cTMS has been particularly useful from a basic neuroscience viewpoint in justifying the assertion that different pulse directions activate different sets of neurones in the cortex. Thus, cTMS can provide a range of stimulus pulse durations that can be used, in conjunction with the recruitment curves, to estimate the strength-duration properties of the stimulated neurones. Because their S-D time constants differ this allows us to conclude that different neurones are activated by different pulse directions. We can also use the same method to test whether the same is true of the inhibitory neurones that are activated by low intensity conditioning pulses in SICI. The ability of cTMS to provide rapid delivery of unidirectional pulse allows us to investigate how unidirectional rTMS differs from the conventional biphasic rTMS. A large number of differences emerge, many of which are likely to be due to the fact that the different directions of stimulation activate different neural elements in the brain. This can have important practical implications for the behavioural after-effects that are seen after rTMS. If the same rules apply outside of motor cortex, then there will be clear implications for many therapeutic applications.