Figure 1.

Conceptual illustration of temporal summation for focal and deep TMS. (A) Three distinct TMS coils, each generating its electric field within the brain, are activated in sequence by three separate stimulators at subthreshold levels. When the intervals between consecutive pulses delivered by two separate coils are adequately brief, areas with the highest electric field overlap experience maximal temporal summation effects, resulting in a suprathreshold response. (B) An experiment designed to prove the concept of temporal summation effect in TMS: a train of pulses is delivered to one single coil at subthreshold intensity and high frequency. A suprathreshold response caused by a subthreshold pulse train is the result of temporal summation.