Posthypnotic Effects on Value-Based Decision-Making
Posthypnotic Effects on Value-Based Decision-Making
Hypnosis can affect perception, motor function and memory. However, so far no study using neuroimaging has investigated whether hypnosis can influence reward processing and decision-making. Here, we assessed whether posthypnotic suggestions can diminish the attractiveness of unhealthy food and whether this is more effective than diminishing attractiveness by one's own effort via autosuggestion. In total, 16 participants were hypnotized and 16 others were instructed to associate a color cue (blue or green) with disgust regarding specific snacks (sweet or salty). Afterwards, participants bid for snack items shown on an either blue or green background during functional magnetic resonance imaging measurement. Both hypnosis and autosuggestion successfully devalued snacks. This was indicated by participants' decision-making, their self-report and by decreased blood oxygen level-dependent signal in the ventromedial prefrontal cortex (vmPFC), a region known to represent value. Different vmPFC subregions coded for cue and snack type. The cue had significantly stronger effects on vmPFC after hypnosis than after autosuggestion, indicating that hypnosis was more effective in genuinely reducing value. Supporting previous findings, the precuneus was involved in the hypnotic effects by encoding whether a snack was sweet or salty during hypnotic cue presentation. Our results demonstrate that posthypnotic suggestions can influence valuation and decision-making.
Hypnosis is a state of altered attention and heightened suggestibility, which is typically induced by verbal instructions. During hypnosis, suggestions can be given to participants, and these may either take effect immediately or after the hypnotic state. In the latter case, they are termed 'posthypnotic' suggestions (Raz et al., 2002, 2005; Wheatley and Haidt, 2005; Iani et al., 2006, 2009). Hypnotic suggestions can lead to strong and genuine effects in susceptible individuals, such as paralysis (Halligan et al., 2000; Cojan et al., 2009), experiencing own movements as externally caused (Blakemore et al., 2003), seeing letters in colors (Cohen Kadosh et al., 2009), sensory pain without an affective component (Rainville et al., 1997), visual illusions (Kosslyn et al., 2000) or auditory hallucinations (Szechtman et al., 1998). Hypnotic suggestions can also affect moral judgments and moral behavior (Wheatley and Haidt, 2005; Brüne et al., 2012). So far, however, no study using neuroimaging has investigated whether hypnosis can also influence reward processing and value-based decision-making. This is a crucial question given the wide use of hypnosis to treat maladaptive decision-making such as in nicotine addiction or obesity (Kirsch et al., 1995; Allison and Faith, 1996; Carmody et al., 2008; Barnes et al., 2010).
It is well established that the subjective value people place on decision options is represented in the ventromedial prefrontal cortex (vmPFC), which includes the rostral anterior cingulate cortex (rACC) and the medial orbitofrontal cortex (mOFC; Kable and Glimcher, 2007; Hare et al., 2008; Lebreton et al., 2009; Basten et al., 2010; Peters and Büchel, 2010; Plassmann et al., 2010; Grabenhorst and Rolls, 2011; Brosch et al., 2012). For example, the greater the activity in vmPFC, the more people are willing to pay for an item (Plassmann et al., 2007; Chib et al., 2009; Janowski et al., 2013), or the more they desire to consume it (Hare et al., 2009; Litt et al., 2011). Some studies have shown that value signals in vmPFC can be modulated by self-control or attention (Hare et al., 2009; Hollmann et al., 2011) or by mindsets (Bhanji and Beer, 2012; for studies on modulating pleasantness of tasting or smelling rewards, see de Araujo et al., 2005; Grabenhorst and Rolls, 2008; Grabenhorst et al., 2008; Plassmann et al., 2008). For example, when participants focus their attention on health aspects of food items, vmPFC responds more strongly to the healthiness of the food, and participants also make healthier decisions (Hare et al., 2011). Moreover, when participants focus on the (negative) long-term rather than the (positive) short-term consequences of consuming food or cigarettes, vmPFC responds less strongly to pictures showing food or cigarettes (Kober et al., 2010). However, overall, evidence regarding experimental manipulations of vmPFC value signals during decision-making has been scarce.
