**4. Discussion**

#### **4.1. Total of VF assessments in the oral and pharyngeal phases and the threshold of electrical sensation**

It was investigated that the relationship between the threshold of sensation and each value in the disease history of each patient. The relationship between the total in the oral phase and the threshold of sensation differed significantly (paired t-test, P<0.05). Furthermore, the relation‐ ship between the total in the pharyngeal phase and the threshold of sensation were statistically significant at P<0.01. The regression curves of each relationship were examined, too. The total scores of the VF assessments in the pharyngeal phase and the threshold of electrical sensation were strongly associated (r2=0.75). However, the total score of the VF assessments in the oral

phase and the threshold of electrical sensation were not strongly associated (r2=0.13) (Figures 4A and 4B).

stimulation indicated a recovery trend for all diseases, separate analysis for each disease was importance to obtain more detailed data. Based on these findings, we believe that the electrical threshold of sensation on the soft plate may reflect the recovery process of swallowing reflex

 

 

 

 

**Figure 3.** Relationship between total scores of VF assessments in (A) the oral phase and (D) the pharyngeal phase and the threshold of electrical sensation. (Aa) VF assessments in the oral phase. (Ab) VF assessments in the pharyngeal phase. (B) Electrical threshold of sensation. Black lines: amyotrophic lateral sclerosis. Red lines: myasthenia gravis. (C,

**4.1. Total of VF assessments in the oral and pharyngeal phases and the threshold of electrical**

It was investigated that the relationship between the threshold of sensation and each value in the disease history of each patient. The relationship between the total in the oral phase and the threshold of sensation differed significantly (paired t-test, P<0.05). Furthermore, the relation‐ ship between the total in the pharyngeal phase and the threshold of sensation were statistically significant at P<0.01. The regression curves of each relationship were examined, too. The total scores of the VF assessments in the pharyngeal phase and the threshold of electrical sensation were strongly associated (r2=0.75). However, the total score of the VF assessments in the oral

 

 

> 

 

disorders.

112 Seminars in Dysphagia

 

 

**4. Discussion**

**sensation**

D) Averages and standard deviations of VF assessments and electrical threshold of sensation.

Because the total scores in the pharyngeal phase and the threshold of sensation showed a strong correlation, the decrease in electrical sensation might be related to recovery of the pharyngeal phase.

**Figure 4.** Relationship between (A) total score in the oral phase and threshold of sensation and (B) total score in the pharyngeal phase and threshold of sensation.

#### **4.2. Relationship between VF assessments and electrical stimulations on the soft palate**

We considered the presence of a relationship between the recovery process and electrical threshold of sensation, as shown in the first experiment. The results were assumed by a close relationship between the two. Why is there a relationship between a decrease in the threshold of electrical sensation and the recovery process? The well-known phenomenon of "active touch" or "haptic perception" is characterized by object perception through touch. It has been believed that sensory organs function by passive touch. However, Asanuma and Arissian [1] reported the functional role of peripheral input to the motor cortex during voluntary move‐ ments in the monkey. Specifically, they proposed that voluntary movements are induced by peripheral sensory inputs. Thus, we believe that measurements of the threshold of electrical sensation are necessary to measure recovery of voluntary movements.

Furthermore, our hypothesis involves the relationship between VF assessment parameters and electrical stimulation in patients with various disorders. VF assessments were divided into the oral and pharyngeal phases because the former is controlled by the first motor cortex of cerebral cortex (M1) and the latter is controlled by the brain stem. In particular, VF assessments of the oral phase are related to voluntary masticatory movements, while VF assessments of the pharyngeal phase are related to the swallowing reflex. We evaluated the relationship between VF assessment parameters and electrical stimulation in patients with various disorders using the swallowing worksheet proposed by Longemann [8], because we utilized measurements in the oral phase (related to masticatory processes) and pharyngeal phase (related to the swal‐ lowing reflex). In oral phase, we measured (1) bolus formation, (2) tongue-to-palate contact, (3) premature bolus loss, (4) residue in oral cavity, and (5) oral transit time. On the other hand, measurements in the pharyngeal phase included (1) lift in the soft palate, (2) triggering of pharyngeal swallow, (3) epiglottic vallecula residue, (4) pyriform sinus residue, (5) pharyngeal transit time, and (6) aspiration. The relationship between total VF assessments in the oral phase and the threshold of electrical sensation showed a weak association with cerebral hemorrhage, cerebral contusion, amyotrophic lateral sclerosis and myasthenia gravis (Figure 4A). However, the relationship between total VF assessments in the pharyngeal phase and the threshold of electrical sensation had a strong association with these disorders (Figure 3B). On the other hand, a decrease in the electrical threshold of sensations following the treatment process was not observed in patients with amyotrophic lateral sclerosis or myasthenia gravis (black and red lines of Figures Aa, Ab and B).

