Normal aging is usually accompanied by several structural and functional physiological changes of the brain, which are closely related to alterations of cognitive functions (e.g., visual short-term memory). As the average age of the population increases, it has become crucial to identify cognitive-behavioural interventions to maintain a healthy level of cognitive performance. Among a variety of approaches, the targeting of specific intrinsic alertness mechanisms has shown a solid rationale and beneficial effects in both healthy and pathological ageing. In a similar vein, the use of non-invasive transcranial electrical stimulation (tES) represents another promising approach to induce an alerting state that can produce advantages in the information processing in the brain and therefore behaviour. Here, we investigated whether time-locked bursts of tES (i.e., transcranial random noise stimulation) were effective in inducing behavioural and physiological changes, consistently with an alertness increase, in both young and older healthy adults. Namely, we expected to find a beneficial alerting effect on visual short-term memory performance as a function of stimulus perceptual salience and tES. The initial results showed that the performance of younger adults was not affected by tES, while older adults scored lower correct responses for high-salience stimuli during real tES with respect to sham stimulation. However, after including a baseline measure of subjective level of alertness in the analyses, a tES-induced memory improvement did emerge in the less alerted younger adults, while only the more alerted older adults were subject to the worsening effect by tES. We discuss these results in consideration of the evidence on critical age-related differences as well as the interaction between neurostimulation and baseline alerting mechanisms.

正常衰老通常伴随着大脑的一些结构和功能生理变化，这些变化与认知功能（例如视觉短期记忆）的改变密切相关。随着人口平均年龄的增加，确定认知行为干预以保持健康的认知表现水平变得至关重要。在各种方法中，针对特定的内在警觉机制已在健康和病理性衰老中显示出坚实的理论基础和有益效果。同样，非侵入性经颅电刺激 (tES) 的使用代表了另一种诱导警觉状态的有前途的方法，这种方法可以在大脑中的信息处理和行为方面产生优势。这里，我们调查了时间锁定的 tES 爆发（即经颅随机噪声刺激）是否能有效诱导年轻和年长健康成年人的行为和生理变化，同时提高警觉性。也就是说，我们希望找到对视觉短期记忆性能的有益警报效果，作为刺激感知显着性和 tES 的函数。最初的结果表明，年轻人的表现不受 tES 的影响，而老年人在真实 tES 期间对假刺激的高显着性刺激的正确反应得分较低。然而，在分析中包括主观警觉水平的基线测量后，tES 诱导的记忆改善确实出现在警觉较少的年轻人中，而只有更警觉的老年人才会受到 tES 的恶化影响。我们在考虑与年龄相关的关键差异的证据以及神经刺激和基线警报机制之间的相互作用的情况下讨论这些结果。