Cognitive and Emotional Deficits in Depression

Proposal details

Title: Cognitive and Emotional Deficits in Depression
Research Area(s): Emotion and Self Regulation
Background: Deficits in cognition (i.e. diminished ability to attend and concentrate) and emotion (i.e. sadness and anhedonia) are well established in subjects suffering from clinical depression (see Rogers, Bradshaw, Pantelis and Philips, 1998 for a review). While sub-clinically depressed individuals are able to function socially (Alison and Burgess, 2003), psychosocial dysfunction has still been reported and such dysfunction may be a prodrome to major depression later in life (See Judd, Schettler and Akiskal, 2002 for a review). It is possible therefore that research focusing on sub-clinically depressed participants will provide valuable information on the cognitive and emotional deficits of depression without the confound of using clinical patients which include co-morbidity, medication effects, remission effects, and the effect of the subtype of depression. The cognitive and emotional deficits displayed in depressed individuals may be understood in the context of the theory of orienting, in which the orienting response is seen to represent the limited information processing capacity and is essential to attention (Dawson, Filion and Schell, 1989). The orienting response has been predominantly measured by physiological means such as an intensification of skin conductance response (SCR) (Schnur, Berstein, Yeager, Smith and Bernstein, 1995). Depression has been known to cause general physiological inhibition, evidenced by lower arousal levels, and the skin conductance response is considered to be the indicator measure of changes in the level of arousal in depression (Miquel, Fuentes, Garcia-Merita and Rojo, 1999). Depressed individuals consistently show a diminished skin conductance response (Bernstein, Riedel, Graae, Seidman, Steele, Connolly and Lubowsky, 1988 and Miquel et. al. 1999), suggesting lower arousal levels and an inadequate orienting response. However, a negativity bias in depression has been observed in previous research, in which the attentional processing of mood congruent information such as negative facial expressions and words may be enhanced (Hasler, Drevets, Manji and Charney, 2004). This negativity bias in depression would affect the performance on tasks that require the processing of negative emotional stimulus but would be suppressed in those tasks that do not require emotional processing. Cognition has largely been viewed in the form of information processing metaphor, embodying how information from the environment is collected, stored, modified and interpreted (Phelps, 2006), all of which rely on attention. Deficits in attention, particularly attention shifting (attention shifting tasks require the participant to switch attention from one set of stimulus to another or from one task to another) is specific to depression, a study that compared the neuropsychological deficits between groups with different disorders (e.g. obsessive compulsive disorder, panic disorder and depression), found deficits in attention, particularly attention shifting was specific to depression (Purcell, Maruff, Kyrios, and Pantelis, 1998). Attention has been frequently studied through the use of the oddball paradigm, a task that combines behavioural and Event Related Potential (ERP) measures. It has been reported that depressed participants have decrease P300 amplitude and increased latency compared to controls when they perform the auditory oddball task (Bruder, Toewy, Steward, Friedman, Tenke and Quitkin, 1991 and Urretavizcaya, Moreno, Benlloch, Cardoner, Serrallonga, Menchon and Vallejo, 2003). This decrease in both amplitude and increase in latency seem to indicate that depressed individuals are not attending to the task as intensely as controls and are taking longer to evaluate the stimulus respectively. The amplitude of the N200 component of ERP has also shown to be affected in depressed participants in an auditory oddball task, and generally shows a decrease (Ogura, Nageishi, Omura, Fukao, Ohta and Kishimoto, 1993). Emotion can assist awareness and attention for environmentally salient stimuli, particularly when attentional resources are limited (Phelps, 2006). It has been found previously in a task that combined face perception and ERPs that the N200 component of ERP is specific to tasks involving faces and not words (Deldin, Keller, Gergen and Miller, 2000). The amplitude of this N200 component has been found to be reduced in depressives in faces tasks when the stimulus presented was mood incongruent, suggestive of a negativity bias (Deldin et. al. 2000). Using intensity of expression as a variable, it was found that depressed subjects had an inverse relationship between the P300 latency and intensity. As intensity decreased, the latency in the P300 component increased (Cavanagh and Geisler, 2005), Indicating that depressives process less intense expressions slower than controls. In normal subjects the P300 component was shown to be reliably replicable and that a reduction in P300 amplitude appear to indicate the inhibition of attention due to emotional factors, since the face depicting no emotion elicited the highest amplitude, then successively decreasing with sadness and anger, with pleasure eliciting the smallest increase in amplitude (Morita, Morita, Yamamoto, Waseda and Maeda, 2001). The P300 component of ERP has been related to orienting and evaluation of the significance of the stimulus, and the N200 component has been related to detection of stimulus change. Therefore, these two components would be affected in both attentional and emotional tasks. Cognitive and emotional impairments in depression have been linked with severity of depression, as more depressed subjects showing more distinct impairment (Silberman, Weingartner, Post, 1983), and the use of both behavioural and neurophysiological measures in a single subject on both attentional and emotional tasks would allow more concrete conclusion to be made regarding the deficits of depression. In this case, an auditory oddball task and a face recognition task will be used to investigate the deficits in attention and emotion respectively.
