Dissociable functional responses along the posterior-anterior gradient of the frontal and parietal cortices revealed by parametric working memory and training.

While the storage capacity is limited, accumulating studies have indicated that working memory (WM) can be improved by cognitive training. However, understanding how exactly the brain copes with limited WM capacity and how cognitive training optimizes the brain remains inconclusive. Given the hierarchical functional organization of WM, we hypothesized that the activation profiles along the posterior-anterior gradient of the frontal and parietal cortices characterize WM load and training effects. To test this hypothesis, we recruited 51 healthy volunteers and adopted a parametric WM paradigm and training method. In contrast to exclusively strengthening the activation of posterior areas, a broader range of activation concurrently occurred in the anterior areas to cope with increased memory load for all subjects at baseline. Moreover, there was an imbalance in the responses of the posterior and anterior areas to the same increment of 1 item at different load levels. Although a general decrease in activation after adaptive training, the changes in the posterior and anterior areas were distinct at different memory loads. Particularly, we found that the activation gradient between the posterior and anterior areas was significantly increased at load 4-back after adaptive training, and the changes were correlated with improvement in WM performance. Together, our results demonstrate a shift in the predominant role of posterior and anterior areas in the frontal and parietal cortices when approaching WM capacity limits. Additionally, the training-induced performance improvement likely benefits from the elevated neural efficiency reflected in the increased activation gradient between the posterior and anterior areas.

Consideraciones clínicas de los implantes en áreas posteriores / Clinical considerations of the implants in posterior areas

Resumen Las restauraciones soportadas por implantes proveen considerables ventajas cuando se comparan con la prótesis parcial removible, en cuanto al soporte, la estabilidad de la oclusión, la preservación ósea, la comodidad, el mejoramiento de la función y el menor costo biológico teniendo en cuenta que los procedimientos sobre la dentición remanente no tienen un carácter invasivo. Hasta el momento la evidencia científica no ha determinado con claridad el número, la longitud, el diámetro y la ubicación de los implantes para restaurar las áreas posteriores. Sin embargo, se han propuesto recomendaciones en algunos casos resultado de la experiencia clínica y el sentido común basadas en las prótesis convencionales. A pesar de la amplia variedad de alternativas protésicas en áreas posteriores existe una carencia de estudios basados en la evidencia para guiar al clínico en la mejor decisión.

Restorations supported by implants provide considerable advantages when compared with removable partial dentures, in terms of support, stability of occlusion, bone preservation, comfort, improved function and lower biological cost considering that the procedures on the remaining dentition do not have an invasive character. To date scientific evidence has not clearly established the number, length, diameter and location of implants in order to restore posterior areas. However, proposed recommendations in some cases result from clinical experience and common sense based on conventional prostheses. Despite the wide variety of prosthetic alternatives in the posterior areas there is a lack of evidence-based studies to guide the clinician in the best decision.