Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy in adults . Up to 50% of patients with epilepsy are associated with cognitive impairment such as memory, executive, and learning , which severely impacts the quality of life. However,the principles and mechanisms of cognition are still not completely understood.
Resting-state functional magnetic resonance imaging (rs-fMRI) has rapidly become one of the most effective research methods to study the pathogenesis of neurological diseases since it is not affected by cognitive impairment and patient cooperation and does not require participants to perform a task. Also, it is often used for the analysis of the spontaneous fluctuations of brain-stimulating activities in resting-state networks (RSNs) .Further, the rs-fMRI provides sensitive biological markings for early diagnosis of nervous system diseases as well as a better understanding of the pathological process of diseases. Previous researches proved that cognitive impairment is closely related to brain network abnormalities in TLE .
Many researchers have divided the RSNs into multiple sub-networks by various methods.Effects on cognitive processing were found in TLE along with the cognitive impairment Furthermore in far-reaching cerebral networks, including the default mode network (DMN),executive control network (ECN), and language networks. Some studies reported increased amplitude of low-frequency fluctuation activation (ALFF)within the cognitive function in the brain areas in CI-TLE patients. In contrast, ALFF increased in the brain area of the ECN and DMN, particularly in the middle temporal gyrus༌ anterior cingulate gyrus༌ inferior parietal lobe, middle frontal gyrus ༌ and superior frontal gyrus. It indicates that changes in these brain activations compensate for cognitive impairment . Also, it was shown that decreased FC between DMN and ECN can be an important characteristic of RSN in intractable unilateral TLE than healthy controls (HCs༉. Spontaneously increased fluctuations in the hippocampal functional MRI signals in cognitively impaired individuals decreased in static hippocampal FC. These alterations result in decreased hippocampal connectivity to bilateral prefrontal and parietal regions in TLE, which may be related to behavior and cognitive impairments.Some studies showed that the primary visual cortex mainly includes the talus sulcus, cuneus, and lingual gyrus area. The secondary visual cortex mainly consists of the superior occipital gyrus, middle occipital gyrus, inferior occipital gyrus, and adjacent temporoparietal regions .
The visual cortex was known to be responsible for visual information processing related tasks. However, in recent studies, it was found that the visual cortex participates in the completion of the implementation and cognitive function in addition to the visual processing process, the visual space cognitive function. There are two distinct attention networks (AN) involved with multimodal processing in the human brain, including the basic structure of the dorsal attention network(DAN) and ventral attention network(VAN). DAN supports ‘top-down’ goal-directed focus, while VAN supports ‘bottom-up’ reorienting to unexpected yet contextually relevant external and internal stimuli . Each is functionally connected with visual networks. The functional connectivity (FC) within the DAN is associated with selective attention or focus and performance on-task. The VAN serves as a gatekeeper to determine if unexpected/distracting stimuli are consistent with task goals but are inhibited by a high working memory load . Limited studies assessed the ANs and VIS networks in patients with CI-TLE.
Abnormal functional connectivity between the attention and VIS networks was related to cognitive dysfunction . Also, many methods were explored to process resting-state data: FC, local consistency, low-frequency amplitude, and independent components analysis(ICA). Among them, the ICA is a typical rs-fMRI analytic method to determine the functional networks , which could reflect the FC of the brain regions. In line with the previous ICA research, evidence of the default mode network(DMN), DAN, visual -auditory, motor -sensory regions, and the self-reference system were found . The FC was investigated to define the interactions between the active brain regions and functional networks using ICA while not determining causal interactions . However,effective connectivity (EC) allows for discussing the relationship between the brain regions of difference .
Granger causality analysis (GCA), requiring no prior knowledge, has been typically used to measure EC and display causal influence flow of information among brain regions . The GCA of the EC has been widely applied in nervous system diseases. For instance, Mengshi Dong et al.  adopted GCA to testify the inhibitory influence disrupted from the left middle frontal gyrus to the right amygdala in generalized anxiety disorder. Previous studies based on GCA indicated that Alzheimer’s disease causes less efficient information transmission . However, in the study, the GCA was not used to study the information flow based on rs-fMRI in CI-TLE patients.
Our study speculated that the EC between the VIS network and AN is interrupted in CI-TLE patients. In order to further understand the patient’s brain network disorders, we analyzed FC and EC alteration between different regions of interest (ROIs) of the resting-state VIS network, VAN and DAN. Also, the GCA method was used to explore possible causal relationships across brain networks. We also investigated the relationship between EC in the VIS network, DAN, VAN, and Montreal cognitive assessment(CoMA) to establish whether cognitive performance variations are related to effective neural network connectivity. The results can provide new insight into the neuropathophysiological mechanisms of visual and attention network dysfunction in CI-TLE patients.