Post-lesionalplasticity of cortical somatosensory maps: A review;Plasticité post-lésionnelle des cartes corticales somatosensorielles: Une revue

Comptes Rendus de l'Academie des Sciences - Serie III

Volumn 321, Issue 2-3, 1998, Pages 135-151

  Xerri, Christian ^a  

^a AIX MARSEILLE UNIVERSITY   (France)

Author keywords

[No Author keywords available]

Indexed keywords

ANIMAL; BRAIN MAPPING; DENERVATION; HUMAN; INJURY; INNERVATION; NERVE CELL PLASTICITY; PHYSIOLOGY; REVIEW; SENSORY NERVE; SKIN; SOMATOSENSORY CORTEX;

AFFERENT PATHWAYS; ANIMALS; BRAIN MAPPING; DENERVATION; HUMANS; NEURONAL PLASTICITY; SKIN; SOMATOSENSORY CORTEX;

EID: 18144433588     PISSN: 07644469     EISSN: None     Source Type: Journal    
DOI: 10.1016/s0764-4469(97)89813-7     Document Type: Article

References (113)

1. Byrne J.A., Calford M.B. 1991. Short-term expansion of receptive fields in rat primary somatosensory cortex after hindpaw digit dencrvation. Brain Res. 565, 218-224.
2. Calford M.B., Tweedale R. 1991. Immediate expansion of receptive fields of neurons in area 3b of macaque monkeys after digit denervation. Somatosens. Mot. Res. 8, 249-260.
3. Kalaska )., Pomeranz B., 1979. Chronic paw denervation causes an age-dependent appearance of novel responses from forearm in paw cortex of kittens and adult cats. Ncurophysiol. 42, 618-633.
4. Merzenich M.M., Kaas J.H., Wall J, Sur M,. Nelson R.J., Felleman DJ. 1983. Progression of change following median nerve section in the cortical representation of the hand in areas 3b and I in adult owl and squirrel monkeys. Neuroscience 10, 639-665.
5. Wall J.T, Cusick C.G. 1984. Cutaneous responsiveness in primary somatosensory (SI) hindpaw cortex before and after partial hindpaw deafferentation in adult rats. J. Neurosci. 4, 1499-1515.
6. Turnbull B.C., Rasmusson D.D. 1990. Acute effects of total or partial digit denervation on raccoon somatosensory cortex. Somatosens. Mot. Res. 7, 365-389.
7. Doetsch G.S., Harrison T.A., MacDonald A.C., Litaker M.S. 1996. Short-term plasticity in primary somatosensory cortex of the rat: rapid changes in magnitudes and latencies of neuronal responses following digit denervation. Exp. Brain Res. 112, 505-512.
8. Kelahan A.M. Doetsch G.S. 1984. Time-dependent changes in the functional organization of somatosensory cerebral cortex following digit amputation in adult raccons. Somatosens. Res. 2, 49-81.
9. Calford M.B., Tweedale R. 1991. Acute changes in cutaneous receptive fields in primary somatosensory cortex after digit denervation in adult flying fox.J. Neurophysiol. 65, 178-187.
10. Dykes R.W., Lamour Y. 1988. Neurons without demonstrable receptive fields outnumber neurons having receptive fields in samples from the somatosensory cortex of anesthetized or paralysed cats and rats. Brain Res. 440, 133-143.
11. Salimi I., Webster H.H., Dykes R.W. 1994. Neuronal activity in normal and deafferented forelimb somatosensory cortex of the awake cat. Brain Res. 656, 263-273.
12. Metzler J., Marks P. S. 1979. Functional changes in cat somatic sensory-motor cortex during short-term reversible epidural blocks. Brain Res. 177, 379-383.
13. Rossini P.M., Martino G., Narici L, Pasquarelli A., Peresson M., Pizzella V., Tecchio F., Torrioli G., Romani G.L. 1994. Short-term 'plasticity' in humans transient finger representation changes in sensory cortex somatotopy following ischémie anesthesia. Brain Res. 642, 169-177.
14. Merzenich M.M., Kaas J.H., Wall )., Nelson R.J., Sur M., Felleman, D.). 1983. Topographic reorganization of somatosensory cortical areas 3b and I in adult monkeys following restricted deaffercntation. Neuroscience 8,33-55.
15. Garraght, P.E., Kaas). H. 1991. Large-scale functional reorganization in adult monkey cortex after peripheral nerve injury. Proc. Njtl. Aad. Sei. U.S.A 88, 6976-6980.
