Somatosensory input in the context of transcranial magnetic stimulation coupled with electroencephalography: An evidence-based overview

• Published in: Neuroscience and biobehavioral reviews Vol. 155; p. 105434
• Main Authors: Mancuso, M., Cruciani, A., Sveva, V., Casula, E.P., Brown, K., Rothwell, J.C., Di Lazzaro, V., Koch, G., Rocchi, L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01-12-2023
• Subjects: Cranial nerves; Electroencephalography; Evoked potentials; Facial nerve; Somatosensory stimulation; TMS-EEG; Transcranial magnetic stimulation; Trigeminal nerve; Transcranial magnetic stimulation; TMS-EEG; Trigeminal nerve; Evoked potentials; Cranial nerves; Facial nerve; Electroencephalography; Somatosensory stimulation
• ISSN: 0149-7634; 1873-7528; 1873-7528
• DOI: 10.1016/j.neubiorev.2023.105434

The transcranial evoked potential (TEP) is a powerful technique to investigate brain dynamics, but some methodological issues limit its interpretation. A possible contamination of the TEP by electroencephalographic (EEG) responses evoked by the somatosensory input generated by transcranial magnetic stimulation (TMS) has been postulated; nonetheless, a characterization of these responses is lacking. The aim of this work was to review current evidence about possible somatosensory evoked potentials (SEP) induced by sources of somatosensory input in the craniofacial region. Among these, only contraction of craniofacial muscle and stimulation of free cutaneous nerve endings may be able to induce EEG responses, but direct evidence is lacking due to experimental difficulties in isolating these inputs. Notably, EEG evoked activity in this context is represented by a N100/P200 complex, reflecting a saliency-related multimodal response, rather than specific activation of the primary somatosensory cortex. Strategies to minimize or remove these responses by EEG processing still yield uncertain results; therefore, data inspection is of paramount importance to judge a possible contamination of the TEP by multimodal potentials caused by somatosensory input.
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•Possible contamination of TEPs by SEPs have been suggested.•SEPs by craniofacial stimulation have not been thoroughly investigated.•We reviewed the evidence and physiology of possible SEPs following this stimulation.•Only activation of craniofacial muscle and free skin nerve endings may induce SEP.•If present, these potentials are represented by vertex multimodal responses.