Understanding how aging affects our cognitive abilities, particularly in relation to auditory processing and memory, is essential for improving quality of life as we age. The latest research into how our brains process musical sequences offers intriguing insights into these changes. In our two recently published studies, focusing on auditory memory, predictive coding, and the impact of aging, we reveal both the resilience and limitations of our cognitive abilities and their neural substrate over the lifespan.

1. The brain spatiotemporal dynamics of auditory sequence recognition

 The first study employed magnetoencephalography (MEG) and magnetic resonance imaging (MRI) to explore how the brain processes and predicts musical sequences. Participants, mostly younger than 30 years old, listened to sequences of five musical notes and identified whether the sequences were familiar or altered versions of previously memorised music.

The study revealed the involvement of a hierarchical network of brain regions, including the auditory cortices, hippocampus, and cingulate gyri. This hierarchical structure remained consistent throughout the sequence, except for the final tone, where the cingulate gyrus, which plays a crucial role in decision-making and evaluation, occupied the highest position in the hierarchy. Although the architecture involved in recognizing both memorized and varied sequences was largely unchanged, the temporal dynamics, signal strength, and polarity differed significantly. The findings suggest that when the upcoming sound aligned with the brain's predicted sound based on stored memory, the auditory cortex, followed by the hippocampus and anterior/medial cingulate gyri, showed positive responses. However, when the upcoming sound deviated from the brain's prediction, a pathway of faster, primarily negative responses appeared within the same brain network.

2. The Effects of Aging on Auditory Recognition

The second study focused on age-related changes in the brain's ability to recognise and predict musical sequences. It compared 39 older adults (over 60 years) with 37 young adults (aged 18-25 years), examining their neural responses during a memory task where they listened to melodies and categorised them as previously memorised or varied. We uncovered age-related changes in the neurophysiology of musical sequence recognition. While older adults could recognise memorised sequences as effectively as younger adults, their brain's functional organisation was significantly reshaped. Older adults exhibited increased early activity in sensory regions such as the left auditory cortex and decreased activity in the medial temporal lobe, suggesting compensatory mechanisms. However, the prediction error in the medial temporal lobe for varied melodies showed a strong reduction with no compensatory mechanisms, leading to reduced performance. This suggests that the neurophysiology of memory and prediction for sequences provides insights into healthy aging beyond behavioural performance

3. Integrating the findings: Implications for understanding auditory processing and memory for temporal sequences across the lifespan

The studies collectively offer a nuanced understanding of the neurophysiology of long-term memory recognition and predictions for music and on the impact of healthy aging on its dynamics. For younger adults, effective recognition and prediction of musical sequences rely on the seamless integration of sensory and higher-order brain regions. This hierarchical processing facilitates robust predictive coding and accurate response to variations in musical stimuli.

In contrast, the findings from the second study reveal a shift in older adults' neural activity patterns. These individuals display increased reliance on early sensory processing, such as heightened activity in the auditory cortex shortly after each note, while showing reduced engagement in higher-order regions, including the hippocampus and prefrontal cortices. This shift suggests a compensatory mechanism where the brain adapts to aging-related declines by enhancing early sensory processing at the expense of higher-order predictive functions.

Behavioural outcomes from both studies complement these neural findings. Younger adults excel in recognizing and predicting both familiar and novel sequences, underlining their efficient integration of sensory and higher-order processing. Older adults, while proficient at recognizing familiar sequences, exhibit notable difficulties with novel sequences, mirroring the observed neural changes. These behavioural patterns highlight the broader impact of aging on cognitive processing, emphasizing the shift from predictive coding and integration in younger adults to compensatory sensory processing in older adults.

4. Practical implications and future directions

Understanding these age-related changes in auditory processing holds potential clinical implications. Notably, the partial discrepancy observed between age-related changes in brain responses and behavioral performance underscores the ability of our methodology to detect more subtle changes in healthy aging, beyond those visible at the behavioral level.

The next step should involve applying our paradigm to patients with dementia. This will allow us to identify the neurophysiological markers that distinguish healthy aging from dementia. Following this, future longitudinal studies can be implemented to uncover potential biomarkers for healthy aging and enable early detection of significant changes in brain function.

Bonetti, L., Fernández-Rubio, G., Carlomagno, F., Dietz, M., Pantazis, D., Vuust, P., & Kringelbach, M. L. (2024). Spatiotemporal brain hierarchies of auditory memory recognition and predictive coding. Nature Communications, 15(1), 4313.

https://doi.org/10.1038/s41467-024-48302-4

Bonetti, L., Fernández-Rubio, G., Lumaca, M., Carlomagno, F., Risgaard Olsen, E., Criscuolo, A., ... & Kringelbach, M. L. (2024). Age-related neural changes underlying long-term recognition of musical sequences. Communications Biology, 7(1), 1036.

https://doi.org/10.1038/s42003-024-06587-7