Reticular formation responses to magnetic brain stimulation of primary motor cortex

Karen M. Fisher, Boubker Zaaimi, Stuart N. Baker*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Transcranial magnetic stimulation (TMS) of cerebral cortex is a popular technique for the non-invasive investigation of motor function. TMS is often assumed to influence spinal circuits solely via the corticospinal tract. We were interested in possible trans-synaptic effects of cortical TMS on the ponto-medullary reticular formation in the brainstem, which is the source of the reticulospinal tract and could also generate spinal motor output. We recorded from 210 single units in the reticular formation of three anaesthetized macaque monkeys whilst TMS was performed over primary motor cortex. Short latency responses were observed consistent with activation of a cortico-reticular pathway. However, we also demonstrated surprisingly powerful responses at longer latency, which often appeared at lower threshold than the earlier effects. These late responses seemed to be generated partly as a consequence of the sound click made by coil discharge, and changed little with coil location. This novel finding has implications for the design of future studies using TMS, as well as suggesting a means of non-invasively probing an otherwise inaccessible important motor centre.

Original languageEnglish
Pages (from-to)4045-4060
Number of pages16
JournalJournal of Physiology
Issue number16
Publication statusPublished - 1 Aug 2012

Bibliographical note

© 2012 The Authors. The Journal of Physiology © 2012 The Physiological Society. This journal is labelled as open access on the publisher's website.


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