Surgical anatomy of facial nerve for revision transmastoid surgery.

We analyze the relationships of the 3 segments of the facial nerve with respect to constant anatomic structures that can be identified during revision surgery via translabyrinthine approach. This study was conducted on 15 formalin-fixed cadavers whose facial nerves were dissected bilaterally under operative microscope via translabyrinthine approach. The distances between the round window niche and the midpoint of the tympanic segment and the beginning of the mastoid segment were 6.64 ± 1.79 mm and 3.99 ± 0.79 mm, respectively. The distances between the tympanic ostium of the eustachian tube and the first and the second genu were 7.02 ± 0.62 mm and 12.25 ± 1.24 mm, respectively. We used the superior semicircular canal, the tympanic ostium of the eustachian tube, and the round window niche as landmarks to identify the facial nerve during revision surgery. Our study also showed that the auricular branch may also be originated from the posterior surface of the facial nerve.

The Sensory Auricular Branch of the Facial Nerve and its Relationship to Landmarks of the Facial Recess.

OBJECTIVE: Delineate the anatomic relationship of the sensory auricular branch (SAB) of the facial nerve to other structures of the facial recess. METHODS: Ten adult cadaveric temporal bones were randomly selected and dissected under operative microscopy. Linear and angular measurements were obtained for the following parameters: (1) the distance from the tip of the short process of the incus to the point of convergence of the SAB and the main trunk of the facial nerve; (2) the distance from the point of convergence of the SAB and the main trunk of the facial nerve to the chorda tympani (CT) division from the main trunk; (3) the distance from the bifurcation of the CT and facial nerve to the crossover point of the SAB/CT; (4) the angle at which the SAB merges with the main trunk (Y°), and (5) the angle at which the CT divides off the main trunk (X°). RESULTS: The mean distance from the tip of the short process of the incus to the SAB takeoff was 8.7 ± 1.83 mm (range 6-13 mm). The mean distance from the SAB to the CT division from the main trunk was 5.9 ± 2.41 mm (range 3-10 mm). The mean angle at which the SAB merged with the main trunk of the facial nerve was 38.5 ± 12.63° (range 25°-68°). The mean CT-main trunk angle was 16 ± 4.24° (range 8°-21°). The branching point of the SAB from the facial nerve approximately bisected the facial recess. CONCLUSION: Recognizing the SAB and knowing its relationships to surrounding anatomy provides a useful adjunctive landmark for the identification of the main trunk of the facial nerve's mastoid segment. LEVEL OF EVIDENCE: 4.

Anatomic limitations of posterior tympanotomy: what is the major radiologic determinant for the view field through posterior tympanotomy?

To radiologically evaluate the anatomic factors that may determine the view field or the accessibility of the posterior tympanotomy into the posterior mesotympanum, a cohort of 30 patients with pneumatic mastoids and 30 patients with unilateral sclerotic mastoids were included. Anatomic relationships were evaluated according to 5 parameters. The reference parameter of the view field through posterior tympanotomy was the maximum view to the stapes area through posterior tympanotomy. Direct distance between the chorda tympani nerve and the facial nerve (FN) and angle between the cortex of the external auditory canal and the FN showed significant positive correlations in pneumatic and sclerotic mastoids. However, the location of the FN was negatively correlated with the maximum view to the stapes area through posterior tympanotomy only in pneumatic mastoids. In particular, the angle between the cortex of the external auditory canal and the FN showed the best correlation with the maximum view to the stapes area through posterior tympanotomy. The angle between the cortex of the external auditory canal and the FN was the most important anatomic determinant for visibility through posterior tympanotomy. This study suggests that pneumatic mastoids, but not sclerotic mastoids, may have a more complex relationship including more factors than those considered in this study. Although this study was performed radiologically, this study can present the insight to surgeons or radiologists.

Surgical anatomy of the chorda tympani: a micro-CT study.

