Mechanism Of Verbal Concreteness Effect: Based On Brain Imaging And Neuromodulation Techniques

Words,the basic units of language,are categorized in different ways from different perspectives.The common classification of words into nouns,verbs,adjectives,etc.known as word class/category,is based mainly on meaning and grammatical features including syntactic functions and morphological forms.Concrete and abstract words are distinguished according to lexical concepts associated with cognition.The semantic representation and processing of concrete and abstract words are one of the research hotspots in linguistics,psychology and cognitive neuroscience,and the difference between the two can,to certain extent,reveal the role of language in human advanced cognition,reflecting the nature of human cognition which is different from that of animals.The processing advantage of concrete words over abstract words is known as the concreteness effect.The dissertation of brain mechanisms of the concreteness effect may provide neurological evidence for exploring advanced complex cognition.Current studies on concreteness effect are based on the techniques of EEG(electroencephalography)and task-state functional magnetic resonance imaging(f MRI),but information on brain activation is limited,which cannot provide a full picture for the neural mechanisms of concreteness effect.This dissertation integrates multimodal brain imaging and neuromodulation techniques to explore the mechanisms of concreteness effect,using structural magnetic resonance imaging(s MRI),resting-state functional connectivity(rs FC),functional magnetic resonance imaging(f MRI)and non-invasive transcranial magnetic stimulation(TMS).The research work is composed of the following five sections:1.Testification of concreteness effect with lexical memory paradigm.The experimental paradigms used in most of the current studies on the concreteness effect are lexical decision and semantic judgment,and only a few studies have explored the concreteness effect from the perspective of memory.These three paradigms are different in terms of the depth of semantic processing and the way of memory retrieval.This dissertation explores the concreteness effect using memory paradigm.The results show that the accuracy and the sensitivity of the concrete words recognition are significantly higher than that of the abstract words.The reaction times of the concrete word recognition are significantly shorter than those of the abstract words.The results indicate a significant memory advantage for concrete words.It provides a reliable behavioral foundation for further investigation with brain imaging and neuromodulation techniques.2.Investigation of concreteness using s MRI.Correlation between gray matter volume and the concreteness effect is studied with whole brain VBM(voxel-based morphometry)analysis.The results show that the concreteness effect is negatively correlated with the gray matter volume in the left inferior frontal gyrus,the right middle temporal gyrus,the right anterior cingulate cortex,and the right supplementary motor area.No positive correlation was found between the size of the gray matter volume and the concreteness effect in any of the brain regions.The results show that the larger the gray matter volume of these brain regions which are semantic hubs or responsible for executive control,the smaller the concreteness effect.It is further demonstrated by internal cross-validation that the gray matter volume of these brain regions could successfully predict the concreteness effect in individuals.3.Investigation of the concreteness effect using rs FC.The regions of interest,the left inferior frontal gyrus,the right middle temporal gyrus,the right anterior cingulate cortex,and the right supplementary motor area derived from the VBM analysis are used as seeds for the correlation analysis of rs FC and concreteness effect.The results show that there is significant positive correlation between the concreteness effect and rs FC seeded in the left inferior frontal gyrus,the right middle temporal gyrus,and the right anterior cingulate cortex,and no correlation is found between concreteness effect and rs FC seeded in the right supplementary motor area.Voxels connected to the left inferior frontal gyrus are mainly located in the default brain network and the visual network.Voxels connected to the right middle temporal gyrus and the right anterior cingulate cortex are mainly located in the frontoparietal network and dorsal attention network.The stronger the resting-state functional connectivity of these three brain regions,the more pronounced the concreteness effect and the greater the difference between concrete and abstract word memory recognition.The results suggest that concrete word processing relies on a wider range of brain regions,whereas abstract word processing is more concentrated in the pivotal regions of language and executive control.Internal cross-validation demonstrates that resting-state functional connectivity of these three brain regions could successfully predict individual concreteness effect.4.Investigation of key brain regions for concreteness effect using f MRI.The f MRI scan in the task state is performed during the concrete and abstract word memory encoding phases to obtain the corresponding brain activation maps.Brain regions coactivated by the encoding of the concrete and abstract words are distributed in the temporal,occipital and frontal lobes.The activation contrast map(abstract > concrete)reveals that the bilateral precuneus and the left posterior cingulate cortex are significantly more activated during the memory encoding phase for abstract words than for concrete words.No brain regions are found to be more activated for concrete word encoding than for abstract word encoding.The results indicate that memory encoding of the abstract words is more regulated by the precuneus and posterior cingulate cortex,hubs for semantic processing and episodic memory.5.Testification of the critical role of the precuneus in abstract word memory processing using TMS.Based on the contrast maps task-state f MRI activation,real and sham TMS stimulations are performed over the left precuneus to confirm the causal relationship between the activity of the precuneus and the concreteness effect.In the sham stimulation condition,the reaction times and sensitivity of the concrete word recognition are significantly different from those of the abstract words.In the real stimulation condition,there is no difference in reaction times or sensitivity of recognition of concrete and abstract words.Real TMS causes significantly faster reaction times for abstract words recognition but has no effect on concrete words.The results suggest that the precuneus has a causal modulatory effect on abstract but not concrete word processing.In summary,this dissertation reveals the neural mechanisms of concrete and abstract word processing from perspectives of brain structure,resting-state functional connectivity,brain activation and neuromodulation.Evidence suggests that abstract word processing relies more on semantic hub regions and regions for executive control to accomplish complex merging operations consistent with higher order cognition,whereas processing of concrete words relies on the support of a broader network.The dissertation of the neural mechanisms of the concreteness effect helps shed light on the role of abstract linguistic operations in human higher cognition.