## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Independent Variable**} & \multicolumn{2}{c}{**Model 1**} & \multicolumn{2}{c}{**Model 2**} & \multicolumn{2}{c}{**Model 3**} \\ \cline{2-7}  & \(\beta\) **(95\% CD)** & \(p\) & \(\beta\) **(95\% CD)** & \(p\) & \(\beta\) **(95\% CD)** & \(p\) \\ \hline Right Caudate & 0.399 (0.147; 0.650) & 0.002 & 0.362 (0.128; 0.595) & 0.003 & 0.315 (0.048; 0.583) & 0.022 \\ Right Thalamus & \(-0.156\) (\(-0.449;\) 0.137) & 0.290 & \(-0.075\) (\(-0.352;\) 0.202) & 0.588 & \(-0.045\) (\(-0.317;\) 0.227) & 0.740 \\ Bilateral Calcarine cortex & \(-0.421\) (\(-0.672;\) 0.171) & 0.001 & \(-0.397\) (\(-0.627;\) 0.167) & 0.001 & \(-0.354\) (\(-0.598;\) \(-0.109\)) & 0.005 \\ Left Percent gyrus & 0.240 (\(-0.043;\) 0.523) & 0.095 & \(0.232\) (\(-0.028;\) 0.492) & 0.079 & 0.216 (\(-0.038;\) 0.470) & 0.094 \\ Left Caudate & 0.301 (0.039; 0.564) & 0.025 & 0.260 (0.015; 0.505) & 0.038 & 0.187 (\(-0.084;\) 0.457) & 0.172 \\ Right Orbitofrontal cortex & \(-0.089\) (\(-0.383;\) 0.204) & 0.544 & \(-0.064\) (\(-0.335;\) 0.207) & 0.638 & \(-0.086\) (\(-0.351;\) 0.178) & 0.517 \\ Left C cingulate gyrus & 0.321 (\(-0.009;\) 0.650) & 0.056 & 0.282 (\(-0.023;\) 0.588) & 0.069 & 0.161 (\(-0.204;\) 0.526) & 0.380 \\ Right Sub-gyral of the temporal lobe & 0.399 (0.094; 0.704) & 0.011 & 0.261 (\(-0.050;\) 0.571) & 0.098 & 0.142 (\(-0.210;\) 0.495) & 0.421 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Association between PSQI score and mean gray matter volume in CSVD patients. GMV of the caudate was associated with sleep disturbance in healthy participants [30; 31]. Diffusion tensor imaging (DTI) studies have revealed that patients with primary insomnia show alterations in topological properties of the caudate and reduced caudal connectivity with frontal regions [32; 33; 34]. A resting-state functional MRI study found that patients with insomnia showed increased resting-state functional connectivity between the left nucleus accumbens and bilateral caudate [35]. In the present study, we found that increased caudate nucleus volume among CSVD patients with poor sleep quality may suggest the presence of neuroplastic compensation that prevents disease progression. Further investigations using a longitudinal design are necessary to determine whether the compensatory mechanisms eventually give way to decompensation during the disease progression. Additionally, we also found that GMV of the bilateral calcarine cortex was decreased in the CSVD-PS group compared to the CSVD-GS group. Further analysis revealed a negative correlation between the GMV of the bilateral calcarine cortex and PSQI score among CSVD patients. The calcarine cortex is also known as the primary visual cortex, which is located near the calcarine fissure of the occipital lobe and is involved in processing visual information [36]. Insomnia is considered to be a state of hyperarousal [37]. Structural and functional alterations in sensory brain regions (including the area of the visual cortex) of patients with insomnia have been previously reported using MRI [38]. [PERSON] et al. suggested that the decreased functional connectivity of the left suprachiasmatic nuclei with the right lingual gyrus and left calcarine sulcus was correlated with early-wakening symptoms in patients with major depressive disorder [39]. Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain and plays an important role in sleep regulation [40]. Previous studies have reported that reduced GABA in the occipital cortex is associated with hyperarousal in insomnia patients [40; 41]. Based on previous findings, we propose that damage to brain regions related to visual processing may be a potential structural basis for the comorbidity of CSVD and sleep disturbance. In the current study, GMV of the sub-gyral temporal lobe was associated with sleep disturbance severity, but the association disappeared after controlling for depression. Among older adult populations, sleep disturbance and depression are highly comorbid [42].