Neurofeedback

Software real time data of neurofeedback training.

Neurofeedback (NFB), also called neurotherapy or neurobiofeedback, is a type of biofeedback that uses real-time displays of brain activity—most commonly electroencephalography (EEG), to teach self-regulation of brain function. Typically, sensors are placed on the scalp to measure activity, with measurements displayed using video displays or sound.

Definition

Neurofeedback is a type of biofeedback that measures brain waves to produce a signal that can be used as feedback to teach self-regulation of brain function.[1] Neurofeedback is commonly provided using video or sound, with positive feedback for desired brain activity and negative feedback for brain activity that is undesirable. Related technologies include hemoencephalography biofeedback (HEG) and functional magnetic resonance imaging (fMRI) biofeedback.

Uses

ADHD

Clinical guidelines on neurofeedback as a treatment for ADHD are mixed. Biofeedback is graded by the American Academy of Pediatrics with their Level 2 evidenced based treatment for ADHD.[2] The NICE guideline for ADHD leaves the efficacy of biofeedback an open question (p. 412). In page 202 states "Biofeedback has been employed as a non-invasive treatment for children with ADHD since the 1970s but is probably not used as a significant intervention in UK clinical practice". However this is unsurprising since in the UK, NICE evaluates whether treatments should be recommended on the basis of the cost of a quality-adjusted life year. SIGN guideline no 112 in page 24 mentions "Neurofeedback is presently considered to be an experimental intervention in children and young people with ADHD/HKD. There are no standardised interventions".[3] Institute for Clinical Systems Improvement guideline on Diagnosis and Management of Attention Deficit Hyperactivity Disorder in Primary Care for School-Age Children and Adolescents in page 41 mentions neurofeedback lacks enough research evidence for efficacy in ADHD.[4]

Overall research into neurofeedback is considered to have been limited and of low quality,[4][5][6] although others have disagreed.[7]

It has been argued there is some indication on the effectiveness of biofeedback for ADHD but that it is not conclusive: several studies have yielded positive results, however the best designed ones have either shown absent or reduced effects.[4][5][5][6][6][8] Other experts have proposed that standard neurofeedback protocols for ADHD, such as theta/beta, SMR and slow cortical potentials neurofeedback are well investigated and have demonstrated specificity.[9] No serious adverse side effects from neurofeedback have been reported.[5]

QEEG has been used to develop EEG models of ADHD. According to this model, persons with ADHD often have too many slow theta brain waves (associated with relaxation) and not enough fast beta wave activity (associated with mental focus).[10] Neurofeedback therapies for ADHD generally attempt to increase the production of betawaves and decrease the number of slower brain waves. This can be accomplished by allowing the patient to view their levels of brain waves on a screen and attempt to alter them, or by integrating brain waves into a video game.[11]

Other medical uses

Research shows neurofeedback may be a potentially useful intervention for a range of brain-related conditions. It has been used for pain,[12] addiction,[13][14][15][16] aggression,[17] anxiety,[11] autism,[18] depression,[19] Schizophrenia,[20][21] epilepsy,[22] headaches,[23] insomnia,[24] Tourette syndrome,[25] and brain damage from stroke,[26] trauma,[27] and other causes.

It is also used to treat other less well known disorders, such as Auditory Processing Disorder and working memory deficit.

Non-medical

The applications of neurofeedback to enhance performance extend to the arts in fields such as music, dance, and acting. A study with conservatoire musicians found that alpha-theta training benefitted the three music domains of musicality, communication, and technique.[28] Historically, alpha-theta training, a form of neurofeedback, was created to assist creativity by inducing hypnagogia, a “borderline waking state associated with creative insights”, through facilitation of neural connectivity.[29] Alpha-theta training has also been shown to improve novice singing in children. Alpha-theta neurofeedback, in conjunction with heart rate variability training, a form of biofeedback, has also produced benefits in dance by enhancing performance in competitive ballroom dancing and increasing cognitive creativity in contemporary dancers. Additionally, neurofeedback has also been shown to instil a superior flow state in actors, possibly due to greater immersion while performing.[29]

However, randomized control trials have found that neurofeedback training (using either sensorimotor rhythm or theta/beta ratio training) did not enhance performance on attention-related tasks or creative tasks.[30] It has been suggested that claims made by proponents of alpha wave neurofeedback training techniques have yet to be validated by randomized, double-blind, controlled studies,[31] a view which even some supporters of alpha neurofeedback training have also expressed.[32]

