Long latency responses in tongue muscle elicited by various stimulation sites in anesthetized humans – New insights into tongue-related brainstem reflexes

• Published in: Brain stimulation Vol. 15; no. 3; pp. 566 - 575
• Main Authors: Szelényi, Andrea, Fava, Enrica
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2022; Elsevier
• Subjects: Adult; Blinking/physiology; Brain Stem/physiology; Brain Stem/surgery; Cranial Nerves/physiology; Direct trigeminal nerve stimulation; Dorsal column stimulation; Electric Stimulation; Long latency responses; Median nerve stimulation; Negative airway pressure reflex; Somatosensory-evoked tongue reflex; Tongue; Transcranial electric stimulation; Trigemino-hypoglossal reflex; Tongue; Tongue/physiology; Electric Stimulation; Humans; Evoked Potentials; Motor/physiology; Long latency responses; Brain Stem/physiology; Direct trigeminal nerve stimulation; Adult; Tongue/innervation; Trigemino-hypoglossal reflex; Somatosensory-evoked tongue reflex; Muscle, Skeletal/innervation; Median nerve stimulation; Negative airway pressure reflex; Cranial Nerves/physiology; Electromyography/methods; Trigeminal Nerve/physiology; Transcranial electric stimulation; Monitoring, Intraoperative/methods; Blinking/physiology; Brain Stem/surgery; Dorsal column stimulation; Muscle, Skeletal/physiology; Reflex/physiology
• ISSN: 1935-861X; 1876-4754
• DOI: 10.1016/j.brs.2022.03.003

Long Latency Responses (LLR) in tongue muscles are a scarcely described phenomenon, the physiology of which is uncertain. The aim of this exploratory, observational study was to describe tongue-LLR elicited by direct trigeminal nerve (DTNS), dorsal column (DoColS), transcranial electric (TES) and peripheral median nerve (MNS) stimulation in a total of 93 patients undergoing neurosurgical procedures under general anesthesia. Bilateral tongue responses were derived concurrently after each of the following stimulations: (1) DTNS applied with single monophasic or train-of-three pulses, ≤5 mA; (2) DoColS applied with a train-of-three pulses, ≤10 mA; (3) TES consisting of an anodal train-of-five stimulation, ≤250 mA; (4) MNS at wrist consisting of single or train-of-three monophasic pulses, ≤50 mA. Polyphasic tongue muscle responses exceeding the latencies of tongue compound muscle action potentials or motor evoked potentials were classified as LLR. Tongue-LLR were evoked from all stimulation sites, with latencies as follows: (1) DTNS: solely ipsilateral 20.2 ± 3.3 msec; (2) DoColS: ipsilateral 25.9 ± 1.6 msec, contralateral 25.1 ± 4.2 msec; (3) TES: contralateral 55.3 ± 10.2 msec, ipsilateral 54.9 ± 12.0 msec; (4) MNS: ipsilateral 37.8 ± 4.7 msec and contralateral 40.3 ± 3.5 msec. The tongue muscles are a common efferent in brainstem pathways targeted by trigeminal and cervical sensory fibers. DTNS can elicit the “trigemino-hypoglossal-reflex”. For the MNS elicited tongue-LLR, we propose the term “somatosensory-evoked tongue-reflex”. Although the origin of the TES related tongue-LLR remains unclear, these data will help to interpret intraoperative tongue recordings. •Intraoperatively, various stimulation sites elicit tongue-long latency responses.•Median nerve and cuneate fascicle stimulations evoke tongue-long latency responses.•The “somatosensory evoked tongue reflex” is a newly described tongue long latency response.•Transcranial electrical stimulation elicits tongue-long latency responses.•Direct trigeminal nerve stimulation elicits the trigemino-hypoglossal reflex.