FFERENT CORTICAL CONNECTIONS OF THE MOTOR CORTICAL
ARYNX AREA IN THE RHESUS MONKEY
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. SIMONYAN1* AND U. JÜRGENS
epartment of Neurobiology, German Primate Center, Kellnerweg 4,-37077 Göttingen, Germany
bstract —The present study describes the cortical input intohe motor cortical larynx area. The retrograde tracer horse-adish peroxidase-conjugated wheat germ agglutinin was in-ected into the electrophysiologically identified motor corticalarynx area in three rhesus monkeys (Macaca mulatta). Ret-ogradely labeled cells were found in the surrounding pre-otor cortex (areas 6V and 6D), primary motor cortex (area
), primary somatosensory cortex (areas 3, 1 and 2), anteriornd posterior secondary somatosensory cortex and the prob-ble homologue of Broca’s area (areas 44 and 45); further-ore, labeling was found in the supplementary motor area,
nterior and posterior cingulate cortex (areas 24 and 23),refrontal and orbital frontal cortex (areas 8A, 46V, 47/12L,7/12O, 13), agranular, dysgranular and granular insula asell as in the cortex within the upper bank of the middle thirdf the superior temporal sulcus (area TPO). The majority ofhese regions are reciprocally connected with the motor cor-ical larynx area [Brain Res 949 (2000) 23]. The laryngealotor cortical input is discussed in relation to the connec-
ey words: motor cortex, larynx representation, vocal foldontrol, phonation, neuroanatomy.
he motor cortical larynx area is located in the most ante-ior part of the ventrolateral part of the motor cortex, bor-ering the tongue, lip and jaw representations. While func-ionally this area is considered as part of the primary motorortex, cytoarchitectonically it belongs to area 6, not 4Brodmann, 1909). In the nomenclature of Vogt and Vogt1919), the primate larynx area corresponds to area 6b�, inhat of Von Bonin and Bailey (1947) to area FCBm and inhat of Matelli et al. (1985) to area F5.
The motor cortical larynx area plays an important rolen voluntary vocal fold control in humans. Bilateral lesionsn this region cause a complete loss of voluntary phonationontrol, while non-verbal emotional vocalizations, such asaughing, crying or moaning, are preserved (for review, see
Present address: Laryngeal and Speech Section, Medical Neurologyranch, National Institute of Neurological Disorders and Stroke, Na-
ional Institutes of Health, Building 10, Room 5D38, Bethesda, MD0892, USA.Correspondence to: K. Simonyan, Laryngeal and Speech Section,edical Neurology Branch, National Institute of Neurological Disor-ers and Stroke, National Institutes of Health, Building 10, RoomD38, Bethesda, MD 20892, USA. Tel: �1-301-402-8129; fax:
ürgens, 2002). Brain imaging studies in humans, further-ore, report activation of the facial motor cortex (including
he larynx area) during speaking and singing (Bookheimert al., 2000; Perry et al., 1999). Electrical stimulation of the
arynx area produces isolated bilateral vocal fold move-ents in man (Foerster, 1936) and non-human primates
Hast and Milojevic, 1966; Hast et al., 1974; Jürgens,974; Leyton and Sherrington, 1917; Sugar et al., 1948;alker and Green, 1938). In non-primate mammals, elec-
rical stimulation of the motor cortex does not yield isolatedocal fold movements (Milojevic and Hast, 1964).
Destruction of the laryngeal motor cortex in the mon-ey, in contrast to man, does not affect vocal communica-ion (Kirzinger and Jürgens, 1982). The reason for thisrobably is that monkey calls are more or less completelyenetically preprogrammed in their acoustic structureHammerschmidt et al., 2001). The production of suchnnate motor patterns does not seem to depend upon anntact motor cortex. The larynx area of the monkey’s motorortex thus probably serves non-vocal laryngeal functions,uch as abdominal straining during defection and delivery,r holding breath during forceful jumps and lifting of heavyeights, rather than vocal functions.
EXPERIMENTAL PROCEDURES
hree adult female rhesus monkeys (Macaca mulatta), weighingetween 3.0 and 6.8 kg, were used. The animals were the sames in the accompanying paper on subcortical connections of theortical larynx area.
