Measuring Mindfulness: A Psychophysiological Approach

Abstract

Mindfulness-based interventions have proved effective in reducing various clinical symptoms and in improving general mental health and well-being. The investigation of the mechanisms of therapeutic change needs methods for assessment of mindfulness. Existing self-report measures have, however, been strongly criticized on various grounds, including distortion of the original concept, response bias, and other. We propose a psychophysiological method for the assessment of the mindfulness learned through time-limited mindfulness-based therapy by people who undergo meditation training for the first time. We use the individual pre-post-therapy changes (dERPi) in the event-related brain potentials (ERPs) recorded in a passive meditation task as a measure of increased mindfulness. dERPi is computed through multivariate assessment of individual participant's ERPs. We tested the proposed method in a group of about 70 recurrently depressed participants, randomly assigned in 1.7:1 ratio to mindfulness-based cognitive therapy (MBCT) or cognitive therapy (CT). The therapy outcome was measured by the long-term change (dDS) relative to baseline in the depression symptoms (DS) assessed weekly, for 60 weeks, by an online self-report questionnaire. We found a strong, highly significant, negative correlation (r = -0.55) between dERPi (mean = 0.4) and dDS (mean = -0.7) in the MBCT group. Compared to this result, the relationship between dDS and the other (self-report) measures of mindfulness we used was substantially weaker and not significant. So was also the relationship between dERPi and dDS in the CT group. The interpretation of dERPi as a measure of increased mindfulness was further supported by positive correlations between dERPi and the other measures of mindfulness. In this study, we also replicated a previous result, namely, the increase (dLCNV) of the late contingent negative variation (LCNV) of the ERP in the MBCT group, but not in the control group (in this case, CT). We interpreted dLCNV as a measure of increased meditative concentration. The relationship between dLCNV and dDS was, however, very week, which suggests that concentration might be relatively unimportant for the therapeutic effect of mindfulness. The proposed psychophysiological method could become an important component of a "mindfulness test battery" together with self-report questionnaires and other newly developed instruments.

Keywords: ERP; MBCT; concentration; depression; event-related potentials; mindfulness; mindfulness-based cognitive therapy; t-CWT.

Figure 1

A flow chart showing the number of (prospective) participants in the different phases of the study. Candidates contacted us per phone or email; “Didn't call again” actually means that they either did not call again, or did not answer our email messages. Two prospective candidates refused further participation after screening, because they did not agree to randomization. Stated causes for drop-out before therapy were most often related to a new job offer or other reason for relocation. In two cases, however, the announced motivation for drop-out was dissatisfaction with study conditions and procedures. Drop-outs during therapy were mostly caused by illness (own or significant other's).

Figure 2

Detailed demographics of participant (sub)samples. N denotes the number of participants in the respective (sub)sample or layer, $\overline{\mathrm{\text{Age}}}$ is the mean age, SD is the standard deviation of the age, and $\overline{N_{\mathrm{\text{DE}}}}$ is the mean number of episodes of major depression. “Highschool” means completed German Realschule or Gymnasium and “Higher edu.” denotes higher education, but not necessarily completed (university students were included in this category). “On meds” refers to the number (and percentage) of participants taking psychopharmaceuticals during diagnostics and therapy. Medication included different kinds of antidepressants and, in two cases, anxiolytics and other psychoactive drugs.

Figure 3

PANAS (section 2.4.3) scores: positive affect (PA, orange circles) and negative affect (NA, purple squares) at three time points: 1, at the beginning of the experimental session; 2, after the mood and rumination induction (section 2.4.4); and 3, after the passive mindfulness meditation task (section 2.4.6). See also Table 3. (A) Never depressed. (B) Recurrently depressed. (C) CT, pre-therapy. (D) MBCT, pre-therapy. (E) CT, post-therapy. (F) MBCT, post-therapy.

Figure 4

Grand average ERPs obtained in the passive mindfulness meditation task (section 2.4.6). (A) ERPs obtained from the CT group before (thin green line) and after (thick brown line) 8 weeks of therapy. (B) ERPs obtained from the MBCT group before (thin green line) and after (thick brown line) 8 weeks of training.

Figure 5

Pre-post-therapy change in the ERPs obtained in the passive mindfulness meditation task (section 2.4.6). (A) Pre-post-therapy difference ERP in the CT group (thin blue line) and in the MBCT group (thick red line). (B) Student's t-test of the difference between the ERP change in the CT group and the that in the MBCT group.

Figure 6

Individual ERP changes of the six MBCT participants (IDs: pwlr4ptg, bruk4khl, auxv6azb, irlk2mdn, uhat8lkg, and uhjd2sed,) whose dERPi and dDS are marked by larger circles in Figure 7. The plots in the first column show the individual average ERPs at Cz obtained in the passive mindfulness meditation task (section 2.4.6) before (thin green line) and after (thick brown line) 8 weeks of training. The plots in the next columns show the corresponding mean difference ERP (second column), Student's t-test of the ERP difference (third column), and the linear discriminant function (LDF, section 2.8.3, fourth column).

Figure 7

Linear regression model (black line) of the relationship between the passive task dERPi and dDS in the MBCT group (red dots). dERPi was computed for each participant as the logarithm of the t-CWT Mahalanobis distance between the ERP before therapy and the ERP after therapy (section 2.8.3). dDS = DSf − DSt, where DSf is the mean DS score during follow-up and DSt is the mean DS score during therapy (section 2.6). The points marked by larger circles drawn around them belong to the six MBCT participants whose individual ERPs are presented in Figure 6.