16. Florence S.L., Wall J.T., KaasJ.H. 1991. Central projections from the skin of the hand in squirrel moukeys. J. Comp. Neural. 311, 563-578.
17. Schroeder C.E., Seto S., Garraghty P.E. 1997. Emergence of radial nea'e dominance in median nerve cortex after median nerve transection in an adult squirrel monkey. J. Neurophysiol. 77, 522-526.
18. Pons T. P., Garragty P.E., Ommaya A.K, KaasJ.H., Taub E., Mishkin M. 1991. Massive cortical reorganization after sensory deafferentation in adult macaques. Science 252,1857-1860.
19. Rausell E., Jones E.G. 1995. Extent of intracortical arborization of thalamocortical axons as a determinant of representational plasticity in monkey somatic sensory cortex. J. NeuroseJ. 15, 4270-4288.
20. Wall J.T., Kaas J.H., Sur M., Nelson R.J., Felleman D.J. Merzenich M.M. 1986. Functional reorganization in somatosensory cortical areas 3b and I of adult monkeys after median nerve repair: Possible relationships to sensory recovery in humans. J. NeuroseJ. 6, 218-233.
21. Manger P.R., Woods T.M., Jones E.G. 1996. Plasticity of the somatosensory cortical map in macaque monkeys after chronic partial amputation of a digit. Proc. R. Soc. Land. 263, 933-939.
22. Merzenich M.M., Nelson R.J., Striker M.P., Cynader M.S., Schopman A., Zook J.M. 1984. Somatosensory cortical map changes following digit amputation in adult monkeys.J. Comp. Ncurol. 224, 591-605.
23. Florence S.L., Kaas J.H. 1995. Large-scale reorganization at multiple levels of the somatosensory pathway follows therapeutic amputation of 'the hand in monkeys. J. NeuroseJ. 15, 8083-8095.
24. Turnbull B.C., Rasmusson D.D. 1991. Chronic effects of total or partial digit denervation on raccoon somatosensory cortex. Somatosens. Mot. Res. 8, 201-213.
25. Kelahan A.M, Ray R.H., Carson C.E., Massey C.E., Doetsch G.S. 1981. Functional reorganization of adult raccoon somatosensory cerebral cortex following neonatal digit amputation. Brain Res. 223, 152-159.
26. Govrin-Lippmann R., Devor M. 1978. Ongoing activity in severed nerves and variation in time. Brain Res. 159, 406-410.
27. Carson L.V., Kelahan A.M., Ray R.H., Massey C.E., Doetsch G.S. 1981. Effects of early peripheral lesions on the somatotopic organization of the cerebral cortex. In : Clinical Neurosurgery (Carmel P.W., ed), Williams and Wilkins, Baltimore, 552-546.
28. Zarzecki P., Wille S., Smits E., Gordon D.C., Kirchberger P., Rasmusson D.D. 1993. Synaptic mechanisms of representational plasticity: somatosensory and corticocortical EPSPs in reorganized raccoon SI cortex. J. Neurophysiol. 5, 1422-1432.
29. Coq J.O., Xerri C. 1997. Acute effects of piracetam after focal brain infarction on the reorganization of the forepaw representation map of the primary somatosensory cortex (SI) in the adult rat. Soc. Neurosci. Abstr.
30. Jenkins W.M., Merzenich M.M. 1987. Reorganization of neocortical representations after brain injury: a neurophysiological model of the bases of recovery from stroke. Progress in Brain Res. 71 (Seil F.J., Herbert E., Carlson B.M., eds.), Elsevier Science Publishers, 249-266.
31. Doetsch G.S., Johnston K.W., Hannan C.J. 1990. Physiological changes in the somatosensory forepaw cerebral cortex of adult raccoons following lesions of a single cortical digit representation. Fxp. Neurol. 108, 162-175.
32. Xerri C, Merzenich M.M., Jenkins W.M., Santucci S., Peterson B. 1998. Plasticity of somatosensory cortex representations paralleling sensorimotor skill recovery from stroke in adult owl and squirrel monkey. I. Neurophysiol. (in press).
33. Nudo R.J., Milliken G.W. 1996. Reorganization of movement representations in primary motor cortex following focal ischémie infarcts in adult squirrel monkeys.J. Neumphysiol. 75, 2144-2149.
