Abstract
Effective estimation of the salience of environmental stimuli underlies adaptive behavior, while related aberrance is believed to undermine rational thought processes in schizophrenia. A network including bilateral frontoinsular cortex (FIC) and dorsal anterior cingulate cortex (dACC) has been observed to respond to salient stimuli using functional magnetic resonance imaging (fMRI). To test the hypothesis that activity in this salience network (SN) is less discriminately modulated by contextually-relevant stimuli in schizophrenia than in healthy individuals, fMRI data were collected in 20 individuals with schizophrenia and 13 matched controls during performance of a modified monetary incentive delay (MID) task. After quantitatively identifying spatial components representative of the FIC and dACC features of the SN, two principal analyses were conducted. In the first, modulation of SN activity by salience was assessed by measuring response to trial outcome. First-level general linear models were applied to individual-specific time-courses of SN activity identified using spatial independent component analysis (ICA). This analysis revealed a significant salience-by-performance-by-group interaction on the best-fit FIC component's activity at trial outcome, whereby healthy individuals but not individuals with schizophrenia exhibited greater distinction between the response to hits and misses in high salience trials than in low salience trials. The second analysis aimed to ascertain whether SN component amplitude differed between the study groups over the duration of the experiment. Independent-samples T-tests on back-projected, percent-signal-change scaled SN component images importantly showed that the groups did not differ in the overall amplitude of SN expression over the entire dataset. These findings of dysregulated but not decreased SN activity in schizophrenia provide physiological support for mechanistic conceptual frameworks of delusional thought formation.
Highlights
The finite capacity of our attentional and behavioral resources necessitates that we assign preferential salience to certain environmental stimuli, while limiting responses to others
We present analyses conducted to assess the explicit hypotheses that: (1) cortical salience network (SN) activity focused in both dorsal anterior cingulate cortex (dACC) and frontoinsular cortex (FIC) will be modulated by the salience of rewarding monetary stimuli at reward outcome in healthy individuals; (2) SN modulation by task and performance will be diminished in schizophrenia; and (3) despite this putative dysregulation in schizophrenia, the cortical SN will be no less evident in these individuals than in healthy controls over the duration of the task
For the current GLM-independent component analysis (ICA) analyses we modeled the timecourse of the blood oxygenationlevel dependent (BOLD) response associated with the presentation of the visual stimuli throughout the task, by convolving a vector of delta functions for the onset and durations of these stimuli with the canonical haemodynamic response function
Summary
The finite capacity of our attentional and behavioral resources necessitates that we assign preferential salience to certain environmental stimuli, while limiting responses to others. Electrophysiological recordings from the macaque striatum show that phasic dopaminergic responses to rewarding stimuli temporally mimic the prediction error of reward-value models, implicating this region as the source of a reinforcement signal required to adjust the probability of subsequent action selection (Schultz et al, 1997). A complementary model of the role of phasic striatal dopamine proposes that the basal ganglia concertedly act as a centralized selection device, allocating attentional resources between competing motor programs in a contextually-relevant manner (Redgrave et al, 1999). The reward findings uphold this model insofar as test animals are generally required to shift attention to rewarding stimuli and carry out a motor program to realize their consumption
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