Ketamine and schizophrenic speech: more difference than originally reported

The Processing of Semantic Complexity and Cospeech Gestures in Schizophrenia: A Naturalistic, Multimodal fMRI Study

Schizophrenia is marked by aberrant processing of complex speech and gesture, which may contribute functionally to its impaired social communication. To date, extant neuroscientific studies of schizophrenia have largely investigated dysfunctional speech and gesture in isolation, and no prior research has examined how the two communicative channels may interact in more natural contexts. Here, we tested if patients with schizophrenia show aberrant neural processing of semantically complex story segments, and if speech-associated gestures (co-speech gestures) might modulate this effect. In a functional MRI study, we presented to 34 participants (16 patients and 18 matched-controls) an ecologically-valid retelling of a continuous story, performed via speech and spontaneous gestures. We split the entire story into ten-word segments, and measured the semantic complexity for each segment with idea density, a linguistic measure that is commonly used clinically to evaluate aberrant language dysfunction at the semantic level. Per segment, the presence of numbers of gestures varied (n = 0, 1, +2). Our results suggest that, in comparison to controls, patients showed reduced activation for more complex segments in the bilateral middle frontal and inferior parietal regions. Importantly, this neural aberrance was normalized in segments presented with gestures. Thus, for the first time with a naturalistic multimodal stimulation paradigm, we show that gestures reduced group differences when processing a natural story, probably by facilitating the processing of semantically complex segments of the story in schizophrenia.

Dissecting the neurobiology of linguistic disorganisation and impoverishment in schizophrenia

Schizophrenia provides a quintessential disease model of how disturbances in the molecular mechanisms of neurodevelopment lead to disruptions in the emergence of cognition. The central and often persistent feature of this illness is the disorganisation and impoverishment of language and related expressive behaviours. Though clinically more prominent, the periodic perceptual distortions characterised as psychosis are non-specific and often episodic. While several insights into psychosis have been gained based on study of the dopaminergic system, the mechanistic basis of linguistic disorganisation and impoverishment is still elusive. Key findings from cellular to systems-level studies highlight the role of ubiquitous, inhibitory processes in language production. Dysregulation of these processes at critical time periods, in key brain areas, provides a surprisingly parsimonious account of linguistic disorganisation and impoverishment in schizophrenia. This review links the notion of excitatory/inhibitory (E/I) imbalance at cortical microcircuits to the expression of language behaviour characteristic of schizophrenia, through the building blocks of neurochemistry, neurophysiology, and neurocognition.

Idea density in the life-stories of people with schizophrenia: Associations with narrative qualities and psychiatric symptoms

Disordered speech and language deficits are well-documented in schizophrenia-spectrum disorders. Researchers often assess speech samples using manualized rating systems, though recently computerized language assessment methods have been used more frequently in the study of speech from people with schizophrenia. Most typically, these computerized assessments measure aspects of expressivity (i.e., pause durations, prosody) or use word-count technology; less attention has focused on similar methods that can capture more sophisticated aspects of linguistic complexity (e.g., idea density). The primary objective of the present study was to assess idea density - via a computerized measure - in the life-story narratives of people with schizophrenia (n=32) compared to a group of community control participants (n=15). In the schizophrenia group, we also examined associations between idea density, narrative qualities rated via a manualized measure, and psychiatric symptoms. Our findings indicate that idea density is diminished in individuals with schizophrenia compared to controls. Further, our results suggest that though people with schizophrenia with richer idea density tended to have more developed insight into illness, they also had higher levels of depression, anxiety, and avolition. Implications of these results and suggestions for future research are discussed.

Using ketamine to model semantic deficits in schizophrenia

Semantic deficits constitute a core cognitive abnormality in schizophrenia. In the current study, the N-methyl-d-aspartate receptor antagonist ketamine was administered to healthy individuals acutely while they performed semantic processing tasks that included word pairs of differing degrees of semantic relatedness. Two dimensions of semantic processing were investigated: (1) explicit versus implicit processing, that is, unconscious versus conscious processing of semantic relationships and (2) direct versus indirect processing, that is, word pairs that are closely (LION-TIGER) or distantly (LION-STRIPES) related. The immediate effects of ketamine (0.8 mg/kg per hour during 80 minutes with approximate target plasma levels of 200 ng/mL) were examined in a placebo-controlled double-blind repeated-measures group design with 19 participants. It was predicted that ketamine would disrupt access to semantic memory as evidenced in schizophrenia, especially the indirectly related word pairs. In addition, implicit processing and explicit processing were predicted to be differentially affected. Ketamine administration did result in an abnormal performance in the reaction time responses to implicitly presented indirectly related word pairs (ie, greater priming) and reduced accuracy for explicit pairs. Performance on the directly related word pair tasks (both implicit and explicit) was similar across ketamine and placebo conditions, except for the suggestion of abnormal semantic matching in the accuracy data in the implicit task. This study confirms that implicit indirect semantic processing is changed under the influences of ketamine akin to schizophrenia. Future research comparing a schizophrenia group and a ketamine group directly about these tasks is needed to determine the similarity of impairments.