All experimental procedures were approved by the Animal Eth-cs Committee of the district government Braunschweig, Loweraxony, Germany. The experiments conformed to the National In-titutes of Health guidelines on the ethical use of animals. Care wasaken to minimize the number of animals used and their suffering.
urgery and injection
ll surgical procedures were carried out as described in the ac-ompanying paper. Briefly, under general anesthesia, the headas fixed in a stereotaxic instrument and a craniotomy of aiameter of 15–20 mm was made above the inferior motor cortex.he motor cortex was explored with electrical brain stimulation,
ooking for sites yielding vocal fold adduction when stimulated.ffective sites were injected with 3% WGA-HRP (lectin fromriticum vulgaris conjugated to horseradish peroxidase). After the
njections, the bone defect was closed and the muscle fascia andkin were sutured.
ixation and histological processing
hree days after the operation, the monkeys were perfused undereep narcosis with 0.9% saline, followed by 1% paraformalde-yde/1.25% glutaraldehyde buffer in 0.1 M phosphate buffer. The
rains were removed and cut at 45 �m in the stereotaxic frontal
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149134
lane on a freezing microtome. Immunohistochemical tracer iden-ification was carried out with tetramethylbenzidine, according to aodification of Mesulam (1978).
ata analysis
he sections were evaluated microscopically under bright andark field illumination. Labeled structures were identified accord-
ng to the stereotaxic atlas of the rhesus monkey brain of Paxinost al. (2000). Photo documentation was made with the help of aigital camera and proper software.
RESULTShe injection sites of all three animals were more or lessound-shaped and were located with their center about
mm above the Sylvian fissure between the inferior
ig. 1. (A) Photograph of the injection site within the laryngeal motorrea. (B–F) Microphotographs of ipsilateral dysgranular insula (B), ipsila
6V (F). Scale bars�5 mm (A); (B) 200 �m; (D) 100 �m; (C–F) 50 �m. All photot al. (2000). For abbreviations, see list.
ranch of the arcuate sulcus rostrally and the subcentralimple posteriorly. There were slight differences in thenterior–posterior extent of the injections. While in the firstnimal, the injection site reached from A 28.2 to A 23.5, the
njection site of the second animal reached from A 28.2 to22.8 and that of the third animal from A 27.8 to A 23.7.ytoarchitectonically, the injection sites corresponded toreas 6VR and ProM of Paxinos et al. (2000) (Figs. 1A, 2And 3, A 28–23.5). The tracer injection, in each case,
nvolved all six cortical layers (Fig. 1A). In animal 3, the twonjection sites merged into each other. All injection sitesere characterized by an intensely labeled central core ofomogeneous reaction product, surrounded by a broadalo. Retrogradely labeled cells outside of the injection site
volving the rostral ventrolateral premotor cortex (6VR) and promotorM (C), ipsilateral area 4 (D), ipsilateral area 44 (E), and ipsilateral area
cortex, interal Pro
graphs were taken from animal 1. Nomenclature according to Paxinos
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149 135
ostly had pyramidal shape and were located in the thirdortical layer. Lower densities of retrogradely labeled cellsere found in the fifth layer (Fig. 1B–F). Anterograde la-eling also was detected in various areas. As the antero-rade projections have been reported already in an earliertudy (Simonyan and Jürgens, 2002), we will limit our-elves in the following to the description of the retrograderojections.
Due to the somewhat different size of the injectionites, the number of retrogradely labeled cortical areasanged between 29 and 40. As one or the other injectionight have invaded non-laryngeal parts of the motor orremotor cortex, we accepted only those projections found
n at least two of the three experimental animals. Alto-ether, 34 cytoarchitectonically distinguishable areas were
ound to be retrogradely labeled in at least two animals.hese areas are listed in Table 1 and are presented iniagrammatic form in Figs. 2 and 3.
Retrograde labeling could be followed from the injec-ion site along the upper bank of the Sylvian fissure into theostral and caudal directions (Fig. 2A and 3). Intense la-eling was found primarily in the lower rostral ventrolateralremotor cortex (area 6VR) and promotor area (arearoM) (Fig. 2A and Fig. 3, A, 28–22). Labeled cells werebserved through the entire anterior–posterior distance inhe second, third and fifth layers, with a dominance in thehird layer. Caudal to the injection site, retrogradely labeledells of lesser density extended to the inferior caudal ven-rolateral premotor cortex (area 6VC; Fig. 2A and Fig. 3, A0.5–17.5). Small clusters of labeled cells were found inhe inferior and intermediate parts of the primary motorortex (area 4) (Fig. 2A and Fig. 3, A 16–11.5). Labeled
Abbreviation
I Agranular insulamt Anterior middle temporal sulcusr Arcuate sulcusrsp Arcuate sulcus spursd Anterior subcentral dimplec Corpus callosumd Caudate nucleusg CingulumG Cingulate gyrusgs Cingulate sulcusr Corona radiatas Central sulcusI Dysgranular insulaIP Depth intraparietal area, GU Gustatory cortexI Granular insula
ar Inferior arcuate sulcusorb Intermediate orbital sulcuspd Inferior precentral dimplePro Insular proisocortexps Intraparietal sulcusf Lateral fissureu Lunate sulcusorb Lateral orbital cortex
orb Medial orbital cortexG Orbital gyrus
lfs Olfactory sulcus
ells in these areas are largely confined to the third layer,ith some cells also in the fifth layer.
