Left Posterior Superior Temporal Sulcus Research Articles

355 Connecting computational models of reading to the brain in post-stroke alexia

OBJECTIVES/GOALS: Many left hemisphere stroke survivors have a reading disorder (alexia), which is experienced as decreasing well-being. Therapies produce inconsistent results, demonstrating a need for treatment response predictors. We are investigating neural correlates of reading computational models to identify biomarkers to improve therapeutic outcomes. METHODS/STUDY POPULATION: Artificial neural network models of reading, mapping between orthography (visual word form), phonology (auditory word form), and semantics (word meaning), are trained to read single words at a healthy, adult capacity. The models are independently damaged to reflect the individual orthography-to-semantics, semantics-to-phonology, and orthography-to-phonology deficits of a sample of left hemisphere stroke survivors (n = 85). These deficits are measured with cognitive tests assessing the intactness of mappings between representations. Model damage is enacted by removing percentages of the connections between representations. For each type of deficit, the percentages of links removed are entered into a voxel-based lesion symptom mapping analysis to identify areas of cortex associated with that mapping. RESULTS/ANTICIPATED RESULTS: We anticipate that the neural correlates of model layers will be localized to a mostly left-lateralized network. Increased damage to the links between semantics and phonology in the model will likely be related to lesions involving the left posterior superior temporal sulcus and inferior frontal gyrus (IFG). Damaged orthography-to-semantic links will be related to the left fusiform gyrus (FG) and IFG. Finally, damage to the orthography-to-phonology links will be related to the left FG and superior temporal gyrus. DISCUSSION/SIGNIFICANCE: Mapping components of language models onto the brain will improve our understanding of the neural networks supporting language processing. Identifying these neural correlates may also produce biomarkers that can be used in predicting reading impairment at the acute stage or optimizing therapy in the chronic stage of stroke.

Long-term changes in cortical representation through perceptual learning of spectrally degraded speech.

Listeners can adapt to acoustically degraded speech with perceptual training. The learning processes for long periods underlies the rehabilitation of patients with hearing aids or cochlear implants. Perceptual learning of acoustically degraded speech has been associated with the frontotemporal cortices. However, neural processes during and after long-term perceptual learning remain unclear. Here we conducted perceptual training of noise-vocoded speech sounds (NVSS), which is spectrally degraded signals, and measured the cortical activity for seven days and the follow up testing (approximately 1year later) to investigate changes in neural activation patterns using functional magnetic resonance imaging. We demonstrated that young adult participants (n = 5) improved their performance across seven experimental days, and the gains were maintained after 10months or more. Representational similarity analysis showed that the neural activation patterns of NVSS relative to clear speech in the left posterior superior temporal sulcus (pSTS) were significantly different across seven training days, accompanying neural changes in frontal cortices. In addition, the distinct activation patterns to NVSS in the frontotemporal cortices were also observed 10-13months after the training. We, therefore, propose that perceptual training can induce plastic changes and long-term effects on neural representations of the trained degraded speech in the frontotemporal cortices. These behavioral improvements and neural changes induced by the perceptual learning of degraded speech will provide insights into cortical mechanisms underlying adaptive processes in difficult listening situations and long-term rehabilitation of auditory disorders.

