Task-dependent functional and effective connectivity during conceptual processing

Conceptual knowledge is central to cognition. Previous neuroimaging research indicates that conceptual processing involves both modality-specific perceptual-motor areas and multimodal convergence zones. For example, our previous functional magnetic resonance imaging (fMRI) study revealed that both modality-specific and multimodal regions respond to sound and action features of concepts in a task-dependent fashion (Kuhnke P, Kiefer M, Hartwigsen G. 2020b. Task-dependent recruitment of modality-specific and multimodal regions during conceptual processing. Cereb Cortex. 30:3938-3959.). However, it remains unknown whether and how modality-specific and multimodal areas interact during conceptual tasks. Here, we asked 1) whether multimodal and modality-specific areas are functionally coupled during conceptual processing, 2) whether their coupling depends on the task, 3) whether information flows top-down, bottom-up or both, and 4) whether their coupling is behaviorally relevant. We combined psychophysiological interaction analyses with dynamic causal modeling on the fMRI data of our previous study. We found that functional coupling between multimodal and modality-specific areas strongly depended on the task, involved both top-down and bottom-up information flow, and predicted conceptually guided behavior. Notably, we also found coupling between different modality-specific areas and between different multimodal areas. These results suggest that functional coupling in the conceptual system is extensive, reciprocal, task-dependent, and behaviorally relevant. We propose a new model of the conceptual system that incorporates task-dependent functional interactions between modality-specific and multimodal areas

Task-dependent recruitment of modality-specific and multimodal regions during conceptual processing

Conceptual knowledge is central to cognitive abilities such as word comprehension. Previous neuroimaging evidence indicates that concepts are at least partly composed of perceptual and motor features that are represented in the same modality-specific brain regions involved in actual perception and action. However, it is unclear to what extent the retrieval of perceptual-motor features and the resulting engagement of modality-specific regions depend on the concurrent task. To address this issue, we measured brain activity in 40 young and healthy participants using fMRI, while they performed three different tasks—lexical decision, sound judgment, and action judgment—on words that independently varied in their association with sounds and actions. We found neural activation for sound or action features of concepts selectively when they were task-relevant in auditory or motor-related brain regions, respectively, as well as in higher-level, multimodal regions which were recruited during both sound and action feature retrieval. For the first time, we show that not only modality-specific perceptual-motor areas, but also multimodal regions are engaged in conceptual processing in a flexible, task-dependent fashion, responding selectively to task-relevant conceptual features

Left posterior inferior frontal gyrus is causally involved in complex sentence comprehension

INTRODUCTION Storage and reordering of words are two core processes required for successful sentence comprehension. Storage is necessary whenever the verb and its arguments (i.e., subject and object) are separated over a long distance, while reordering is necessary whenever the argument order is atypical (e.g., object-first order in German, where subject-first order is typical). Previous neuroimaging work (Meyer et al., 2012) has associated storage with the left planum temporale (PT), and reordering with the left posterior inferior frontal gyrus (pIFG). However, it is unclear whether left PT and pIFG are indeed causally relevant for storage and reordering, respectively. Here, we tested the necessity of the PT and pIFG for storage and reordering using repetitive transcranial magnetic stimulation (rTMS). METHODS We applied either effective online rTMS (5 pulses at 10 Hz) over PT or pIFG, or sham rTMS, while subjects listened to sentences that independently manipulated storage demands (short vs. long argument–verb distance) and reordering demands (subject– vs. object-first argument order). We employed behavioral modeling, using a drift diffusion model, to assess rTMS-induced disruption of sentence comprehension. RESULTS We found that rTMS over pIFG, but not PT, selectively impaired reordering during the processing of sentences with a long argument–verb distance. Specifically, relative to sham rTMS, rTMS over pIFG significantly increased the performance decline for object– vs. subject-first long-distance sentences (t23 = 2.86; p = 0.009). This effect was anatomically specific as the same comparison for PT stimulation was far from significant (t23 = −0.11; p = 0.9), and a direct across-sites comparison showed that the pIFG effect was significantly stronger (t23 = −2.62; p = 0.015). CONCLUSION Our results provide the first causal evidence that the left pIFG supports the reordering of arguments in long-distance sentences. We thereby substantially extend previous neuroimaging studies that showed a correlation between pIFG activation and reordering demands. Together with previous evidence (Lauro et al., 2010), our findings indicate that the left pIFG crucially supports the comprehension of syntactically complex sentences. These results might extend to other domains, such as music (Maess et al., 2001) and action (Clerget et al., 2009), indicating a domain-general role of left pIFG in the processing of hierarchically-structured sequences