34. Nudo R.J., Wise B.M., SiFuentes F., Milliken G.W. 1996. Neural substrate for the effects of rehabilitative training on motor recovery after ischémie infarct. Science 272, 1791-1794.
35. Wall, P.D. 1977. The presence of ineffective synapses and the circumstances which unmask them. Phil. Trans. R. Soc. Lond. B/ol. 278, 361-372.
36. Killackey H.P. 1989. Static and dynamic aspects of cortical somatotopy : A critical review. J. Cogn. Neurosci. 1, 3-11.
37. KaasJ.H., Merzenich M.M., Killackey H.P. 1983. The reorganization of somatosensory cortex following peripheral nerve damage in adult and developing mammals. Annu. Rev. Neurosci. 6, 325-356.
38. Jacobs K., DonoghueJ.P. 1991. Reshaping the cortical motor map by unmasking latent intracortical connections. Science 251, 944-947.
39. Lund J.P., Sun G.D., Lamarre Y. 1994. Cortical reorganization and deafferentation in adult macaques. 5c/ence 265, 546-548.
40. Garraghty P., Pons T., Sur M., Kaas J.H. 1989. The arbors of axons terminating in middle cortical layers of somatosensory area 3b in owl monkeys. Somatosens. Mot. Res. 6, 401-411.
41. [41) Garraghty P.E., SurM. 1990 Morphology of single intracellularly stained axons terminating in area 3b of macaque monkeys. J. Comp. Neurol. 294, 583-593.
42. Jensen K.F, Killackey H.P. 1987. Terminal arbors of axons projecting to the somatosensory cortex of the adults rat. I. The normal morphology of specific thalamocortical afférents. J. Neurosci.7, 3529-3543.
43. Landry P., Diadori P., Leclerc S., Dykes R.W. 1987. Morphological and electrophysiological characteristics of somatosensory thalamocortical axones studied with intra-axonal staining and recording in the cat. Exp. Brain Res. 65, 317-330.
44. Chagnac-Amitai Y., Connors B.W. 1989. Horizontal spread of synchronized activity in neocortex and its control by GABA-mediated inhibition. J. Neurophysiol. 4, 747-758.
45. Hicks T.P., Dykes R.W. 1983. Receptive field size for certain neurons in primary somatosensory cortex is determined by GABA-mediated intracortical inhibition. Brain Res. 274, 160-164.
46. Dykes R.W, Landry P., Metherate R., Hicks T.P. 1984. Functional role of GABA in cat primary somatosensory cortex : Shaping receptive fields of cortical neurons.J. Neurophysiol. 52, 1066-1093.
47. Kaneko T., Hicks T.P. 1988. Baclofen and gama-aminobutyric acid differentially suppress the cutaneous responsiveness of primary somatosensory cortical neurones. Brain Res. 443, 360-366.
48. Alloway K.D., Rosenthal P., Burton H. 1989. Quantitative measurements of receptive field changes during antagonism of GABAergic transmission in primary somatosensory cortex, fxp. Brain Res. 78, 514-532.
49. Jones E.G. 1993. GABAergic neurons and their role in cortical plasticity in primates. Cereb. Cortex 3, 361-372.
50. Welker E., Soriano E., Dorn J, Van der Loos H. 1989. Plasticity in the barrel cortex of the adult mouse: Transient increase of GAD-immunoreactivity following sensory stimulation. Exp. Brain Res. 78, 659-664.
51. Welker E., Soriano E., Dörfl J., Van der Loos H., 1989. Plasticity in the barrel cortex of the adult mouse : Effects of peripheral deprivation on GAD-immunoreactivity. fxp. Brain Res. 74, 441-452.
52. Hendry S.H., Jones E.G. 1986 Reduction in number of immunostained GABAergic neurons in deprived eye dominance columns of monkey area 17. Nature 320, 750-753.
53. Malenka R.C., Nicoll R.A. 1997. Silent synapses speak up. Neuron 19, 473-476.
54. Metherate R., Tremblay N., DyCes R.W. 1988. Transient and prolonged effects of acetylcholine on responsiveness of cat somatosensory cortical neurons. J. Neurophysiol. 59, 1253-1276.
