Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Deanna M Barch
Schizophrenia (SCZ) is characterized by severe cognitive impairments and amotivation, generally referred to as negative symptoms, including anhedonia and/or avolition. Amotivation tends to exist in prodromal patients and persist over the illness course regardless of successful antipsychotic medications, which are known to reduce positive symptoms, including hallucination and delusions (e.g., (Horan, Blanchard, Clark, & Green, 2008; Tarbox et al., 2013). Importantly, amotivation is a promising predictor for later social functioning in SCZ, even after accounting for patients' cognitive impairments (e.g., (Evensen et al., 2012; Faerden et al., 2010). Despite this crucial impact on functioning outcome in SCZ, to date, no study has systematically investigated neural mechanism underlying amotivation in SCZ.
To date, it has been well documented that many of cognitive impairments in SCZ may reflect a core deficit of non-emotional context processing, supported by the dorsolateral prefrontal cortex (DLPFC), and defined by the ability to maintain non-emotional context information necessary to regulate upcoming behavioral response towards goal-directed behavior (e.g., (Cohen, Barch, Carter, & Servan-Schreiber, 1999). Recent evidence from both animal and healthy human neuroimaging work suggests that the DLPFC plays a crucial role in representing and integrating reward-related context information. However, it has been unexplored whether individuals with SCZ can represent and integrate reward-related contextual information to modulate cognitive control function implicated in the DLPFC.
Thirty-six individuals with SCZ and twenty-seven healthy controls (HC) underwent behavioral and fMRI data collection at 3Tsela while performing a modified response conflict processing task under two contexts, that is, no-reward baseline and reward contexts. Participants first performed baseline conditions without any knowledge regarding the future potential for incentives (Baseline-Context; BCXT). Each trial started with a baseline cue, "XX" that was pre-instructed to participants as being irrelevant to the task. After each cue, "XX," either a house or building picture (with overlaid words that are either congruent or incongruent) was presented to each participant one at a time. The job of the task was to categorize each picture as either a house or a building by pressing a certain button while ignoring the overlaid word. Following the baseline condition, participants performed additional reward blocks on which they were told that they could win money on some trials by performing fast (faster than their median correct reaction times (RT) in the baseline and accurately). Each trial was then preceded either by a "$20" cue (Reward-Cue; RC), indicating that a fast and correct response would be rewarded or by a "XX" cue (Reward-Context; RCXT), indicating zero money would be possible on the trial. After the target stimulus, participants received immediate feedback regarding the reward points they earned on the trials, as well as their cumulative earning in points.
As such, this response conflict task paradigm enabled examination of: (1) reward context effects by comparing performance and brain activity when the cue, "XX" was presented in the baseline context versus in the reward context (BCXT vs. RCXT trials cued by the same cue, "XX") and (2) reward cue effects by comparing performance during RC (cued by "$20") versus RCXT (cued by "XX") within reward blocks. Importantly, by employing a mixed state-item fMRI design, I investigated both sustained (block-based) context-dependent and transient (trial-by-trial) reward-related cue activity at both behavioral and neural levels.
Chung, Yu Sun, "Sustained and Transient Reward Effect on Cognitive Control in Schizophrenia: The Relevance of Negative Symptoms" (2014). All Theses and Dissertations (ETDs). 1377.