The effects of individualized theta burst stimulation on the excitability of the human motor system.
BACKGROUND
Theta burst stimulation (TBS) is a pattern of repetitive transcranial magnetic stimulation that has been demonstrated to facilitate or suppress human corticospinal excitability when applied intermittently (iTBS) or continuously (cTBS), respectively. While the fundamental pattern of TBS, consisting of bursts of 50 Hz stimulation repeated at a 5 Hz theta frequency, induces synaptic plasticity in animals and in vitro preparations, the relationship between TBS and underlying cortical firing patterns in the human cortex has not been elucidated.


OBJECTIVE
To compare the effects of 5 Hz iTBS and cTBS with individualized TBS paradigms on corticospinal excitability and intracortical inhibitory circuits.


METHODS
Participants received standard and individualized iTBS (iTBS 5; iTBS I) and cTBS (cTBS 5; cTBS I), and sham TBS, in a randomised design. For individualized paradigms, the 5 Hz theta component of the TBS pattern was replaced by the dominant cortical frequency (4-16 Hz; upper frequency restricted by technical limitations) for each individual.


RESULTS
We report that iTBS 5 and iTBS I both significantly facilitated motor evoked potential (MEP) amplitude to a similar extent. Unexpectedly, cTBS 5 and cTBS I failed to suppress MEP amplitude. None of the active TBS protocols had any significant effects on intracortical circuits when compared with sham TBS.


CONCLUSIONS
In summary, iTBS facilitated MEP amplitude, an effect that was not improved by individualizing the theta component of the TBS pattern, while cTBS, a reportedly inhibitory paradigm, produced no change, or facilitation of MEP amplitude in our hands.
The School of Physical Education, Sport and Exercise Sciences, University of Otago, New Zealand; The Brain Health Research Centre, University of Otago, New Zealand.
Philip W
PW
Brownjohn
The Brain Health Research Centre, University of Otago, New Zealand; Department of Anatomy, University of Otago, New Zealand.
John N J
JN
Reynolds
The Brain Health Research Centre, University of Otago, New Zealand; Department of Anatomy, University of Otago, New Zealand.
Natalie
N
Matheson
The School of Physical Education, Sport and Exercise Sciences, University of Otago, New Zealand; The Brain Health Research Centre, University of Otago, New Zealand.
Jonathan
J
Fox
The School of Physical Education, Sport and Exercise Sciences, University of Otago, New Zealand; The Brain Health Research Centre, University of Otago, New Zealand. Electronic address: jon.shemmell@otago.ac.nz.
Jonathan B H
JB
Shemmell
D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
Cortical plasticity; Electroencephalography; Primary motor cortex; Transcranial magnetic stimulation