55. Kurosawa M., Sato A., Sato Y. 1989. Stimulation of the nucleus basalis of Meynert increases acetylcholine release in the cerebral cortex of the rat. Neurosci. Lett. 98, 45-50.
56. Tremblay N., Warren R.A., Dykes R.W. 1990. Electrophysiological studies of acetylcholine and the role of the basal forebrain in the somatosensory cortex of the cat II. Cortical neurons excited by somatic stimuli. J. Neurophysiol. 64, 1212-1222.
57. Juliano S.L., Ma W., Bear M.F., Eslin D. 1990. Cholinergic manipulation alters stimulus-evoked metabolic activity in cat somatosensory cortex. J. Comp. Neural. 297, 106-120.
58. Juliano S.L., Ma W., Eslin D. 1991. Cholinergic depletion prevents expansion of topographic maps in somatosensory cortex. Proc. Natl. Acad. Sei. U.S.A. 88, 78-784.
59. Dykes R.W. 1997. Mechanisms controlling neuronal plasticity in somatosensory cortex. Can. I. Physiol. Pharmacol. 75, 535-545.
60. Freund T.F., Meskenaite V. 1992. Gamma-aminqbutyric acid containing basal forebrain neurons innervate inhibitory interneurons in the neocortex. Proc. Natl. Acad. Sei. USA 89, 738-742.
61. Webster H.H., Hanisch U.K., Dykes R.W., Biesold D. 1991. Basal forebrain lesions with or without reserpine injection inhibit cortical reorganization in rat hindpavv primary somatosensory cortex following sciatic nerve section. Somatosens. Mot. Res. 8, 327-346.
62. Sillito A.M., Murphy P.C. 1987. The Cholinergic modulation of cortical function. In : Cerebral Cortex Vol VI, Further Aspects of Cortical Function, including Hippocampus (Jones E.G., Peters A., eds), Plenum Press, New York, 161-185.
63. Verdier D., Maalouf M., Myasnikov A.A., Dykes R.W. 1995. Longterm Cholinergic enhancement: a form of LTP in the rat somatosensory cortex. 5oc. Neurosci. Abstr. 21, 442.
64. Lee S.M., Weiissfopf M.G., Ebner F.F. 1991. Horizontal long-term potentiation of responses in rat somatosensory cortex. Brain Res. 544, 303-310.
65. LeeS.M., Ebner F.F. 1992. Induction of high frequency activity in the somatosensory thalamus of rats in vivo results in long-term potentîation of responses in SI. cortex. Exp. Brain Res. 90, 253-261.
66. Kano M., lino K., KanoM. 1991. Functional reorganization of adult cat somatosensory cortex is dependent on NMDA receptors. Neuroreport 2, 77-80.
67. Garraghty P. E., Muja N. 1996. NMDA receptors and plasticity in adult primate somatosensory cortex. J. Comp. Neurol. 367, 319-326.
68. Cruikshank S.J., Weinberger N.M. 1996. Evidence for the hebbian hypothesis in experience-dependent physiological plasticity of neocortex: A critical review. Brain Res. Rev. 22, 191-228.
69. Benett E.L., Diamond M.C., Krech D., Rosenzweig M.R. 1964. Chemical and anatomical plasticity of brain. Science 146, 610-619.
70. Richardson R.T., Delong M.R. 1986. Nucleus basalis of Meynert neuronal activity during a delayed response task in the monkey. Brain Res. 399, 364-368.
71. Acquas E., Wilson C, Fibiger H.C. 1996. Conditionned and unconditioned stimuli increase frontal cortical and hippocampal acetylcholine release : effects of novelty, habituation and fear. J. Neurosci. 16, 3089-3096.
72. Inglis P.M., Fibiger H.C. 1995. Increases in hippocampal and frontal cortical acetylcholine release associated with presentation of sensory stimuli. Neuroscience 66, 81-86.
73. Butt A.E., Testylier G., Dykes R.W. 1997. Acetylcholine release in rat frontal and somatosensory cortex is enhanced during tactile discrimination learning. Psychobiology 25, 18-33.
74. Inglis F.M., Day J.C., Fibiger H.C. 1994. Enhanced acetylcholine release in hippocampus and cortex during the anticipation and consumption of a palatable meal. Neuroscience 62, 1049-1056.
75. Metherate R., Cox C.L., Ashe J.H. 1992. Cellular bases of neocortical activation : modulation of neuronal oscillation by the nucleus basalis and endogenous acetycholine. J. Neurosci. 12, 4701-4711.
