Developmental and evolutionary data from vertebrates are beginning to elucidate the origin of the sensorimotor pathway that links gravity and motion detection to image-stabilizing eye movements - the vestibulo-ocular reflex (VOR). Conserved transcription factors coordinate the development of the vertebrate ear into three functional sensory compartments (graviception/translational linear acceleration, angular acceleration and sound perception). These sensory components connect to specific populations of vestibular and auditory projection neurons in the dorsal hindbrain through undetermined molecular mechanisms. In contrast, a molecular basis for the patterning of the vestibular projection neurons is beginning to emerge. These are organized through the actions of rostrocaudally and dorsoventrally restricted transcription factors into a ‘hodological mosaic' within which coherent and largely segregated subgroups are specified to project to different targets in the spinal cord and brain stem. A specific set of these regionally diverse vestibular projection neurons functions as the central element that transforms vestibular sensory signals generated by active and passive head and body movements into motor output through the extraocular muscles. The large dynamic range of motion-related sensory signals requires an organization of VOR pathways as parallel, frequency-tuned, hierarchical connections from the sensory periphery to the motor output. We suggest that eyes, ears and functional connections subserving the VOR are vertebrate novelties that evolved into a functionally coherent motor control system in an almost stereotypic organization across vertebrate taxa.

Angelaki DE, Cullen KE (2008): Vestibular system: the many facets of a multimodal sense. Annu Rev Neurosci 31:125-150.
Baker R (1998): From genes to behavior in the vestibular system. Otolaryngol Head Neck Surg 119:263-275.
Beraneck M, Pfanzelt S, Vassias I, Rohregger M, Vibert N, Vidal P, Moore L, Straka H (2007): Differential intrinsic response dynamics determine synaptic signal processing in frog vestibular neurons. J Neurosci 27:4283-4296.
Birinyi A, Straka H, Matesz C, Dieringer N (2001): Location of dye-coupled second order and of efferent vestibular neurons labeled from individual semicircular canal or otolith organs in the frog. Brain Res Bull 921:44-59.
Bosley TM, Oystreck DT, Robertson RL, al Awad A, Abu-Amero K, Engle EC (2006): Neurological features of congenital fibrosis of the extraocular muscles type 2 with mutations in PHOX2A. Brain 129:2363-2374.
Bouchard M, de Caprona D, Busslinger M, Xu P, Fritzsch B (2010): Pax2 and Pax8 cooperate in mouse inner ear morphogenesis and innervation. BMC Dev Biol 10:89.
Briscoe J, Ericson J (2001): Specification of neuronal fates in the ventral neural tube. Curr Opin Neurobiol 11:43-49.
Brunet JF, Pattyn A (2002): Phox2 genes - from patterning to connectivity. Curr Opin Genet Dev 12:435-440.
Budelmann BU (1988): Morphological diversity of equilibrium receptor systems in aquatic invertebrates; in Atema J, Fay RR, Popper AN, Tavolga WN (eds): Sensory Biology of Aquatic Animals. New York, Springer, pp 757-782.
Budelmann B (1992): Hearing in nonarthropod invertebrates; in Webster DB, Fay RR, Popper AN (eds): The Evolutionary Biology of Hearing. New York, Springer, pp 141-155.
Budelmann BU, Bleckmann H (1988): A lateral line analogue in cephalopods: water waves generate microphonic potentials in the epidermal head lines of Sepia and Lolliguncula. J Comp Physiol A 164:1-5.
Budelmann BU, Young JZ (1993): The oculomotor system of decapod cephalopods: eye muscles, eye muscle nerves, and the oculomotor neurons in the central nervous system. Philos Trans R Soc Lond B Biol Sci 340:93-125.
Burighel P, Caicci F, Manni L (2011): Hair cells in non-vertebrate models: lower chordates and molluscs. Hear Res 273:14-24.
Cambronero F, Puelles L (2000): Rostrocaudal nuclear relationships in the avian medulla oblongata: a fate map with quail chick chimeras. J Comp Neurol 427:522-545.
