Abstract
Associative memory is one of the first cognitive functions negatively affected by healthy and pathological aging processes. Non-invasive brain stimulation (NIBS) techniques are easily administrable tools to support memory. However, the optimal stimulation parameters inducing a reliable positive effect on older adult’s memory performance remain mostly unclear. In our randomized, double-blind, cross-over study, 28 healthy older adults (16 females; 71.18 + 6.42 years of age) received anodal transcranial direct (tDCS), alternating current in the theta range (tACS), and sham stimulation over the left ventrolateral prefrontal cortex (VLPFC) each once during encoding. We tested associative memory performance with cued recall and recognition tasks after a retention period and again on the following day. Overall, neither tDCS nor tACS showed effects on associative memory performance. Further analysis revealed a significant difference for performance on the cued recall task under tACS compared to sham when accounting for age. Our results suggest that tACS might be more effective to improve associative memory performance than tDCS in higher aged samples.
Highlights
The decline of episodic memory performance is one of the most prominent changes in cognitive function in aging (Grady, 2012)
Our key goal was to evaluate the efficacy of the Non-invasive brain stimulation (NIBS) techniques anodal transcranial direct current stimulation (tDCS) and theta transcranial alternating current stimulation (tACS) for associative memory enhancement in healthy elderly adults
We compared the fixed age effects between the stimulation conditions using conditional t-tests, revealing a significant difference between the age effect under tACS and the age effect under sham stimulation [β = 1.18, 95%-CI: (0.16, 2.2), t(48) = 2.17, p < 0.05, Figure 5], whereas there was no significant difference between tDCS and sham [β = 1.05, 95%-CI: (−0.02, 2.12), t(48) = 1.9, p = 0.07, Figure 5]
Summary
The decline of episodic memory performance is one of the most prominent changes in cognitive function in aging (Grady, 2012). According to the associative memory deficit hypothesis, this decline is specific to difficulties in connecting unrelated units into one cohesive episode (NavehBenjamin et al, 2003). Aging negatively affects this ability to form and retrieve links between different chunks of information given by items and their contexts, e.g., spatial location and color of an item. The association of names or occupations with faces is a common test of associative memory (Vannini et al, 2011). Using the association of occupations and faces creates a broader semantic context, that can be used as a cue for later retrieval (Duss et al, 2011)
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