History and application

In 1924, the German psychiatrist Hans Berger connected a couple of electrodes (small round discs of metal) to a patient's scalp and detected a small current by using a ballistic galvanometer. During the years 1929-1938 he published 14 reports about his studies of EEGs, and much of our modern knowledge of the subject, especially in the middle frequencies, is due to his research.[33] Berger analyzed EEGs qualitatively, but in 1932 G. Dietsch applied Fourier analysis to seven records of EEG and became the first researcher of what later is called QEEG (quantitative EEG).[33]

Later, Joe Kamiya popularized neurofeedback in the 1960s when an article[34] about the alpha brain wave experiments he had been conducting was published in Psychology Today in 1968. Kamiya’s experiment had two parts. In the first part, a subject was asked to keep his eyes closed and when a tone sounded to say whether he thought he was in alpha. He was then told whether he was correct or wrong. Initially the subject would get about fifty percent correct, but some subjects would eventually develop the ability to better distinguish between states.[35] In the second part of the study, subjects were asked to go into alpha when a bell rang once and not go into the state when the bell rang twice. Once again some subjects were able to enter the state on command. Alpha states were connected with relaxation, and alpha training had the possibility to alleviate stress and stress-related conditions.

Despite these claims, the universal correlation of high alpha density to a subjective experience of calm cannot be assumed. Alpha states do not seem to have the universal stress-alleviating power indicated by early observations.[36] At one point, Martin Orne and others challenged the claim that alpha biofeedback actually involved the training of an individual to voluntarily regulate brainwave activity.[37] James Hardt and Joe Kamiya, then at UC San Francisco's Langley Porter Neuropsychiatric Institute published a paper that supported biofeedback.[38]

In the late sixties and early seventies, Barbara Brown, one of the most effective popularizers of Biofeedback, wrote several books on biofeedback, making the public much more aware of the technology. The books included New Mind New Body, with a foreword from Hugh Downs, and Stress and the Art of Biofeedback. Brown took a creative approach to neurofeedback, linking brainwave self-regulation to a switching relay which turned on an electric train.[39]

The work of Barry Sterman, Joel F. Lubar and others has been relevant on the study of beta training, involving the role of sensorimotor rhythmic EEG activity.[40] This training has been used in the treatment of epilepsy,[41][42] attention deficit disorder and hyperactive disorder.[43] The sensorimotor rhythm (SMR) is rhythmic activity between 12 and 16 hertz that can be recorded from an area near the sensorimotor cortex. SMR is found in waking states and is very similar if not identical to the sleep spindles that are recorded in the second stage of sleep.

For example, Sterman has shown that both monkeys and cats who had undergone SMR training had elevated thresholds for the convulsant chemical monomethylhydrazine. These studies indicate that SMR may be associated with an inhibitory process in the motor system.[42]

Within the last 5–10 years, neurofeedback has taken a new approach in taking a look at deep states.[44] Alpha-theta training has been tried with patients with alcoholism,[45] other addictions as well as anxiety.[45] This low frequency training differs greatly from the high frequency beta and SMR training that has been practiced for over thirty years and is reminiscent of the original alpha training of Elmer Green and Joe Kamiya.[45] Beta and SMR training can be considered a more directly physiological approach, strengthening sensorimotor inhibition in the cortex and inhibiting alpha patterns, which slow metabolism. Alpha-theta training, however, derives from the psychotherapeutic model and involves accessing of painful or repressed memories through the alpha-theta state.[46] The alpha-theta state is a term that comes from the representation on the EEG.

A recent development in the field is a conceptual approach called the Coordinated Allocation of Resource Model (CAR) of brain functioning which states that specific cognitive abilities are a function of specific electrophysiological variables which can overlap across different cognitive tasks.[47] The activation database guided EEG biofeedback approach initially involves evaluating the subject on a number of academically relevant cognitive tasks and compares the subject's values on the QEEG measures to a normative database, in particular on the variables that are related to success at that task.

Organizations

The Association for Applied Psychophysiology and Biofeedback (AAPB) is a non-profit scientific and professional society for biofeedback and neurofeedback. The International Society for Neurofeedback and Research (ISNR) is a non-profit scientific and professional society for neurofeedback.[48] The Biofeedback Foundation of Europe (BFE) sponsors international education, training, and research activities in biofeedback and neurofeedback.