Task-dependent recruitment of modality-specific and multimodal regions during conceptual processing

Conceptual knowledge is central to cognitive abilities such as word comprehension. Previous neuroimaging evidence indicates that concepts are at least partly composed of perceptual and motor features that are represented in the same modality-specific brain regions involved in actual perception and action. However, it is unclear to what extent the retrieval of perceptual-motor features and the resulting engagement of modality-specific regions depend on the concurrent task. To address this issue, we measured brain activity in 40 young and healthy participants using fMRI, while they performed three different tasks—lexical decision, sound judgment, and action judgment—on words that independently varied in their association with sounds and actions. We found neural activation for sound or action features of concepts selectively when they were task-relevant in auditory or motor-related brain regions, respectively, as well as in higher-level, multimodal regions which were recruited during both sound and action feature retrieval. For the first time, we show that not only modality-specific perceptual-motor areas, but also multimodal regions are engaged in conceptual processing in a flexible, task-dependent fashion, responding selectively to task-relevant conceptual features

Meta-analytic evidence for a novel hierarchical model of conceptual processing

Conceptual knowledge plays a pivotal role in human cognition. Grounded cognition theories propose that concepts consist of perceptual-motor features represented in modality-specific perceptual-motor cortices. However, it is unclear whether conceptual processing consistently engages modality-specific areas. Here, we performed an activation likelihood estimation (ALE) meta-analysis across 212 neuroimaging experiments on conceptual processing related to 7 perceptual-motor modalities (action, sound, visual shape, motion, color, olfaction-gustation, and emotion). We found that conceptual processing consistently engages brain regions also activated during real perceptual-motor experience of the same modalities. In addition, we identified multimodal convergence zones that are recruited for multiple modalities. In particular, the left inferior parietal lobe (IPL) and posterior middle temporal gyrus (pMTG) are engaged for three modalities: action, motion, and sound. These “trimodal” regions are surrounded by “bimodal” regions engaged for two modalities. Our findings support a novel model of the conceptual system, according to which conceptual processing relies on a hierarchical neural architecture from modality-specific to multimodal areas up to an amodal hub

Adaptive plasticity in the healthy reading network investigated through combined neurostimulation and neuroimaging

The reading network in the human brain comprises several regions, including the left inferior frontal cortex (IFC), ventral occipito-temporal cortex (vOTC) and dorsal temporo-parietal cortex (TPC). The left TPC is crucial for phonological decoding, i.e., for learning and retaining sound-letter mappings. Here, we tested the causal contribution of this area for reading with repetitive transcranial magnetic stimulation (rTMS) and explored the response of the reading network using functional magnetic resonance imaging (fMRI). 28 healthy adult readers overtly read simple and complex words and pseudowords during fMRI after effective or sham TMS over the left TPC. Behaviorally, effective stimulation slowed pseudoword reading. A multivariate pattern analysis showed a shift in activity patterns in the left IFC for pseudoword reading after effective relative to sham TMS. Furthermore, active TMS led to increased effective connectivity from the left vOTC to the left TPC, specifically for pseudoword processing. The observed changes in task-related activity and connectivity suggest compensatory reorganization in the reading network following TMS-induced disruption of the left TPC. Our findings provide first evidence for a causal role of the left TPC for overt pseudoword reading and emphasize the relevance of functional interactions in the healthy reading network for successful pseudoword processing

