RESUMEN
OBJECTIVE: Transcranial focused ultrasound (TUS) can suppress human motor cortical excitability. However, it is unclear whether the TUS may interact with transcranial magnetic stimulation (TMS) when they co-delivered in multiple trials. METHODS: Nineteen subjects received three different TUS-TMS co-stimulation protocols to the motor cortex including concurrent stimulation (TUS-TMS-C), separated stimulation (TUS-TMS-S), and TMS only. In each condition, two runs of 30 stimulation trials were conducted with a five-minute rest between runs. Motor-evoked potentials (MEP) were recorded during stimulation and at 0, 10, 20, and 30 min after stimulation. The MEP amplitudes after intervention were normalized to the mean pre-intervention MEP amplitude and expressed as MEP ratios. An additional test with TUS alone was applied to all participants to assess whether TUS itself can elicit after-effects. RESULTS: There were no significant after-effects of all three interventions on MEP ratios. However, 11 subjects who showed online inhibition (OI + ) during the TUS-TMS-C protocol, defined as having MEP ratio less than 1 during TUS-TMS-C, showed significant MEP suppression at 10, 20 and 30 min after TUS-TMS-C. In 8 subjects did not show online inhibition (OI-), defined as having MEP ratios greater than 1 during TUS-TMS-C, showed no significant inhibitory after-effects. OI + and OI- status did not change in a follow-up repeat TUS-TMS-C test. TUS alone did not generate inhibitory after-effects in either OI + or OI- participants. CONCLUSIONS: Our results showed that co-delivery of TUS and TMS can elicit inhibitory after-effect in subjects who showed online inhibition, suggesting that TUS and TMS may interact with each other to produce plasticity effects. SIGNIFICANCE: TUS and TMS may interact with each other to modulate cortical excitability.
RESUMEN
The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.