Candiani S, Moronti L, De Pietri Tonelli D, Garbarino G, Pestarino M (2011): A study of neural-related microRNAs in the developing amphioxus. Evodevo 2:15.
Chagnaud BP, Simmers J, Straka H (2012): Predictability of visual perturbation during locomotion: implications for corrective efference copy signaling. Biol Cybern 106:669-679.
Chang W, Lin Z, Kulessa H, Hebert J, Hogan BL, Wu DK (2008): Bmp4 is essential for the formation of the vestibular apparatus that detects angular head movements. PLoS Genet 4:e1000050.
Chen J, Streit A (2013): Induction of the inner ear: stepwise specification of otic fate from multipotent progenitors. Hear Res 297:3-12.
Christophorou NA, Mende M, Lleras-Forero L, Grocott T, Streit A (2010): Pax2 coordinates epithelial morphogenesis and cell fate in the inner ear. Dev Biol 345:180-190.
Cochran SL, Dieringer N, Precht W (1984): Basic optokinetic-ocular reflex pathways in the frog. J Neurosci 4:43-57.
Combes D, Le Ray D, Lambert FM, Simmers J, Straka H (2008): An intrinsic feed-forward mechanism for vertebrate gaze stabilization. Curr Biol 18:241-243.
Consi TR, Macagno ER, Necles N (1987): The oculomotor system of Daphnia magna. The eye muscles and their motor neurons. Cell Tissue Res 247:515-523.
Coppola E, Pattyn A, Guthrie SC, Goridis C, Studer M (2005): Reciprocal gene replacements reveal unique functions for Phox2 genes during neural differentiation. EMBO J 24:4392-4403.
Cullen K (2011): The neural encoding of self-motion. Curr Opin Neurobiol 21:587-595.
Dasen J (2013): Hox genes: choreographers in neural development, architects of circuit organization. Neuron 80:12-34.
de Burlet HM (1934): Vergleichende Anatomie des statoakustischen Organs. a) Die innere Ohrsphäre; in Bolk L, Göppert E, Kallius E, Lubosch W (eds): Handbuch der vergleichenden Anatomie der Wirbeltiere. Berlin, Urban & Schwarzenberg, vol 2, pp 1293-1432.
Di Bonito M, Glover JC, Studer M (2013): Hox genes and region-specific sensorimotor circuit formation in the hindbrain and spinal cord. Dev Dyn 242:1348-1368.
Díaz C, Glover JC (2002): Comparative aspects of the hodological organization of the vestibular nuclear complex and related neuron populations. Brain Res Bull 57:307-312.
Díaz C, Glover JC, Puelles L, Bjaalie J (2003): The relationship between hodological and cytoarchitectonic organization in the vestibular complex of the 11-day chicken embryo. J Comp Neurol 457:87-105.
Díaz C, Puelles L (2003): Plurisegmental vestibulocerebellar projections and other hindbrain cerebellar afferents in midterm chick embryos: biotinylated dextranamine experiments in vitro. Neuroscience 117:71-82.
Díaz C, Puelles L, Marin F, Glover JC (1998): The relationship between rhombomeres and vestibular neuron populations as assessed in quail-chick chimeras. Dev Biol 202:14-28.
Duncan JS, Fritzsch B (2012): Evolution of sound and balance perception: innovations that aggregate single hair cells into the ear and transform a gravistatic sensor into the organ of Corti. Anat Rec (Hoboken) 295:1760-1774.
Eatock RA, Xue J, Kalluri R (2008): Ion channels in mammalian vestibular afferents may set regularity of firing. J Exp Biol 211:1764-1774.
Ferrario JE, Baskaran P, Clark C, Hendry A, Lerner O, Hintze M, Allen J, Chilton JK, Guthrie SC (2012): Axon guidance in the developing ocular motor system and Duane retraction syndrome depends on Semaphorin signaling via alpha2-chimaerin. Proc Natl Acad Sci USA 109:14669-14674.
Fetcho JR (1992): The spinal motor system in early vertebrates and some of its evolutionary changes. Brain Behav Evol 40:82-97.
Fritzsch B (1996): Similarities and differences in lancelet and craniate nervous systems. Isr J Zool 42:147-160.