In summary, the criteria for evaluating recovery of the swallowing reflex may be covered by the electrical threshold of sensation on the soft palate, and acceptance of the electrical stimu‐ lation will produce a reduction in the bombing experience. Why dose the threshold of electrical sensation reflect recovery of the swallowing reflex? The reflex arc progresses as follows: receptor organ, afferent fiber, central nerve for the reflex, efferent fiber and effector organ. In particular, initiation of the swallowing reflex starts from the regions that induce swallowing (primarily the soft palate, posterior part of tongue, and posterior wall of the pharynx). VF assessments of the pharyngeal phase exhibited the swallowing reflex, and this reflex was initiated by stimulation of the regions that induce swallowing. We consider that the stimulation of these regions involves perception by sensory organs, and the swallowing reflex is then evoked by the sensory stimulation.

#### **4.3. Relationship between electrical sensation and voluntary movement or reflex**

When we execute hand movements (especially during search behavior), we take notice of a keen sense in the fingers. Namely, our cutaneous sensation is excited before the execution of movements. This helps us to understand the inaccuracy and inadequacy of movements in patients with sensation disorders. In particular, when the patients with unilateral lingual nerve disease (e.g., secondary to sensory nerve damage during wisdom teeth extraction) are promoted to perform tongue protrusion, the tongue bends toward the diseased side. Further‐ more, monkeys with tactile agnosia after blocking of the first somatosensory cortex (SI) exhibit poor performance in gripping an object (Hikosaka et al.) [4]. Nelson [9] reported somatosen‐ sory neuronal activity in the SI prior to movement. These results indicate that sensory information in the SI is necessary for the initiation and preparatory of the start of movements. Based on these findings, it is understandable that the somatosensory information obtained prior to movement excites the facial, intraoral, and pharyngeal regions. Sessle et al. [10]. Sessle [11], Stohr and Petruch [12] and Stohr et al. [13] reported that a close relationship between the facial motor and sensory cortices is needed during facial and tongue movements. We assumed the presence of a relationship between electrical sensation and the recovery process based on our findings in the orofacial region. However, two patients in the present study (nos. 7 and 8, Table 2) exhibited no change with electrical stimulation treatment. Both of these patients had muscular atrophy, a degenerative disease. These results may suggest that progressive deterioration of the muscle and spinal cord make reconstruction difficult. On the other hand, although a close relationship between VF assessment of the pharyngeal phase and electrical stimulation on the soft palate was observed (cumulating tendency), there was a week rela‐ tionship between VF assessment of the oral phase and electrical stimulation on the soft palate (scattering tendency) (Figures 4A and 4B). VF assessments of the oral phase involved stimu‐ lation of various regions of masticatory movements controlled by the M1. Because disorders of these regions become diffuse around the orofacial region, the electrical sensation of the soft palate cannot cover the entire disease region. However, VF assessments of the pharyngeal phase showed that the swallowing reflex was initiated by stimulation of the regions involved in induction of swallowing (primarily the soft palate, root of tongue, and posterior portion of wall of pharynx). We believe that this conclusion can be drawn from our experimental data: measurement of the electrical threshold can be performed as a substitute for VF assessment in the pharyngeal phase, and patients can undergo less radiation. Namely, the swallowing reflex, nasopharyngeal closure, elevation of hyoid bone and pharynx (laryngeal elevation), laryngeal closure (downward movement of the epiglottis), and esophageal sphincter relaxation are accomplished by serial processing after the initiation of sensory stimulation in the induced regions. We arrived at this conclusion from our experimental data.

Measurement of the electrical threshold can be performed as a substitute for VF assessment in the pharyngeal phase, and patients can undergo less radiation as a consequence.
