The effects of transcranial alternating current stimulation (tACS) at individual alpha peak frequency (iAPF) on motor cortex excitability in young and elderly adults.

Fresnoza, Shane, Monica Christova, Theresa Feil, Eugen Gallasch, Christof Körner, Ulrike Zimmer, & Anja Ischebeck. 2018. The effects of transcranial alternating current stimulation (tACS) at individual alpha peak frequency (iAPF) on motor cortex excitability in young and elderly adults. Experimental Brain Research. 236: 2573-88.
 
Summary: In this study experimenters collected a variety of cortical excitability measures using a combination of TMS and tACS presented at individualized alpha frequencies compared to sham. The researchers compared participants in two age groups (18-28 & 56-67 years old) to determine if the alpha-tACS changed later in adulthood where alpha is shown to reduce in power and frequency. MEP amplitudes increased for both older and younger adults, but SICI was found to show differential patterns between the groups. SICI shifted to facilitation in the younger group 60 minutes after alpha-TACS, whereas the older group started out showing facilitation effects at SICI latencies, then shifting to the more traditionally seen inhibition at 60 minutes. These findings highlight the potential for using tACS in older populations to normalize cortical activity patterns that 
 
Pro:  

• Individualized, high amplitude stimulation.
• Characterized excitability across lifespan

 
Open Questions:  

• Are the mixed facilitation/inhibition effects during putative SICI related to changes in the underlying timing of inhibition in the cortex or to a net shift in the balance between cortical excitation and inhibition?
• Should we tailor tACS treatments and protocols to different age groups?

 
Contributed by: Christopher Walker, PhD