Transcranial Direct Current Stimulation Combined With Listening to Preferred Music Alters Cortical Speech Processing in Older Adults.

Emerging evidence suggests transcranial direct current stimulation (tDCS) can improve cognitive performance in older adults. Similarly, music listening may improve arousal and stimulate subsequent performance on memory-related tasks. We examined the synergistic effects of tDCS paired with music listening on auditory neurobehavioral measures to investigate causal evidence of short-term plasticity in speech processing among older adults. In a randomized sham-controlled crossover study, we measured how combined anodal tDCS over dorsolateral prefrontal cortex (DLPFC) paired with listening to autobiographically salient music alters neural speech processing in older adults compared to either music listening (sham stimulation) or tDCS alone. EEG assays included both frequency-following responses (FFRs) and auditory event-related potentials (ERPs) to trace neuromodulation-related changes at brainstem and cortical levels. Relative to music without tDCS (sham), we found tDCS alone (without music) modulates the early cortical neural encoding of speech in the time frame of ∼100-150 ms. Whereas tDCS by itself appeared to largely produce suppressive effects (i.e., reducing ERP amplitude), concurrent music with tDCS restored responses to those of the music+sham levels. However, the interpretation of this effect is somewhat ambiguous as this neural modulation could be attributable to a true effect of tDCS or presence/absence music. Still, the combined benefit of tDCS+music (above tDCS alone) was correlated with listeners' education level suggesting the benefit of neurostimulation paired with music might depend on listener demographics. tDCS changes in speech-FFRs were not observed with DLPFC stimulation. Improvements in working memory pre to post session were also associated with better speech-in-noise listening skills. Our findings provide new causal evidence that combined tDCS+music relative to tDCS-alone (i) modulates the early (100-150 ms) cortical encoding of speech and (ii) improves working memory, a cognitive skill which may indirectly bolster noise-degraded speech perception in older listeners.

Effects of transcranial direct current stimulation combined with listening to preferred music on memory in older adults.

Listening to autobiographically-salient music (i.e., music evoking personal memories from the past), and transcranial direct current stimulation (tDCS) have each been suggested to temporarily improve older adults' subsequent performance on memory tasks. Limited research has investigated the effects of combining both tDCS and music listening together on cognition. The present study examined whether anodal tDCS stimulation over the left dorsolateral prefrontal cortex (2 mA, 20 min) with concurrent listening to autobiographically-salient music amplified subsequent changes in working memory and recognition memory in older adults than either tDCS or music listening alone. In a randomized sham-controlled crossover study, 14 healthy older adults (64-81 years) participated in three neurostimulation conditions: tDCS with music listening (tDCS + Music), tDCS in silence (tDCS-only), or sham-tDCS with music listening (Sham + Music), each separated by at least a week. Working memory was assessed pre- and post-stimulation using a digit span task, and recognition memory was assessed post-stimulation using an auditory word recognition task (WRT) during which electroencephalography (EEG) was recorded. Performance on the backwards digit span showed improvement in tDCS + Music, but not in tDCS-only or Sham + Music conditions. Although no differences in behavioural performance were observed in the auditory WRT, changes in neural correlates underlying recognition memory were observed following tDCS + Music compared to Sham + Music. Findings suggest listening to autobiographically-salient music may amplify the effects of tDCS for working memory, and highlight the potential utility of neurostimulation combined with personalized music to improve cognitive performance in the aging population.

Breaking down unitization: Is the whole greater than the sum of its parts?

Memory impairments are often observed in aging. Specifically, older adults have difficulty binding together disparate elements (relational memory). We have recently shown that a cognitive strategy known as unitization can mitigate impaired relational learning in the transverse patterning task (TP) in both amnesia and healthy aging. This strategy allows items to be fused together through an interaction such that one item acts upon another. In the context of TP, unitization is comprised of three component processes: (1) fusion, (2) motion, and (3) semantic comprehension of action/consequence sequences. Here, we examine which of these components are sufficient to mitigate age-related impairments. Four groups of older adults were given either the full unitization strategy or one of the three component strategies. Each group of older adults showed impairments in memory for the relations among items under standard training instructions relative to a threshold that marks learning of a winner-take-all rule (elemental threshold). However, participants who were given either the full unitization strategy or the action/consequence-only strategy showed improved performance, which was maintained following the 1-hour delay. Therefore, semantically rich action/consequence interactions are sufficient to mitigate age-related relational memory impairments.

Human anterolateral entorhinal cortex volumes are associated with cognitive decline in aging prior to clinical diagnosis.

We investigated whether older adults without subjective memory complaints, but who present with cognitive decline in the laboratory, demonstrate atrophy in medial temporal lobe (MTL) subregions associated with Alzheimer's disease. Forty community-dwelling older adults were categorized based on Montreal Cognitive Assessment (MoCA) performance. Total gray/white matter, cerebrospinal fluid, and white matter hyperintensity load were quantified from whole-brain T1-weighted and fluid-attenuated inversion recovery magnetic resonance imaging scans, whereas hippocampal subfields and MTL cortical subregion volumes (CA1, dentate gyrus/CA2/3, subiculum, anterolateral and posteromedial entorhinal, perirhinal, and parahippocampal cortices) were quantified using high-resolution T2-weighted scans. Cognitive status was evaluated using standard neuropsychological assessments. No significant differences were found in the whole-brain measures. However, MTL volumetry revealed that anterolateral entorhinal cortex (alERC) volume-the same region in which Alzheimer's pathology originates-was strongly associated with MoCA performance. This is the first study to demonstrate that alERC volume is related to cognitive decline in undiagnosed community-dwelling older adults.