Recent findings suggest that brain-stimulating activities may have beneficial effects on both Mild Cognitive Impairment (MCI) and Alzheimer’s Disease (AD). However, whether cognitive interventions merely enhance cognitive reserve or truly attenuate, or even reverse, the disease’s pathophysiology is still controversial. The aim of the present article is to discuss the potential for brain-stimulating activities, including cognitive stimulation (CS), cognitive rehabilitation (CR), and cognitive training (CT), to be symptomatic or disease-modifying interventions in the context of cognitive decline. While emerging evidence indicates that CT can enhance synaptic plasticity, suggesting a potential role in augmenting cognitive reserve, its impact on AD pathology remains uncertain. Small-scale studies suggest that CT and CS may slow down neurodegeneration in MCI patients and that multidomain interventions combining physical activity with CT may benefit Aβ pathology. However, the considerable heterogeneity across studies limits the comparability of findings. It underscores the necessity for a more standardized approach to cognitive interventions in future guidelines for preventing and managing cognitive decline.