This study aims to investigate the effects of a single session of bright light treatment (BLT) on emotional information processing in healthy volunteers. We hypothesised that BLT can acutely push the processing of emotional information towards a prioritisation of positive (relative to negative) input. To test this hypothesis, healthy volunteers were randomly allocated to receive either bright light treatment or sham-placebo treatment and study participants as well as investigators were blind as to which treatment was used. After treatment, all participants underwent testing with the Oxford Emotional Test Battery, an established set of psychological tasks that allow to assess how emotional information is processed.

Background:

Bright light treatment (BLT) is an efficacious treatment for depressive disorders but the causal mechanisms by which it exerts its clinical effects are largely unknown. According to the cognitive neuropsychological model of antidepressant treatment action, one way by which antidepressant treatments lead to clinical effects is by acutely inducing a relatively increased preferential processing of positive (as compared to negative) emotional stimuli. Whether BLT has the potential to induce such positive biases is not known to date.

Aim of study:

To investigate the influence of single-dose BLT on emotion-related information processing in healthy volunteers.

Methods:

Using a double-blind, parallel-group design, fifty healthy volunteers (male and female) were randomly allocated to a single session (60 minutes) of treatment with either bright light (10 000 lux) or a credible placebo-sham condition (deactivated negative ion generator). After treatment, all participants underwent testing with the Oxford Emotional Test Battery, an established battery of behavioural tasks that allow to assess emotional information processing in multiple cognitive domains. This battery consists of a facial expression recognition task, an emotional categorization task, an emotional dot probe task, an emotional recall task and an emotional recognition task. Before and after treatment, subjective state was assessed using different questionnaires.

Hypotheses:

Our working hypothesis, in line with the cognitive neuropsychological model of antidepressant treatment action, is that one-time BLT can induce biases towards positive stimuli in multiple cognitive domains and this bias will be present even in the absence of observable changes in subjective state.

Implications of the study:

This study will show whether a single dose of BLT can influence emotion-related information processing in a similar way as previously observed for antidepressant drugs. If this is the case, then the clinical effects of BLT could be explained through its acute effects on emotional processing. On a broader level, the results of this study will also add to our understanding of any potential effects that acute exposure to bright light (e.g. sunlight) could have on the healthy human mind.

Entry criteria:

1. Female or male
2. Age: 18 to 65 years
3. Good general health
4. Competency to give informed consent

Exclusion criteria:

1. Any current or past psychiatric disorder
2. Any first-degree relative with a diagnosis of schizophrenia-spectrum or other psychotic disorder, bipolar disorder, or depressive disorder
3. Any severe medical condition not stabilized at the time of the experiment (e.g. asthma, heart disease)
4. Any condition which precludes treatment with bright light (e.g. retinal disorder, intake of photo-sensitizing medication)
5. Any current or past physical illness that has the potential to significantly affect mental functioning (e.g. stroke, Parkinson's disease)
6. Pregnant, lactating, or sexually active women who do not use any medically accepted method of contraception
7. Any history of seizures or any condition with the potential to manifest with seizures (e.g. epilepsy)
8. Diagnosis of diabetes (because of potential risk of retinal disorder)
9. Current intake of medication that has a significant potential to affect mental functioning, or intake of such medication in the previous 3 months (e.g. antidepressants, neuroleptics, tranquilizers)
10. Any intake of recreational drugs in the last 3 months before the experiment
11. Excessive alcohol consumption up to three days before the experiment
12. Previous use of bright light treatment or negative ion treatment
13. Participant usually (more than 5 days a week) gets up later than 10.00 a.m.
14. Necessity to wear tinted glasses
15. Any kind of sun exposure in the last month that is unusually high for local conditions (e.g. beach vacation, skiing holidays)
16. The researchers decide to exclude a participant for any other reason (because participation could be harmful to a participant, or a participant can't properly interact with the researchers or could bias the study results)