Fritzsch B (1998): Evolution of the vestibulo-ocular system. Otolaryngol Head Neck Surg 119:182-192.
Fritzsch B, Beisel KW, Jones K, Farinas I, Maklad A, Lee J, Reichardt LF (2002): Development and evolution of inner ear sensory epithelia and their innervation. J Neurobiol 53:143-156.
Fritzsch B, Beisel KW, Pauley S, Soukup G (2007): Molecular evolution of the vertebrate mechanosensory cell and ear. Int J Dev Biol 51:663-678.
Fritzsch B, Glover JC (2007): Evolution of the deuterostome central nervous system: an intercalation of developmental patterning processes with cellular specification processes; in Kaas JH (ed): Evolution of Nervous Systems. Oxford, Academic Press, vol 2, pp 1-24.
Fritzsch B, Gregory D, Rosa-Molinar E (2005): The development of the hindbrain afferent projections in the axolotl: evidence for timing as a specific mechanism of afferent fiber sorting. Zoology (Jena) 108:297-306.
Fritzsch B, Nichols DH (1993): DiI reveals a prenatal arrival of efferents at the differentiating otocyst of mice. Hear Res 65:51-60.
Fritzsch B, Nichols DH, Echelard Y, McMahon AP (1995): Development of midbrain and anterior hindbrain ocular motoneurons in normal and Wnt-1 knockout mice. J Neurobiol 27:457-469.
Fritzsch B, Northcutt RG (1993a): Cranial and spinal nerve organization in amphioxus and lampreys: evidence for an ancestral craniate pattern. Acta Anat (Basel) 148:96-109.
Fritzsch B, Northcutt RG (1993b): Origin and migration of trochlear, oculomotor and abducent motor neurons in Petromyzon marinus L. Brain Res Dev Brain Res 74:122-126.
Fritzsch B, Pan N, Jahan I, Duncan JS, Kopecky BJ, Elliott KL, Kersigo J, Yang T (2013): Evolution and development of the tetrapod auditory system: an organ of Corti-centric perspective. Evol Dev 15:63-79.
Fritzsch B, Sonntag R, Dubuc R, Ohta Y, Grillner S (1990): Organization of the six motor nuclei innervating the ocular muscles in lamprey. J Comp Neurol 294:491-506.
Fritzsch B, Signore M, Simeone A (2001): Otx1 null mutant mice show partial segregation of sensory epithelia comparable to lamprey ears. Dev Genes Evol 211:388-396.
Fritzsch B, Straka H (2014): Evolution of mechanosensory hair cells and inner ears: toward identifying stimuli that select mutation driven altered morphologies. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 200:5-18.
Gehring WJ (2011): Chance and necessity in eye evolution. Genome Biol Evol 3:1053-1066.
Gilland E, Baker R (1993): Conservation of neuroepithelial and mesodermal segments in the embryonic vertebrate head. Acta Anat (Basel) 148:110-123.
Gilland E, Baker R (2005): Evolutionary patterns of cranial nerve efferent nuclei in vertebrates. Brain Behav Evol 66:234-254.
Glover JC (1994): The organization of vestibulo-ocular and vestibulospinal projections in the chicken embryo. Eur J Morphol 32:193-200.
Glover JC (2000): Neuroepithelial ‘compartments' and the specification of vestibular projections. Prog Brain Res 124:3-21.
Glover JC (2003): The development of vestibulo-ocular circuitry in the chicken embryo. J Physiol (Paris) 97:17-25.
Glover JC, Petursdottir G (1991): Regional specificity of developing reticulospinal, vestibulospinal and vestibulo-ocular projections in the chicken embryo. J Neurobiol 22:353-376.
Goldberg JM (2000): Afferent diversity and the organization of central vestibular pathways. Exp Brain Res 130:277-297.
Grocott T, Tambalo M, Streit A (2012): The peripheral sensory nervous system in the vertebrate head: a gene regulatory perspective. Dev Biol 370:3-23.
Hammond KL, Whitfield TT (2006): The developing lamprey ear closely resembles the zebrafish otic vesicle: Otx1 expression can account for all major patterning differences. Development 133:1347-1357.
