Neural and cognitive response to emotional faces in dizygotic twins at familial risk of depression

Materials and methods

Participants and recruitment

Forty-two healthy, never-depressed DZ twins from same-gender twin-pairs were included in the study as a part of a high-risk study elucidating risk factors for affective disorder in a large twin cohort (N=234) approved by the Danish Ministry of Health, Danish Scientific Ethics Committee and Data Protection Agency (see Vinberg et al. 2013a). In brief, the original cohort was recruited through record linkage between the Danish Twin Registry, the Danish Psychiatric Central Research Register and the Danish Civil Registration System and took part in a cross-sectional baseline study in 2003–2005 (see Christensen et al. 2006, 2007). Participants were then followed for a 7-year period with contact every six months and telephone interviews in 2010–2012, on which occasion they were asked to participate in the present fMRI study. The included twenty-two DZ twins had a co-twin history of hospital admission for major depression (high-risk), while the remaining 20 twins had no first-degree family history of psychiatric illness (low-risk).

Experimental design

Participants attended one test session at the Danish Research Center for Magnetic Resonance (DRCMR). They completed a set of questionnaires for measurement of their mood and subjective state, personality traits and coping style which was followed by fMRI assessing neural response to emotional faces. After the scan, participants completed a faces dot-probe and a facial expression recognition task on a test computer. The experimenters were blinded to risk status and blinding was maintained throughout data management and analysis.

Emotional face processing task during fMRI

Neural response to emotional faces was assessed with an incidental face processing task from the Emotional Test Battery (ETB; P1Vital Oxford). Pictures of happy or fearful faces were projected from a computer using e-prime software (version 1.2) onto an opaque screen at the foot end of the scanner bed, which participants viewed through an angled mirror. Happy and fearful faces were presented in blocks of 25 seconds. Each block consisted of 10 faces displayed for 200 milliseconds followed by a fixation cross shown for 2300 milliseconds. Face blocks were interleaved by 16 second inter-blocks with a central fixation cross. There were four blocks of each emotion condition and eight inter-blocks which lasted together 5 minutes 28 seconds. During this time, participants performed a gender discrimination task by pressing the keys of a response pad with their right middle and index fingers for ‘male’ and ‘female’ respectively. Responses were recorded and used for the calculation of mean reaction times (RT) and accuracy.

Behavioural tasks outside the scanner

Faces dot-probe task

Vigilance to happy and fearful facial expressions was investigated with a faces dot-probe task from the ETB. Pairs of faces consisting of an emotional and a neutral expression or two neutral expressions of the same person were presented on the computer. An equal number of three types of face pairs were presented: happy-neutral, fearful-neutral and neutral-neutral in masked (subliminal) and unmasked (supraliminal) conditions. In the masked condition, the emotional faces were shown for 17 milliseconds immediately replaced by a neutral face mask for 83 milliseconds, while face pairs were shown for 100 milliseconds in the unmasked condition. In each trial, one face was immediately replaced by two dots presented vertically (:) or horizontally (^{. .}). Participants indicated the orientation of the dots by pressing labelled keys on the keyboard. There were 192 trials, consisting of 64 masked and unmasked happy-neutral pairs, 64 masked and unmasked fear-neutral pairs, 64 neutral-neutral pairs. Eight blocks of unmasked trials and eight blocks of masked trials (with 12 trials per block) were presented in an alternating order (for more details see (Murphy et al. 2008). RT for correct responses and accuracy were recorded. Outcome measures were vigilance to masked and unmasked fearful and happy faces, as reflected by differences in RTs for dots replacing neutral vs. emotional probes.

Facial expression recognition task

The facial expression recognition task from the ETB involved presentation of faces on a computer screen expressing happiness, surprise, sadness, fear, anger or disgust. Stimuli from Ekman and Friesen (Ekman and Friesen 1979) were presented in randomized order for 500 ms immediately replaced by a blank screen. Participants determined each expression by pressing the corresponding key on the keyboard. The faces were morphed at 10% steps in shape and texture differences between a neutral face (0%) and a full emotion face (100%), for more details see (Harmer et al. 2004). There were 250 stimuli presentations consisting of four examples of every emotion at each intensity level and a neutral face for every emotion. RT for correct responses, accuracy and misclassifications were recorded. Outcome measures were accuracy of facial expression recognition and RTs for correctly identified expressions.

Mood and subjective state

Mood and subjective state were assessed with the State and Trait Anxiety Inventory (STAI) (Spielberger 1983), the Beck Depression Inventory (BDI; Beck et al. 1961) and visual analogue scales (VAS) of relevant mood states (happiness, sadness, arousal, anxiety, dizziness and nausea). Neuroticism was assessed with the Eysenck Personality Questionnaire (EPQ) (Eysenck and Eysenck 1975) and coping styles with the Coping Inventory for Stressful Situations (CISS) (Endler and Parker 1999). The number of severe stressful life events (LEs) in the lifetime before were obtained at baseline (2003-05) with a Danish version of the questionnaire by Kendler and colleagues (Kendler et al. 1995). Participants completed the Kendler LE questionnaire annually in the follow-up period between baseline and the present study (see Vinberg et al. 2013a).
Magnetic resonance imaging

MRI data were collected with a 3 Tesla Siemens Trio MR scanner using an eight-channel head array coil. BOLD-sensitive fMRI applied a T2*-weighted gradient echo spiral echo-planer imaging (EPI) sequence with a repetition time (TR) with a duration of 2.49 seconds, a flip angle of 90˚ and an echo time of (ET) of 30 ms. A total of 128 brain volumes were collected in a single fMRI session, and each of these consisted of 42 slices with a slice thickness of 3 mm and a field of view (FOW) of 256 x 256 mm, using a 64 x 64 grid. High-resolution three-dimensional T1-weighted spin echo images were obtained after the first session of blood-oxygen level dependent (BOLD) fMRI (T1=800; TE=3.93; TR=1540 milliseconds, flip angle 90°; 256 x 256 FOV; 192 slices).
Statistical analysis of demographic, behavioral and mood data

Visual analogue scale ratings of mood, coping styles and behavioural performance on the facial expression recognition test were analysed with repeated measures analysis of variance (ANOVA) with mood ratings/ coping styles/ behavioural performance as the within-subject factors and group as the between-subjects factor. We used Greenhouse-Geisser correction for non-sphericity when appropriate. Significant interactions were followed up by simple main effect analyses (t-tests for normally distributed data and Mann-Whitney U tests for non-normally distributed data). Bech Depression Inventory and STAI ratings, demographic variables, neuroticism and behavioural performance on the dot-probe test (fear and happiness vigilance scores) were compared between groups using independent sample t-tests for normally distributed data and Mann-Whitney U tests for non-normally distributed data. Signal detection theory was applied to obtain a measure of accuracy for facial expression recognition corrected for response tendency (d’) (Grier 1971). The alpha-level used to determine significance was p<0.05 (two-tailed). Statistical analyses were performed with the Statistical Package for Social Sciences (SPSS; version 22; IBM Corporation, Armonk, New York, United States).