Though old age has long been associated with structural changes within certain regions of the brain, a new study indicates that even when this does not occur, older adults tend to use different types of brainwaves to their sprightlier counterparts. As such, the study authors suggest that changes to the ways in which neurons fire may provide a particularly reliable marker of age-related brain functioning.

Brainwaves are produced by rhythmic electric impulses being sent between neurons, which tend to fire at different speeds depending on the type of task the brain is performing. For instance, theta waves are relatively slow, with a speed of between 3 and 8 Hertz, and are associated with learning and memory.

Researchers devised an experiment in which participants were required to remember the position of items on a visual display, before being tested on their ability to recall the spatial relationships between these objects – a task known as relational binding. Meanwhile, the study authors recorded their brainwaves using a process called magnetoencephalography, paying particular attention to increases in theta power within the hippocampus – a brain region associated with memory formation.

Participants were split into two groups, with median ages of 24.8 and 65.9 years respectively. Crucially, the researchers made sure to select older individuals who did not display lower hippocampal volumes than those in the younger group, and used functional magnetic resonance imaging (fMRI) to confirm this.

Presenting their findings in the journal Neurobiology of Learning and Memory, the study authors report an increase in theta power within the hippocampus of younger adults while performing the task, adding that success rates within this group were proportional to these theta increases.

^{Older participants elicited more alpha power, rather than theta power, when performing the task. Nerthuz/Shutterstock}

However, older adults were found to elicit alpha rather than theta brainwaves. These are faster waves, with a speed of 8 to 12 Hertz, and are often associated with fixing and maintaining attention on a particular element. As such, the researchers propose that members of this group may not have been engaging in relational binding, but were instead dedicating a greater amount of energy to filtering out distractions.

Furthermore, these alpha waves were found to be widespread throughout the brain, rather than concentrated within the hippocampus. Consequently, the researchers suggest that hippocampal recruitment of theta waves during relational binding may be disrupted in older people, indicating a decreased ability to selectively recruit neurons for the performance of certain cognitive tasks.

However, in spite of these findings, those in the older group performed no worse than those in the younger group when tested on their ability to remember the spatial positioning of the items on the screen. As such, the study authors concede that the differences in brainwaves between the two groups may actually reflect a shift towards an alternative cognitive strategy that doesn’t involve relational binding in older adults.

Either way, the results appear to show with significant clarity that the brains of older and younger participants operate on highly contrasting wavelengths.