Location and baseline score interaction: Physiology of memory
CARPENTER, SECONDARY, CORTEX
As previously mentioned, LB subjects benefited from the combined WM task with spTMS over M1, while MB subjects benefited from the combined WM task with spTMS over the hippocampus. This finding revealed that these two cortical areas are involved in numerical and visuospatial WM task performance. We hypothesize that the hierarchy of cognitive processes in WM determines the brain location where combined-stimuli intervention will be effective.Completing a WM masking-task requires encoding and retaining the associations between the presented items and correct matrix locations. Thus, we can infer that this task utilizes WM based on the coding, storage and manipulation processes involved [The motor cortex is associated with sequence order coding. Carpenter et al. observed activity in the motor cortex of monkeys during sequential association. They reported different profiles of cellular responses within the motor cortex that responded to specific temporal and spatial positions as well as the interaction of these two variables [To perform the presented WM task, individuals require at least two cognitive processes: first, coding items and their order, presumably relying on the motor cortex, and second, retaining the associated information between spatial locations, presumably relying on the hippocampus.We hypothesize that in LB participants, the neural pathway encoding the numbers and their order is mainly activated in M1 and is less efficient than in MB and HB subjects. Pairing TMS repeatedly with active neuronal cells in the M1 may induce plastic mechanisms, which would enhance M1 function to encode and process items. HIP intervention would not facilitate memorization because of lower spatial information retention and hippocampal activity.Conversely, the MB participants’ coding process may be functional, while the retention of spatial information is not significantly strengthened. In this case, HIP intervention would enhance the hippocampal neural ensembles in charge of retaining spatial information. Through the strengthening of synapses, the retention and manipulation of information capacity can be improved. Then, the MOT intervention would not be significantly effective because these subjects already encoded items and their order efficiently.However, we have to consider that the LB group is significantly different from the MEM group and, despite having an improvement compared to the SHAM and HIP groups, the difference is not statistically significant. The fact that there is no significant difference could suggest that there are other variables in these groups but not in the MEM group (such as the sound of the TMS) that could be affecting the results. Due to the significance of the baseline variable in the effect of combined stimulation, the sample that is divided into groups and subgroups is ultimately small and therefore, to clarify these secondary variabilities, this protocol should be tested in a larger sample in the future.Nevertheless, further research is needed to investigate the plastic changes that may involve WM task outcome changes found in this study.