ABSTRACT
Objective: Two subregions of the dorsolateral prefrontal cortex have been identified as effective repetitive transcranial magnetic stimulation (rTMS) targets for the "anxiosomatic" and "dysphoric" symptoms, respectively. We aimed to develop a convenient approach to locate these targets on the scalp. Materials and methods: In a discovery experiment, the two personalized targets were precisely identified on 24 subjects using a neuronavigation system. Then, a localized approach was developed based on individual scalp landmarks. This "landmark-based approach" was replicated and validated in an independent cohort (N = 25). Reliability of the approach was tested by calculating the correlation of both the inter-rater and intra-rater results. Validity was tested by comparing the mean distance between the personalized and landmark-based targets to the TMS spatial resolution (i.e., 5 mm). We further conducted a total of 24 sham rTMS sessions to estimate the misplacement between the coil center and target during a 10-min stimulation without neuronavigation. Results: The parameters of the "landmark-based approach" in the discovery experiment were replicated well in an independent cohort. Using discovery parameters, we successfully identified the symptom-specific targets in the independent cohort. Specifically, the mean distance between the personalized and landmark-based targets on the cortex was not significantly larger than 5 mm. However, the personalized and landmark-based targets distance exceeded 5 mm in more than 50% of subjects. During the 10-min sham rTMS session, the average coil misplacement was significantly larger than 5 mm. Conclusion: The "landmark-based approach" can conveniently and reliably locate the two symptom-specific targets at group level. However, the accuracy was highly varied at individual level and further improvement is needed.
ABSTRACT
Associative memory (AM) is an essential function of everyday life, but is often disrupted in many neurological diseases. Recent studies have found that repetitive transcranial magnetic stimulation (rTMS) can effectively enhance AM and have shown its potential in clinical applications. In this study, we aimed to reproduce the 5-day rTMS effect on AM in a Chinese version of a face-cued word recall task. In an open-label experiment, AM scores were significantly improved after active 20-Hz rTMS on individualized inferior parietal lobule (IPL) targets. To exclude the placebo effect, we performed a second experiment and added rTMS of the pre-supplementary motor area (preSMA) as an active control. In this within-subject crossover experiment, participants received active rTMS on IPL and preSMA targets, separated by at least 2 weeks. A Stroop task was included as a control test, which was more likely to be modulated by preSMA stimulations. We found that stimulations on IPL targets significantly improved AM, but this change did not significantly higher than that induced by preSMA stimulations. No significant change in Stroop measures were found in either IPL or preSMA condition. In summary, this study did not support that the 5 days of rTMS on individualized IPL targets could improve AM more than placebo rTMS. Further work is required to improve the rTMS paradigms to enhance the aftereffects in memory.