Certification

The Biofeedback Certification International Alliance (formerly the Biofeedback Certification Institute of America) is a non-profit organization that is a member of the Institute for Credentialing Excellence (ICE). BCIA certifies individuals who meet education and training standards in biofeedback and neurofeedback and progressively recertifies those who satisfy continuing education requirements. BCIA offers biofeedback certification, neurofeedback (also called EEG biofeedback) certification, and pelvic muscle dysfunction biofeedback certification. BCIA certification has been endorsed by the Mayo Clinic,[49] the Association for Applied Psychophysiology and Biofeedback (AAPB), the International Society for Neurofeedback and Research (ISNR), and the Washington State Legislature.[50]

The BCIA didactic education requirement includes a 36-hour course from a regionally accredited academic institution or a BCIA-approved training program that covers the complete Neurofeedback Blueprint of Knowledge and study of human anatomy and physiology. The Neurofeedback Blueprint of Knowledge areas include: I. Orientation to Neurofeedback, II. Basic Neurophysiology and Neuroanatomy, III. Instrumentation and Electronics, IV. Research, V. Psychopharmalogical Considerations, VI. Treatment Planning, and VII. Professional Conduct.[51]

Applicants may demonstrate their knowledge of human anatomy and physiology by completing a course in biological psychology, human anatomy, human biology, human physiology, or neuroscience provided by a regionally accredited academic institution or a BCIA-approved training program or by successfully completing an Anatomy and Physiology exam covering the organization of the human body and its systems.

Applicants must also document practical skills training that includes 25 contact hours supervised by a BCIA-approved mentor designed to them teach how to apply clinical biofeedback skills through self-regulation training, 100 patient/client sessions, and case conference presentations. Distance learning allows applicants to complete didactic course work over the internet. Distance mentoring trains candidates from their residence or office.[52] They must recertify every 4 years, complete 55 hours of continuing education (30 hours for Senior Fellows) during each review period or complete the written exam, and attest that their license/credential (or their supervisor’s license/credential) has not been suspended, investigated, or revoked.[53]

Neuroplasticity

In 2010, a study provided some evidence of neuroplastic changes occurring after brainwave training. Half an hour of voluntary control of brain rhythms led in this study to a lasting shift in cortical excitability and intracortical function.[54] The authors observed that the cortical response to transcranial magnetic stimulation (TMS) was significantly enhanced after neurofeedback, persisted for at least 20 minutes, and was correlated with an EEG time-course indicative of activity-dependent plasticity.[55]

