| Paper authors: | Florinda Ferreri, Andrea Guerra, Luca Vollero, David Ponzo, Sara Maatta, Esa Mervaala, Giulio Iannello, Vincenzo Di Lazzaro |
| Year of paper publication: | 2017 |
| Post authors: | Alice Erchov, Lisa Ridgway, Fidel Vila-Rodriguez |
| Download the research article: | Ferreri et al. (2017) Age-related changes of cortical excitability and connectivity in healthy humans: non-invasive evaluation of sensorimotor network by means of TMS-EEG |
Introduction
It may be well-known that aging affects nearly every part of our lives – both good and bad. In particular, there have been a growing number of studies that look to see how aging impacts our brain, which is a field of research capable of driving our idea of what is “successful” aging, and how we might be able to support people’s health across the lifespan.
In general, the brain has been shown to be a greatly adaptive structure, constantly remodelling connections to preserve its function as we age. However, the motor system, in particular, appears to be especially vulnerable to age-related deficits: decreased physical ability and coordination are common in older age. Some studies have suggested that this is due to the brain, on the whole, becoming “less active” or responsive to the neurochemical and electrical signaling that neurons use to communicate. In the neuroscientific sense, this relative sensitivity is called “excitability” and we know relatively little about this phenomenon. Ferrari et al. (2017) aim to investigate this by comparing a group of healthy and older individuals using novel neurophysiological techniques combined with repetitive transcranial magnetic stimulation (rTMS).
Methods
The authors compared a group of 25 older individuals (between 59-81 years old) and 12 young adults (18-30 years old). To measure the brain’s excitability, the authors combined 2 methods simultaneously:
- Electroencephalography (EEG): a series of electrodes are placed on the scalp that measure the electrical activity of the brain over time
- rTMS: used to stimulate the primary motor cortex (the key region involved in executing movement) via a magnetic coil placed on the scalp
Participants received 80 single rTMS pulses, with the brain’s reactivity to them measured using EEG at the same time. The authors then compared the two groups based on the brain’s (1) overall excitability and (2) electrode-specific reactions to rTMS, at different time points.
Results
Hypoexcitability = less excitability
Hyperexcitability = more excitability
- Overall, the brains of older people were hypoexcitabile when compared to younger adults
- But, at some time points – older people had hyperexcitability in specific regions of the brain in response to rTMS, when compared to younger adults
- About ~30 milliseconds after rTMS older individuals had more activity in the frontal region of the brain. This area is usually associated with cognitive (thinking) ability, attention, and other “higher” brain functions
- This hyperexcitability was also shown in the premotor cortex, which is involved in planning and preparing movements
- Comparatively, at the same time, there was hypoexcitability in the primary motor cortex, which is involved in the actual execution of movement
- This was also found at the next time point, ~44 ms after rTMS
Discussion
The authors’ theory is that the effects of rTMS were “spread” from the primary motor cortex, where it was delivered, to more frontal and premotor cortices in older individuals. This may be possible through changes in underlying brain structures or connections. It is also possible that the premotor cortex began to compensate by becoming more active, when the primary motor cortex began declining in function with age.
Conclusion
This study adds to previous findings that, on average, the brain may be less excitable/active as we age. However, this appears to be specific to certain regions. Hypoexcitability was especially pronounced in the primary motor cortex – possibly related to worsening movement and coordination in old age. But the brain appears to be highly flexible and adaptive: there were other regions, primarily in the front of the brain, that were hyperexcitable in older individuals in response to rTMS – suggesting that these regions may be compensating for the primary motor cortex in some way.
This study adds to previous findings that, on average, the brain may be less excitable/active as we age. However, this appears to be specific to certain regions. Hypoexcitability was especially pronounced in the primary motor cortex – possibly related to worsening movement and coordination in old age. But the brain appears to be highly flexible and adaptive: there were other regions, primarily in the front of the brain, that were hyperexcitable in older individuals in response to rTMS – suggesting that these regions may be compensating for the primary motor cortex in some way.