BOLD fMRI response to direct stimulation (transcranial magnetic stimulation) of the motor cortex shows no decline with age

Previous studies using BOLD fMRI to examine age-related changes in cortical activation used tasks that relied on peripheral systems to activate the brain. They were unable to distinguish between alterations due to age-related changes in the periphery and actual changes in cortical physiology. Transcranial magnetic stimulation (TMS), which allows direct, non-invasive stimulation of cortical neurons, was interleaved with BOLD fMRI to study 6 young and 5 old subjects. Three different tasks were compared: direct stimulation by TMS, indirect active stimulation produced by a motor task, and indirect passive stimulation produced by hearing the TMS coil discharge. Direct neuronal stimulation by TMS produced similar fMRI signal increases in both groups, suggesting that cortical physiology itself may not necessarily decline with age.