Effects of brief mindfulness training on the neural activity associated with processing food cues Público
Chen, Jing (Summer 2019)
Abstract
A functional magnetic resonance imaging experiment assessed effects of a brief mindfulness intervention on the neural mechanisms that underlie food cue processing. In a blocked design, an initial training phase asked participants to either normally view or mindfully attend to images of tasty and healthy foods. In a fast event-related design, a subsequent choice phase asked participants to make speeded choices about whether to eat pictured foods (both tasty and healthy, half from the training phase, half novel). The results largely supported our hypotheses. Using the breadth of activation relative to well-matched active baselines (rather than signal intensity relative to resting state baselines), we established a large distributed neural network for food processing that grounds the diverse aspects of food consumption simulations, including the ventral food reward network (taste, olfaction, reward, attention), mentalizing (along the cortical midline), and embodiment including action (across the motor system). This distributed network was active for both training and choice, for both tasty and healthy foods, for both repeated and novel foods. Left-hemisphere language areas were also active (although not predicted), implicating linguistic processing of food cues, especially during the training phase for the mindful attention group. As predicted, tasty foods produced greater neural activity across food processing areas than healthy foods during the training phase. Surprisingly the choice phase exhibited the opposite pattern, with healthy foods producing larger activations. Most importantly, mindful attention, relative to normal viewing, produced more neural activity while processing foods during the training phase, but much less neural activity during the subsequent choice phase. Increased up-front processing for mindful attention during training later led to a large processing off-load during food choice. Moreover, this effect of mindful attention was much larger for tasty foods than for healthy foods, perhaps because tasty foods offer more conceptual content for mindful attention to process. Finally, mindful attention operated both as a general cognitive set (generalizing to novel foods) and also via food-specific memories (repetition effect), suggesting two mechanisms that underlie mindful attention effects. These results shed new light on the mechanisms that underlie early mindfulness practice, while raising many issues for future research.
Table of Contents
1. Introduction......................................................................................................................... 1
1.1.The problem................................................................................................................ 1
1.2. The neural mechanisms that underlie the processing of food cues............................ 3
1.2.1. Adopting the perspective of grounded cognition............................................... 3
1.2.2. The neural network underlying food consumption............................................. 4
1.2.3. The neural network underling food cue processing............................................ 6
1.2.4. Enhanced activations in (part of) the ventral reward pathway
for high-calorie food cues............................................................................................. 9
1.2.5. Altered activations in food networks with increased BMI (body mass index)10
1.2.6. Enhanced activations in (part of) the ventral reward pathway when hungry... 11
1.3. Interventions designed to moderate food cue processing......................................... 11
1.4. Mindfulness interventions relevant to food cue processing..................................... 12
1.4.1. Brief mindful attention training on other aspects............................................. 14
1.4.2. Brief mindful attention training on food cue processing.................................. 15
1.4.3. Neural mechanisms that underlie brief mindful attention training
in emotion regulation and smoking............................................................................ 17
1.5. Assessing the neural mechanisms that underlie
a brief mindfulness intervention for stress processing.................................................... 18
1.5.1. Summary of Lebois et al.’s (2015) methods..................................................... 19
1.5.2. Summary of Lebois et al.’s (2015) results........................................................ 21
1.6. Experiment overview and hypotheses...................................................................... 22
1.6.1. Experiment goals.............................................................................................. 22
1.6.2. Experiment overview........................................................................................ 24
1.6.3. Methodological similarities and differences with Lebois et al. (2015)............ 26
1.6.3.1. The observe perspective.................................................................... 26
1.6.3.2. Active baseline tasks.......................................................................... 27
1.6.3.3. Scrambled non-food object images in the active baseline tasks........ 28
1.6.3.4. Breadth of activations above the active baseline............................... 29
1.6.3.5. Departures from Lebois et al. (2015)................................................. 30
1.6.4. Hypotheses........................................................................................................ 30
2. Methods.............................................................................................................................. 33
2.1. Design....................................................................................................................... 33
2.2. Participants............................................................................................................... 34
2.3. Materials................................................................................................................... 35
2.3.1. The training phase............................................................................................. 35
2.3.2. The food choice phase...................................................................................... 36
2.3.3. The pre-scan and post-scan questionnaires...................................................... 37
2.4. Procedure.................................................................................................................. 38
2.4.1. Active baseline task for the training phase....................................................... 38
2.4.2. Learning the observe or normal viewing perspective....................................... 39
2.4.3. Learning food blocks........................................................................................ 40
2.4.4. The training phase in the scanner..................................................................... 40
2.4.5. The food choice phase in the scanner............................................................... 41
2.4.6. Post-scan questionnaires................................................................................... 42
2.5. Image acquisition...................................................................................................... 42
2.6. Image preprocessing................................................................................................. 43
2.7. Data analysis............................................................................................................. 44
2.7.1. Conjunction analyses........................................................................................ 46
2.7.2. Binomial tests between conditions................................................................... 46
2.7.3. Conjunction analysis overview......................................................................... 48
2.7.4. Region of interest masks................................................................................... 48
3. Results................................................................................................................................. 49
3.1. Preliminary behavioral results.................................................................................. 49
3.1.1. Hunger measures.............................................................................................. 49
3.1.2. Individual difference measures......................................................................... 50
3.1.3. Food measures.................................................................................................. 50
3.1.4. Ratings on perspective effectiveness during the training phase....................... 50
3.2. Mixed-effects regressions on the behavioral data during the choice phase............. 50
3.3. Whole brain analyses................................................................................................ 52
3.3.1. Overview........................................................................................................... 52
3.3.2. Hypothesis 2..................................................................................................... 53
3.3.3. Hypothesis 3..................................................................................................... 55
3.3.4. Hypothesis 4..................................................................................................... 56
3.3.5. Assessing whole brain activations for tasty vs. healthy foods......................... 57
3.4. ROI analyses............................................................................................................. 59
3.4.1. Overview........................................................................................................... 59