Hill A, Boll W, Ries C, Warner L, Osswalt M, Hill M, Noll M (2010): Origin of Pax and Six gene families in sponges: single PaxB and Six1/2 orthologs in Chalinula loosanoffi. Dev Biol 343:106-123.
Hwang CH, Simeone A, Lai E, Wu DK (2009): Foxg1 is required for proper separation and formation of sensory cristae during inner ear development. Dev Dyn 238:2725-2734.
Jahan I, Kersigo J, Pan N, Fritzsch B (2010): Neurod1 regulates survival and formation of connections in mouse ear and brain. Cell Tissue Res 341:95-110.
Joyce Tang W, Chen JS, Zeller RW (2013): Transcriptional regulation of the peripheral nervous system in Ciona intestinalis. Dev Biol 378:183-193.
Kaminski HJ, Richmonds CR, Kusner LL, Mitsumoto H (2002): Differential susceptibility of the ocular motor system to disease. Ann NY Acad Sci 956:42-54.
Kopecky B, Santi P, Johnson S, Schmitz H, Fritzsch B (2011): Conditional deletion of N-Myc disrupts neurosensory and non-sensory development of the ear. Dev Dyn 240:1373-1390.
Kozmik Z, Daube M, Frei E, Norman B, Kos L, Dishaw LJ, Noll M, Piatigorsky J (2003): Role of Pax genes in eye evolution: a cnidarian PaxB gene uniting Pax2 and Pax6 functions. Dev Cell 5:773-785.
Lamb TD (2013): Evolution of phototransduction, vertebrate photoreceptors and retina. Prog Retin Eye Res 36:52-119.
Lambert FM, Beck JC, Baker R, Straka H (2008): Semicircular canal size determines the developmental onset of angular vestibuloocular reflexes in larval Xenopus. J Neurosci 28:8086-8095.
Lambert FM, Combes D, Simmers J, Straka H (2012): Gaze stabilization by efference copy signaling without sensory feedback during vertebrate locomotion. Curr Biol 22:1649-1658.
Lewis ER, Leverenz EL, Bialek WS (1985): The Vertebrate Inner Ear. Boca Raton, CRC Press.
Lorente de Nó R (1933): Vestibulo-ocular reflex arc. Arch Neurol Psychiatry 30:245-291.
Maklad A, Fritzsch B (2002): The developmental segregation of posterior crista and saccular vestibular fibers in mice: a carbocyanine tracer study using confocal microscopy. Brain Res Dev Brain Res 135:1-17.
Maklad A, Fritzsch B (2003a): Partial segregation of posterior crista and saccular fibers to the nodulus and uvula of the cerebellum in mice, and its development. Brain Res Dev Brain Res 140:223-236.
Maklad A, Fritzsch B (2003b): Development of vestibular afferent projections into the hindbrain and their central targets. Brain Res Bull 60:497-510.
Maklad A, Kamel S, Wong E, Fritzsch B (2010): Development and organization of polarity-specific segregation of primary vestibular afferent fibers in mice. Cell Tissue Res 340:303-321.
Markl H (1974): The perception of gravity and of angular acceleration in invertebrates; in Kornhuber HH (ed): Handbook of Sensory Physiology: vol VI/1 Vestibular System. Berlin, Springer, pp 17-74.
Mazan S, Jaillard D, Baratte B, Janvier P (2000): Otx1 gene-controlled morphogenesis of the horizontal semicircular canal and the origin of the gnathostome characteristics. Evol Dev 2:186-193.
Murakami Y, Pasqualetti M, Takio Y, Hirano S, Rijli FM, Kuratani S (2004): Segmental development of reticulospinal and branchiomotor neurons in lamprey: insights into the evolution of the vertebrate hindbrain. Development 131:983-995.
Nichols DH, Pauley S, Jahan I, Beisel KW, Millen KJ, Fritzsch B (2008): Lmx1a is required for segregation of sensory epithelia and normal ear histogenesis and morphogenesis. Cell Tissue Res 334:339-358.