The role of the angular gyrus in semantic cognition: A synthesis of five functional neuroimaging studies

Semantic knowledge is central to human cognition. The angular gyrus (AG) is widely considered a key brain region for semantic cognition. However, the role of the AG in semantic processing is controversial. Key controversies concern response polarity (activation vs. deactivation) and its relation to task difficulty, lateralization (left vs. right AG), and functional-anatomical subdivision (PGa vs. PGp subregions). Here, we combined the fMRI data of five studies on semantic processing (n = 172) and analyzed the response profiles from the same anatomical regions-of-interest for left and right PGa and PGp. We found that the AG was consistently deactivated during non-semantic conditions, whereas response polarity during semantic conditions was inconsistent. However, the AG consistently showed relative response differences between semantic and non-semantic conditions, and between different semantic conditions. A combined analysis across all studies revealed that AG responses could be best explained by separable effects of task difficulty and semantic processing demand. Task difficulty effects were stronger in PGa than PGp, regardless of hemisphere. Semantic effects were stronger in left than right AG, regardless of subregion. These results suggest that the AG is engaged in both domain-general task-difficulty-related processes and domain-specific semantic processes. In semantic processing, we propose that left AG acts as a "multimodal convergence zone" that binds different semantic features associated with the same concept, enabling efficient access to task-relevant features

One-dimensional metal chains on Pt vicinal surfaces

High-density arrays (5 x 10(6) cm(-1)) of parallel nanowires have been grown using the vicinal Pt(997) surface as a template. Single monatomic rows of Ag and Cu can be deposited with subrow precision. We demonstrate real-time monitoring and characterization of the growth of the atomic chains as a function of temperature by thermal energy helium atom scattering. Scanning tunneling microscopy provides further insight into the structure of the metal rows. Growth mode and alloying with the Pt substrate are discussed as a function of temperature. Our results provide the basis for the creation of surfaces with a uniform distribution of wires having the same average width for the investigation of the electronic, magnetic, and chemical properties of one-dimensional and quasi-one-dimensional metal structures

Frenkel and charge transfer excitons in C60

We have studied the low energy electronic excitations of C60 using momentum dependent electron energy-loss spectroscopy in transmission. The momentum dependent intensity of the gap excitation allows the first direct experimental determination of the energy of the 1Hg excitation and thus also of the total width of the multiplet resulting from the gap transition. In addition, we could elucidate the nature of the following excitations - as either Frenkel or charge transfer excitons.Comment: RevTEX, 3 Figures, to appear in Phys. Rev.

Gold chain formation via local lifting of surface reconstruction by hot electron injection on H_2(D_2)/Au(111)

The hexagonal close packed surface of gold shows a 22 x root 3 "herringbone" surface reconstruction which makes it unique among the (111) surfaces of all metals. This long-range energetically favored dislocation pattern appears in response to the strong tensile stress that would be present on the unreconstructed surface. Adsorption of molecular and atomic species can be used to tune this surface stress and lift the herringbone reconstruction. Here we show that herringbone reconstruction can be controllably lifted in ultrahigh vacuum at cryogenic temperatures by precise hot electron injection in the presence of hydrogen molecules. We use the sharp tip of a scanning tunneling microscope (STM) for charge carrier injection and characterization of the resulting chain nanostructures. By comparing STM images, rotational spectromicroscopy and ab initio calculations, we show that formation of gold atomic chains is associated with release of gold atoms from the surface, lifting of the reconstruction, dissociation of H_2 molecules, and formation of surface hydrides. Gold hydrides grow in a zipper-like mechanism forming chains along the [1 (1) over bar0] directions of the Au(111) surface and can be manipulated by further electron injection. Finally, we demonstrate that Au(111) terraces can be transformed with nearly perfect terrace selectivity over distances of hundreds of nanometers