Older adults with aging brains have more difficulty learning and making decisions. Healthy aging is associated with loss of brain cells and reduces cognitive function. Neuroscientists have found that people can rewire the connections in their brains to compensate for cognitive decline associated with aging. During this process, known as compensatory scaffolding, people’s brains connect new regions, strengthen existing bonds between regions, and even create new brain cells. However, researchers don’t understand how these new connections work and interact, or what their limits are.
Leonardo Bonetti and colleagues have previously shown that young people rely mostly on the right half of their brains to process and understand auditory information like music. As a follow-up, Bonetti’s research team hypothesized that healthy older adults would have more compensatory scaffolding and less single-sided activity in regions of their brains involved in memory and task handling during music-based tasks. They explained that previous researchers showed these areas of the brain decline faster than others.
To test their hypothesis, Bonetti and colleagues explored whether age affected how people’s brains underwent compensatory scaffolding while they processed music. The researchers recruited 37 volunteers aged 18 to 25 years old and 39 volunteers greater than 60 years old, and created “maps” of each person’s brain activity while they listened to music. To create these maps, they imaged the participants’ brains using 2 devices: one that records magnetic fields in the brain, known as a magnetoencephalograph, and one that combines these magnetic fields with radio waves to create a map, known as a magnetic resonance imager. The researchers focused on 8 regions of the brain known to be involved in processing sound and decision-making, including parts of the temporal lobe, frontal lobe, and hippocampus.
The researchers asked the participants to memorize a 10-second audio clip of Johann Sebastian Bach’s Prelude No. 2 in C minor. Then they took 27 sequences of 5 notes from the audio clip and changed the notes after the first or third note. They called these new sequences NT1 and NT3, meaning they changed notes after Tone 1 or Tone 3, respectively. After the researchers modified the tunes, they had 27 original note sequences and 54 modified note sequences.
Next, they asked the participants to listen to these sequences and determine which were the original versions versus the modified versions, NT1 or NT3. While the patients listened, the researchers imaged their brain activity in the regions of interest and noted any differences between individuals and between age groups.
They found the older group had less brain activity than the younger group while listening to the musical sequences in all the regions they tested except in their left auditory cortexes. The older participants’ brains were more active in this region when recognizing the original tune and NT1 starting notes. The researchers proposed that reduced activity in memory regions like the hippocampus and temporal lobe impaired the older group’s ability to correctly identify modified note patterns. However, the increased left auditory cortex activity showed that healthy aging brains can restructure to maintain function.
In addition, they found the younger group’s brains were more active in regions associated with memory and detecting change, like the hippocampus, and in regions associated with working memory, like the frontal lobe. They suggested more activity in these regions allowed the younger group to detect the modified tunes better than the older group.
Finally, they asked the participants to complete a survey reporting how many years of education and formal musical training they had. They also completed a series of tasks assessing their cognitive skills like comprehension, problem-solving, reasoning, learning, and working memory. Previous researchers have shown that strong working memory can protect against mild cognitive impairment and dementia. They found that participants with good working memories were able to recognize modified tune sequences more consistently than their counterparts in both age groups.
The researchers confirmed that parts of people’s brains associated with memory and data processing, like the hippocampus and frontal lobe, lose function as we age. Their results also provide evidence that healthy aging reorganizes our brains to alter functional decline. In particular, Bonetti’s study showed that regions of our brains that process sound, like the left auditory cortex, are brought on board to help distribute the workload. They explained that this result challenges earlier researchers’ theories that aging does not reorganize brain pathways and structures related to memory and executive functions like decision-making, planning, and mood control.