Nolte C, Krumlauf R (2006): Expression of Hox genes in the nervous system of vertebrates; in Papageorgiou S (ed): Hox Gene Expression. Austin, Landes Bioscience & Springer, pp 14-41.
Pan N, Kopecky B, Jahan I, Fritzsch B (2012): Understanding the evolution and development of neurosensory transcription factors of the ear to enhance therapeutic translation. Cell Tissue Res 349:415-432.
Pani AM, Mullarkey EE, Aronowicz J, Assimacopoulos S, Grove EA, Lowe CJ (2012): Ancient deuterostome origins of vertebrate brain signalling centres. Nature 483:289-294.
Pasqualetti M, Díaz C, Renaud JS, Rijli F, Glover JC (2007): Fate-mapping the mammalian hindbrain: segmental origins of vestibular projection neurons assessed using rhombomere-specific Hoxa2 enhancer elements in the mouse embryo. J Neurosci 27:9670-9681.
Pauley S, Lai E, Fritzsch B (2006): Foxg1 is required for morphogenesis and histogenesis of the mammalian inner ear. Dev Dyn 235:2470-2482.
Pflieger JF, Dubuc R (2004): Vestibulo-reticular projections in adult lamprey: their role in locomotion. Neuroscience 129:817-829.
Pierce ML, Weston MD, Fritzsch B, Gabel HW, Ruvkun G, Soukup GA (2008): MicroRNA-183 family conservation and ciliated neurosensory organ expression. Evol Dev 10:106-113.
Prince VE, Price AL, Ho RK (1998): Hox gene expression reveals regionalization along the anteroposterior axis of the zebrafish notochord. Dev Genes Evol 208:517-522.
Puelles L (1978): A Golgi-study of oculomotor neuroblasts migrating across the midline in chick embryos. Anat Embryol (Berl) 152:205-215.
Puzdrowski RL (1998): Innervation of the medial rectus muscle in the ratfish, Hydrolagus colliei. J Comp Neurol 400:571-579.
Rota-Stabelli O, Campbell L, Brinkmann H, Edgecombe GD, Longhorn SJ, Peterson KJ, Pisani D, Philippe H, Telford MJ (2011): A congruent solution to arthropod phylogeny: phylogenomics, microRNAs and morphology support monophyletic Mandibulata. Proc Biol Sci 278:298-306.
Rubel EW, Fritzsch B (2002): Auditory system development: primary auditory neurons and their targets. Annu Rev Neurosci 25:51-101.
Simpson JI, Graf W (1985): The selection of reference frames by nature and its investigators; in Berthoz A, Melvill Jones G (eds): Adaptive Mechanisms in Gaze Control: Facts and Theories. Amsterdam, Elsevier, pp 3-16.
Soukup GA, Fritzsch B, Pierce ML, Weston MD, Jahan I, McManus MT, Harfe BD (2009): Residual microRNA expression dictates the extent of inner ear development in conditional Dicer knockout mice. Dev Biol 328:328-341.
Straka H, Biesdorf S, Dieringer N (1997): Canal-specific excitation and inhibition of frog second order vestibular neurons. J Neurophysiol 78:1363-1372.
Straka H (2010): Ontogenetic rules and constraints of vestibulo-ocular reflex development. Curr Opin Neurobiol 20:689-695.
Straka H, Baker R (2013): Vestibular blueprint in early vertebrates. Front Neural Circuits 7:182.
Straka H, Baker R, Gilland E (2001): Rhombomeric organization of vestibular pathways in larval frogs. J Comp Neurol 437:42-55.
Straka H, Baker R, Gilland E (2002a): The frog as a unique vertebrate model for studying the rhombomeric organization of functionally identified hindbrain neurons. Brain Res Bull 57:301-305.
Straka H, Beraneck M, Rohregger M, Moore LE, Vidal PP, Vibert N (2004): Second-order vestibular neurons form separate populations with different membrane and discharge properties. J Neurophysiol 92:845-861.
Straka H, Dieringer N (2004): Basic organization principles of the VOR: lessons from frogs. Prog Neurobiol 73:259-309.
