Neural changes in early visual processing after 6 months of mindfulness training in older adults

Age-related decline in attentional performance is a significant concern. Mindfulness training, which involves focused attention and metacognitive monitoring, has shown promise in improving attention. While short-term effects of mindfulness training on late-latency EEG event-related potentials (ERPs) have been reported, the long-term stability and impact on early stages of information processing remain unclear. This study aimed to investigate the long-term stability of mindfulness training effects on neural activation in older adults, focusing on both early and late stages of visual information processing, and comparing it to the effects of a computer-based attention training control group. The study's importance lies in its potential to reveal mechanisms through which mindfulness enhances cognitive function in aging, offering insights into interventions for age-related cognitive decline and neurodegenerative diseases. The researchers hypothesized that both mindfulness and computer training would improve attention and alter late-latency ERPs, and that mindfulness training would also lead to earlier ERP changes with prolonged practice.

Existing research suggests that mindfulness training enhances attentional performance by repeatedly activating neural circuitry involved in information processing and attentional control. Mindfulness cultivates sustained attention through metacognitive monitoring and control processes, resisting distractions. Studies have shown improvements in sustained attention, selective attention, and executive inhibitory control with increased activation in brain regions such as the anterior cingulate cortex and right dorsolateral prefrontal cortex following mindfulness interventions. EEG ERPs, sensitive temporal measures of information processing, are suitable for studying these effects, tracing visual processing through sensory encoding (50-80ms), early discrimination (100-200ms), and later cognitive processing (200-400ms). While some studies have reported changes in long-latency N2 and P3 components following mindfulness training, the long-term stability and impact on earlier stages are less understood. Cross-sectional studies of long-term practitioners have shown changes in both short and long-latency ERP components, suggesting that with prolonged practice, mindfulness may affect earlier stages of processing. However, longitudinal studies were needed to examine the training trajectory of these ERP changes. Age-related slowing of visual processing is linked to deterioration in white matter microstructure, particularly in the magnocellular pathway. Cognitive training interventions also improve attentional performance and modify long-latency ERPs in older adults, but it is unclear whether these changes share mechanisms with mindfulness.

This study employed a longitudinal, active-controlled, randomized controlled trial (RCT) with healthy older adults (N=120 initially, 81 completed all three timepoints). Participants were randomly assigned to either an 8-week mindfulness training (MT) program or a computer-based cognitive training (CT) control program. Both interventions involved weekly group sessions and daily home practice (20-45 min/day). The MT program used a standardized mindfulness technique focused on cultivating unbiased attention to present-moment experience, while the CT program involved game-based tasks designed to activate similar attentional processes. EEG was recorded at three time points: baseline (T1), immediately after the 8-week intervention (T2), and 6 months later (T3). Participants completed a breath-counting task (measuring mindfulness) and the Attentional Network Test (ANT) (measuring attention). High-density EEG data were analyzed using a non-parametric cluster-based permutation approach to assess spatiotemporal ERP dynamics in response to cue and target stimuli within the ANT. Statistical analyses included independent samples t-tests for baseline comparisons, mixed-model ANOVAs for behavioral data, and cluster-based permutation tests for ERP data. Brain-behavior correlations were conducted to examine relationships between ERP activity and reaction times. Ethical approval was obtained, and all procedures adhered to relevant guidelines.

No significant pre-intervention differences were found between the MT and CT groups. The CT group engaged in slightly more daily training than the MT group (approximately 2-3 minutes more per day on average across the intervention and 6-month follow-up periods). The MT group showed significant improvements in breath-counting accuracy from baseline to both post-intervention and 6-month follow-up, indicating improved mindfulness skills. Both groups showed improved attentional performance (reduced errors and increased stability of attentional deployment) on the ANT across timepoints. However, only the MT group exhibited significant reductions in errors from baseline to both post-intervention and 6-month follow-up. ERP analysis revealed no significant changes immediately after the 8-week intervention. However, at the 6-month follow-up, the MT group showed significant increases in ERP amplitude at early latencies (P1 and N1) associated with sensory encoding and perceptual processing of the cue stimulus. These effects were localized to left parieto-occipital and parietal-temporal regions. The CT group showed a significant increase in N1-P2 amplitude at later latencies in occipital and centroparietal regions. In the MT group, the target stimulus elicited increased P3 amplitude at 6-months follow up, reflecting enhanced neural activation during post-perceptual processing. Brain-behavior correlations in the MT group revealed significant associations between cue N1 amplitude and target RT, and between target P3 amplitude and RT, indicating that enhanced early perceptual processing was linked to faster response times. There was also a significant correlation between cue N1 and target P3 activity in the MT group.

The findings indicate that mindfulness training leads to enduring changes in the neural mechanisms underlying visual processing and attention. The significant ERP changes observed at the 6-month follow-up, particularly the increased activity in early sensory and perceptual processing, suggest that mindfulness training may enhance the efficiency of neural pathways involved in bottom-up visual processing. This might result from improved white matter microstructure integrity, a factor known to decline with age. The enhanced ability to mobilize top-down attentional processes during perceptual and post-perceptual processing is evident in the increased P3 amplitude. The observed correlation between early cue-related activity (N1) and later target-related activity (P3) suggests a functional link between these processes. In contrast, the CT group, while showing attentional improvements, only demonstrated ERP changes indicative of enhanced visual discrimination, highlighting the unique impact of mindfulness training on attentional processes. The absence of immediate effects in the MT group might be attributed to the design of the mindfulness intervention, which focused solely on core mindfulness practices, excluding ancillary components that might have contributed to more rapid changes.

This longitudinal study provides strong evidence for the long-term benefits of mindfulness training on neural processing in older adults. The enhanced early and late-latency ERP components, along with improvements in sustained attention, suggest that mindfulness training may help mitigate age-related cognitive decline by improving the efficiency of neural pathways involved in visual processing and attentional control. Future research could explore the mechanisms underlying these effects, including examining white matter microstructure changes and investigating the generalizability of these findings to other cognitive domains and clinical populations.

The study's relatively small sample size, particularly in the CT group after attrition, limits the statistical power and generalizability of the findings. The specific mindfulness training technique used may not be fully generalizable to all mindfulness practices. The absence of a no-training control group makes it difficult to completely rule out practice effects, although the use of RTCV as a robust measure of sustained attention, and evidence regarding the high test-retest reliability of ERPs, mitigate this concern. Future studies should address these limitations by incorporating larger samples and comparing various mindfulness training techniques against no-intervention control groups.