PURPOSE: Iatrogenic injury of the chorda tympani is a well-known complication of middle ear surgery, yet few studies have investigated the intraosseous course of the nerve. The aim of this study was to accurately delineate the posterior canaliculus in the temporal bone, particularly its relationship to the tympanic annulus, which is critical during the insertion of subannular ventilation tubes. METHODS: Forty temporal bones from 27 cadavers (15 male, mean age 75 years, 13 bilateral) were scanned using a micro-CT scanner, and standardised 3-D multiplanar reconstructions were generated using a software platform. The posterior canaliculus was measured in relation to reproducible bony landmarks. RESULTS: In 6 (15%) specimens, the chorda tympani originated from the facial nerve outside the skull and in 34 (85%) from within the facial canal at a mean of 3.2 ± 1.8 mm above the stylomastoid foramen. The posterior canaliculus was 12.3 ± 3.8 mm long and converged on the tympanic sulcus cranially. It entered the middle ear at 62 ± 10% of the height of the tympanic membrane. CONCLUSIONS: This novel micro-CT study defines the precise anatomy of the posterior canaliculus housing the chorda tympani and provides data that may help the otologic surgeon protect the nerve from iatrogenic injury.

CT-scan imaging of iron marked chorda tympani nerve: anatomical study and educational perspectives.

The chorda tympani nerve (CTN) is the last collateral branch of the facial nerve in its third intraosseous portion just over the stylomastoid foramen. After a curved course against the medial aspect of the tympanum where it is likely to be injured in middle ear surgery, CTN reaches the lingual nerve in the infratemporal fossa. Knowledge of CTN topographic anatomy is not easily achieved by the students because of the deep location of this thin structure. The aim of this study was to assess the spatial relationships of the CTN in the infratemporal fossa. Therefore, ten nerves were dissected in five fresh cadavers. All the nerves were catheterized with a 3/0 wire. After a meticulous repositioning of surrounding structures, standard X-ray and CT scan examinations were performed with multiplanar acquisitions and three-dimensional surface rendering reconstructions. Ventral projection of the CTN corresponded to the middle of the maxillary sinus. Lateral landmark was the mandibular condyle. The CTN was present and unique in all the dissections. The average length of the nerve, as measured on CT scans, was 31.8 mm (29-34, standard deviation of 1.62); the anastomosis of the CTN to the lingual nerve was located at a mean 24.9 mm below the skull base (24-27, standard deviation of 0.99), approximately in the same horizontal plane as the lower part of the mandibular notch. The acute angle opened dorsally and cranially between CTN and LN measured mean 63.2° (60-65, standard deviation of 1.67). Three-dimensional volumetric reconstructions using surface rendering technique provided realistic educational support at the students' disposal.

Ossification of the petrotympanic fissure: morphological analysis and clinical implications.

The petrotympanic fissure, a narrow slit in the temporal bone, allows the temporomandibular joint (TMJ) and the middle ear to communicate. Both the chorda tympani and the ligament cross the fissure between the posterior region of the joint disk and the malleolar ossicle. The parasympathetic fibers of the chorda tympani spread into the major salivary glands and are responsible for the taste sensibility on the anterior two-thirds of the tongue. After chronological identification of 30 human skulls, petrotympanic fissures were macroscopically and stereomicroscopically analyzed for the presence and disposition of ossification areas. Digitalized images were analyzed using computer program UTHSCSA ImageTool 3.0 (developed by the Department of Dental Diagnostic Science at The University of Texas Health Science Center, San Antonio, Texas). The total extension of the fissures and ossification areas was measured. The macroscopic analysis did not constitute an appropriated method for this evaluation and the ossification of the fissures increased with aging, suggesting its influence on the causes of otalgia in cases of TMJ dysfunction.

Anatomical variations of the mandibular nerve and its branches correlated to clinical situations.

AIM: The mandibular division of the trigeminal nerve is the largest of the three major divisions of the trigeminal nerve (fifth cranial nerve). In this way, many health professionals belonged to different fields are commonly evaluating patients suffering with orofacial pain and stomatognatic dysfunction associated to this structure. But, in the most cases, it is difficult to establish a correct diagnosis due to the anatomical complexity of the head and neck surfaces, especially when the focus is the trigeminal nerve. Thus, the objective of this research was to present the anatomical variations of the mandibular nerve and its branches correlated to more common clinical situations. METHODS: For this purpose, 20 human heads were anatomically dissected, so to study their structures, an external, medial and endocranial view. RESULTS: No significant variations related to ophthalmic and maxillary nerves were observed. Anatomical variations were observed in 20% of the total human heads dissected, all related to mandibular nerve and its branches: masseter, temporal, auriculotemporal and lingual. Variations in three to seven, on the number of the following nerves ramus, masseter and temporal were described. CONCLUSIONS: According to the present data using the described methodology, it was possible to conclude that anatomical variations are present in many subjects and they can explain many clinical situations that involve the stomatognathic structures.