Longitudinal changes in the brain language system as amyloid accumulates

AbstractBackgroundLanguage dysfunction is common in Alzheimer disease (AD). There is increasing interest in the preclinical phase of AD. Here we tested longitudinally how activity in the associative‐semantic language network, measured with task‐based fMRI, changes in relation to increases in amyloid load, measured with 18F‐flutemetamol and 11C‐PIB. The main hypothesis was that an increase in amyloid would be associated with changes in activity in left or right posterior superior temporal sulcus (STS) and/or medial temporal gyrus (GTm).MethodA cohort of 35 cognitively intact older adults (mean age=65.4; range: 52‐78 years, 54.3% APOE‐ε4) participated who all received a task‐based fMRI and amyloid PET in 2009‐2011 and a repeat scan for both modalities in 2016‐2017. As primary analysis, we examined how longitudinal change in amyloid, measured using Centiloids (CL), relates to longitudinal activation change in the posterior temporal nodes of the associative‐semantic language network. The left and right posterior STS and GTm were defined as regions of prior interest using the Fan Brainnetome atlas, based on prior studies in amnestic mild cognitive impairment (MCI) and clinically probable AD using the same functional paradigm (Nelissen et al., 2007; Vandenbulcke et al., 2007; Adamczuk et al., 2016). Within this VOI, significance was determined based on SPM12 small volume correction. As a secondary analysis, we also performed a voxelwise whole‐brain analysis with a FWE whole‐brain corrected threshold <0.05. We also examined how the change in amyloid and the change in fMRI activation related to changes in offline language measures.ResultIn the right posterior STS, the change in response amplitude during the associative‐semantic versus the visuoperceptual task showed a positive correlation with the change in amyloid load (x=51 mm, y=‐31 mm, z=5 mm; Z=3.47, Pcorr=0.010; Fig. 1). The change in response amplitude also correlated with longer offline confrontation naming reaction times (RT; r=0.42, P=0.035; Fig. 2). In addition, in the whole‐brain analysis we observed a decrease in response in the right inferior frontal sulcus with increasing amyloid load (x=3 mm, y=20 mm, z=56 mm; Z=4.64, Pcorr=0.021).ConclusionThis study confirms the central role of the posterior STS as area of predilection in the earliest stages of AD.

Dissociating the functions of three left posterior superior temporal regions that contribute to speech perception and production

Prior studies have shown that the left posterior superior temporal sulcus (pSTS) and left temporo-parietal junction (TPJ) both contribute to phonological short-term memory, speech perception and speech production. Here, by conducting a within-subjects multi-factorial fMRI study, we dissociate the response profiles of these regions and a third region – the anterior ascending terminal branch of the left superior temporal sulcus (atSTS), which lies dorsal to pSTS and ventral to TPJ. First, we show that each region was more activated by (i) 1-back matching on visually presented verbal stimuli (words or pseudowords) compared to 1-back matching on visually presented non-verbal stimuli (pictures of objects or non-objects), and (ii) overt speech production than 1-back matching, across 8 types of stimuli (visually presented words, pseudowords, objects and non-objects and aurally presented words, pseudowords, object sounds and meaningless hums). The response properties of the three regions dissociated within the auditory modality. In left TPJ, activation was higher for auditory stimuli that were non-verbal (sounds of objects or meaningless hums) compared to verbal (words and pseudowords), irrespective of task (speech production or 1-back matching). In left pSTS, activation was higher for non-semantic stimuli (pseudowords and hums) than semantic stimuli (words and object sounds) on the dorsal pSTS surface (dpSTS), irrespective of task. In left atSTS, activation was not sensitive to either semantic or verbal content. The contrasting response properties of left TPJ, dpSTS and atSTS was cross-validated in an independent sample of 59 participants, using region-by-condition interactions. We also show that each region participates in non-overlapping networks of frontal, parietal and cerebellar regions. Our results challenge previous claims about functional specialisation in the left posterior superior temporal lobe and motivate future studies to determine the timing and directionality of information flow in the brain networks involved in speech perception and production.

The roles of the LpSTS and DLPFC in self‐prioritization: A transcranial magnetic stimulation study

The Self‐Attention Network (SAN) has been proposed to describe the underlying neural mechanism of the self‐prioritization effect, yet the roles of the key nodes in the SAN—the left posterior superior temporal sulcus (LpSTS) and the dorsolateral prefrontal cortex (DLPFC)—still need to be clarified. One hundred and nine participants were randomly assigned into the LpSTS group, the DLPFC group, or the sham group. We used the transcranial magnetic stimulation (TMS) technique to selectively disrupt the functions of the corresponding targeted region, and observed its impacts on self‐prioritization effect based on the difference between the performance of the self‐matching task before and after the targeted stimulation. We analyzed both model‐free performance measures and HDDM‐based performance measures for the self‐matching task. The results showed that the inhibition of LpSTS could lead to reduced performance in processing self‐related stimuli, which establishes a causal role for the LpSTS in self‐related processing and provide direct evidence to support the SAN framework. However, the results of the DLPFC group from HDDM analysis were distinct from the results based on response efficiency. Our investigation further the understanding of the differentiated roles of key nodes in the SAN in supporting the self‐salience in information processing.

Increased Connectivity among Sensory and Motor Regions during Visual and Audiovisual Speech Perception.

