The Effect of D-cycloserine on Emotional Processing

Participants are presented with positive and negative personality descriptors and are asked to classify the valence of each word. These words describe either extremely agreeable/positive characteristics (e.g. "cheerful", "honest", "optimistic") or extremely disagreeable/negative characteristics (e.g. "domineering", "untidy", "hostile") and are presented individually in the centre of the screen. Participants are instructed to imagine themselves overhearing someone describing them with each of the words and to indicate as quickly and accurately as possible whether they would like or dislike to be described with each of the words. Responses are made by pressing a correspondingly labelled key on a button box. Reaction times for correct classifications are measured separately for positive and negative words.

Pictures of positive and negative emotional stimuli (happy and fearful facial expressions) are presented individually together with a matched neutral stimulus (neutral face). On each trial, one stimulus is shown above and the other below a central fixation point. Subsequently, a probe appears behind one of the stimuli and participants have to correctly classify the probe as quickly and as accurately as possible. Stimuli can be masked (i.e. presented very briefly and followed by a jumbled face) or unmasked (i.e. presented for a longer period without a subsequent masking stimulus). Reaction times for correct responses are recorded and vigilance scores are calculated for masked and unmasked positive and negative stimuli by subtracting reaction time data from trials when the probe appeared in the same position as the emotional stimulus (congruent trials) from trials when the probe appeared in the opposite position to the emotional stimulus (incongruent trials).

3 hours after drug/placebo administration

The computer stress task is designed to induce psychological stress.It is presented as a series of mental arithmetic, verbal and visuospatial challenges on the screen which participants are required to solve. In the stress condition, there is a time limit for completing each challenge, which is displayed on the screen as a time bar. To induce a high failure rate, the timing for each challenge is set depending on individual's previous performance at 10% less than the time that it took to previously correctly solve challenges. The difficulty of the challenges is automatically varied to ensure that participants are getting only 20-40% of the challenges correctly completed within the time. To ensure a high failure rate, some of the verbal challenges (anagrams) are impossible to solve. Participants are given feedback on their performance on the screen which indicates that they are performing badly.

Participants are presented with individual pictures of facial expressions of emotions. Each presented face displays one of six basic emotions (anger, disgust, fear, happiness, sadness, or surprise). Each emotional expression is presented at different levels of intensity which have been created by combining shape and texture features of the two extremes "neutral" (0%) and "full prototypical emotion" (100%) to varying degrees. Examples of neutral facial expressions are presented as well. Participants are instructed to correctly classify each facial expression as angry, disgusted, fearful, happy, sad, surprised or neutral both as quickly and as accurately as possible. Responses are made by pushing one out of seven labelled keys on a response box. Hit rates, false alarm rates, and reaction times for correct classifications are measured separately for each emotion.

Participants are asked to recall and write down as many words as possible from yesterday's emotional categorization task. Numbers of correctly and incorrectly recalled positive and negative words are measured.

The autobiographical memory cues are presented visually on computer screen in a fixed order, with positive, negative, and neutral words alternating, each word will be presented only once. Participants are instructed that, for each cue word, they should respond with a memory of an autobiographical event which had lasted less than 1 day and which had occurred at a specific time and place. They are told that the event could have occurred recently or a long time ago and could have been important or trivial but that no responses should be repeated for a subsequent word. Correct and incorrect examples are given. Responses are tape-recorded for subsequent coding.