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La meditazione buddista conferisce una completa e superiore stabilità visiva
December 9th, 2010 by admin

Effects of meditation on perceptual switching
Fig. 1: Effects of meditation on perceptual switching

Lo stato mentale può influire sull’esperienza visiva cosciente.

Le capacità di meditazione dei monaci buddisti rivelano indizi sui processi mediante i quali il cervello regola l’attenzione e la consapevolezza. Con un’insolita ma fruttuosa collaborazione fra monaci tibetani buddisti e neuroscienziati, alcuni ricercatori hanno svelato indizi su come gli stati mentali – e i meccanismi neurali che vi stanno alla base – possono influire sull’esperienza visiva cosciente. Nello studio, pubblicato sulla rivista “Current Biology“, Olivia Carter e Jack Pettigrew dell’Università del Queensland hanno trovato le prove che le capacità sviluppate dai monaci buddisti nella loro pratica di un certo tipo di meditazione può influenzare fortemente la loro esperienza di un fenomeno, chiamato “rivalità percettiva”, che ha a che fare con l’attenzione e la consapevolezza. La rivalità percettiva ha origine normalmente quando a ciascun occhio vengono presentate due differenti immagini, e si manifesta come una fluttuazione – di solito nell’arco di pochi secondi – nell’immagine “dominante” che viene percepita coscientemente. Gli eventi neurali alla base della rivalità percettiva non sono ancora del tutto compresi, ma si ritiene che siano coinvolti i meccanismi cerebrali che regolano l’attenzione e la consapevolezza. .. Alcuni studi precedenti avevano suggerito che la meditazione potesse alterare determinati aspetti dell’attività neurale dl cervello. Ora, con il beneplacito del Dalai Lama, 76 monaci tibetani hanno partecipato a uno studio condotto presso i loro ritiri montuosi nell’Himalaya e in India. L’addestramento meditativo dei monaci variava da 5 a 54 anni, e fra di essi ce n’erano tre con almeno 20 anni di esperienza di totale isolamento. Misurando la rivalità percettiva dei monaci durante la pratica di due tipi di meditazione, gli scienziati hanno scoperto che alcuni di essi presentavano una completa stabilità visiva superiore ai soggetti di controllo. I risultati suggeriscono che i processi particolarmente associati con il tipo di meditazione nel quale si mantiene l’attenzione su un singolo oggetto o pensiero contribuiscono alla prolungata stabilità percettiva sperimentata dai monaci. Gli individui addestrati alla meditazione possono alterare considerevolmente le normali fluttuazioni nello stato conscio che vengono indotte dalla rivalità percettiva. Lo studio, dunque, confermerebbe che la rivalità percettiva possa essere modulata da influenze neurali top-down di alto livello. Fonte http://lescienze.espresso.repubblica.it/articolo/Meditazione_buddista_e_rivalità_percettiva/1284714

Current Biology, Volume 15, Issue 11, R412-R413, 7 June 2005

O.L. Carter1, D.E. Presti2C. Callistemon1Y. Ungerer1G.B. Liu1 and J.D. Pettigrew1,

Vision, Touch and Hearing Research Centre, University of Queensland, St Lucia, Australia 4072.
University of California, Berkeley, California 94720, USA.

Neuroscientific studies of the mind are likely to benefit from the insights and skills of Tibetan Buddhist monks who have practiced the historic tradition of meditative

Figure 2. Frequency of respective disappearance intervals during motion-induced blindness for monks tested in the current study (red) compared to a group of 61 meditation-naive volunteers (blue).

Figure 2. Frequency of respective disappearance intervals during motion-induced blindness for monks tested in the current study (red) compared to a group of 61 meditation-naive volunteers (blue).

training over many years a point made recently at a forum between a selection of Buddhist leaders and distinguished scientists [1]. Perceptual rivalries, such as binocular rivalry [2] and motion induced blindness [3], are being used to study the neural mechanisms underlying consciousness and attention [2,4], as they involve fluctuations in conscious awareness despite unchanging external stimulation. Tapping into the ability of Tibetan Buddhist monks to control the flow of items being attended to and accessing consciousness, we found that meditation alters the inherent fluctuations in conscious state associated with perceptual rivalry.