Here we investigated whether posthypnotic suggestions can influence the value people place on unhealthy food during decision-making, as indicated by behavior, self-report and vmPFC activation. We further asked whether hypnosis can achieve stronger effects than self-controlled down-regulation of the attractiveness of food, termed here 'autosuggestion' (Baudouin, 2003; Coué, 2009). Autosuggestion refers to the process of implementing a mental change in oneself (e.g. by repeating suggestions to oneself and by engaging in goal-directed imagery). It is a novel approach to use an autosuggestion (or self-control) group as a comparison group for hypnosis. Previous studies have typically used control participants who were either instructed to 'simulate' hypnotic behavior (Cojan et al., 2009) or who received the same suggestions as the hypnotized group without a hypnotic induction (Iani et al., 2006). Another approach is to compare hypnotic effects between highly suggestible and less suggestible participants (Raz et al., 2002). Here, we compared hypnosis to autosuggestion, because it is clinically and practically relevant to determine if hypnosis is more effective than attempts to implement a mental change by oneself.
We further assessed whether the hypnotic manipulation of value-based decision-making involves the precuneus. Previous findings indicated that the precuneus is important for hypnotic effects. In a study by Cojan et al. (2009), participants were given hypnotic suggestions for left-hand paralysis. When they were instructed to move their left hand—which they were unable to do—there was precuneus activation; and precuneus showed enhanced functional connectivity with primary motor cortex. The authors related their findings to studies showing that the precuneus is involved in mental imagery and self-related processing (Lou et al., 2004; Cavanna and Trimble, 2006). They proposed that during hypnotic effects, behavior is guided by increased self-monitoring processes and by internal representations produced by imagery and by the hypnotic suggestions.
We hypothesized that hypnosis would be able to change decision-making about unhealthy snacks behaviorally, and that this would be reflected in diminished value signals in vmPFC during those decisions. We further predicted that hypnosis would lead to stronger effects than autosuggestion. Finally, we hypothesized that the precuneus would be functionally involved in the hypnotic effects by encoding relevant information about the content of the suggestions.
Abstract and Introduction
Abstract
Hypnosis can affect perception, motor function and memory. However, so far no study using neuroimaging has investigated whether hypnosis can influence reward processing and decision-making. Here, we assessed whether posthypnotic suggestions can diminish the attractiveness of unhealthy food and whether this is more effective than diminishing attractiveness by one's own effort via autosuggestion. In total, 16 participants were hypnotized and 16 others were instructed to associate a color cue (blue or green) with disgust regarding specific snacks (sweet or salty). Afterwards, participants bid for snack items shown on an either blue or green background during functional magnetic resonance imaging measurement. Both hypnosis and autosuggestion successfully devalued snacks. This was indicated by participants' decision-making, their self-report and by decreased blood oxygen level-dependent signal in the ventromedial prefrontal cortex (vmPFC), a region known to represent value. Different vmPFC subregions coded for cue and snack type. The cue had significantly stronger effects on vmPFC after hypnosis than after autosuggestion, indicating that hypnosis was more effective in genuinely reducing value. Supporting previous findings, the precuneus was involved in the hypnotic effects by encoding whether a snack was sweet or salty during hypnotic cue presentation. Our results demonstrate that posthypnotic suggestions can influence valuation and decision-making.
Introduction
Hypnosis is a state of altered attention and heightened suggestibility, which is typically induced by verbal instructions. During hypnosis, suggestions can be given to participants, and these may either take effect immediately or after the hypnotic state. In the latter case, they are termed 'posthypnotic' suggestions (Raz et al., 2002, 2005; Wheatley and Haidt, 2005; Iani et al., 2006, 2009). Hypnotic suggestions can lead to strong and genuine effects in susceptible individuals, such as paralysis (Halligan et al., 2000; Cojan et al., 2009), experiencing own movements as externally caused (Blakemore et al., 2003), seeing letters in colors (Cohen Kadosh et al., 2009), sensory pain without an affective component (Rainville et al., 1997), visual illusions (Kosslyn et al., 2000) or auditory hallucinations (Szechtman et al., 1998). Hypnotic suggestions can also affect moral judgments and moral behavior (Wheatley and Haidt, 2005; Brüne et al., 2012). So far, however, no study using neuroimaging has investigated whether hypnosis can also influence reward processing and value-based decision-making. This is a crucial question given the wide use of hypnosis to treat maladaptive decision-making such as in nicotine addiction or obesity (Kirsch et al., 1995; Allison and Faith, 1996; Carmody et al., 2008; Barnes et al., 2010).