3.4.2. Contrasting tasty vs. healthy foods................................................................... 63
3.4.3. Contrasting the normal viewing vs. observe perspective................................. 65
3.4.4. Contrasting repeated vs. novel trials during the choice phase.......................... 66
4. Discussion........................................................................................................................... 66
4.1. Summary of results................................................................................................... 66
4.1.1. Hypothesis 1..................................................................................................... 66
4.1.2. Hypothesis 2..................................................................................................... 68
4.1.3. Hypothesis 3..................................................................................................... 69
4.1.4. Hypothesis 4..................................................................................................... 69
4.2. Possible roles of the cortical midline and self-relevance in food processing........... 69
4.2.1. The cortical midline and self-relevance processing......................................... 70
4.2.2. The importance of self-identity for foods......................................................... 70
4.2.3. How might participants have been mentalizing about food?........................... 71
4.2.4. Previous studies on mindful attention and the cortical midline........................ 71
4.2.5. Self-relevance processing during the choice phase.......................................... 73
4.3. Language areas and their roles in food processing
(especially during the training phase).............................................................................. 74
4.3.1. Roles of the left IFG and left lateral MTG in language processing................. 74
4.3.2. Language processing during mindful attention................................................ 75
4.3.3. Differences between perspectives and phases in language-related areas......... 76
4.4. Grounded cognition and food processing................................................................. 77
4.4.1. Establishing the breadth of activations associated with food processing......... 78
4.4.2. Olfaction and food processing.......................................................................... 79
4.4.3. Embodiment and food processing.................................................................... 79
4.4.4. The parahippocampal gyrus and food processing............................................ 80
4.4.5. Summary........................................................................................................... 81
4.5. How does mindful attention work?.......................................................................... 81
4.5.1. Decentering and mindful attention................................................................... 82
4.5.2. Mindful attention in the training and choice phases:
Up-front vs. off-loaded processing............................................................................. 82
4.5.3. “Top-down” or “bottom-up” processing.......................................................... 84
4.5.4. Mindful attention exhibits stronger effects for tasty foods............................... 84
4.5.5. Repetition effects for mindful attention training.............................................. 85
4.5.6. Summary........................................................................................................... 86
4.6. Stronger activations for healthy foods during the choice phase
(especially for the normal viewing group)...................................................................... 86
4.7. Limitations................................................................................................................ 88
4.8. Future directions....................................................................................................... 91
4.8.1. Short-term effect vs. long-term effects of mindful attention training.............. 91
4.8.2. Other populations.............................................................................................. 92
4.8.3. Functional connectivity during mindful attention processing.......................... 92
References............................................................................................................................... 94
Appendices
Appendix A.................................................................................................................... 114
Table A1........................................................................................................................ 115
Table A2........................................................................................................................ 116
Appendix B.................................................................................................................... 117
Table B1........................................................................................................................ 118
Table B2........................................................................................................................ 118
Table B3........................................................................................................................ 119
Appendix C.................................................................................................................... 120
Table C1........................................................................................................................ 121
Appendix D.................................................................................................................... 123
Appendix E.................................................................................................................... 141
Appendix F.................................................................................................................... 146
Table F1......................................................................................................................... 147
Appendix G.................................................................................................................... 148
Table G1........................................................................................................................ 149
Table G2........................................................................................................................ 154
Table G3........................................................................................................................ 159
Tables
Table 1........................................................................................................................... 164
Table 2........................................................................................................................... 165
Table 3........................................................................................................................... 166
Table 4........................................................................................................................... 167
Table 5........................................................................................................................... 168
Table 6........................................................................................................................... 169
Table 7........................................................................................................................... 170
Figures
Figure 1.......................................................................................................................... 171
Figure 2.......................................................................................................................... 172
Figure 3.......................................................................................................................... 173
Figure 4.......................................................................................................................... 174
Figure 5.......................................................................................................................... 175
Figure 6.......................................................................................................................... 176
Figure 7.......................................................................................................................... 177
Figure 8.......................................................................................................................... 178
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Figure 10........................................................................................................................ 180
Figure 11........................................................................................................................ 181
Figure 12........................................................................................................................ 182
Figure 13........................................................................................................................ 183
Figure 14........................................................................................................................ 184
Figure 15........................................................................................................................ 185
Figure 16........................................................................................................................ 186
Figure 17........................................................................................................................ 187
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