Temporal resolution
In cognitive neuroscience the chronometrics of information processing are central to many theories and experiments. For cognitive studies then, an understanding of the temporal resolution of TMS is at least as important as an account of its spatial selectivity. When a TMS pulse is delivered over an area of cortex, the effect is to simultaneously activate many neurons. At the point of maximal activation, the stimulated area will have its lowest signal-to-noise ratio with respect to the task it is trying to perform. However, as neurons recover, the signal will increase, and whether or not TMS continues to have an effect will depend on the level of signal required for the task. Note that the interaction between the TMS signal and the contribution of an area to a task makes it highly unlikely that the time at which TMS has its maximal effect will correspond with the peak times reported in event-related potential (ERP) or subtractive or magneto-encephalographic (MEG) experiments.
An effectively disruptive pulse will interfere with processes that contribute to the build up of the ERP/MEG signal, so if the signal represents a neural event that is essential to the task, the time of TMS interference will typically precede ERP peaks and is more likely to coincide with single unit data. In other words, where an ERP result reports a peak at, say 300 ms, this may reflect the contribution of more than one neural event with a group maximum at 300 ms. When TMS is applied over the areas that contribute to this signal, it may disrupt processing of the individual components that may be maximal before, at, or after the reported peak at 300 ms.
