Anorexia Nervosa and Deep Brain Stimulation: Philosophical Analysis of Potential Mechanisms

By Hannah Maslen, Jonathan Pugh and Julian Savulescu

 

According to the NHS, the number of hospital admissions across the UK for teenagers with eating disorders has nearly doubled in the last three years. In a previous post, we discussed some ethical issues relating to the use of deep brain stimulation (DBS) to treat anorexia nervosa (AN). Although the trials of this potential treatment are still in very early, investigational stages (and may not necessarily become an approved treatment), the invasive nature of the intervention and the vulnerability of the potential patients are such that anticipatory ethical analysis is warranted. In this post, we show how different possible mechanisms of intervention raise different questions for philosophers to address. The prospect of intervening directly in the brain prompts exploration of the relationships between a patient’s various mental phenomena, autonomy and identity.

DBS could achieve treatment effects in different ways depending on the stimulation site. Which of these potential mechanisms would promote an anorexic patient’s ability to direct their life and express their self in their decisions regarding their eating behavior, and which might potentially compromise these abilities, is in large part a philosophical question. We here discuss three potential mechanisms alluded to in the neuroscientific literature: 1) modification of hedonic properties of food, 2) reduction of the drive towards compulsive behavior, and 3) regulation of aversive mood and affect. The associated consequences for philosophical assessment are, correspondingly, 1) the alteration of a first-order desire for food, 2) the promotion of comparative cognitive control over behavior, 3) the modification of emotional symptoms or traits. In the remainder of the post we distinguish these three mechanisms and explain why mechanism could matter for the patient’s autonomy and personal identity.

Imposition or exacerbation of a first-order desire

Park and colleagues explain that a few single case reports on individuals with Anorexia nervosa given DBS to the Nucleus Accumbens (part of the Ventral Striatum directly implicated in reward processing) suggest positive outcomes in terms of weight recovery and resolution of both anorexia and comorbid pathology.[1] Indeed, as Treasure and Schmidt report:

The importance of the subthalamic nucleus for the control of eating is shown by the emergence of binge eating as a possible side-effect of DBS in that region for the treatment of Parkinson’s disease.[2]

The suggestion seems to be that stimulating a part of the brain implicated in the hedonic properties of food would increase the desirability of the food and/or the motivation to eat. Determining precisely how this works will be important. Park and colleagues point out that there is an important – and neurologically supported – distinction between ‘wanting’ and ‘liking’ in anorexia. Whilst ‘wanting’ is associated with motivational salience, ‘liking’ simply denotes hedonic pleasure taken in the object. Park and colleagues argue that wanting and liking – usually working in concert – can cease to work in concert in anorexia nervosa.

An additional distinction between the explicit (conscious) and implicit (subconscious) levels at which wanting and liking can operate further complicate the picture. Park and colleagues note that implicit ‘wanting’ can occur in the absence of cognitively driven, explicit wanting, or even in conflict to it. This leads to their hypothesis that such a conflict ‘could be the case in AN where there is a cognitive preoccupation with dietary restraint which may be function to counter the implicit processes at work. In this situation, desires can become dreads’.[3]

The idea that DBS could be used to alter a desire for food is therefore actually a very complicated proposition. It could be that the intervention makes explicit an otherwise implicit desire (wanting), thereby rendering it accessible to the patient. In a sense, on this understanding, DBS might be understood to reveal to the patient what she ‘really’ wants. Whether the patient rationally endorses this desire at a higher order level will be of great significance to whether the intervention works to promote their autonomy or frustrate it.

Further, the psychological consequences of a conflict between first-order desires and higher order evaluations could be distressing for the patient. Indeed, some of those involved in the research have warned that ‘Normalization of body weight after DBS for AN does not necessarily imply normalization of the distorted body image’ nor other psychological features associated anorexia. [4] They worry that DBS may have the consequence of increasing body weight without changing body image, and that ‘a “psychological hell” for the patient may result from this’. Whilst such an outcome has not yet been reported, the manipulation of first-order desires without attending to the patient’s evaluation of thinness presents a risk of psychological harm.