Straka H, Holler S, Goto F (2002b): Patterns of canal and otolith afferent input convergence in frog second order vestibular neurons. J Neurophysiol 88:2287-2301.
Straka H, Holler S, Goto F, Kolb FP, Gilland E (2003): Differential spatial organization of otolith signals in frog vestibular nuclei. J Neurophysiol 90:3501-3512.
Straka H, Lambert FM, Pfanzelt S, Beraneck M (2009): Vestibulo-ocular signal transformation in frequency-tuned channels. Ann NY Acad Sci 1164:37-44.
Straka H, Vibert N, Vidal PP, Moore LE, Dutia MB (2005): Intrinsic membrane properties of vertebrate vestibular neurons: function, development and plasticity. Prog Neurobiol 76:349-392.
Streit A (2007): The preplacodal region: an ectodermal domain with multipotential progenitors that contribute to sense organs and cranial sensory ganglia. Int J Dev Biol 51:447-461.
Suwa H, Gilland E, Baker R (1996): Segmental organization of vestibular and reticular projections to spinal and oculomotor nuclei in the zebrafish and goldfish. Biol Bull 191:257-259.
Szentagothai J (1950): The elementary vestibulo-ocular reflex arc. J Neurophysiol 13:395-407.
Tischfield MA, Baris HN, Wu C, Rudolph G, Van Maldergem L, He W, Chan WM, Andrews C, Demer JL, Robertson RL, Mackey DA, Ruddle JB, Bird TD, Gottlob I, Pieh C, Traboulsi EI, Pomeroy SL, Hunter DG, Soul JS, Newlin A, Sabol LJ, Doherty EJ, de Uzcategui CE, de Uzcategui N, Collins ML, Sener EC, Wabbels B, Hellebrand H, Meitinger T, de Berardinis T, Magli A, Schiavi C, Pastore-Trossello M, Koc F, Wong AM, Levin AV, Geraghty MT, Descartes M, Flaherty M, Jamieson RV, Moller HU, Meuthen I, Callen DF, Kerwin J, Lindsay S, Meindl A, Gupta ML Jr, Pellman D, Engle EC (2010): Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance. Cell 140:74-87.
Trinajstic K, Sanchez S, Dupret V, Tafforeau P, Long J, Young G, Senden T, Boisvert C, Power N, Ahlberg PE (2013): Fossil musculature of the most primitive jawed vertebrates. Science 341:160-164.
Uchino Y, Ikegami H, Sasaki M, Endo K, Imagawa M, Isu N (1994): Monosynaptic and disynaptic connections in the utriculo-ocular reflex arc of the cat. J Neurophysiol 71:950-958.
Uchino Y, Sasaki M, Sato H, Imagawa M, Suwa H, Isu N (1996): Utriculoocular reflex arc of the cat. J Neurophysiol 76:1896-1903.
Vaage S (1969): The segmentation of the primitive neural tube in chick embryos (Gallus domesticus). A morphological, histochemical and autoradiographical investigation. Ergeb Anat Entwicklungsgesch 41:3-87.
von Uckermann G, Le Ray D, Combes D, Straka H, Simmers J (2013): Spinal efference copy signaling and gaze stabilization during locomotion in juvenile Xenopus frogs. J Neurosci 33:4253-4264.
Vopalensky P, Pergner J, Liegertova M, Benito-Gutierrez E, Arendt D, Kozmik Z (2012): Molecular analysis of the amphioxus frontal eye unravels the evolutionary origin of the retina and pigment cells of the vertebrate eye. Proc Natl Acad Sci USA 109:15383-15388.
Wada H (1998) Evolutionary history of free-swimming and sessile lifestyles in urochordates as deduced from 18S rDNA molecular phylogeny. Mol Biol Evol 15:1189-1194.
Wahl CM, Noden DM, Baker R (1994): Developmental relations between sixth nerve motor neurons and their targets in the chick embryo. Dev Dyn 201:191-202.
Young GC (2008): Number and arrangement of extraocular muscles in primitive gnathostomes: evidence from extinct placoderm fishes. Biol Lett 4:110-114.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.