In everyday conversation, we usually process the talker's face as well as the sound of the talker's voice. Access to visual speech information is particularly useful when the auditory signal is degraded. Here, we used fMRI to monitor brain activity while adult humans (n = 60) were presented with visual-only, auditory-only, and audiovisual words. The audiovisual words were presented in quiet and in several signal-to-noise ratios. As expected, audiovisual speech perception recruited both auditory and visual cortex, with some evidence for increased recruitment of premotor cortex in some conditions (including in substantial background noise). We then investigated neural connectivity using psychophysiological interaction analysis with seed regions in both primary auditory cortex and primary visual cortex. Connectivity between auditory and visual cortices was stronger in audiovisual conditions than in unimodal conditions, including a wide network of regions in posterior temporal cortex and prefrontal cortex. In addition to whole-brain analyses, we also conducted a region-of-interest analysis on the left posterior superior temporal sulcus (pSTS), implicated in many previous studies of audiovisual speech perception. We found evidence for both activity and effective connectivity in pSTS for visual-only and audiovisual speech, although these were not significant in whole-brain analyses. Together, our results suggest a prominent role for cross-region synchronization in understanding both visual-only and audiovisual speech that complements activity in integrative brain regions like pSTS.SIGNIFICANCE STATEMENT In everyday conversation, we usually process the talker's face as well as the sound of the talker's voice. Access to visual speech information is particularly useful when the auditory signal is hard to understand (e.g., background noise). Prior work has suggested that specialized regions of the brain may play a critical role in integrating information from visual and auditory speech. Here, we show a complementary mechanism relying on synchronized brain activity among sensory and motor regions may also play a critical role. These findings encourage reconceptualizing audiovisual integration in the context of coordinated network activity.

Improving speech perception in noise in young and older adults using transcranial magnetic stimulation

Normal aging is associated with speech perception in noise (SPiN) difficulties. The objective of this study was to determine if SPiN performance can be enhanced by intermittent theta-burst stimulation (iTBS) in young and older adults. MethodWe developed a sub-lexical SPiN test to evaluate the contribution of age, hearing, and cognition to SPiN performance in young and older adults. iTBS was applied to the left posterior superior temporal sulcus (pSTS) and the left ventral premotor cortex (PMv) to examine its impact on SPiN performance. ResultsAging was associated with reduced SPiN accuracy. TMS-induced performance gain was greater after stimulation of the PMv compared to the pSTS. Participants with lower scores in the baseline condition improved the most. DiscussionSPiN difficulties can be reduced by enhancing activity within the left speech-processing network in adults. This study paves the way for the development of TMS-based interventions to reduce SPiN difficulties in adults.

Social brain networks: Resting-state and task-based connectivity in youth with and without epilepsy

Individuals with epilepsy often experience social difficulties and deficits in social cognition. It remains unknown how disruptions to neural networks underlying such skills may contribute to this clinical phenotype. The current study compared the organization of relevant brain circuits—the “mentalizing network” and a salience-related network centered on the amygdala—in youth with and without epilepsy. Functional connectivity between the nodes of these networks was assessed, both at rest and during engagement in a social cognitive task (facial emotion recognition), using functional magnetic resonance imaging. There were no group differences in resting-state connectivity within either neural network. In contrast, youth with epilepsy showed comparatively lower connectivity between the left posterior superior temporal sulcus and the medial prefrontal cortex—but greater connectivity within the left temporal lobe—when viewing faces in the task. These findings suggest that the organization of a mentalizing network underpinning social cognition may be disrupted in youth with epilepsy, though differences in connectivity within this circuit may shift depending on task demands. Our results highlight the importance of considering functional task-based engagement of neural systems in characterizations of network dysfunction in epilepsy.

Native non-prototypicality in vowel perception induces prominent neuromagnetic mismatch intensities in non-native speakers: a pilot study.

