The role of the right temporal lobe in neural network mechanisms during working memory encoding

Background Visual working memory (vWM) impairment is common in patients with temporal lobe epilepsy (TLE) and is more severe in those with right TLE (RTLE), suggesting the significant role of right temporal lobe in WM processes. Methods We recruited patients with left TLE (LTLE group, n = 20), RTLE (RTLE group, n = 20) and 35 healthy controls (Control), and examined their vWM performance while simultaneously recording task-based EEG. The alterations in the neural oscillations and neural network were analyzed during the WM encoding phase. In addition, we examined the relationship between the neural oscillations and WM performance, as well as the relationship between the neural network and WM performance, to further explore the role of the right temporal lobe in WM encoding. Results Remarkably lower accuracy (both p < 0.001) and significantly longer response times (LTLE vs. Control: p = 0.026; RTLE vs. Control: p < 0.001) were found in both LTLE and RTLE groups compared with controls. The RTLE group experienced notably delayed response time in comparison to the LTLE group ( p = 0.026). In comparison to the LTLE group, the RTLE group displayed reduced theta power spectral density for the frontal ( p = 0.024) and occipital ( p = 0.011) regions, along with the Fz channel ( p = 0.047). DTF F_outflow and DTF Fz_outflow values in the RTLE group displayed reduction relative to the LTLE group (DTF F_outflow : p = 0.026; DTF Fz_outflow : p = 0.037). The LTLE group showed weakened information flow from Fz to P3 (IF Fz → P3 , ANOVA, F = 3.45, p = 0.037; LSD, LTLE vs. Control: p = 0.013), whereas the RTLE group exhibited weakened information flow from Fz to P4 (IF Fz → P4 ; ANOVA, F = 3.78, p = 0.028; LSD, RTLE vs. Control: p = 0.029), Fz to T4 (IF Fz → T4 ; ANOVA, F = 4.67, p = 0.012; LSD, RTLE vs. Control: p = 0.009), and Fz to TP8 (IF Fz → TP8 ; ANOVA, F = 3.11, p = 0.050 ; LSD, RTLE vs. Control: p = 0.017), which were positively associated with accuracy and inversely associated with response time. Conclusion Abnormal information transfer from the dorsomedial prefrontal cortex to the superior parietal lobe during the encoding phase may causes WM deficits; damage to information transfer from the dorsomedial prefrontal cortex to the right middle temporal and right inferior temporal gyri exacerbates WM impairments.