With the support of His Holiness the Dalai Lama, a total of 76 Tibetan Buddhist monks varying in experience from 5 to 54 years of training (including three retreatist meditators, each with at least 20 years experience in isolated mountain retreats) were tested using non-intrusive perceptual measures at, or near, their mountain retreats in the Himalaya, Zanskar and Ladakhi Ranges of India. Binocular rivalry was induced with head-mounted display goggles (Figure 1A) that presented horizontal and vertical green stationary gratings to the right and left eye, respectively (see Supplemental data available with this article online). In cases where coordinated button-press responses were not possible, verbal reports were recorded.

Figure 1: Effects of meditation on perceptual switching. (A) Retreatist meditator wearing display goggles. (B) Proportion of monks reporting changes in rivalry switch rate during compassion (Comp) meditation, after and during one-point meditation (slower, light blue; faster, red; stabilization, dark blue; white, no change). (C) A representative frequency histogram showing phase duration (time between perceptual switch) for horizontal, vertical and mixed (grey) percepts after no meditation and (D) the same monk showing longer durations after one-point meditation.

Harnessing the skills of highly trained monks to control their mental state, we report results from 23 monks corresponding to two types of meditation, approximately translated as compassion (a non-referential contemplation of suffering within the world combined with the emanation of loving kindness) and one-point (through the maintained focus of attention on a single object, the mind is calmed and the distracting influences of other internal and external events is reduced).

Consistent with a recent study [5] linking different types of meditation with distinct patterns of neural activity, we found compassion and one-point meditation had similarly differential functional effects on the visual switching during rivalry. In contrast to compassion meditation, which led to no observable change in rivalry rate, one-point meditation led to extreme increases in perceptual dominance durations that were reported by 50% of monks after a period of one-point meditation (reports collected via button-press, as shown in Figure 1C,D, or verbally).

Additional prolongation/ stabilization was reported (verbally) by the monks when they viewed the rivalry display during one-point meditation (Figure 1B). Within this group, three (including two of the retreatists ) reported complete perceptual stability throughout the entire 5minute meditation period. There was no consistent pattern in the dominant orientation favored. During periods of stabilization, the reported percepts often differed from either of the two presented gratings, with qualitative changes in depth, color and width.

In some cases the perceptual dominance was complete; in other cases the non-dominant image remained partially visible. For example, one monk reported the stable dominance of the vertical gratings appearing as three-dimensional columns that were wider, brighter and closer than during normal viewing conditions. During this time the horizontal gratings remained faintly visible: set back in depth, they appeared thin and pale with a slight blue coloration. These results contrast sharply with the reported observations of over 1000 meditation-naive individuals tested previously.

Because most of the monks served as their own controls by participating in the different meditation conditions, the finding that the increase in prolongation/ stabilization was specific to only one of the meditation types (Figure 1B) suggests that the effect is real, rather then simply reflecting miscommunication or a general incapability to perform the task. Furthermore it suggests that the prolongation of rivalry dominance observed results from the intense attentional focus and the practiced ability to stabilize the mind during one-point meditation, rather than the process of meditation per se.

Volunteers were also tested on motion induced blindness prior to any meditation (see Supplemental data for details) and the mean disappearance duration reported was 4.1s (s.d. 3.9 s), compared to 2.6 s (s.d. 1.6 s) recorded from a group of 61 meditation-naive volunteers tested previously [6] (t = 2.8, p < 0.001) (Figure 2). The most extreme finding came from the retreatist volunteer with the most experience at meditation (25 years intense practice in mountain retreats). After a period of passive viewing he commented that he could maintain the disappearance indefinitely. So we suggested he attempt to actively maintain the disappearance and after recommencing, he reported the first reappearance of any of the three yellow target dots after 723s of sustained motion induced blindness disappearance!