Anatomical and functional aspects of ligaments between the malleus and the temporomandibular joint.

The aim of this paper is to investigate the anatomical topography and the relationship between the ligaments, malleus and temporomandibular joint (TMJ) and to determine the role of these ligaments on the movement of the malleus. The malleus, incus, petrotympanic fissure (PTF), chorda tympani, anterior malleolar ligament (AML), discomallear ligament (DML), malleomandibular ligament, sphenomandibular ligament and articular disc were explored in 15 skulls. Traction and tension tests were carried out to clarify their role in malleolar movement. In 12 of the cases, two separate ligaments were connected to the anterior of the malleus, whereas a single ligament from the anterior of the malleus to the PTF was observed in 3 cases. In 12 cases, the DML united the retrodiscal tissues. In the other 3 cases, the medial and the lateral parts of the ligament were connected to the retrodiscal tissue after passing through the PTF. The thickness of the ligaments differed among specimens. When tension was applied to the DML no malleolar movement occurred, but when the AML was overstretched, significant movement was observed in 5 cadavers; little movement in 6 cadavers, and no movement in 4 cadavers. This study suggests that extreme stretching of the condyle in conjunction with the ligaments between the ossicles of the inner ear and the TMJ could be the reason for unexplained otological problems.

Temporomandibular joint and correlated fissures: anatomical and clinical consideration.

An anatomical study of the fissures related to the temporomandibular joint (TMJ) was performed in 40 dry human skulls. The length of the squamotympanic fissure (X), as well as those of the petrotympanic fissure (Y) and the (descending part of) the petrosquamous fissure (Z), into which the first of them (as a rule) branches, was measured. The distances between the point of this bifurcation and the deepest point of the glenoid fossa (A), the articular tubercle (B), and the styloid process (C) of the TMJ were also measured. The distances measured presented a significant variability among different specimens. In particular, the lengths (X, Y, and Z) of some fissures measured twice as great compared to other ones. All distance measurements were expressed in mm. Dysfunction of the TMJ may lead to a variety of ear symptoms, i.e., otalgia, tinnitus, hearing loss, possibly vertigo and, less often, to tongue symptoms (collectively characterized as temporomandibular syndrome). These symptoms often relate to the important anatomic structures (anterior malleolar ligament, anterior tympanic artery and chorda tympani nerve) coursing (mainly) through the petrotympanic fissure, whose length and position may exert considerable impact. The measured distances (hardly assessable through a plain radiogram) may also be considered as parameters that need to be taken into account in view of an eventual replacement of a poorly functioning TMJ by a suitable prosthesis.

Development of the anterior chordal canal.

Resent advances have led to the reexamination of the intraosseous pathway of the chorda tympani a few years ago and they stated that the nerve never enters the mandibular fossa and its exit the skull base in the sphenopetrosal fissure. In our report, 58 temporal bones were investigated after maceration and formalin fixation in order to understand the development of the anterior chordal canal. Our study revealed that the chorda tympani leaves the tympanic cavity through the tympanosquamosal fissure before formation of the anterior chordal canal of Huguier. This canal is situated parallel to and in front of the musculotubal canal and formed by the processus inferior tegminis tympani and the sphenoid bone between the second and fifth years of age. Prior to the age of 2, only the exit of the bony canal exists which is gradually followed by the appearance of a groove in the growing processus inferior tegminis tympani. The borders of the groove elevate and develop to upper and lower plates which lengthen with similar plates of the sphenoid bone, completing the anterior chordal canal by the fifth postnatal year. The entrance of the canal develops above the petrotympanic fissure and similar to the canal itself, it is also completely formed in the fifth year. In case of an incomplete development the anterior chordal canal remains partially opened laterally which might allow the head of the mandibula to effect the chorda tympani mechanically causing Costen's syndrome.

Subannular tube insertion: anatomical considerations.

OBJECTIVES: To assess the distance between the bony groove created during subannular tubes placement and the chorda tympani, and examine the depth of the hypotympanum and retrotympanum. METHOD: Grooves drilled in cadaver temporal bones at two levels were imaged to measure: the distance between the chorda tympani nerve and the tympanic sulcus, and the depth of the hypotympanum and the retrotympanum relative to the annulus. RESULTS: The chorda tympani was between 0 and 5 mm from the groove cut across the annulus. The hypotympanum average depth was 2 mm (0.44-6.40 mm) and the retrotympanum average depth was 1 mm (0-2.53 mm). CONCLUSION: Grooves drilled across the tympanic sulcus should be placed at a point 20 per cent of the height of the tympanic membrane or lower; this will ensure least risk of injury to the chorda tympani nerve. The depth of the hypotympanum and retrotympanum dictates that the posteroinferior part of a subannular tube flange should be approximately 2 × 1 mm.

