Theta burst stimulation

It has proved possible in experimental animals to manipulate synaptic efficiency using direct electrical stimulation. The introduction of transcranial methods of non-invasively stimulating the human brain raised hopes that similar effects could be produced in humans, with the potential for eventual therapeutic application in disease states. However, human subjects often require lengthy conditioning with traditional repetitive transcranial magnetic stimulation (rTMS), and even then effects are often weak, variable and have only mild benefits in a therapeutic setting. To address some of these concerns, we developed novel rTMS paradigms, which can swiftly produce relatively strong and controllable long-term changes in the excitability of cortical circuits after only a few minutes of conditioning. They are based on theta burst stimulation (TBS) patterns of neuronal firing occurring in the hippocampus of animals and use low-intensity (80% of active motor threshold) stimulation to produce long-term depression-like and long-term potentiation-like effects on the motor system of conscious humans. These can be measured at an electrophysiological and behavioural level as effects that outlast the period of stimulation by over an hour. In particular, we have found that the pattern of delivery of TBS (continuous versus intermittent) is crucial in determining the direction of change in synaptic efficiency.