Neural mismatch response resulting from the difference between prediction and observation is related to change detection and discrimination. Robust neuromagnetic brain activity of auditory mismatch-related perception occurs in response to non-prototypical vowels inacross-category contrasts for first-language speakers. However, whether this non-prototypicality effect applies to within-category vowel perception remains to be elucidated. Here, healthy Japanese adults (n = 7) were subjected to magnetoencephalography (MEG) while watching a silent movie, and passively listened to synthesized English vowels /i/. We observed the source-level mismatch effect to the mid-high near-front vowel deviant [ɪ] with the most non-prototypical, unspecified feature in the participants' native language system. The mismatch effect recruited the left posterior superior temporal sulcus with a peak latency of 225ms post-stimulus onset. We further studied whether a longer F1 distance between vowel pairs would increase mismatch-activated intensities, however, we did not observe neuromagnetic changes when the prototypical anchor standard [i] was compared with three non-prototypical deviants differing in first resonance frequency (F1) values. Our results indicate that an F1 increase in within-category upper front vowel perception is a strong activator of mismatch responses measured by source-level activated intensities for non-native listeners.

Altered Local Gyrification Index and Corresponding Functional Connectivity in Medication Free Major Depressive Disorder.

A lot of previous studies have documented that major depressive disorder (MDD) is a developmental disorder. The cortical surface measure, local gyrification index (LGI), can well reflect the fetal and early postnatal neurodevelopmental processes. Thus, LGI may provide new insight for the neuropathology of MDD. The previous studies only focused on the surface structural abnormality, but how the structural abnormality lead to functional connectivity changes is unexplored. In this study, we investigated LGI and corresponding functional connectivity difference in 28 medication-free MDD patients. We found significantly decreased LGI in left lingual gyrus (LING) and right posterior superior temporal sulcus (bSTS), and the changed LGI in bSTS was negatively correlated with disease onset age and anxiety scores. The following functional connectivity analyses identified decreased functional connectivities between LING and right LING, precentral gyrus, and middle temporal gyrus. The decreased functional connectivities were correlated with disease duration, onset, and depression symptoms. Our findings revealed abnormal LGI in LING and bSTS indicating that the abnormal developmental of visual and social cognition related brain areas may be an early biomarker for depression.

Aberrant posterior superior temporal sulcus functional connectivity and executive dysfunction in adolescents with internet gaming disorder.

Background and aimsThe clinical significance of Internet gaming disorder (IGD) is spreading worldwide, but its underlying neural mechanism still remains unclear. Moreover, the prevalence of IGD seems to be the highest in adolescents whose brains are in development. This study investigated the functional connectivity between large-scale intrinsic networks including default mode network, executive control network, and salience network. We hypothesized that adolescents with IGD would demonstrate different functional connectivity patterns among large-scale intrinsic networks, implying neurodevelopmental alterations, which might be associated with executive dysfunction.MethodsThis study included 17 male adolescents with Internet gaming disorder, and 18 age-matched male adolescents as healthy controls. Functional connectivity was examined using seed-to-voxel analysis and seed-to-seed analysis, with the nodes of large-scale intrinsic networks used as region of interests. Group independent component analysis was performed to investigate spatially independent network.ResultsWe identified aberrant functional connectivity of salience network and default mode network with the left posterior superior temporal sulcus (pSTS) in adolescents with IGD. Furthermore, functional connectivity between salience network and pSTS correlated with proneness to Internet addiction and self-reported cognitive problems. Independent component analysis revealed that pSTS was involved in social brain network.Discussion and conclusionsThe results imply that aberrant functional connectivity of social brain network with default mode network and salience network was identified in IGD that may be associated with executive dysfunction. Our results suggest that inordinate social stimuli during excessive online gaming leads to altered connections among large-scale networks during neurodevelopment of adolescents.

Musicians use speech-specific areas when processing tones: The key to their superior linguistic competence?

It is known that musicians compared to non-musicians have some superior speech and language competence, yet the mechanisms how musical training leads to this advantage are not well specified.This event-related fMRI study confirmed that musicians outperformed non-musicians in processing not only of musical tones but also syllables and identified a network differentiating musicians from non-musicians during processing of linguistic sounds.Within this network, the activation of bilateral superior temporal gyrus was shared with all subjects during processing of the acoustically well-matched musical and linguistic sounds, and with the activation distinguishing tones with a complex harmonic spectrum (bowed tone) from a simpler one (plucked tone). These results confirm that better speech processing in musicians relies on improved cross-domain spectral analysis.Activation of left posterior superior temporal sulcus (pSTS), premotor cortex, inferior frontal and fusiform gyrus (FG) also distinguishing musicians from non-musicians during syllable processing overlapped with the activation segregating linguistic from musical sounds in all subjects. Since these brain-regions were not involved during tone processing in non-musicians, they could code for functions which are specialized for speech. Musicians recruited pSTS and FG during tone processing, thus these speech-specialized brain-areas processed musical sounds in the presence of musical training.This study shows that the linguistic advantage of musicians is linked not only to improved cross-domain spectral analysis, but also to the functional adaptation of brain resources that are specialized for speech, but accessible to the domain of music in the presence of musical training.

