Entrainment of neural activity using transcranial magnetic stimulation.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Chanes et al. Transcranial magnetic stimulation (TMS) is one of the most valuable tools at the disposal of cognitive neuroscientists due to its ability to perturb brain function with high temporal precision. To date, TMS has primarily been applied to disturb normal processing nonspecifically, similar to a " virtual lesion. " Notwithstanding the creative studies that have allowed researchers to make important progress using this approach, the usefulness of TMS could be greatly increased by developing new applications to modulate specific features of neural processing. One particularly promising application of TMS relates to entrainment of brain activity at specific frequencies. It has been theorized that neuronal oscillation and synchronization is critical for communication between separate brain regions (Fries, 2005). In a seminal paper, Thut et al. (2011) demonstrated that rhythmic TMS at the alpha frequency (8 –14 Hz, i.e., one pulse every 70 –125 ms) could be used to " entrain " brain oscillations in the parietal cortex. Other studies have shown that such alpha-frequency rhythmic TMS affects be-used TMS to entrain neural oscillations at higher frequencies. The researchers applied four consecutive pulses separated by 34 ms (a stimulation rate of 30 Hz, or high beta frequency) or 20 ms (a stimulation rate of 50 Hz, gamma frequency). In addition, the authors used two non-frequency-specific conditions that featured a larger gap between the second and third pulses thus ensuring that no single frequency was preferentially entrained. The non-frequency-specific conditions matched the rhythmic TMS conditions for the number of pulses and the total stimulation duration but not for the rhythm of application. Chanes and colleagues (2013) stimulated the frontal eye field (FEF), a region involved in eye movement and spatial attention. To investigate the behavioral effects of rhythmic TMS, participants were asked to complete two tasks. In the first task, observers judged whether a briefly presented Gabor patch, a sinewave grating with a Gaussian contrast envelope, was tilted in a clockwise or counterclockwise direction (discrimination task). The Gabor patch could appear left or right of fixation or not appear at all. In the second task, participants were further asked …