Peripheral interactions among single papilla inputs to gustatory nerve fibers.

Recordings were made from single fibers of the rat chorda tympani nerve while the peripheral receptor fields were mapped using a stimulator developed to stimulate single fungiform papillae which in the rat contain a solitary taste bud. The results indicate that several fungiform papillae may supply input to a single fiber, and the most sensitive papilla of these provided, on the average, about one-half of the response of that fiber to stimulation of the entire tongue. The magnitude of the response to each concentration of stimulus and the shape of the concentration-response curves differ among papillae innervated by the same fiber. If one of the papillae supplying input to the fiber was stimulated individually with NaCl solution, application of this stimulus to the tongue surface surrounding the isolated papilla resulted in enhancement of the fiber response. If the papilla was stimulated with NaCl and potassium benzoate solution was applied to the surround, a depression of the response occurred. The excitatory input of the cationic stimuli and the depressing influence of the anionic stimuli interacted to determine the resultant steady-state impulse frequency of the single afferent fiber. A hypothetical model involving the summation of generator currents along the unmyelinated terminals of the single afferent neuron is presented as a speculative explanation of the integration of inputs from several receptors innervated by the same single fiber.

High resolution CT study of the chorda tympani nerve and normal anatomical variation.

OBJECTIVE: The aim of this study was to define the normal anatomical variation of the course of the CTN through the mastoid temporal bone on high resolution CT (HRCT). MATERIALS AND METHODS: Retrospective review of 27 consecutive normal HRCT bilateral temporal bones (n = 54, 14 males and 13 females, mean age 41 years) reconstructed at 0.4-mm slice thickness specifically measuring (1) origin of CTN from the posterior genu of the facial nerve (CNVII) and (2) the lateral-most position of the CTN from the mastoid segment of CNVII. RESULTS: The mean distance of the CTN origin from the mastoid segment of CNVII was 11.5 mm (standard deviation, SD = 3.2, 95% CI 10.7-12.3) with no statistically significant difference between the left and right side observed (p = 0.08). The most lateral distance of the CTN from CNVII was a mean of 1.3 mm (SD = 0.6, 95% CI 1.2-1.7), range 0-2.5 mm and again no statistical significance between contralateral sides was observed (p = 0.11). These measurements demonstrated an excellent level of agreement between observers as assessed by intraclass correlation calculation. CONCLUSIONS: Reproducible measurements demonstrate variability of the CTN in both its origin from the mastoid segment of CNVII and its lateral-most course. Precise description of the course of the CTN with HRCT may be useful for planning of otologic surgery and limiting inadvertent nerve injury.

Glaser Fissure, Huguier Canal, and Civinini Canal: A Confused Eponymical Imbroglio.

Huguier canal or Civinini canal is a canaliculus in the Glaser fissure allowing the exit of the chorda tympani from the tympanic cavity. The aim of this study is to try to put some order in the origins and relations of these different eponyms, and to evaluate their pertinence in the actual anatomical terminology. This study demonstrates that Huguier and Civinini are not the first to describe this canal in the 1830s. Furthermore, it confirms that Glaser does not describe the related fissure in 1680. In conclusion, Glaser, Civinini, and Huguier no longer have a place in the actual anatomical nomenclature of the fine details of the temporal bone. To avoid confusion and errors, they must be replaced by anterior canaliculus for the chorda tympani and petrotympanic fissure.

The motor nuclei and primary projections of the facial nerve in the monitor lizard Varanus exanthematicus.

