Abstract
Disruptions in reward processing and anhedonia have long been observed in Anorexia Nervosa (AN). Interoceptive deficits have also been observed in AN, including reduced tactile pleasure. However, the extent to which this tactile anhedonia is specifically liked to an impairment in a specialised, interoceptive C-tactile system originating at the periphery, or a more top-down mechanism in the processing of tactile pleasantness remains debated. Here, we investigated differences between patients with and recovered from AN (RAN) and healthy controls (HC) in the perception of pleasantness of touch delivered in a CT-optimal versus a CT-non-optimal manner, and in their top-down, anticipatory beliefs about the perceived pleasantness of touch. To this end, we measured the anticipated pleasantness of various materials touching the skin and the perceived pleasantness of light, dynamic touch applied to the forearm of 27 women with AN, 24 women who have recovered and 30 HCs using C Tactile (CT) afferents-optimal (slow) and non-optimal (fast) velocities. Our results showed that both clinical groups anticipated tactile experiences and rated delivered tactile stimuli as less pleasant than HCs, but the latter difference was not related to the CT optimality of the stimulation. Instead, differences in the perception of CT-optimal touch were predicted by differences in top-down beliefs, alexithymia and interoceptive sensibility. Thus, tactile anhedonia in AN might persist as a trait even after otherwise successful recovery of AN and it is not linked to a bottom-up interoceptive deficit in the CT system, but rather to a learned, defective top-down anticipation of tactile pleasantness.
Highlights
Anorexia Nervosa (AN) is an eating disorder characterised by restriction of energy intake, by either avoiding food consumption, or purging, intense fear of gaining weight, disturbances in the experience of one’s own body weight or shape, and unawareness of such disturbances (DSM-5, 2013)
This study aimed to investigate (1) whether the anticipation and perception of pleasant touch would be reduced in patients who have recovered from AN as well as in patients with acute AN compared to healthy controls (HC); (2) whether this tactile anhedonia will be best explained by deficits in the CT-afferent system, top-down beliefs about the pleasantness of affective touch, or their combination
The three groups did not differ significantly in their age; as expected, the BMI was significantly higher in the HC and recovered from AN (RAN) groups compared to the AN group (AN vs. RAN: U = 17; p < 0.01; AN vs. HC: U = 5, p < 0.01; RAN vs. HC: U = 235.5, p = 0.10)
Summary
Anorexia Nervosa (AN) is an eating disorder characterised by restriction of energy intake, by either avoiding food consumption ( in the ‘‘restricting-type” of AN), or purging ( in the ‘‘binge-eating/purging-type”), intense fear of gaining weight, disturbances in the experience of one’s own body weight or shape, and unawareness of such disturbances (DSM-5, 2013). The associated malnutrition can have both cognitive (e.g. altered judgment and decision making) and physiological consequences (e.g. amenorrhea, reviewed by Zakzanis et al, 2010). Y These authors have shared the first authorship. Increasing evidence suggests that AN is associated with deficits in interoception (reviewed by Martin et al, 2019), recently re-defined as the perception of the physiological status of the body (Craig, 2002). As we review below, the definition of interoceptive modalities and their relation to other, long documented deficits in AN such as reward and emotional abnormalities remains debated and warrants further investigation.
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