Further caudally, the laryngeal motor cortex is con-ected with the most inferior primary somatosensory cor-ex, involving all four subareas, that is, areas 3a, 3b, 1 and
(Fig. 2A and Fig. 3, A 22–13). Labeled cells are concen-rated mainly in the third layer, with a few seen also in thefth and sixth layers.
Dorsally to the injection site, small clusters of labeledells in the third and fifth layers were observed in the
ntermediate part of the rostral dorsolateral premotor cor-ex (area 6DR) and caudal dorsolateral premotor cortexarea 6DC) in the region around the superior precentralimple (Fig. 2A and Fig. 3, A 26.5–23.5 and A 20.5–17.5).
In the prefrontal cortex, heavy labeling was found in theentral two thirds of the ventrolateral prefrontal cortexarea 47/12L), with a gradual decline toward the lateralrbital frontal cortex (area 47/12O), orbital proisocortexnd central orbital frontal cortex (area 13) (Fig. 2A, D andig. 3, A 37–23.5). In the latter areas, labeled cells occur iniscrete patches in both the third and fifth layers. Labelingid not invade the neighboring granular area 11.
Scattered labeling of medium density was detected inhe lower prearcuate cortex and rostral bank of the inferiorrcuate sulcus (area 45) as well as in the lower part of theaudal bank of the inferior arcuate sulcus (area 44) (Fig.B and Fig. 3, A 34–25). Labeled cells were located pre-ominantly in the third layer of these regions.
Small clusters of labeled cells were also found in thepper prearcuate cortex in the region around the superiorrcuate sulcus and in the depth of the arcuate sulcus spurarea 8A) as well as in the lower bank of the principal
the figures
AI Orbital periallocortexro Orbital proisocortex
Superior parietal cortexAnterior inferoparietal cortex
G Inferoparietal cortexOp Anterior inferoparietal cortex
K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149136
ig. 2. Schematic diagrams of the rhesus monkey brain showing (A) lateral views of the left and right hemisphere, (B) unfolded cortex of the principalnd arcuate sulci, (C) unfolded cortex within the Sylvian fissure, (D) ventral views of the left and right hemisphere, (E) medial views of the left and rightemisphere with unfolded sulcus cinguli. Dots indicate regions in which retrogradely labeled neurons were found in at least two of the threexperimental animals (for quantitative differences between animals as well as structures, see Table 1). The injection site common to all three animals
s indicated by the solid black area on the lateral view. In all diagrams, the left hemisphere represents the injection side. Brain diagrams and
ytoarchitectonic nomenclature based on Paxinos et al. (2000). For abbreviations, see list.
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149 137
ulcus (area 46V) and in the depth of the central third of therincipal sulcus (area 46V/46D) (Fig. 2B and Fig. 3, A 37–2.5 and 20.5). Here, labeling was restricted to the third layer.
In the mediofrontal cortex, retrogradely labeled cells were
Fig. 2
ound in the central third of the supplementary motor area w
SMA; area 6M) and the underlying cingulate cortex (Fig. 2End Fig. 3, A 34–11.5). Here, labeling reached from the levelf the genu of the corpus callosum (area 24) to the posterioringulate gyrus (area 23). A major part of the labeled cells
ued).
ere located in the depth of the cingulate sulcus, invading the
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149138
pper as well as lower lips of the sulcus, with the most denseabeling in the areas 24b, 24c, and medium to weak labelingn the areas 24d, 24a, 23c and 23b. Labeling within theingulate cortex was predominantly of pyramidal cells in the
Fig. 2
hird layer with fewer cells in the fifth layer. a
The cortical larynx area also receives an extensivenput from the cortex within the Sylvian fissure. In therontoparietal operculum, labeling of medium density wasound in a scattered form from the most rostral part of the
ued).
nterior secondary somatosensory cortex (area PV) into
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149 139
he inferior part of the posterior secondary somatosensoryortex (area SII) (Fig. 2C and Fig. 3, A 20.5–17.5 and4.5–7). Heavy labeling was found in the agranular, dys-ranular and granular insula (areas AI, DI, GI) throughout
ts entire rostro-caudal extent. In the insular proisocortex,abeled cells formed a narrow band along the upper part ofhis area (Fig. 2C and Fig. 3, A 23.5–7). Labeled cells wererominent in the third layer with a few cells in the fifth layer.