The location of the motor nuclei and the projection of the primary afferent fibers of the facial nerve of the reptile Varanus exanthematicus were studied by means of the HRP method and the anterograde degeneration technique. The motor nuclei are located ventrolaterally in the rhombencephalon and are constituted by a medial cell group consisting of large, polygonal cells and a lateral cell group consisting of medium-sized, spindle-shaped, and multipolar cells. From HRP applications to the various branches of the facial nerve it could be concluded that the medial cell group represents the branchiomotor nucleus and the lateral cell group the superior salivatory nucleus. The efferent axons from the motor nuclei course dorsomedially toward the fourth ventricle, where they form a genu, and exit from the brainstem in the ventral fiber bundle of the facial nerve. The primary afferent fibers enter the brainstem in the dorsal bundle of the facial nerve. This bundle courses medially, enters the solitary tract, and diverges into rostrally and caudally running fibers. Part of the caudally directed fibers leave the solitary tract and course laterally toward the descending trigeminal tract. Some fibers enter the nucleus of this tract. There was no noticeable terminal degeneration in the solitary tract or in the descending trigeminal tract or its nucleus.

Central origins of cranial nerve parasympathetic neurons in the rat.

The location of central neurons that contribute preganglionic parasympathetic axons to cranial nerves VII, IX, and X in rats has been identified using horseradish peroxidase (HRP) tracing methods. Collectively, these neurons form an uninterrupted dorsal column that extends over the entire length of the medulla. The cephalic end of this column turns ventrally with neurons scattered in the parvicellular reticular formation between the rostral pole of the nucleus of the solitary tract (NST) and the facial motor nucleus. Applying HRP crystals to the cut cervical vagus labels neurons in the classically defined dorsal motor nucleus. Rostrally, this distribution continues along the medial edge of NST, ending just caudal to neurons exiting in the lingual-tonsilar branch of IX. At the rostral pole of the NST and ventral to it, neurons occur that serve the lingual-tonsilar and tympanic branches of IX, as well as the chorda tympani and greater superficial petrosal (GSP) branches of VII. Central neurons of the chorda tympani and tympanic nerves spread ventrally from NST into a sparse but largely coextensive distribution in the reticular formation lateral to the ascending radiations of the facial motor nucleus. Immediately ventral to this distribution, a dense accumulation of GSP efferent neurons appears rostrolateral to the facial motor nucleus. Although they vary considerably in number and packing density, the neurons of the dorsal efferent column and those extending from it into the reticular formation have similar morphological characteristics. The somata are medium-sized, fusiform, or multipolar, but with usually no more than five or six major processes.

The nucleus of the solitary tract in the monkey: projections to the thalamus and brain stem nuclei.

The projections of the nucleus of the solitary tract (NST) were studied by autoradiographic anterograde fiber-tracing and horseradish peroxidase (HRP) retrograde cell-labeling. Tritiated proline and leucine were deposited in electrophysiologically identified regions of NST. Injections of NST at levels caudal to where the vagus enters the nucleus, from which responses were evoked by stimulation of cranial nerves IX and X, revealed topographically organized bilateral projections to, most prominently, the ventrolateral medullary reticular formation which contains neurons of the ambiguus complex, and to the lateral and medial parabrachial nuclei, including a small portion of the medially adjacent central gray substance. Labeled fibers in the ventrolateral reticular formation were present from the nucleus retroambigualis rostralward to the retrofacial nucleus, with the densest concentration located over the nucleus ambiguus proper. The parabrachial projection was confirmed using HRP and shown to originate from cells in the medial subdivision of NST. Due to the problem of fibers en passant, it was not possible to interpret conclusively the cell-labeling seen around the solitary tract after HRP injections made in the region of the nucleus ambiguus. Labeled fibers were also traced from caudal NST to the dorsal motor nucleus of the vagus, but their origin could not be determined with certainty. Other labeled axons, traced to circumscribed parts of the inferior olivary complex and via the contralateral medial lemniscus to VPL of the thalamus, were shown in HRP experiments to originate from the dorsal column nuclei rather than NST. No labeled fibers were traced into the spinal cord, nor were any cells labeled in NST after large HRP deposits in upper cervical segments. Isotope deposits at levels of NST rostral to the entrance of the vagus, from which responses were evoked by rapid stimulation of the tongue, revealed an ipsilateral projection which ascends as a component of the central tegmental tract to the parvicellular part of the ventral posteromedial thalamic nucleus (VPMpc). After small HRP deposits in VPMpc, labeled cells in NST were restricted to the rostral part of the lateral subdivision. No labeled axons were traced from rostral NST to the ambiguus complex or parabrachial area. Injections of 3H-amino acids at intermediate levels of NST resulted in fiber-labeling in VPMpc, the parabrachial area, and the ambiguus complex.

Anatomy of the gustatory system in the hamster: central projections of the chorda tympani and the lingual nerve.