76. Recanzone G.H., Merzenich M.M., Jenkins W.M., Crajski K.A., Dinse H.R. 1992. Topographic reorganization of the hand representation in cortical area 3b owl monkeys trained in a frequency-discrimination task. J. Neurophysiol. 67, 1031-1056.
77. Rosenzweig M.R., BennetE.L. 1978. Experiential influences on brain anatomy and brain chemistry in rodents. In : Studies on the Development of Behavior and of the Nervous System. Early Influences (Gottlieb G. ed.). Vol 4. Academic Press, New York, 289-327,
78. Diamond M.C, Law F., Rhodes H., Lindner B., Rosenzweig M.R., Krech D., Bennett E.L. 1966. Increases in cortical depth and glia numbers in rats subjected to enriched environment. J. Comp. Neurol. 123, 117-125.
79. Katz H., Davies C.A. 1984. Effects of differential environments on the cerebral anatomy of rats as a function of previous and subsequent housing conditions. Exp. Neurol. 83, 274-287.
80. Turner A.M., Greenough VV.T. 1985. Differential rearing effects on rat visual cortex synapses. I. Synaptic and neuronal density and synapses per neuron. Brain Res. 329, 195-203.
81. SirevaagA.M., Greenough VV.T. 1988. A multivariate stastitical summary of synaptic plasticity measures in rats exposed to complex, social and individual environments. Brain Res. 441, 386-392.
82. Greenough VV.T, Volkmar F.R., Juraska J.M. 1973. Effects of rearing complexity on dendritic branching in frontolateral and temporal cortex of the rat. Exp. Neurol. 41, 371-378.
83. Withers G.S., Greenough VV.T. 1989. Reach training selectively alters dendritic branching in subpopulations of layer ll-lll pyramids in rat motorsomatosensory forelimb cortex. Neuropsychology 27, 61-69.
84. Greenough W.T., Larson J.R., Withers G.S. 1994. Effects of unilateral and bilateral training in a reaching task on dendritic branching of neurons in the rat motor-sensory forelimb cortex. Behav. Neural. Biol. 44,301-314.
85. Globus A., Rozensweig M.R., Bennet E.L., Diamond M.C. 1973. Effects of differential experience on dendritic spine counts in rat cerebral cortex. I. Comp. Physiol. Psych. 82, 175-181.
86. Schapiro S., Vukovich K.R. 1970. Early experience effects upon cortical dendrites: a proposed model for development. Science 167,292294.
87. Möllgaard K., Diamond M.C, Bennett E.L., Rosenzweig M.R., Lindner B. 1971. Quantitative synaptic changes with differential experience in rat brain. Int. J. Neurosci. 2, 113-128.
88. Vrensen G., Cardozo J.N. 1981. Changes in size and shape of synaptic connections after visual training: An ultrastructural approach of synaptic plasticity. Brain Res. 218, 79-97.
89. Kozlowski D.A., James D.C., Schauert T. 1996. Use-dependent exaggerations of neuronal injury after unilateral sensorimotor cortex lesions. J. Neurosci. 16, 4776-4786.
90. BeaulieuC, ColonnierM. 1988. Richness of environment affects the number of contacts formed by boutons containing flat vesicles but does not alter the number of these boutons per neuron. J. Comp. Neurol. 274, 347-356.
91. Keller A., Arissian K., Asanuma H. 1992. Synaptic proliferation in the motor cortex of adult cats after long-term thalamic stimulation. J. Neurophysiol. 68, 295-308.
92. Struble R.G., Riesen A.H. 1978. Changes in cortical dendritic branching subsequent to partial social isolation in stumptailed monkeys. Dev. Psychobiol. 11,479486.
93. Stell M., Riesen A. 1987. Effects of early environments on monkey cortex neuroanatomical changes following somatomotor experience effects on layer III pyramidal cells in monkey cortex. Behav. Neurosci. 101(3), 341-346.
94. Wellman C.L., Sengelaub D.R. 1995. Alterations in dendritic morphology of frontal cortical neurons after basal forebrain lesions in adult and aged rats. Brain Res. 669, 48-58.