Very few labeled cells were found within the centralart of the dorsal bank of the superior temporal sulcus (Fig.C and Fig. 3, A 17.5). These cells were mainly found in
he third layer.Contralateral to the injection side, only 14 out of the 34
egions labeled ipsilaterally contained labeled cells in ateast two animals (Table 1). All these regions showed a
uch weaker labeling than the corresponding ipsilateralegions. Crossing anterogradely labeled WGA-HRP fibersere only found in the corpus callosum, not the anterior
able 1. Brain structures with output to the cortical larynx areaa
���, Heavy projection; ��, medium projection; �, weak projection;hat contained labeled cells in at least two of the three animals on at leall animals.
ommissure. The contralateral labeling was limited almost c
xclusively to the third and fifth layer; but these laminaeere not always labeled together in the same region.
Scattered groups of labeled cells were found in the rostralentrolateral premotor cortex (area 6VR), promotor cortexProM), lower post- and prearcuate cortex (areas 44, 45),entrolateral prefrontal cortex (area 47/12L), lateral orbitalrontal cortex (area 47/12O), agranular, dysgranular andranular insula as well as secondary somatosensory cortexarea SII) (Fig. 2A, B, D and Fig. 3, A 32.5–17.5 and 13).
On the medial surface, some labeled cells were lo-ated in the SMA (area 6M), anterior cingulate cortexareas 24b, c) and lower bank of posterior cingulate sulcusarea 14; Fig. 2E and Fig. 3, A 32.5–13).
DISCUSSION
otor input
he cortical larynx area receives input from essentially five
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149140
on-laryngeal primary motor cortex, supplementary motorrea, anterior and posterior cingulate motor areas and the
ig. 3. Frontal sections of the rhesus monkey brain, showing the retroells. Each section shows the distribution of labeled cells at the planiagrams and nomenclature are based on Paxinos et al. (2000). For
entrolateral premotor cortex. Input from the primary motor d
ortex comes from its tongue, lip and jaw representation.hese regions border the larynx area caudally and caudome-
abeled areas in animal 1. Each dot represents one to several labeledd as well as planes up to 0.5 mm anterior and posterior to it. Brain
ions, see list.
gradely le indicate
ially. Their electrical stimulation induces movements of the
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149 141
espective organs (Huang et al., 1988; Woolsey et al., 1952).ingle-unit recording reveals tongue, lip and jaw movement-
elated neuronal activity (Murray and Sessle, 1992). Inactiva-ion of these regions affects learned oral movements (Murray
Fig. 3
t al., 1991). In addition to the input from the motor cortical n
ace area, we found an input from a motor cortical regionigher up in the precentral cortex, probably representing
runk muscles (Woolsey et al., 1952). As several behavioratterns, such as phonation, coughing, swallowing, abdomi-
ued).
al pressing and breath holding, demand the cooperation of
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149142
aryngeal with oral and respiratory muscles, it makes sensehat the motor cortical larynx area is connected with theongue, lip, jaw and trunk area of the motor cortex.
Recent brain imaging studies, furthermore, have shown
Fig. 3
hat during speaking, there is a global activation of the facial i
nd laryngeal motor area, together with the trunk motor areaBookheimer et al., 2000; Herholz et al., 1994; Hirano et al.,996). Brain activation during speaking is bilateral. In theresent study, the left cortical larynx area received a direct
ued).
nput from the right cortical larynx area. A comparison with
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149 143
ur anterograde projection study (Simonyan and Jürgens,002) makes clear that left and right cortical areas are recip-ocally connected. No reciprocal projections, however, seemo exist between cortical larynx area of the one side and face
Fig. 3
r trunk area of the other side. S
The SMA is another source of cortical input into theotor cortical larynx area. The input is not limited to the
arynx area, but connects all parts of the primary motorortex with the SMA (Luppino et al., 1991; Muakkassa and
ued).
