J Psychiatry Neurosci 2013; 38(6): 388-397
Elizabeth I. Cawley, MSc; Sarah Park, MSc; Marije aan het Rot, PhD; Kimberley Sancton, BSc; Chawki Benkelfat, MD, DERBH; Simon N. Young, PhD; Diane B. Boivin, MD, PhD; Marco Leyton, PhD
Cawley, Park, Sancton, Benkelfat, Young, Boivin, Leyton — Department of Psychiatry, McGill University, Montréal, Que., Canada; ann het Rot — Department of Psychology and School of Behavioral and Cognitive Neurosciences, University of Groningen, Groningen, the Netherlands; Leyton — Centre for Studies in Behavioral Neurobiology, Concordia University, Montréal, Que., Canada
Background: Despite evidence that bright light can improve mood, the neurobiology remains poorly understood. Some evidence implicates the catecholamines. In the present study, we measured the effects of transiently decreasing dopamine (DA) synthesis on mood and motivational states in healthy women with mild seasonal mood changes who were tested in either bright or dim light.
Methods: On 2 test days, participants slept overnight in a light-controlled room. On the morning of each session, half of the participants awoke to gradual increases of bright light, up to 3000 lux, and half to dim light (10 lux). For all participants, DA was reduced on 1 of the test days using the acute phenylalanine/tyrosine depletion (APTD) method; on the other day, they ingested a nutritionally balanced control mixture (BAL). Beginning 4 hours postingestion, participants completed subjective mood questionnaires, psychological tests and a progressive ratio breakpoint task during which they worked for successive units of $5.
Results: Thirty-two women participated in our study. The APTD lowered mood, agreeableness, energy and the willingness to work for monetary reward. The effects on energy and motivation were independent of light, while the effects on mood and agreeableness were seen in the dim condition only, being prevented by bright light.
Limitations: Acute phenylalanine/tyrosine depletion might affect systems other than DA. The sample size was small.
Conclusion: These results suggest that increased DA function may be responsible for some of the beneficial effects of light, while adding to the evidence that the neurobiology of mood and motivational states can be dissociated.
Submitted Sept. 7, 2012; Revised Jan. 25, 2013; Accepted Feb. 13, 2013.
Acknowledgements: We acknowledge the valuable support of Abdel Azzoug, Dr. Zia Choudhry, Itamar Danziger, Dr. Mimi Israel , Milla Kerusenko and Franceen Lenoff during various stages of the study. We also thank Dr. Paul Clarke for his feedback on an earlier version of the manuscript.
Competing interests: None declared for E.I. Cawley, S. Park, K. Sancton and S.N. Young. Over the past 3 years, M. aan het Rot has received compensation from the Innovational Research Incentives Scheme Veni from the Netherlands Organisation for Scientific Research (NWO). D.B. Boivin has received travel grants and speaker honoraria from Servier and is Founder/CEO of Alpha Logik Consult ants, Inc. C. Benkelfat and M. Leyton hold research chairs at McGill University.
Contributors: M. aan het Rot, C. Benkelfat, S.N. Young, D.B. Boivin and M. Leyton designed the study. E. Cawley, S. Park, K. Sancton and M. Leyton acquired the data, which E. Cawley, S. Park, M. aan het Rot, S.N. Young and M. Leyton analyzed. E. Cawley, S. Park and M. Leyton wrote the article, which all authors reviewed and approved for publication.
Correspondence to: M. Leyton, Department of Psychiatry, McGill University, 1033 Pine Ave. W, Montréal QC H3A 1A1; firstname.lastname@example.org