Brain Mechanisms Supporting the Modulation of Pain by Mindfulness Meditation

En studie som gir en tydelig beskrivelse av hvor mye mindfulness demper smerte. De fant ingen korrelasjon mellom pustefrekvens og smertereduksjon, men det kan være flere faktorer som spiller inn der.  I denne studien gjorde de f.eks. kun 20 min meditasjon i 4 dager, med mennesker som ikke har meditert først. De andre studiene inkluderer mennesker som har meditert lenge. I tillegg kan man tydelig se at etter 4 dager med meditasjon så blir pustefrekvensen lavere når man blir påført vond varme, noe som tyder på at de begynner å bruke pusten som smertereduksjon. Det var motsatt før de hadde fått instruksjon i meditasjon.

After 4 d of mindfulness meditation training, meditating in the presence of noxious stimulation significantly reduced pain unpleasantness by 57% and pain intensity ratings by 40% when compared to rest.

Meditation-induced reductions in pain intensity ratings were associated with increased activity in the anterior cingulate cortex and anterior insula, areas involved in the cognitive regulation of nociceptive processing. Reductions in pain unpleasantness ratings were associated with orbitofrontal cortex activation, an area implicated in reframing the contextual evaluation of sensory events. Moreover, reductions in pain unpleasantness also were associated with thalamic deactivation, which may reflect a limbic gating mechanism involved in modifying interactions between afferent input and executive-order brain areas. Together, these data indicate that meditation engages multiple brain mechanisms that alter the construction of the subjectively available pain experience from afferent information.

Mindfulness-based mental training.

Mindfulness-based mental training was performed in four separate, 20 min sessions conducted by a facilitator with >10 years of experience leading similar meditation regimens. Subjects had no previous meditative experience and were informed that such training was secular and taught as the cognitive practice of Shamatha or mindfulness meditation. Each training session was held with one to three participants.

On mindfulness meditation training day 1, subjects were encouraged to sit with a straight posture, eyes closed, and to focus on the changing sensations of the breath occurring at the tips of their nostrils. Instructions emphasized acknowledging discursive thoughts and feelings and to return their attention back to the breath sensation without judgment or emotional reaction whenever such discursive events occurred. On training day 2, participants continued to focus on breath-related nostril sensations and were instructed to “follow the breath,” by mentally noting the rise and fall of the chest and abdomen. The last 10 min were held in silence so subjects could develop their meditative practice. On training day 3, the same basic principles of the previous sessions were reiterated. However, an audio recording of MRI scanner sounds was introduced during the last 10 min of meditation to familiarize subjects with the sounds of the scanner. On the final training session (day 4), subjects received minimal meditation instruction but were required to lie in the supine position and meditate with the audio recording of the MRI sounds to simulate the scanner environment. Contrary to traditional mindfulness-based training programs, subjects were not required to practice outside of training.

Subjects also completed the Freiburg Mindfulness Inventory short-form (FMI), a 14-item assessment that measures levels of mindfulness, before psychophysical pain training and after MRI session 2. The FMI is a psychometrically validated instrument with high internal consistency (Cronbach α = 0.86) (Walach et al., 2006). Statements such as “I am open to the experience of the present moment” are rated on a five-point scale from 1 (rarely) to 5 (always). Higher scores indicate more skill with the mindfulness technique.

Decreases in respiration rate have been reported previously to predict reductions in pain ratings (Grant and Rainville, 2009Zautra et al., 2010). In the present data (MRI session 2; n = 14), no significant relationship between the decreased respiration rates and pain intensity (p = 0.22, r = −0.35), pain unpleasantness (p = 0.41, r = −0.24), or FMI ratings (p = 0.42, r = 0.24) was found.

CBF Respiration rate Heart rate
Session 1
    Rest: neutral 74.12 (3.01) 19.97 (1.29) 72.53 (2.33)
    Rest: heat 71.51 (2.93) 20.45 (1.11) 74.79 (2.39)
    ATB: neutral 70.69 (3.56) 17.05 (1.00) 70.46 (1.79)
    ATB: heat 67.90 (3.08) 19.32 (1.33) 74.07 (2.19)
Session 2
    Rest: neutral 68.57 (3.17) 16.72 (0.82) 74.82 (3.08)
    Rest: heat 66.82 (2.59) 17.12 (0.93) 77.32 (2.95)
    Meditation: neutral 65.09 (3.59) 11.55 (0.74) 73.62 (2.77)
    Meditation: heat 65.47 (3.86) 9.47 (0.67)a 75.38 (2.70)

In the present investigation, meditation reduced all subjects’ pain intensity and unpleasantness ratings with decreases ranging from 11 to 70% and from 20 to 93%, respectively.

Meditation likely modulates pain through several mechanisms. First, brain areas not directly related to meditation exhibited altered responses to noxious thermal stimuli. Notably, meditation significantly reduced pain-related afferent processing in SI (Fig. 5), a region long associated with sensory-discriminative processing of nociceptive information (Coghill et al., 1999). Executive-level brain regions (ACC, AI, OFC) are thought to influence SI activity via anatomical pathways traversing the SII, insular, and posterior parietal cortex (Mufson and Mesulam, 1982Friedman et al., 1986;Vogt and Pandya, 1987). However, because meditation-induced changes in SI were not specifically correlated with reductions in either pain intensity or unpleasantness, this remote tuning may take place at a processing level before the differentiation of nociceptive information into subjective sensory experience.

Second, the magnitude of decreased pain intensity ratings was associated with ACC and right AI activation (Fig. 6). Activation in the mid-cingulate and AI overlapped between meditation and pain, indicating a likely substrate for pain modulation. Converging lines of evidence suggest that these regions play a major role in the evaluation of pain intensity and fine-tuning afferent processing in a context-relevant manner (Koyama et al., 2005Oshiro et al., 2009;Starr et al., 2009). Such roles are consistent with the aspect of mindfulness meditation that involves reducing appraisals that normally impart significance to salient sensory events.

Third, OFC activation was associated with decreases in pain unpleasantness ratings (Fig. 6). The OFC has been implicated in regulating affective responses by manipulating the contextual evaluation of sensory events (Rolls and Grabenhorst, 2008) and processing reward value in the cognitive modulation of pain (Petrovic and Ingvar, 2002). Meditation directly improves mood (Zeidan et al., 2010a), and positive mood induction reduces pain ratings (Villemure and Bushnell, 2009). Therefore, meditation-related OFC activation may reflect altered executive-level reappraisals to consciously process reward and hedonic experiences (e.g., immediate pain relief, positive mood) (O’Doherty et al., 2001Baliki et al., 2010Peters and Büchel, 2010).

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