Neural Basis of Professional Pride in the Reaction to Uniform Wear.

Professional pride is a positive emotion that includes self-reflection or evaluation and attitude toward one’s own occupational group. Uniforms can encourage the wearer to have professional pride. The current study aimed to elucidate the neural basis of professional pride using an experimental task related to the self in uniform and functional magnetic resonance imaging (fMRI). The person-adjective matching task, in which a participant or other in uniform or casual wear was presented with positive and negative words, was used for scanning fMRI. Imaging data from 21 adults who had an occupation requiring a uniform were analyzed to identify the main and interaction effects of individual (self vs. other), clothes (uniform vs. casual wear), and valence (positive vs. negative). Identified brain activities were correlated with psychological scales including the Rosenberg Self-esteem Scale and Group Environment Questionnaire. Whole brain analyses found that the interaction between individual and clothes was present in multiple regions such as the right ventrolateral prefrontal cortex (VLPFC), left dorsolateral prefrontal cortex, left middle and inferior temporal gyri, left posterior superior temporal sulcus, right temporoparietal junction, left lingual gyrus, left calcarine cortex, right insula, left caudate, and right putamen. In particular, activities in the right VLPFC, left calcarine cortex, and right putamen in the self/uniform condition were positively correlated with several psychological scales. These results suggest that professional pride may be represented through multiple brain networks related to empathy, reward, and emotion regulation as well as the theory-of-mind network. The neural basis of professional pride is closely related to positive self-evaluation and group cohesion.

The structural and functional correlates underlying individual heterogeneity of reading the mind in the eyes

Mentalizing is an essential component in human social interactions and the sources of individual variation in mentalizing are still very poorly understood. Utilizing the “reading the mind in the eyes” test (RMET), we examined the neuroanatomical basis of these differences with voxel-based morphometry and found that the gray matter density in the left posterior superior temporal sulcus (pSTS) could positively predict individuals’ RMET scores. Furthermore, we found that the pSTS-amygdala functional connection was positively correlated to individuals’ RMET scores. A test-validation procedure confirmed that the imaging results could be replicated and validated in another independent sample. Finally, mediation analysis revealed that pSTS-amygdala functional connection could account for the relationship between pSTS gray matter density and RMET scores. Present results demonstrate the contribution of brain structure of pSTS to individual variations in RMET performance and reveal an important implication of the neural circuit between core imitation and emotion regions in REMT.

Encoding Praise and Criticism During Social Evaluation Alters Interactive Responses in the Mentalizing and Affective Learning Networks.

Verbal communication with evaluative characters of different emotional valence has a considerable impact on the extent to which social relations are facilitated or undermined. Here using functional magnetic resonance imaging, we investigated how the brain acts in response to social praise and criticism, leading to differential affective judgments. We engaged thirty men and women in a task associating sex-balanced, neutral faces with praising or criticizing comments targeting others or objects. A whole-brain analysis revealed that criticism as compared to praise enhanced the activation in the medial prefrontal cortex (mPFC), particularly its dorsal portion, whereas the right amygdala displayed an opposite pattern of changes. Comments on others relative to objects increased the reactivity in the left posterior superior temporal sulcus and posterior cingulate cortex (PCC) such that both praise and criticism of others produced stronger activation in these two regions than their object-targeted counterparts. The interaction of valence and target was identified in the mPFC with greater reactivity in the contrasts of criticism vs. praise in the social context and others- vs. object-targeted criticism. Comments also modulated the functional connectivity of prior activated regions with the left temporoparietal junction, bilateral caudate and left PCC/precuneus showing reduced connectivity in response to social criticism but greatly strengthened connectivity for social praise as compared to non-social counterparts. These neural effects subsequently led to altered likeability ratings for the faces. Neither behavioral nor neural effects observed were influenced by the gender of participants. Taken together, our findings suggest a fundamental interactive role of the mentalizing and affective learning networks in differential encoding of individuals associated with praising or criticizing others, leading to learning of valenced traits and subsequent approach or avoidance responses in social interactions.

