Associations between schizotypy and cerebral laterality

What happens to the inhibitory control functions of the right inferior frontal cortex when this area is dominant for language?

A low number of individuals show an atypical brain control of language functions that differs from the typical lateralization in the left cerebral hemisphere. In these cases, the neural distribution of other cognitive functions is not fully understood. Although there is a bias towards a mirrored brain organization consistent with the Causal hypothesis, some individuals are found to be exceptions to this rule. However, no study has focused on what happens to the homologous language areas in the right frontal inferior cortex. Using an fMRI-adapted stop-signal task in a healthy non right-handed sample (50 typically lateralized and 36 atypically lateralized for language production), our results show that atypical lateralization is associated with a mirrored brain organization of the inhibitory control network in the left hemisphere: inferior frontal cortex, presupplementary motor area, and subthalamic nucleus. However, the individual analyses revealed a large number of cases with a noteworthy overlap in the inferior frontal gyrus, which shared both inhibitory and language functions. Further analyses showed that atypical lateralization was associated with stronger functional interhemispheric connectivity and larger corpus callosum. Importantly, we did not find task performance differences as a function of lateralization, but there was an association between atypical dominance in the inferior frontal cortex and higher scores on schizotypy and autistic spectrum traits, as well as worse performance on a reading accuracy test. Together, these results partially support the Causal hypothesis of hemispheric specialization and provide further evidence of the link between atypical hemispheric lateralization and increased interhemispheric transfer through the corpus callosum.

Clarifying the roles of schizotypy and psychopathic traits in lexical decision performance

INTRODUCTION

Some studies suggest that lexical recognition is impaired in people with schizophrenia, psychopathy and/or antisocial personality disorders, but not affective disorders. We examined the extent to which various traits dimensionally linked to one or more of these disorders are associated with lexical recognition performance in the general population.

METHODS

Seventy-eight healthy English-speaking participants completed self-report measures of schizotypy, psychopathy, impulsivity, depression, anxiety and stress. All participants were assessed on a one-choice variant of a lexical decision task (LDT).

RESULTS

Meanness and Boldness traits of psychopathy (Triarchic Psychopathy Measure), and positive schizotypy (Unusual Experiences, Oxford-Liverpool Inventory of Feelings and Experiences) were associated with poor word-nonword accuracy, and predicted a significant amount of unique variance (Meanness, 12%; Boldness, 4.8%; Positive Schizotypy, 4.4%; total 21%) in performance. Higher motor impulsivity predicted 30% of the variance in low-frequency words recognition accuracy, but only in non-native English speakers. Affective traits were not associated with LDT performance.

CONCLUSION

Psychopathic traits show stronger negative associations with lexical recognition performance than schizotypal traits, and impulsivity may differently influence lexical decision performance in native and non-native speakers. Further studies are needed to replicate these findings, especially the influence of language familiarity in the impulsivity-performance relationship, and to clarify the influence of corresponding symptom dimensions in lexical recognition abilities, taking language familiarity, migration status, and comorbidity into account, in people with schizophrenia, psychopathy, and/or antisocial personality disorders.

Meaning in meaninglessness: The propensity to perceive meaningful patterns in coincident events and randomly arranged stimuli is linked to enhanced attention in early sensory processing

Perception of objectively independent events or stimuli as being significantly connected and the associated proneness to perceive meaningful patterns constitute part of the positive symptoms of schizophrenia, which are associated with altered attentional processes in lateralized speech perception. Since perceiving meaningful patterns is to some extent already prevalent in the general population, the aim of the study was to investigate whether the propensity to experience meaningful patterns in co-occurring events and random stimuli may be associated with similar altered attentional processes in lateralized speech perception. Self-reported and behavioral indicators of the perception of meaningful patterns were assessed in non-clinical individuals, along with EEG auditory evoked potentials during the performance of an attention related lateralized speech perception task (Dichotic Listening Test). A greater propensity to perceive meaningful patterns was associated with higher N1 amplitudes of the evoked potentials to the onset of the dichotically presented consonant-vowel syllables, indicating enhanced automatic attention in early sensory processing. The study suggests that more basic mechanisms in how people associate events may play a greater role in the cognitive biases that are manifest in personality expressions such as positive schizotypy, rather than that positive schizotypy moderates these cognitive biases directly.