The Construction And Applications Of The Thalamocortical Pathway: DTI-Based Study

The thalamus works with other brain regions and plays a key role in sensorimotor and higher-order cognitive functions.Meanwhile,as the interaction with multiple neurotransmitter systems(such as dopamine,glutamate),the thalamic circuits also occupy a prominent position in the neurology and psychiatry disease such as epilepsy and schizophrenia.Therefore,studies of this circuit help us to understand the origin of human specific cognitive ability,as well as the pathological mechanism of the thalamocortical circuit involved in various diseases.Neurophysiological studies have shown that this loop is mainly rely on the white matter fibers of the thalamocortical radiations to transmit information.With the advancement of magnetic resonance imaging(MRI)-based brain imaging sequences and the development of data analysis methods,we can use non-invasive methods such as diffusion MRI(dMRI)to construct the thalamocortical pathway and investigate its connectivity pattern,and to explore its effects on cognition and disease.This study will investigate the thalamic cortex loop from the following aspects:First,we reviewed and implemented several classical methods for the construction of the thalamocortical circuit.Basically,the most typical method is thalamic parcellation based on connectivity with subsequent circuit construction.This also makes it possible to investigate the subdivision of the thalamocortical circuit and its effects on cognition processes and brain diseases.By reviewing the data-driven parcellation of the thalamus and the hypothesis-driven division of the thalamus,we conclude that seeking a rational approach to merging and categorizing the nuclei of the thalamus at the appropriate scale maybe a good choice to investigate the detail of thalamocortical circuit and its effects on pathological processes.Subsequently,we parcellated the somatosensory motor cortex,and examined the effects of the thalamocortical circuit for motion control,and the potential modulating on EEG signal of the spatial distribution pattern in the cerebral cortex of this circuit.Briefly,based on the individual's high-resolution anatomical images,we divided individual's somatosensory motor cortex into two parts,the sulci and gyrus.Then,using dMRIbased white matter tractography,the white matter pathway of the basal ganglia-thalamicsomatomotor cortex was constructed.By investigating the white matter connectivity of the above pathway in gyrus and sulci of cortex,a measurement named G-S-ratio was proposed.This indicator can reflect the spatial distribution pattern of this circuit on cerebral cortex.Combined with correlation analysis and support vector regression,the potential relationship between the white matter pathway of the human brain and the generation of EEG signals duration motor imagery is revealed,meanwhile the BCI performance was found to be successfully predicted by white matter information.This study also indicates the importance of subdividing the cortex during the investigation of the white matter circuit.At last,a pure data-driven and a hypothesis-driven approaches to construct the subcomponents of the thalamocortical circuit.Then specific changes of this circuit in two disease models(schizophrenia and general idiopathic epilepsy)were examined.Specifically,a data-driven method was adopted to combine the structural and functional connectivity to segment the thalamus into six sub-regions that are bilaterally symmetric,based on MRI data of schizophrenia patients and corresponding control groups.When each of the thalamus sub-regions was used as a seed,functional connectivity changes are detected in several sub-components of this circuit.Besides,it was also found that functional integration intra thalamus was affected by the disease.Most of the thalamic sub-regions that exhibit altered functional connections were located at the medial-dorsal nucleus and ventral nucleus of the thalamus.The result revealed that the altered functional connectivity of the thalamocortical circuit in patients may come from different nuclei in the thalamus.In addition,via the thalamus,the cerebellum and basal ganglia modulating the cortex,forming important parts of the thalamocortical projection circuit.However,in patients with idiopathic generalized seizure,the regulation role of cerebellum and basal ganglia on this circuit are not fully understood.Therefore,we obtained the projection maps of the cerebellum and basal ganglia inner the thalamus based on dMRI data.Correspondingly,the thalamocortical circuit is split into two parts,the BTC(basal ganglia thalamocortical circuit)and the CTC(cerebellar thalamocortical circuit)circuits.Alterations in the functional and structural connectivity of BTC and CTC were examined in patients with epilepsy comparing to the controls.The results of this study demonstrated a combined effect of the two circuits on sensory motor and cognitive systems in patients with epilepsy,providing new clues for understanding the role of the basal ganglia and cerebellum in the thalamocortical circuit,which may be helpful in comprehending the pathological mechanism and clinical manifestations of the patient.In summary,through this dissertation,we discussed the construction of the thalamocortical circuit by using MRI,especially the dMRI,and compared various connectivitybased thalamic parcellation methods,then subdivided the cortex and thalamus respectively.Through this subdividing,in thalamus,we located the subregions of thalamus which changes in epilepsy and schizophrenia patients,revealed the specific alteration between different thalamic subregions and cerebral cortex;in cerebral cortex,we investigated the individual spatial pattern of thalamocortical white matter connection,then measured the effects of this pattern on scalp EEG signal.The method of the dissertation provided new ideas for delicately inspecting the role the thalamocortical circuit on cognition and diseases;the results and conclusions of this dissertation supplied more information for understanding the origin of cognition functions and the pathological mechanism of brain diseases.