Difference between revisions of "Bilateral Trigeminal neuromotor organic symmetry"

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| autore = Gianni Frisardi

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Normalization is computed by dividing the EMG from a specific task or event by the EMG from a reference contraction of the same muscle.<ref name=":0">Clarys JP, Cabri J (1993) Electromyography and the study of sports movements: a review. J Sports Sci 11: 379-448.</ref> Additionally, in healthy individuals, normalizing EMGs by using the EMG recorded from a maximal voluntary contraction (MVC), as the reference value may allow the electromyographer to assess what percentage of the maximal activation capacity of the muscle is represented by the EMG task.<ref>Allison GT, Godfrey P, Robinson G (1998) EMG signal amplitude assessment during abdominal bracing and hollowing. J Electromyogr Kinesiol 8: 51-57.</ref>

To avoid the MVC limitations described above, another EMG model has been proposed as normalization factor.

The jaw-stretch reflex is the short-latency excitatory response in the jaw-closing muscles after the application of a sudden stretch. It is considered the trigeminal equivalent of the monosynaptic spinal stretch reflex in limb muscles.<ref>Lund JP, Lamarre Y, Lavigne G, Duquet G (1983) Human jaw reflexes. Adv Neurol 39: 739-755.</ref> The simplest way to provoke a jaw stretch reflex is by tapping the chin with a reflex hammer.<ref>Murray GM, Klineberg IJ (1984) A standardized system for evoking reflexes in human jaw elevator muscles. J Oral Rehabil 11: 361-372.</ref><ref>Cruccu G, Frisardi G, van Steenberghe D (1992) Side asymmetry of the jaw jerk in human craniomandibular dysfunction. Arch Oral Biol 37: 257-262.</ref>

Some authors have tried to test the hypothesis that normalization of the jaw-stretch reflex amplitude with respect to the voluntary EMG activity preceding the reflex stimulus (EMG pre-stimulus) makes the amplitude more independent by the electrode location over the masseter muscle. In this experimental study, the reflex amplitude was also normalized with respect to the mean pre-stimulus EMG activity.<ref>Koutris M, Naeije M, Lobbezoo F, Wang K, Arendt-Nielsen L, et al. (2010) Normalization reduces the spatial dependency of the jaw-stretch reflex activity in the human masseter muscle. Muscle Nerve 41: 78-84.</ref>

The technical execution of <math>M-wave</math> for the trigeminal nervous system is much more painful and invasive than that of the spinal cord. To evoke a direct response from the masseter muscle, in fact, it is necessary to insert an insulated in-tip needle electrode about 2 cm deep in the temporal fossa and this makes the technique not clinically applicable, although it could obtain more detailed information for the neurophysiological interpretation data.

===_maximalAbsolute Neural Evoked Energy <math>_mANEE</math>===

[[File:Potenziale Evocato della Radice Trigeminale.jpg|left|thumb|'''Figure 3:''' The figure shows the signal saturation of the root with respect to latency and amplitude.]]

In this model of normalization, the purpose is not the decomposition of the signal/noise ratio, that we prefer to consider as an entropic phenomenon,<ref>Xie HB, Guo JY, Zheng YP (2010) Fuzzy approximate entropy analysis of chaotic and natural complex systems: detecting muscle fatigue using electromyography signals. Ann Biomed Eng 38: 1483-1496.</ref> but to decouple the contents of the central drive <ref>Inghilleri M, Berardelli A, Cruccu G, Priori A, Manfredi M (1989) Corticospinal potentials after transcranial stimulation in humans. J Neurol Neurosurg Psychiatry 52: 970-974.</ref> from the peripheral drive<ref>Cruccu G, Iannetti GD, Marx JJ, Thoemke F, Truini A, et al. (2005) Brainstem reflex circuits revisited. Brain 128: 386-394.</ref><ref>Kennelly KD (2012) Electrodiagnostic approach to cranial neuropathies. Neurol Clin 30: 661-684.</ref>by normalizing them with the organic content extrapolated from the _bR-MEPs.

===_bR-MEPs stability and synchronicity===

[[File:TCS - Motor Evoked Potentials of trigeminal roots in open bite patient.jpg|thumb|'''Figure 2''': Motor evoked potentials elicited by transcranial electrical stimulation of both trigeminal roots]]

Another essential element to support the proposed normalization factor is its stability and synchronicity in the neuromuscular response.

We have to add to these biases an even more limiting phenomenon than the intracranial current distribution with vectorial summation and collision current phenomena. However, the morphology of the _bR-MEPs (Figure 2) and the difference in latency and amplitude (0.04 msec and 400 μV, respectively) reported in Table 2, confirm the high stability and synchronicity of the _bR-MEPs. Keep in mind that, in order to extract the maximum efficiency from the normalization model proposed, any functional tests, such as trigeminal reflexes, must be performed in the same session and, therefore, with the same electrode arrangement. This way it will significantly reduce distortion due to the recording geometry.

====Organic symmetry====

A reflex opening of the jaw, resulting from the simultaneous relaxation of jaw closers and contraction of jaw openers, not only helps to avoid injuries to the oral tissues, but also could contribute to coordinating rhythmic masticatory movements.<ref>Shigenaga Y, Yoshida A, Mitsuhiro Y, Tsuru K, Doe K (1988) Morphological and functional properties of trigeminal nucleus oralis neurons projecting to the trigeminal motor nucleus of the cat. Brain Res 461: 143-149.</ref>The stimulus applied to one side evokes the reflex bilaterally in a nearly symmetrical fashion. The symmetrical output is characteristic of most of the jaw movements induced by sensory signals both from the peripheral tissue and from those generated by signals coming from the cerebral cortex.

It has been demonstrated that in the masticatory system, where symmetrical motor output is the rule, employing neurons with bifurcating axons as a pre-motor element might be a common strategy for mediation of both peripheral and central signals.