterior parts of the brain at an SOA of 150ms. Our finding of ERP signatures at very short SOAs provides the first neural evidence that affective pictures can exert an automatic influence on the evaluation of affective target words.

Receptor architecture of human cingulate cortex: evaluation of the four-region neurobiological model

The structural and functional organization of the human cingulate cortex is an ongoing focus; however, human imaging studies continue to use the century-old Brodmann concept of a two region cingulate cortex. Recently, a four-region neurobiological model was proposed based on structural, circuitry, and functional imaging observations. It encompasses the anterior cingulate, midcingulate, posterior cingulate, and retrosplenial cortices (ACC, MCC, PCC, and RSC, respectively). For the first time, this study performs multireceptor autoradiography of 15 neurotransmitter receptor ligands and multivariate statistics on human whole brain postmortem samples covering the entire cingulate cortex. We evaluated the validity of Brodmann's duality concept and of the four-region model using a hierarchical clustering analysis of receptor binding according to the degree of similarity of each area's receptor architecture. We could not find support for Brodmann's dual cingulate concept, because the anterior part of his area 24 has significantly higher AMPA, kainate, GABA(B), benzodiazepine, and M(3) but lower NMDA and GABA(A) binding site densities than the posterior part. The hierarchical clustering analysis distinguished ACC, MCC, PCC, and RSC as independent regions. The ACC has highest AMPA, kainate, alpha(2), 5-HT(1A), and D(1) but lowest GABA(A) densities. The MCC has lowest AMPA, kainate, alpha(2), and D(1) densities. Area 25 in ACC is similar in receptor-architecture to MCC, particularly the NMDA, GABA(A), GABA(B), and M(2) receptors. The PCC and RSC differ in the higher M(1) and alpha(1) but lower M(3) densities of PCC. Thus, multireceptor autoradiography supports the four-region neurobiological model of the cingulate cortex.

Physical activity and memory functions: an interventional study

Previous studies have suggested beneficial effects of physical activity on cognition. Here, we asked in an interventional approach if physical activity performed at different intensity levels would differentially affect episodic memory function. Additionally, we tried to identify mechanisms mediating these changes. Sixty-two healthy elderly individuals were assessed for level of physical activity, aerobic fitness, episodic memory score, neurotrophin and catecholamine levels, and received a magnetic resonance image of the brain at baseline and after a six months intervention of medium or low-intensity physical activity or control. Increase in total physical activity was positively associated with increase in memory score over the entire cohort, without significant differences between intensity groups. It was also positively associated with increases in local gray matter volume in prefrontal and cingulate cortex, and BDNF levels (trend). In conclusion, we showed that physical activity conveys the beneficial effects on memory function independently of its intensity, possibly mediated by local gray matter volume and neurotrophic factors. Our findings may carry significant implications for prevention of cognitive decline in the elderly.

Dopaminergic neuromodulation of semantic processing: a 4-T FMRI study with levodopa

There is emerging evidence that alterations in dopaminergic transmission can influence semantic processing, yet the neural mechanisms involved are unknown. The influence of levodopa (L-DOPA) on semantic priming was investigated in healthy individuals (n = 20) using event-related functional magnetic resonance imaging with a randomized, double-blind crossover design. Critical prime-target pairs consisted of a lexical ambiguity prime and 1) a target related to the dominant meaning of the prime (e.g., bank-money), 2) a target related to the subordinate meaning (e.g., fence-sword), or 3) an unrelated target (e.g., ball-desk). Behavioral data showed that both dominant and subordinate meanings were primed on placebo. In contrast, there was preserved priming of dominant meanings and no significant priming of subordinate meanings on L-DOPA, the latter associated with decreased anterior cingulate and dorsal prefrontal cortex activity. Dominant meaning activation on L-DOPA was associated with increased activity in the left rolandic operculum and left middle temporal gyrus. These findings suggest that L-DOPA enhances frequency-based semantic focus via prefrontal and temporal modulation of automatic semantic priming and through engagement of anterior cingulate mechanisms supporting attentional/controlled priming.