Impact of meditation on emotional processing—A visual ERP study
Highlights
► Visual ERPs reveal altered emotional processing in meditation practitioners. ► At high processing levels meditators are less affected by adverse emotional stimuli. ► Conversely, processing of positive stimuli remains unchanged.
Introduction
Traditional practices commonly referred to as “meditation”, present in various cultures, are alleged to lead to heightened awareness, more balanced emotional behavior and other health benefits. The practices take different forms, however common features include detached observation of one's introspective phenomena (“open monitoring” or “mindfulness” meditation) and focus on a simple object (“focused attention” or “concentrative” meditation; Lutz et al., 2008). Recently a distinct category of meditation – “automatic self-transcending” – has been proposed (Travis and Shear, 2010, Josipovic, 2010).
The putative advantages of meditation have drawn increased clinical and scientific interest, such that it recently merited extensive reviews (including one commissioned by the U.S. Department of Health and Human Services; Ospina et al., 2007). The findings corroborate some effects of meditation, but, while encouraging further investigation, also criticize the frequent low quality of original research, precluding firmer conclusions (Chiesa and Serretti, 2009, Ospina et al., 2007, Cahn and Polich, 2006).
Original studies that do support the effects of meditation have shown, for example, that the practice of meditation has influence on the immune, endocrine and autonomic system, e.g. it causes a decrease in respiration rate, heart rate and spontaneous skin conductance response (Dillbeck and Orme-Johnson, 1987, Infante et al., 2001, Davidson et al., 2003). Aftanas and Golosheykin (2005) suggested that meditators have better capabilities to moderate intensity of emotional arousal. They argued that greater desynchronization in EEG alpha band combined with gamma band synchronization over anterior cortical sites in non-meditating control subjects during watching an emotionally adverse movie clip represented heavier emotional workload on the controls than on meditators. Effects of meditation were reported to include increased theta/alpha band activity (e.g. Travis et al., 2002), while individuals exhibiting greater theta activity tended to have lower state and trait anxiety scores (Inanaga, 1998).
Impact of meditation on emotional processing has not, however, to our knowledge, been a subject of visual event-related potential (ERP) study, while visual ERPs have been consistently shown to reflect emotional processes triggered by the emotional load of the stimulus (scene, picture), and thus provide a good research tool of the human brain's emotional responses. Particularly, the so-called late positive potential (LPP, a sustained positive component of the ERP waveform starting ca. 400–500 ms post-stimulus) was shown to increase with the emotional potency carried by the stimuli (Codispoti et al., 2007, Olofsson and Polich, 2007, Hajcak and Olvet, 2008; for review see Olofsson et al., 2008). It was also sensitive to regulation of emotions and top-down modulation related to evaluation of the affective stimuli (Hajcak et al., 2006, Moser et al., 2006, Carretié et al., 2006), diminished LPP being associated with suppression of emotional reaction (Moser et al., 2006).
The goal of the present experiment was therefore to investigate how meditation influences visual ERPs evoked by emotionally arousing stimuli. Rather than transient alterations appearing during actual meditation sessions (i.e. states), we intended to capture long-term effects of meditation practice, revealing lasting reorganization of emotional processes (i.e. traits).
Section snippets
Participants
Twenty six individuals were included in the study. Thirteen (7 men and 6 women; aged 38.7 ± 9.8 years, mean ± standard deviation), who have been practicing Buddhist meditation, formed a ‘meditators’ group. The ‘control’ group (n = 13, 5 men and 8 women; aged 34.6 ± 6.5 years) were recruited from healthy volunteers with no experience of meditation. There were no significant age differences between the groups (p = 0.40, Wilcoxon's rank sum test), nor did the gender ratios in the groups differ significantly
Results
Fig. 1 illustrates group mean (i.e. grand average) ERPs registered in our study. There is, as expected (see Section 1), an evident increase of the LPP amplitude in response to stimulus negativity in control subjects (Fig. 1A). However, interestingly, there is no such effect, or only an inconspicuous increase, in meditators’ group (Fig. 1B). On the other hand, stimulus positivity elicited only modest LPP variations in both groups, which were similar in both control (Fig. 1C) and meditators’ (
Discussion
The present visual ERP study provides evidence for a long-term effect of meditation practice on the brain's emotional processing. We found that – in contrast to the control subjects – meditators’ ERPs, specifically over frontal regions, were not impacted by negative pictures (there was no increase in the LPP components of ERP). On the other hand, we found no difference in LPP response to emotional positivity of images between meditators and control participants. This allows us to posit that
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