Discussion
STM
This study presents the design and research of an innovative methodology based on the combined application of spTMS and endogenous hippocampal activity during the coding phase of a WM task. The present results show that the application of this new protocol significantly improves memorization capacity.The WM task, utilized as part of the combined protocol, was characterized without interactions (TMS or Sham) to define the average capacity to memorize items in a single session. The outcome score of the MEM group increased significantly in the POST30 time-block in comparison with the PRE time-block. Nevertheless, the MOT intervention had a significant potentiating effect that improved the ability to memorize and perform the WM task in LB subjects, and the HIP intervention had a significant potentiating effect on MB subjects.LB subjects showed greater improvement even without active stimulation compared to MB and HB subjects. Even so, LB subjects in the MOT group, with an improvement of 42%, performed the memorization task 1.66 times better than LB subjects in the SHAM group (25% of improvement) and 3 times better than LB subjects in the MEM group (14% of improvement). MB subjects of the HIP group (23%) improved their memorization capacity by 2.5 times compared to the SHAM group (9%) and 3.75 times compared to the MEM group (6%). In HB subjects, neither the HIP nor the MOT intervention induced changes in the memorization capacity of the subjects compared to the SHAM or MEM groups. Thus, we conclude that at baseline, HB subjects performed close to their maximum capacity, and a ceiling effect was likely to occur because neither training (SHAM and MEM) nor combined-stimuli facilitation (HIP and MOT) improved memorization in HB subjects.The idea that brain resources supporting Short-Term Memory (STM) or WM are limited is not new [In our study, memorization involved nine visuospatial items. In the MEM group at POST30, the mean retention capacity ranged between 3.04 items (a LB subject) and 7.84 items (a HB subject). The average retention capacity in all groups of HB subjects was 5.34 items at PRE and 5.78 items at POST30, while LB subjects in the MOT group memorized on average 3.23 items at PRE and 5 items at POST30, and MB subjects in the HIP group memorized on average 3.91 items at PRE and 5.15 items at POST30. Seven subjects memorized a mean of 7 or more items at POST30; six of these participants were HB subjects and one was an LB subject in the MOT group who started with a memorization capacity of 3.08 items. Based on these data, we characterized the intrasession memorization capacity of this WM task as 5±2 items.Given that differences between groups in HB subjects were not statistically significant and due to the limited capacity of WM neural function, we conclude that this combined-stimuli protocol promotes an improvement in those resources that are not fully potentiated in LB and MB subjects. Overall, we deduce that this combined protocol enhances the neuronal pathway responsible for memorization no more than the maximum functionality of the subjects’ neural capacity. However, further research is needed to demonstrate cortical plasticity induction by this combined-stimuli intervention.