See also

References

  1. Napoletano, Margo. "Neurofeedback: Frequently Asked Questions". Child and Family Counseling Center. Retrieved 19 April 2016.
  2. http://www.braintrainuk.com/wp-content/uploads/2013/07/How-AAP-reached-conclusion-other-recent-evidence-July-2013-V3.pdf
  3. Scottish Intercollegiate Guidelines Network (2009). Management of attention deficit and hyperkinetic disorders in children and young people: A national clinical guideline. NHS Quality Improvement Scotland. p. 24.
  4. 1 2 3 Dobie C,; Donald WB; Hanson M; Heim C; Huxsahl J; Karasov R; Kippes C; Neumann A; Spinner P; Staples T; Steiner L. (2012). Diagnosis and Management of Attention Deficit Hyperactivity Disorder in Primary Care for School-Age Children and Adolescents. Institute for Clinical Systems Improvement. p. 41.
  5. 1 2 3 4 Moriyama TS, Polanczyk G, Caye A, Banaschewski T, Brandeis D, Rohde LA (July 2012). "Evidence-based information on the clinical use of neurofeedback for ADHD". Neurotherapeutics. 9 (3): 588–98. PMC 3441929Freely accessible. PMID 22930416. doi:10.1007/s13311-012-0136-7.
  6. 1 2 3 Holtmann, M; Sonuga-Barke, E; Cortese, S; Brandeis, D (Oct 2014). "Neurofeedback for ADHD: A Review of Current Evidence.". Child and adolescent psychiatric clinics of North America. 23 (4): 789–806. PMID 25220087. doi:10.1016/j.chc.2014.05.006.
  7. Arns, M., de Ridder, S., Strehl, U., Breteler, M., & Coenen, A. (2009). "Efficacy of neurofeedback treatment in ADHD: the effects on inattention, impulsivity and hyperactivity: a meta-analysis.". Clinical EEG and Neuroscience. 40 (3): 180–189. PMID 19715181. doi:10.1177/155005940904000311.
  8. Lofthouse N, Arnold LE, Hurt E (October 2012). "Current status of neurofeedback for attention-deficit/hyperactivity disorder". Curr Psychiatry Rep. 14 (5): 536–42. PMID 22890816. doi:10.1007/s11920-012-0301-z.
  9. Arns M, Hartmut G, Strehl U (2014). "Evaluation of neurofeedback in ADHD: The long and winding road". Biological Psychology, in press. 95: 108–115. doi:10.1016/j.biopsycho.2013.11.013.
  10. Butnik, Steven M. "Neurofeedback in adolescents and adults with attention deficit hyperactivity disorder." Journal of Clinical Psychology, May 2005. Vol. 61 Issue 5, p621-625
  11. 1 2 Karidis, Arlene. "Neurofeedback – The Scientific Evidence Grows". Perth Brain Centre. Perth Brain Centre. Retrieved 19 April 2016.
  12. Christopher deCharms R; et al. (2005). "Control over brain activation and pain learned by using real-time functional MRI". Proceedings of the National Academy of Sciences of the United States of America. 102 (51): 18626–18631. Bibcode:2005PNAS..10218626D. PMC 1311906Freely accessible. PMID 16352728. doi:10.1073/pnas.0505210102.
  13. Peniston EG, Kulkosky PJ (1989). "Alpha-theta brainwave training and beta-endorphin levels in alcoholics.". Alcoholism: Clinical and Experimental Research. 13 (2): 271–279. PMID 2524976. doi:10.1111/j.1530-0277.1989.tb00325.x.
  14. William C. Scott; David Kaiser; Siegfried Othmer; Stephen I. Sideroff (2005). "Effects of an EEG Biofeedback Protocol on a Mixed Substance Abusing Population.". The American Journal of Drug and Alcohol Abuse. 31 (3): 455–469. PMID 16161729. doi:10.1081/ADA-200056807.
  15. Rostami R, Dehghani-Arani F (2015). "Training as a New Method in Treatment of Crystal Methamphetamine Dependent Patients: A Preliminary Study.". Appl Psychophysiol Biofeedback. 40 (3): 151–61. PMID 25894106. doi:10.1007/s10484-015-9281-1.
  16. Dehghani-Arani F; Rostami R; Masoud Nostratabadi. (2010). "Effectiveness of Neurofeedback Training as a Treatment for Opioid Dependent Patients". Clinical EEG and Neuroscience. 41 (3): 170–177. PMID 20722354. doi:10.1177/155005941004100313.
  17. Arani, FD; Rostami, R; Nostratabadi, M (Jul 2010). "Effectiveness of neurofeedback training as a treatment for opioid-dependent patients.". Clin EEG Neurosci. 41 (3): 170–7. PMID 20722354. doi:10.1177/155005941004100313.