Aims: The aim for this study is to determine whether the severity of subthreshold depression affects performance in an attentional (auditory oddball) and emotional task (face recognition). Neurophysiological measures (the ERP components) and behavioural scores, such as number correct and reaction time (RT) will both be analysed. The ERP components which particular attention will be paid to would be the P300 and N200 in the auditory oddball task and the face perception task; both components are located in the frontal regions of the brain. It is hypothesised that as the severity of subthreshold depression increases, neurophysiological performance on cognitive task would decrease, but the performance on the emotions task would be increased for negative emotions and decreased for positive emotions. The SCR indicating orienting is hypothesised to be present for the negatively valenced faces in the face perception task but not present in the auditory oddball task due to the lack of negative stimuli. In the auditory oddball task, the P300 amplitude would be expected to decrease and the latency would increase. Decreases are also expected in the amplitude of the N200 component in auditory oddball. In the face perception task there would be a similar expected decrease in P300 amplitude and increase in latency, as well as a decrease in N200 amplitude for positive emotions and show the opposite pattern for negative emotions. These two components have been implicated in orienting, evaluation of significance of the stimulus and detection of stimulus change respectively, and hence implicated in both attentional and emotional tasks. Performance on behavioural measures would also be hypothesised to decrease with the severity of subthreshold depression due to the predicted increase in cognitive and emotional impairment, except in cases of negatively valenced emotional stimuli in which the depressed participants are expected to perform at or better than normal levels due to the negativity bias. It is also hypothesised that in the same participant, the neuropsychological and neurophysiological performance on the auditory oddball and the faces task should be similar because they both require orienting, but as the severity of subthreshold depression increases the disparity in performance between the two tasks would also increase. With auditory oddball performance declining while performance on the face perception task improving.
Method: Participants will first be required to complete a web-based questionnaire, which includes demographic items such as age and sex and the Depression Anxiety and Stress Scales (DASS). Preceding testing, participants will be asked to avoid stimulants for at least two hours before the test session begins. They will then be administered a computerised auditory oddball and the faces task after being fitted with an electrode cap for ERP recordings. The data will be acquired from 26 EEG channels and 4 EOG channels (for eye movements) continuously at 500Hz. Data will be recorded relative to averaged mastoid and an electrode on the forehead acting as a ground. Participants will be seated in a sound and light controlled room, at a constant temperature of 24C. Pre-recorded test instructions will be delivered through headphones and communication between the participant and experimenter will be though a two-way intercom system. The auditory oddball task requires participants to press buttons with the index finger of each hand in response to ?target? tones (presented at 1000 Hz) but not to respond to ?background? tones (presented at 500 Hz). All participants will be given a practice session to distinguish between target and background tones, and both speed and accuracy of the response will both be emphasised. Overall, there will be 280 background and 60 target tones that will be presented in a random order, with two targets never appearing consecutively. All the tones are presented binaurally via headphones and the task lasts approximately 6 minutes. The face perception task involves presentation of a series of grey-scale images displaying facial expressions relating to one of six emotions (neutral, happy, fear, anger, disgust, sadness), which has been selected from a standardized set of facial emotion stimuli (Gur, Schroeder, Turner, McGrath, Chan, Turetsky, Alsop, Maldjian and Gur, 2002). Blocks of face stimuli will be presented to participants and each block will contain eight stimulus pictures depicting one of the six emotions in random order. There will be four repeat blocks for each expression, making a total of 32 stimuli per expression. The task will take approximately 11 minutes. Following the ERP recordings, participants will be asked to identify the facial expression of emotion depicted on each of the 48 faces presented by circling the emotion label that best describes the facial expression from a choice of six options (neutral, happy, fear, anger, disgust, sadness) and to rate the intensity of emotion on a forced-choice rating scale of 1 (weak intensity) to 5 (very intense).