Action-related dynamic changes in inferior frontal cortex effective connectivity: A TMS/EEG coregistration study

Humans show exquisite abilities to perform versatile finger movements. The inferior frontal cortex (IFC) plays a pivotal role in the visual control of such movements through connections with other sensorimotor regions. Yet, the dynamics of IFC effective connectivity during action execution are still poorly understood. Using single-pulse TMS and simultaneous EEG recording (i.e., TMS-EEG coregistration), we stimulated the left posterior IFC at rest and during a visuomotor task. We recorded TMS-evoked potentials (TEPs) to assess action-related changes in IFC connectivity and localized their sources using sLORETA. We found two key time windows at ∼60 and ∼80 msec after IFC stimulation in which TEPs were modulated by task conditions in remote electrodes. In the first time window (∼60 msec), action-related changes in TEP amplitudes were observed over frontal and temporo-parietal electrodes, reflecting increased IFC connectivity with fronto-parietal motor areas and decreased IFC connectivity with visual occipito-temporal areas. In the second time window (∼80 msec), action-related TEP increases were observed in frontal, temporal and parietal regions partially overlapping with the default-mode network. No similar effects were observed when TMS was administered over a non-motor control area (the left posterior superior temporal sulcus, STS). These findings highlight dynamic changes in IFC connectivity with motor, sensory and default-mode networks. They suggest sequential stages of task-related changes in IFC connectivity possibly related to controlling and sensing actions and inhibiting default-mode brain activity during motor performance.

Alterations of Gray Matter Volume and White Matter Integrity in Maternal Deprivation Monkeys

Maternal deprivation (MD) in rhesus monkeys has been demonstrated to be an effective model to mimic early adversity in humans because of the close phylogenetic similarity affinity. Although behavioral and hormonal abnormalities have been observed in MD monkeys, the neurobiological underpinning of the long-term deleterious effect of MD on monkeys is still unclear. In this study, we assessed emotional changes and socio-behavioral abnormalities induced by long-term MD and assessed structural alterations of gray matter volume (GMV) and white matter integrity (WMI) in 15 MD rhesus monkeys and in 15 age-, gender-matched normal controls (NC) using voxel-based morphology and voxel-based analysis methods. We found increased stereotypical behavioral durations and decreased social grooming durations in MD monkeys. Reduced GMV in the primary visual cortex (V1) and increased fractional anisotropy (FA) in the left posterior superior temporal sulcus (pSTS) was also found in MD monkeys. Moreover, the mean FA values in pSTS showed positive correlation with the stereotypical behavioral durations in MD monkeys and negative correlation with social grooming durations in NC monkeys. Our findings indicated that the deleterious effects of MD on rhesus monkeys resulted in structural abnormalities in the visual cortex and premature myelination in the pSTS. These findings provide new insights into understanding the impact of maternal deprivation on the neurological basis of brain development.

Affective and cooperative social interactions modulate effective connectivity within and between the mirror and mentalizing systems.

Decoding the meaning of others' actions, a crucial step for social cognition, involves different neural mechanisms. While the "mirror" and "mentalizing" systems have been associated with, respectively, the processing of biological actions versus more abstract information, their respective contribution to intention understanding is debated. Processing social interactions seems to recruit both neural systems, with a different weight depending on cues emphasizing either shared action goals or shared mental states. We have previously shown that observing cooperative and affective social interactions elicits stronger activity in key nodes of, respectively, the mirror (left posterior superior temporal sulcus (pSTS), superior parietal cortex (SPL), and ventral/dorsal premotor cortex (vPMC/dPMC)) and mentalizing (ventromedial prefrontal cortex (vmPFC)) systems. To unveil their causal organization, we investigated the effective connectivity underlying the observation of human social interactions expressing increasing cooperativity (involving left pSTS, SPL, and vPMC) versus affectivity (vmPFC) via dynamic causal modeling in 36 healthy human subjects. We found strong evidence for a model including the pSTS and vPMC as input nodes for the observed interactions. The extrinsic connectivity of this model undergoes oppositely valenced modulations, with cooperativity promoting positive modulations of connectivity between pSTS and both SPL (forward) and vPMC (mainly backward), and affectivity promoting reciprocal positive modulations of connectivity between pSTS and vmPFC (mainly backward). Alongside fMRI data, such divergent effective connectivity suggests that different dimensions underlying the processing of social interactions recruit distinct, although strongly interconnected, neural pathways associated with, respectively, the bottom-up visuomotor processing of motor intentions, and the top-down attribution of affective/mental states.