  18. Coben R, Linden M, Myers TE (2010). "Neurofeedback for autistic spectrum disorder: a review of the literature.". Applied Psychophysiology and Biofeedback. 35 (1): 83–105. PMID 19856096. doi:10.1007/s10484-009-9117-y.
  19. Linden DE, Habes I, Johnston SJ, Linden S, Tatineni R, Subramanian L, Sorger B, Healy D, Goebel R (2012). "Real-time self-regulation of emotion networks in patients with depression". PLoS ONE. 7 (6): e38115. Bibcode:2012PLoSO...738115L. PMC 3366978Freely accessible. PMID 22675513. doi:10.1371/journal.pone.0038115.
  20. Surmeli, Tanju (2012), "Living Health Center for Research and Education, Istanbul, Turkey." (PDF), Schizophrenia and the efficacy of qEEG-guided neurofeedback treatment:a clinical case series, California State University, San Bernandino
  21. Surmeli, Tanju (2012), "Schizophrenia and the efficacy of qEEG-guided neurofeedback treatment:a clinical case series", Clin EEG Neurosci, US National Library of Medicine National Institutes of Health, 43 (2): 133–44, PMID 22715481, doi:10.1177/1550059411429531 |contribution= ignored (help)
  22. Tan G, Thornby J, Hammond DC, Strehl U, Canady B, Arnemann K, Kaiser DA (2009). "Meta-analysis of EEG biofeedback in treating epilepsy.". Journal of Clinical EEG & Neuroscience. 40 (3): 173–179. PMID 19715180. doi:10.1177/155005940904000310.
  23. Jeffrey A. Carmen (2005). "Passive Infrared Hemoencephalography: Four Years and 100 Migraines.". Journal of Neurotherapy. 8 (3): 23–51. doi:10.1300/J184v08n03_03.
  24. Cortoos A, De Valck E, Arns M, Breteler MH, Cluydts R (2010). "An exploratory study on the effects of tele-neurofeedback and tele-biofeedback on objective and subjective sleep in patients with primary insomnia.". Applied Psychophysiology and Biofeedback. 35 (2): 125–134. PMID 19826944. doi:10.1007/s10484-009-9116-z.
  25. Messerotti Benvenuti S, Buodo G, Leone V, Palomba D (2011). "Neurofeedback training for tourette syndrome: an uncontrolled single case study.". Applied Psychophysiology and Biofeedback. 36 (4): 281–288. PMID 21915704. doi:10.1007/s10484-011-9169-7.
  26. Mihara M, Hattori N, Hatakenaka M, Yagura H, Kawano T, Hino T, Miyai I (2013). "Near-infrared spectroscopy-mediated neurofeedback enhances efficacy of motor imagery-based training in poststroke victims: a pilot study.". Stroke. 44 (4): 1091–1098. PMID 23404723. doi:10.1161/STROKEAHA.111.674507.
  27. Thornton KE, Carmody DP (208). "Efficacy of traumatic brain injury rehabilitation: interventions of QEEG-guided biofeedback, computers, strategies, and medications.". Applied Psychophysiology and Biofeedback. 33 (2): 101–124. PMID 18551365. doi:10.1007/s10484-008-9056-z.
  28. Egner, Tobias; Gruzelier, John H (1 July 2003). "Ecological validity of neurofeedback" (PDF). NeuroReport. 14 (9): 1221–1224. doi:10.1097/00001756-200307010-00006.
  29. 1 2 Gruzelier, John (1 July 2011). "Neurofeedback and the performing arts". Neuroscience Letters. 500: e15. doi:10.1016/j.neulet.2011.05.106.
  30. Doppelmayr, Michael; Weber, Emily (20 May 2011). "Effects of SMR and Theta/Beta Neurofeedback on Reaction Times, Spatial Abilities, and Creativity". Journal of Neurotherapy. 15 (2): 115–129. doi:10.1080/10874208.2011.570689.
  31. Beyerstein, Barry L (1990). "Brainscams: Neuromythologies of the New Age". International Journal of Mental Health. 19 (3): 27–36. doi:10.1080/00207411.1990.11449169.
  32. Vernon, D; Dempster, T; Bazanova, O; Rutterford, N; Pasqualini, M; Andersen, S (30 Nov 2009). "Alpha Neurofeedback Training for Performance Enhancement: Reviewing the Methodology". Journal of Neurotherapy. 13 (4): 214–227. doi:10.1080/10874200903334397.
  33. 1 2 Kaiser David A (2005). "Basic Principles of Quantitative EEG". Journal of Adult Development. 12 (2/3).
  34. Kamiya, J. (1971). "Operant Control of the EEG Alpha Rhythm and Some of its Reported Effects on Consciousness". Biofeedback and Self-Control: an Aldine Reader on the Regulation of Bodily Processes and Consciousness.