trick, 1979). The connections are reciprocal (Wiesendan-
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149144
er, 1986). There is some disagreement in the literaturebout the existence of a somatotopy in SMA. While someuthors describe a gross somatotopy, with the head rep-esented rostrally and the legs caudally (Luppino et al.,
Fig. 3
991; Muakkassa and Strick, 1979; Woolsey et al., 1952), t
thers deny such a somatotopy (Macpherson et al., 1982;enfield and Welch, 1951). In the present study, retro-radely labeled cells were limited to the central third of theMA. In brain imaging studies, the SMA has been shown
ued).
o be active during the execution of learned complex motor
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149 145
equences, including speech and singing (Bookheimer etl., 1995; Herholz et al., 1994; Hirano et al., 1996; Perry etl., 1999; Price, 2000). By electrical stimulation of theMA, vocal utterances can be produced in human pa-
Fig. 3
ients, but not in monkeys (Jürgens and Ploog, 1970; Pen- (
eld and Welch, 1951). Bilateral lesions in the SMA do notffect monkey call production (Kirzinger and Jürgens,982), but severely reduce the motivation to speak inumans, a syndrome called transcortical motor aphasia
ued).
Erickson and Woolsey, 1951; Gelmers, 1983; Rubens,
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149146
982). These findings suggest that the SMA is involved inhe control of speech and song, but not in monkey callroduction.
In the cingulate cortex, two motor areas have been
Fig. 3
istinguished: one in the lower lip of the anterior cingulate t
ulcus, corresponding to area 24c; the other in the lower lipf the posterior cingulate sulcus, corresponding to area3c (Morecraft and Van Hoesen, 1992; Picard and Strick,996). Both areas contained retrogradely labeled cells in
ued).
he present study. Marked labeling, in addition, was found
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K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149 147
n the anterior cingulate cortex below the cingulate sulcusarea 24b). This area has been shown in electrical stimu-ation experiments to produce species-specific vocalizationn the rhesus monkey, squirrel monkey, cat and bat (foreview, see Jürgens, 2002). Bilateral lesions in the anterioringulate cortex have been reported to abolish condi-ioned, but not unconditioned, vocalization in the rhesusonkey (Aitken, 1981; Sutton et al., 1974) and reduce theumber of spontaneous vocal utterances in the squirrelonkey (MacLean and Newman, 1988). In humans, bilat-ral lesions in the anterior cingulate cortex affect the vol-ntary control of emotional vocal utterances (Jürgens andon Cramon, 1982).
Cortical input reaches the motor cortical larynx arealso from the rostrally bordering peri-arcuate cortex. Thisegion is considered by some authors to be homologous toroca’s area (areas 44 and 45) (Paxinos et al., 2000;etrides and Pandya, 1994, 2001). From single-unit re-ording studies, it is known that the neurons in the rostralentrolateral premotor cortex have very complex reactionharacteristics. Some of them are active during the exe-ution of specific mouth movements and, at the same time,o the observation of corresponding oral movements inonspecifics (Ferrari et al., 2003). In humans, brain imag-
ng studies have shown an activation in Broca’s area dur-ng complex, but not simple, speech tasks. Specifically, if aerson is asked to repeat simple phonemes or the monthsf the year, no activity using positron emission tomographyPET) is found in Broca’s area. If, in contrast, a person issked to recite a memorized prose passage, activity isound (Bookheimer et al., 2000). Lesions in Broca’s area,ontrary to those in the lower primary motor cortex, do notause a paresis of the oral muscles (Mohr et al., 1978).roca’s area in humans and its counterpart, the inferioreri-arcuate cortex in the monkey, seem to provide theotor cortex with information necessary for the imitation ofral behavior and the long-term organization of learnedromotor sequences.
ensory input
omatosensory input of cortical origin reaches the larynxrea from the primary and secondary somatosensory cor-ices. Within the primary somatosensory cortex, retro-radely labeled cells were limited to its lateralmost part.his region receives somatosensory input from the facend intraoral regions (Dreyer et al., 1975; Lin et al., 1994).abeling was found in all four subareas, that is, Brodmannreas 3a, 3b, 1 and 2. Area 3a is known to receive inputainly from deep receptors, such as muscle spindles and
endon organs, while areas 3b and 1 receive primarily inputrom surface receptors, such as Merkel cells and Meiss-er’s corpuscles, and area 2 receives mixed input (Jonesnd Porter, 1980; Kaas et al., 1979; Manger et al., 1996;elson et al., 1980; Pons et al., 1985; Wiesendanger andiles, 1982). The fact that the cortical larynx area receivesn input from all four subareas suggests that vocal foldontrol relies on information coming from various types of
echanoreceptors. a
Somatosensory input reaches the cortical larynx arealso from two areas hidden in the depth of the Sylvianssure: the anterior secondary somatosensory area PVnd the posterior secondary somatosensory area SII. Ac-ording to Krubitzer et al. (1995), both areas show a so-atotopy, with the face representation bordering the face
epresentation of the primary somatosensory cortex andhe arm and leg representation following the face repre-entation toward the insula. In the present study, labeledells were distributed over large parts of PV and SII.