95. Black ).E., Isaacs K.R., Anderson B.J., Alcantara A.A, 1990. Learning causes synaptogenesis, whereas motor activity causes angiogenesis. In : Cerebellar Cortex of Adult Rats (Grecnough VV.T, ed.), Neurobiol. 87, 5568-5572.
96. Wallace C.S., Kilman V.L., Withers G.S., Greenough W.T. 1992. Increases in dendritic length in occipital cortex after 4 days of differential housing in weanling rats. Behav. Neural. Biol. 58, 64-68.
97. Camel J.E., Withers G.S., Greenough W.T. 1986. Persistence of visual cortex dendritic alterations induced by postweaning exposure to a superenriched environment in rats. Behav. Neurosci. 100, 810-813.
98. Hwang H.M., Greenough W. 1986. Synaptic plasticity in adult rat occipital cortex following short term, long term, and reversal of differential housing environmental complexity. 5oc. Neurosci. Abstr. 12, 1284.
99. Kleim )., Vij K., Ballard D.H., Greenough W.T. 1997. Learning-dependent synaptic modifications in the cerebellar cortex of the adult rat persist for at least four weeks. J. Neurosci. 17, 717-721.
100. Kolb B., Wishaw I.Q. 1989. Plasticity in the neocortex : mechanisms underlying recovery from early brain damage. Prog. Neurobiol. 32, 235-276.
101. Kolb B., Gibb R. 1991. Environmental enrichment and cortical injury : behavioral and anatomical consequences of frontal cortex lesions. Ccreb.Cort. 1, 189-198.
102. Jones T.A., Schauert T. 1994. Use-dependent growth of pyramidal neurons after neocortical damage. J. Neurophysiol. 14, 2140-2152.
103. Jenkins W.M., Merzenich M.M., Ochs M.T., Allard T., Guic-Robles E. 1990 Functional reorganization of primary somatosensory cortex in adult owl monkeys after behaviorally controlled tactile stimulation. J. Neurophysiol. 63, 82-104.
104. Xerri C, Merzenich M.M., Jenkins W.M., Santucci S., Peterson B. 1998. Representational plasticity in cortical area 3b paralleling tactualmotor skill acquisition in adult monkeys. Cereb. Cortex (in press,).
105. Xerri C, Stern J.M., Merzenich M.M. 1994. Alterations of the cortical representation of the rat ventrum induced by nursing behavior. J. NeuroseJ. 14, 1710-1721.
106. Allard T., Clark S.A., Jenkins W.M., Merzenich M.M. 1991. Reorganization of the somatosensory area 3b representations in adult owl monkeys after digital syndactyly. J. Neurophysiol. 66, 1048-1058.
107. Molginer A, Grossman J.A.I., Ribory U., Joliet M., Volkmann J., Rapaport D., Bensley R.W., Llinas R. 1993. Somatosensory cortical plasticity in adult humans revealed by magnetoencephalography. Proc. Natl. AcadSci. USA 90, 3593-3597.
108. Wang X., Merzenich M.M., Sameshima K., Jenkins W.M. 1995. Remodelling of hand representation in adult cortex determined by timing of tactile stimulation. 378,71-75.
109. Byl N.N., Merzenich M.M., CheungS., Bedenbaugh P., Nagarajan S.S., Jenkins W.M. 1997. A primate model for studying focal dystonia and repetitive strain injury: effects on the primary somatosensory cortex. Physical Therapy 77, 269-84.
110. Diamond M.E., Armstrong-James M., Ebner F.F. 1993. Experiencedependent plasticity in adult rat barrel cortex. Proc. Natl. Acad. Sei. USA. 90, 2082-2086.
111. Armstrong-James M., Diamond M.E., Ebner F.F. 1994. An innocuous bias in whisker use in adult rats modifies receptive fields of barrel cortex neurons. J. Neurose!. 14, 6978-6991.
112. Hebb D.O. 1949. Tfte organization of behavior: A ncuropsychological theory. New York, Wiley.
113. Snow P.J., Wilson P. 1991. Plasticity in the somatosensory system of developping and mature mammals. The effects of injury to the central and peripheral nervous system. Progress in sensory physiology II (Ottoson D., ed., Springer-Verlag, Berlin, Heidelberg.