Figure 2: Histogram showing the frequency of respective disappearance intervals during motion-induced blindness for monks tested in the current study (red) compared to a group of 61 meditation-naive volunteers (blue) tested previously (for details see [6]). The two extreme values were not included in the statistical analysis reported in the text.

The primary result of this study is that individuals trained in meditation can measurably alter the normal fluctuations in conscious state induced by binocular rivalry and motion-induced blindness. The meditation specific changes in visual function observed here provide new evidence in support of recent electrophysiological studies suggesting that different types of meditation and training duration lead to distinguishable short- and long-term changes at the neural level [5,7]. Furthermore, the reported association between focused styles of meditation and changes in neural activity in prefrontal regions of the cortex [7,8] regions that have been similarly implicated in sustained attentional [9] and binocular rivalry [10] supports claims of high-level, top-down modulatory effects in perceptual rivalry [2], and strengthens recent links between rivalry and attentional mechanisms [4].

This study offers an initial contribution towards increased understanding of the biological processes underlying meditation and rivalry, while additionally highlighting the synergistic potential for further exchange between practitioners of meditation and neuroscience in the common goal of understanding consciousness.

Acknowledgments This investigation was financially supported by the Heffter Research Institute, Santa Fe, New Mexico, USA, and a Stanley Foundation grant to J. D. Pettigrew. We would like to thank His Holiness the Dalai Lama for his support and help in facilitating the study, Tenzin Geyche and Tenzin Sherab for essential logistical assistance and Tsering Topgyal for recruitment of monks. We would also like to thank Tashi Choephel, Kelsang Wangmo, Ngodup Burkhar, Tenzin Sherab and Dorjee Dhondup who assisted with Tibetan and Ladakhi translations and the monks from the Institute of Buddhist Dialectics and the Namgyal and Thiksey monasteries for their participation.

References

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Blake, R., and Logothetis, N. (2002). Visual competition. Nat. Rev. Neurosci. 3, 13 21. PubMed

3 Bonneh, Y., Cooperman, A., and Sagi, D. (2001). Motion induced blindness in normal observers. Nature 411, 798 801. CrossRef | PubMed

4 Mitchell, J., Stoner, G., and Reynolds, J. (2004). Object-based attention determines dominance in binocular rivalry. Nature 429, 410 413. CrossRef | PubMed

5 Lehmann, D., Faber, P.L., Achermann, P., Jeanmonod, D., Gianotti, R.R., and Pizzagalli, D. (2001). Brain sources of EEG gamma frequency during volitionally meditation-induced, altered states of consciousness, and experience of the self. Psychiatry Res. 108, 111 121. PubMed

6 Carter, O., and Pettigrew, J. (2003). A common oscillator for perceptual rivalries?. Perception 32, 295 305. CrossRef | PubMed

7 Lutz, A., Greischar, L.L., Rawlings, N.B., Ricard, M., and Davidson, R. (2004). Long-term meditators self-induce high-amplitude gamma synchrony during mental practice. Proc. Natl. Acad. Sci. USA 101, 16369 16373. CrossRef | PubMed

8 Newberg, A., Alavi, A., Baime, M., Pourdehnad, M., Santanna, J., and d Aquili, E. (2001). The measurement of regional cerebral blood flow during the complex cognitive task of meditation: a preliminary SPECT study. Psychiatry Res. 106, 113 122. PubMed

9 Pardo, J.V., Fox, P.T., and Raichle, M.E. (1991). Localization of a human system for sustained attention by positron emission tomography. Nature 349, 61 64. CrossRef | PubMed

10 Lumer, E.D., Friston, K.J., and Rees, G. (1998). Neural correlates of perceptual rivalry in the human brain. Science 280, 1930 1934. CrossRef | PubMed http://www.cell.com/current-biology/fulltext/S0960-9822(05)00558-0

Meditation alters perceptual rivalry in Tibetan Buddhist monks


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