The larynx area does not only receive sensory infor-ation of the somatosensory type. A small group of retro-radely labeled cells was also found in the depth of theuperior temporal sulcus. This region represents multimo-al association cortex, receiving auditory, visual as well asomatosensory input (Baylis et al., 1987; Hikosaka et al.,988). It is still unclear in which way this multimodal infor-ation is used by the cortical larynx area in laryngeal
ontrol. Brain imaging studies show that the cortex of theuperior temporal sulcus is active during listening to wordss well as reading a text. The activation is stronger duringpeaking than during listening to words (Price, 2000). Thisoints to an interaction between language perception and
anguage production in the superior temporal sulcal cortex.
refrontal, orbital frontal and insular input
hile the premotor cortex, SMA, primary and secondaryomatosensory cortices as well as cingulate sulcal cortexepresent “classical” input structures of the primary motorortex, this does not hold for the prefrontal, orbital frontalnd insular cortices (Ghosh et al., 1987; Godschalk et al.,984; Leichnetz, 1986; Muakkassa and Strick, 1979; Pan-ya and Kuypers, 1969). The reason that the latter struc-ures contained retrogradely labeled cells in the presenttudy, but were not found by other authors to project to therimary motor cortex, is the special position of the larynxepresentation within the motor cortex. While all the otherotor cortical body representations (face, arms, trunk,
egs, tail) are lined up along the central sulcus, the larynxepresentation lies far more rostrally, occupying area 6,nstead of area 4. Laterally as well, the larynx area takesn extreme position. Together with the caudally adjacentongue representation, the larynx representation has theateralmost position of all body representations. As a con-equence, the larynx area shows projections, which haveeen considered to be typical of the premotor and peri-ylvian cortex, but not the motor cortex. Specifically, theremotor cortex is one of the classical target structures ofhe prefrontal cortex, the insula is directly connected withhe peri-Sylvian cortex, and the orbital frontal cortex haseen shown to project to regions combining a peri-Sylvianith a premotor position (Augustine, 1996; Barbas andandya, 1987; Deacon, 1992; Matelli et al., 1986; More-raft and Van Hoesen, 1993; Tokuno et al., 1997).
While the prefrontal and orbital frontal cortex is as-umed to be involved in vocal control only in a very indirectay (Price, 1996), the insula seems to play a more specific
ole. The insula, similar to the facial sensorimotor cortex
nd SMA, is regularly activated in PET studies during
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M
K. Simonyan and U. Jürgens / Neuroscience 130 (2005) 133–149148
peaking, singing and whispering (Bookheimer et al.,000; Paus et al., 1996; Perry et al., 1999). Lesions in the
nsula cause speech apraxia, a syndrome characterized bympairment in the coordination of speech movementsDronkers, 1996).
eciprocal connections
comparison between the retrograde projections of theresent study and the anterograde projections reported inur previous study (Simonyan and Jürgens, 2002) showshat almost all cortical connections of the motor corticalarynx area are reciprocal. More specifically, the larynxrea receives massive projections from and projectseavily into the neighboring inferior premotor, prefrontalnd motor cortex, anterior cingulate cortex, secondary so-atosensory cortex and insula. Weaker reciprocal connec-
ions exist, in addition, with the dorsolateral premotor, pre-rontal and motor cortex, the SMA, primary somatosensoryortex and cortex within the superior temporal sulcus. Thenly region projecting to the larynx area without receivingn input from it is the central orbital frontal cortex (area 13).his projection, however, is a very weak one. Anterograderojections of the larynx area, that are not reciprocated, goo the inferior parietal cortex (areas inferoparietal cortex,osterior inferoparietal cortex), posterior parietoopercularortex (areas anterior inferoparietal cortex, posterior pari-toopercular cortex) and cortex within the intraparietalulcus.
cknowledgment—Supported by the Deutsche Forschungsge-einschaft, GRK 289.
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(Accepted 18 August 2004)(Available online 28 October 2004)