P141 Contribution of the motor system to McGurk effect-event-related fMRI and TMS studies

Question ”McGurk effect” is known as an auditory illusion caused by interference from unmatched visual inputs. For example, a combination of auditory/Pa/ and visual/Ka/ results in the perception of a third syllable of/Ta/. Recent neuroimaging studies proposed that left posterior superior temporal sulcus (pSTS), a hub region of audiovisual integration, is concerned with McGurk effect. However, the mechanisms still remain under debate. Methods 27 right-handed healthy volunteers received audiovisual incongruent (auditory/Ba//Pa/ and visual/Ga//Ka/) and congruent (both/Ba//Pa/) perceptual tasks, and then they were asked the syllables listened to. We investigated activated brain regions in event-related functional magnetic resonance imaging (fMRI) study. In addition, we applied single-pulse transcranial magnetic stimulation (TMS) over the lip or foot area of the primary motor cortex (M1) in an event-related design and we measured McGurk susceptibility. Results Behaviorally, audiovisual incongruent trials resulted in higher illusion susceptibility and longer reaction time than congruent trials. FMRI study revealed brain activations in audiovisual areas, dorsal premotor cortex (dPMC) and inferior frontal gyrus (IFG), bilaterally in both audiovisual stimuli. Activations in dPMC and IFG were more prominent in incongruent task, whereas stronger activations of the pSTS in congruent task. Left IFG activation correlated negatively with McGurk susceptibility. Psychophysiological interaction analysis demonstrated increased effective connectivity between the left IFG and M1 lip area in incongruent task. Event-related TMS over M1 lip area showed significant reduction of McGurk susceptibility when compared with TMS over M1 foot area or the control condition (no TMS). Conclusions We showed that the motor system contributes to recognition of audiovisual inputs and it is more active in incongruent condition, while the pSTS is more active in congruent condition. The left IFG-M1 network plays some roles in detecting and resolving multisensory incompatibility to reduce illusion.

The role of the IFG and pSTS in syntactic prediction: Evidence from a parametric study of hierarchical structure in fMRI

Sentences encode hierarchical structural relations among words. Several neuroimaging experiments aiming to localize combinatory operations responsible for creating this structure during sentence comprehension have contrasted short, simple phrases and sentences to unstructured controls. Some of these experiments have revealed activation in the left inferior frontal gyrus (IFG) and posterior superior temporal sulcus (pSTS), associating these regions with basic syntactic combination. However, the wide variability of these effects across studies raises questions about this interpretation. In an fMRI experiment, we provide support for an alternative hypothesis: these regions underlie top-down syntactic predictions that facilitate sentence processing but are not necessary for building syntactic structure. We presented stimuli with three levels of structure: unstructured lists, two-word phrases, and simple, short sentences; and two levels of content: natural stimuli with real words and stimuli with open-class items replaced with pseudowords (jabberwocky). While both the phrase and sentence conditions engaged syntactic combination, our experiment only encouraged syntactic prediction in the sentence condition. We found increased activity for both natural and jabberwocky sentences in the left IFG (pars triangularis and pars orbitalis) and pSTS relative to unstructured word lists and two-word phrases, but we did not find any such effects for two-word phrases relative to unstructured word lists in these areas. Our results are most consistent with the hypothesis that increased activity in IFG and pSTS for basic contrasts of structure reflects syntactic prediction. The pars opercularis of the IFG showed a response profile consistent with verbal working memory. We found incremental effects of structure in the anterior temporal lobe (ATL), and increased activation only for sentences in the angular gyrus (AG)/temporal–parietal junction (TPJ) – both regions showed these effects for stimuli with all real words. These findings support a role for the ATL in semantic combination and the AG/TPJ in thematic processing.