Promotion of comparative cognitive control

An alternative hypothesized mechanism is that DBS may aid recovery of both weight and AN pathology by normalizing aberrant control over compulsive behavior. Outlining the neurocircuitry – specifically, a cortico-striatal thalamic circuit (CSTC) – involved, Park and colleagues explain that research suggest that different neural components are responsible for, on the one hand, the (bottom-up) driving of compulsive behavior and, on the other hand, the (top-down) control or inhibition of this behavior. Abnormalities in either of these components (hypoactivity/hyperactivity) may result in an increase in compulsive behaviours.

Drawing comparisons with the behavior exhibited in obsessive compulsive disorder (OCD), they hypothesise that anorexic patients might suffer from hyperactive weight-loss compulsion. Although weight loss behaviors might start out as goal-driven, these behaviours themselves (as opposed to their effects on weight) become rewarding and are thereby reinforced until they become habits. Consequently, habitual weight-loss behavior becomes dissociated from the original goals and is difficult to exert control over. The argument seems to be that what starts out as goal-driven becomes habit driven, in a way that is difficult to resist. Extending the comparison with OCD, Park and colleagues note that ‘Symptomatic alleviation in treatment resistant OCD and addictions following DBS targeted within the CSTC circuit […] supports the involvement of these circuits in compulsivity. There are preliminary suggestions that this circuit may indicate potential targets for DBS for severe enduring AN’.[5]

Such an intervention clearly could promote the patient’s autonomy, if the weight loss is driven by reinforced habits that no longer align with the patient’s autonomously chosen goals. In such a scenario, DBS could be used to reduce a compulsive drive towards over-learnt behaviours that no longer serve the patient’s goals. If the compulsion to engage in weight-loss behavior is reduced, the patient regains control over her actions, and can decide whether or not to engage in behavior that previously was difficult to resist.

Modification of emotional traits

The final mechanism we consider is drawn from a study that examined the effects of using DBS to modify emotional traits of patients with anorexia. Lipsman et al. believe that anorexia is ‘predominantly a disorder of emotional processing’ on the grounds that it is, according to their model, primarily the limbic structures that are implicated in the disorder. Anorexia, they point out is a disorder ‘marked by high rates of depressed mood and affective dysregulation’.[6]

Lipsman and colleagues stimulated the subcallosal cingulate, which has a key role in modulating emotional states and projects cortically, to medial- and orbitofrontal cortex, as well as subcortically to nucleus accumbens. They reported as follows:

Our initial study in a small group of treatment-refractory patients (N.6; average age: 38 years; average illness duration: 18 years) showed DBS to be reasonably safe, and associated with improvements in comorbid mood and anxiety symptoms.[7]

Although they found that three of their six patients had achieved and maintained a BMI greater than their historical baselines after 9 months, Lipsman and colleagues speculated that these effects were achieved indirectly via a primary effect on mood, anxiety and affective regulation. Improved mood, they suggest, enhanced the uptake and effectiveness of conventional anorexia treatment, which consequently lead to increases in weight.

The nature of this intervention leaves the patient’s drives and desires less directly affected, although there is obviously a relationship between how we feel and what we are motivated to do. In cases where the intervention acts on an agent’s mood and emotions, the intervention may raise concerns pertaining to the patient’s narrative identity. Whilst it seems intuitively plausible to claim that raised mood and decreased anxiety are the sorts of changes that people will welcome, we should not forget that they can be closely bound up with our sense of identity in ways that clinicians should at least be aware of. The following quotation from a qualitative study conducted by Tan et al. illustrates this in relation to anorexia:

Interviewer:     If your anorexia nervosa magically disappeared, what would be different from right now?

Participant:     Everything. My personality would be different.

Interviewer:     Really!

Participant:     It’s been, I know it’s been such a big part of me, and—I don’t think you can ever get rid of it, or the feelings, you always have a bit—in you. […]

Interviewer:     Let’s say you’ve got to this point, and someone said they could wave a magic wand and there wouldn’t be anorexia any more.

Participant:     I couldn’t.

Interviewer:     You couldn’t.

Participant:     It’s just a part of me now.

Interviewer:     Right. So it feels like you’d be losing a part of you.