It is well established that the subjective value people place on decision options is represented in the ventromedial prefrontal cortex (vmPFC), which includes the rostral anterior cingulate cortex (rACC) and the medial orbitofrontal cortex (mOFC; Kable and Glimcher, 2007; Hare et al., 2008; Lebreton et al., 2009; Basten et al., 2010; Peters and Büchel, 2010; Plassmann et al., 2010; Grabenhorst and Rolls, 2011; Brosch et al., 2012). For example, the greater the activity in vmPFC, the more people are willing to pay for an item (Plassmann et al., 2007; Chib et al., 2009; Janowski et al., 2013), or the more they desire to consume it (Hare et al., 2009; Litt et al., 2011). Some studies have shown that value signals in vmPFC can be modulated by self-control or attention (Hare et al., 2009; Hollmann et al., 2011) or by mindsets (Bhanji and Beer, 2012; for studies on modulating pleasantness of tasting or smelling rewards, see de Araujo et al., 2005; Grabenhorst and Rolls, 2008; Grabenhorst et al., 2008; Plassmann et al., 2008). For example, when participants focus their attention on health aspects of food items, vmPFC responds more strongly to the healthiness of the food, and participants also make healthier decisions (Hare et al., 2011). Moreover, when participants focus on the (negative) long-term rather than the (positive) short-term consequences of consuming food or cigarettes, vmPFC responds less strongly to pictures showing food or cigarettes (Kober et al., 2010). However, overall, evidence regarding experimental manipulations of vmPFC value signals during decision-making has been scarce.
Here we investigated whether posthypnotic suggestions can influence the value people place on unhealthy food during decision-making, as indicated by behavior, self-report and vmPFC activation. We further asked whether hypnosis can achieve stronger effects than self-controlled down-regulation of the attractiveness of food, termed here 'autosuggestion' (Baudouin, 2003; Coué, 2009). Autosuggestion refers to the process of implementing a mental change in oneself (e.g. by repeating suggestions to oneself and by engaging in goal-directed imagery). It is a novel approach to use an autosuggestion (or self-control) group as a comparison group for hypnosis. Previous studies have typically used control participants who were either instructed to 'simulate' hypnotic behavior (Cojan et al., 2009) or who received the same suggestions as the hypnotized group without a hypnotic induction (Iani et al., 2006). Another approach is to compare hypnotic effects between highly suggestible and less suggestible participants (Raz et al., 2002). Here, we compared hypnosis to autosuggestion, because it is clinically and practically relevant to determine if hypnosis is more effective than attempts to implement a mental change by oneself.
We further assessed whether the hypnotic manipulation of value-based decision-making involves the precuneus. Previous findings indicated that the precuneus is important for hypnotic effects. In a study by Cojan et al. (2009), participants were given hypnotic suggestions for left-hand paralysis. When they were instructed to move their left hand—which they were unable to do—there was precuneus activation; and precuneus showed enhanced functional connectivity with primary motor cortex. The authors related their findings to studies showing that the precuneus is involved in mental imagery and self-related processing (Lou et al., 2004; Cavanna and Trimble, 2006). They proposed that during hypnotic effects, behavior is guided by increased self-monitoring processes and by internal representations produced by imagery and by the hypnotic suggestions.
We hypothesized that hypnosis would be able to change decision-making about unhealthy snacks behaviorally, and that this would be reflected in diminished value signals in vmPFC during those decisions. We further predicted that hypnosis would lead to stronger effects than autosuggestion. Finally, we hypothesized that the precuneus would be functionally involved in the hypnotic effects by encoding relevant information about the content of the suggestions.
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