Abstract
To the Editor
Reduced dopamine levels in anorexia nervosa (AN) have been reported utilising invasive procedures such as lumbar punctures and positron emission tomography. A far more passive and non-invasive measurement is spontaneous blink rate (SBR) which shows a positive relationship with central dopaminergic activity. Although decreased dopaminergic activity has been demonstrated in AN, one study reported increased SBR during a 2-minute electrooculography recording while participants faced a blank wall, following a 3-minute accommodation period (Barbato et al., 2006). Given the positive relationship between fatigue and SBR, and that individuals with AN are easily fatigued due to their physical state, this study sought to improve on this methodology by (1) analysing the first minute of recordings and (2) administering a more engaging task requiring fixation on a central stimulus. As increased cognitive demand is reported to result in decreased SBR, a further aim was to determine the effect of cognitive load on SBR in AN by contrasting results from this fixation task to a more cognitively demanding task (prosaccade/antisaccade/no-go task).
The study was primarily approved by St Vincent’s Hospital Human Research Ethics Committee (Melbourne, Australia). The sample assessed is described in detail elsewhere (Phillipou et al., 2014). Briefly, 24 AN and 21 healthy controls (HC) participated (all right-handed females). Vertical electrooculography was recorded on the right eye. Blinks were identified using the same criteria as Barbato et al. (2006), and the first minute of data was analysed for each task.
Significantly lower SBR was found in AN, relative to HCs during the fixation task (AN: M = 8.50(5.04); HC: M = 13.40(8.62); F(1, 36) = 4.44, p = 0.04). Groups were not found to differ in SBR during the saccade task (AN: M = 7.30(4.96); HC: M = 7.17(3.11); F(1, 36) = 0.01, p = 0.92). SBR did not correlate with illness duration in AN, or with age, body mass index or Eating Disorder Examination Questionnaire scores in either group, for either task.
These findings suggest that although individuals with AN may have reduced levels of central dopaminergic activity at rest, dopaminergic activity may function in a similar manner to healthy individuals when engaged in cognitively demanding tasks. This is consistent with our previous research demonstrating a lack of deficits in neurocognitive abilities in AN (Phillipou et al., 2015). The findings also provide potential considerations for the use of dopamine agonists to increase low baseline dopamine levels in AN. Patients in this study were, however, on a number of different medications as is typical with AN. As such, future research should aim to assess medication-naïve patients to further elucidate dopaminergic activity in AN.
Footnotes
Acknowledgements
The authors would like to thank Chia Huang, Richard Newton, Lynley Gervasoni, Michelle Snell, Helen Shepherd, Philippa Harrison and Felicity Lawrence for their assistance in recruiting participants. The authors also would like to thank everyone who took the time to participate in the study.
Declaration of Conflicting Interests
Prof. Castle reports grants and personal fees from Eli Lilly, Janssen-Cilag, Roche, Allergen, Bristol-Myer Squibb, Pfizer, Lundbeck, AstraZeneca and Hospira during the conduct of the study and personal fees from Eli Lilly, Bristol-Myer Squibb, Lundbeck, Janssen Cilag, Pfizer, Organon, Sanofi-Aventis, Wyeth, Hospira and Servier, outside the submitted work. A/Prof. Abel reports personal fees from Actelion Pharmaceuticals, Switzerland, outside the submitted work. Dr Phillipou, Dr Woods, Prof Rossell, Dr Hughes and Dr Gurvich report no conflicts of interest.
Funding
This research was supported by the Jack Brockhoff Foundation (L.A.A., S.L.R., D.J.C. and A.P.; grant no. 3410); the Dick and Pip Smith Foundation (A.P., L.A.A., S.L.R. and D.J.C.); an Australian Postgraduate Award (A.P.) and the David Hay Memorial Fund Award (A.P.).