Participant:     Because it was my identity. (Participant I)[8]

From the philosophical to the practical

In our earlier post we raised concerns about the possible coerciveness of the situation in which patients might consent to the neurosurgery, and the consequent implications for the validity of that consent. In saying that the situation might be coercive, we did not mean that surgery would be forced on the patient without any attempt to gain consent. Rather, we suggested that the beliefs a patient could have about their set of options might adversely affect the voluntariness of that patient’s choice to undergo surgery. If a patient (rightly or wrongly) believes that if they do not undergo surgery then there is a high possibility of aversive compulsory treatment further down the line, then they might consent to surgery on the grounds that it is the least bad of two completely unwelcome options. Indeed, the concept of ‘perceived coercion’ in the treatment of anorexia has been described elsewhere.[9] Similarly, the concern we raised pertained to the possible subjective perception of there being no viable option to refuse surgical intervention, given the even less attractive alternative. For patients who value nothing higher than thinness or rejection of food, the options might appear thus, even if the actual trajectory is unlikely to end in aversive compulsory treatment. What the patient believes about their options is of paramount importance to the quality of any consent given.

As noted above, DBS is still at the experimental stage of treatment development for Anorexia Nervosa. Indeed, ongoing research on the mechanisms to optimize neural targets (Park et al 2014) is important. At present there is not even any consensus on which area of the brain should be stimulated, nor on precisely how stimulation of different regions will affect symptoms and the underlying pathology. The phase 1 trials will provide researchers and clinicians with much new data on anorexia nervosa and its complex neurological underpinnings, rather than simply representing attempts to test a potential treatment. However, the few case studies that are available suggest a range of different interventional mechanisms, and further hypotheses have been presented in the neuroscientific review literature. In this post, our aim was simply to outline the philosophical implications of three different possible intervention mechanisms, drawn from the preliminary data and discussion.

Conclusion

DBS is undoubtedly a powerful new medical technology, and existing studies suggests that it has at least some promise as a potential new therapy for anorexia nervosa. An adequate ethical analysis of the potential use of this technology should focus first on the quality of the patient’s consent to undergo the intervention. However, assuming that a patient has validly consented to undergoing the intervention, the primary ethical considerations that the use of DBS in this context raises depend on the precise neural effects, which may vary according to neural targets. Whilst the manipulation of some processes may plausibly enhance the patient’s ability to make autonomous decisions with regards to her eating behavior, the use of this technology to alter first-order motivating desires or the patient’s emotional traits also raises some potential for significant harms as well as potential benefits, which need to be borne in mind in research and clinical development protocols.

 

References

[1] Park, R. J., Godier, L. R., & Cowdrey, F. A. (2014). Hungry for reward: How can neuroscience inform the development of treatment for Anorexia Nervosa?. Behaviour research and therapy, 62, 47-59.

[2] Treasure, J., & Schmidt, U. (2013). DBS for treatment-refractory anorexia nervosa. The Lancet, 381(9875), 1338-1339.

[3] Park, R. J., Godier, L. R., & Cowdrey, F. A. (2014). Hungry for reward: How can neuroscience inform the development of treatment for Anorexia Nervosa?. Behaviour research and therapy, 62, 47-59.

[4] Wu H, Van Dyck-Lippens PJ, Santegoeds R, et al. Deep-brain stimulation for anorexia nervosa. World Neurosurg 2012; published online June 25. DOI:10.1016/j.wneu.2012.06.039.

[5] Park, R. J., Godier, L. R., & Cowdrey, F. A. (2014). Hungry for reward: How can neuroscience inform the development of treatment for Anorexia Nervosa?. Behaviour research and therapy, 62, 47-59.

[6] Lipsman, N., & Lozano, A. M. (2014). Targeting emotion circuits with deep brain stimulation in refractory anorexia nervosa. Neuropsychopharmacology, 39(1), 250-251.

[7] Lipsman, N., & Lozano, A. M. (2014). Targeting emotion circuits with deep brain stimulation in refractory anorexia nervosa. Neuropsychopharmacology, 39(1), 250-251.

[8] Tan, J. O., Hope, T., Stewart, A., & Fitzpatrick, R. (2006). Competence to make treatment decisions in anorexia nervosa: thinking processes and values. Philosophy, psychiatry, & psychology: PPP, 13(4), 267., p. 276

[9] Tan, J. O., Stewart, A., Fitzpatrick, R., & Hope, T. (2010). Attitudes of patients with anorexia nervosa to compulsory treatment and coercion. International journal of law and psychiatry, 33(1), 13-19.