  35. Frederick, J. (2012). "Psychophysics of EEG Alpha State Discrimination" (PDF). Consciousness and Cognition. 21 (3): 1345–1354. doi:10.1016/j.concog.2012.06.009.
  36. Hardt, J.V.; Kamiya, J. (1978). "Anxiety change through electroencephalographic alpha feedback seen only in high anxiety subjects". Science. 201 (4350): 79–81. Bibcode:1978Sci...201...79H. PMID 663641. doi:10.1126/science.663641.
  37. Paskewitz, D.A.; Orne, M.T. (1973). "Visual Effects on Alpha Feedback Training". Science. 181 (4097): 360–363. Bibcode:1973Sci...181..360P. PMID 4719909. doi:10.1126/science.181.4097.360.
  38. Hardt, J.V.; Kamiya, J. (1976). "Conflicting results in EEG alpha feedback studies" (PDF). Applied Psychophysiology and Biofeedback. 1 (1): 63–75. doi:10.1007/bf00998691. Retrieved 2007-12-05.
  39. Forghan, Bahamin. "Investigation brain Neuro biofeedback". Academia. Retrieved 19 April 2016.
  40. Sterman, M.B.; Clemente, C.D. (1962). "Forebrain inhibitory mechanisms: cortical synchronization induced by basal forebrain stimulation". Exp Neurol. 6 (2): 91–102. PMID 13916975. doi:10.1016/0014-4886(62)90080-8.
  41. Sterman, M.B.; Friar, L. (1972). "Suppression of seizures in an epileptic following sensorimotor EEG feedback training". Electroencephalogr Clin Neurophysiol. 33 (1): 89–95. PMID 4113278. doi:10.1016/0013-4694(72)90028-4.
  42. 1 2 Sterman, M.B. (2000). "Basic concepts and clinical findings in the treatment of seizure disorders with EEG operant conditioning". Clin Electroencephalogr. 31 (1): 45–55. PMID 10638352. doi:10.1177/155005940003100111.
  43. Lubar, J.F.; Swartwood, M.O.; Swartwood, J.N.; O'Donnell, P.H. (1995). "Evaluation of the effectiveness of EEG neurofeedback training for ADHD in a clinical setting as measured by changes in TOVA scores, behavioral ratings, and WISC-R performance" (PDF). Applied Psychophysiology and Biofeedback. 20 (1): 83–99. doi:10.1007/bf01712768. Retrieved 2007-12-05.
  44. Hammond, D. Corydon. "Neurotherapy also called Neurofeedback or EEG Biofeedback". Applied Neuroscience Society of Australasia. Applied Neuroscience Society of Australasia. Retrieved 19 April 2016.
  45. 1 2 3 Sokhadze, Tato M.; Cannon, Rex L.; Trudeau, David L. (Mar 2008). "EEG Biofeedback as a Treatment for Substance Use Disorders: Review, Rating of Efficacy, and Recommendations for Further Research". Appl Psychophysiol Biofeedback. 33 (1): 1–28. PMC 2259255Freely accessible. PMID 18214670. doi:10.1007/s10484-007-9047-5.
  46. Reel, Justine J. (2013). Eating Disorders: An Encyclopedia of Causes, Treatment, and Prevention. ABC-CLIO. p. 300. ISBN 978-1-4408-0058-0.
  47. Thornton K.; Carmody D. (2009). "Eyes-Closed and Activation QEEG Databases in Predicting Cognitive Effectiveness and the Inefficiency Hypothesis". Journal of Neurotherapy. 13 (1): 1–22. doi:10.1080/10874200802429850.
  48. http://www.bfe.org/
  49. Neblett R.; Shaffer F.; Crawford J. (2008). "What is the value of Biofeedback Certification Institute of America certification?". Biofeedback. 36 (3): 92–94.
  50. Washington State Legislature WAC 296-21-280 Biofeedback Rules.
  51. Gevirtz, R. (2003). The behavioral health provider in mind-body medicine. In D. Moss, A. McGrady, T. C. Davies, & I. Wickramasekera (Eds.). Handbook of mind-body medicine for primary care. Thousand Oaks, CA: Sage Publications, Inc.
  52. De Bease C (2007). "Biofeedback Certification Institute of America certification: Building skills without walls". Biofeedback. 35 (2): 48–49.
  53. Shaffer, F., & Schwartz, M. S. (in press). Entering the field and assuring competence. In M. S. Schwartz, & F. Andrasik (Eds.). Biofeedback: A practitioner's guide (4th ed.). New York: The Guilford Press.
  54. Science Daily
  55. Ros T.; Munneke M.A.M.; Ruge D.; Gruzelier J.H.; Rothwell J.C. (2010). "Endogenous Control of Waking Brain Rhythms Induces Neuroplasticity in Humans". European Journal of Neuroscience. 31 (4): 770–778. PMID 20384819. doi:10.1111/j.1460-9568.2010.07100.x.

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