Increased Activation of the Auditory Cortex in Schizophrenia in Thought Generation and Perception
Résumé
Dysfunction in the cognitive processes involved in generation of thoughts has been linked to schizophrenia, partly due to the presence of symptoms involving self-other or inner-outer confusion, such as hallucinations and Schneiderian delusions. In the present study, we investigated the neural underpinnings of verbal thought generation and verbal auditory perception using fMRI. Constrained principal component analysis (CPCA; Takane & Hunter, 1991; Hunter & Takane, 2002; Woodward et al., 2006) was used to identify networks of cerebral activation associated with generating thoughts and auditory perception in schizophrenia patients. Two experimental conditions were examined. In the first condition, participants were required to mentally generate a definition of a common word presented on the screen. In the second condition, they were required to listen to the definition of a common word presented on the screen. All definitions started with the phrase "Something you" (e.g., pen: something you use for writing). An overt generation practice session using a different set of words was performed to familiarize the participants with the task. Each condition consisted of 30 words. Five schizophrenia patients and ten healthy controls participated. All were right-handed and native speakers of English. An event-related fMRI protocol was used during two 9.25 minute scanning sessions in a 3T scanner for a total of 440 images. Preprocessing was performed using SPM5 and statistical analyses were carried out using constrained principal component analysis (CPCA) with a finite impulse response (FIR) model, and an orthogonal rotation applied on both conditions simultaneously.Four reliable components were extracted. The first component extracted (Figure 1) included the visual cortex and showed a higher intensity for the thought generation condition relative to the auditory perception condition, but did not differ between groups. The second component (Figure 2) mainly involved the superior temporal cortex (and primary auditory cortex), and showed a greater hemodynamic response for patients relative to controls regardless of condition. The third component (Figure 3) involved the task negative network (Fox et al., 2005) and did not differ between conditions or groups. The fourth component (Figure 4) represented the task positive network (Fox et al., 2005) and differed between conditions, whereby higher activity was found for the thought generation condition compared to the auditory perception condition. These results suggest that, regardless of groups and relative to the auditory perception condition, the thought generation involves more visual cortex activation as well as an overall intensified task positive network. With regards to the task negative network, both conditions and groups showed similar patterns of activation. One component, involving the bilateral superior temporal cortices (and primary auditory cortices) showed a greater hemodynamic response for patients relative to controls regardless of condition. This indicates that schizophrenia patients activate the auditory cortex more when mentally generating thoughts as well as in auditory perception. The finding suggests that overactivation of the primary auditory cortex is characteristic of schizophrenia (Frith et al., 1995), and may be a necessary (but not sufficient) state for the presence of hallucinations and/or Schneiderian delusions.