The sensory modalities of taste and touch, for the anterior tongue, are relegated to separate cranial nerves. The lingual branch of the trigeminal nerve mediates touch: the chorda tympani branch of the facial nerve mediates taste. The chorda tympani also contains efferent axons which originate in the superior salivatory nucleus. The central projections of these two nerves have been visualized in the hamster by anterograde labelling with horseradish peroxidase (HRP). Afferent fibers of the chorda tympani distribute to all rostral-caudal levels of the solitary nucleus. They synapse heavily in the dorsal half of the nucleus at its rostral extreme; synaptic endings are sparser and located laterally in caudal regions. These taste afferents travel caudally in the solitary tract and reach different levels by a series of collateral branches which extend medially in the the solitary nucleus, where they exhibit preterminal and terminal swellings. Taste afferent axons range in diameter from 0.2 micrometer to 1.5 micrometers. The thickest axons project exclusively to the rostral and intermediate subdivisions of the solitary nucleus; the find ones may distribute predominantly to the caudal subdivision. Afferent fibers of the lingual nerve terminate heavily in the dorsal one-third of the spinal nucleus of the trigeminal nerve and also as a dense patch in the lateral solitary nucleus at the midpoint between its rostral and caudal poles. This latter projection overlaps that of the chorda tympani. Thus the two sensory nerves which subserve taste and touch from coincident peripheral fields on the tongue converge centrally on the intermediate subdivision of the solitary nucleus. Efferent neurons of the superior salivatory nucleus were labelled retrogradely following application of HRP to the chorda tympani. These cells are located ipsilaterally in the medullary reticular formation ventral to the rostral pole of the solitary nucleus; their dendrites are oriented dorsoventrally. The efferent axons course dorsally, form a genu lateral to the facial somatomotor genu, and course ventrolaterally through the spinal nucleus of the trigeminal nerve to exit the brain ventral to the entering facial afferents.

Central distribution of afferent and efferent components of the chorda tympani in the cat as revealed by the horseradish peroxidase method.

Central distribution of afferent and efferent components of the chorda tympani (CT) in the cat was examined by using the anterograde and retrograde tracing techniques of horseradish peroxidase (HRP). HRP was applied to the CT in the tympanic cavity. HRP-labeled CT fibers were traced to the brain stem along the ventral surface of the vestibular nerve. The afferent CT fibers were divided into ascending and descending components. The rostrally directed ascending fibers ended within and around the dorsomedial portions of the principal sensory trigeminal nucleus. The descending fibers entered the solitary tract to run caudally as far as the levels slightly rostral to the obex, giving terminals to the solitary nucleus. A cluster of HRP-labeled neurons were seen ipsilaterally in the lateral reticular formation medial to the spinal trigeminal nucleus; it was observed from the caudalmost levels of the exiting root of the facial nerve to the caudal levels of the facial nucleus. HRP-labeled axons arising from the HRP-labeled neurons firstly ran dorsomedially and then medially under the genu of the facial nerve to form a small genu at the region medial to the genu of the facial nerve. Subsequently the labeled axons ran laterally and ventrolaterally to join other CT fibers at the dorsomedial aspect of the spinal trigeminal tract.

Convergence of afferent inputs from the chorda tympani, lingual-tonsillar and pharyngeal branches of the glossopharyngeal nerve, and superior laryngeal nerve on the neurons in the insular cortex in rats.

The responses of single neurons in the insular cortex to electrical stimulation of the chorda tympani (CT), lingual-tonsillar branch of the glossopharyngeal (LT-IXth) nerve, pharyngeal branch of the glossopharyngeal (PH-IXth) nerve, and superior laryngeal (SL) nerve were recorded in anaesthetized and paralyzed rats. Ninety-four neurons responding to stimulation of at least one of the four nerves were identified from the insular cortex. Most of the neurons were located in the posterior portion of the insular cortex; the mean location was 0.8 mm anterior to the anterior edge of the joining of the anterior commissure (AC) and was 1.4 mm dorsal to the rhinal fissure (RF). Of the 94 neurons, 84 (89%) received convergent inputs from two or more nerves, and the remaining 10 (11%) received inputs from one nerve. The neurons responding to the CT stimulation were distributed more anteriorly than those responding to other three nerves in the anterior-posterior dimension. Our results indicate that the neurons recorded mainly from the posterior portion of the insular cortex receive convergent inputs from the oropharyngolaryngeal regions.