The influence of tobacco consumption on the relationship between schizotypy and hemispheric asymmetry

Abstract

Tobacco use is positively associated with severity of symptoms along the schizophrenia spectrum. Accordingly it could be argued that neuropsychological performance, formerly thought to be modulated by schizotypy, is actually modulated by drug use or an interaction of drug use and schizotypy. We tested whether habitual cigarette smokers as compared to non-smokers would show a neuropsychological profile similar to that observed along the schizophrenia spectrum and, if so, whether smoking status or nicotine dependence would be more significant modulators of behavior than schizotypy. Because hemispheric dominance has been found to be attenuated along the schizophrenia spectrum, 40 right-handed male students (20 non-smokers) performed lateralized left- (lexical decisions) and right- (facial decision task) hemisphere dominant tasks. All individuals completed self-report measures of schizotypy and nicotine dependence. Schizotypy predicted laterality in addition to smoking status: While positive schizotypy (Unusual Experiences) was unrelated to hemispheric performance, Cognitive Disorganization predicted reduced left hemisphere dominant language functions. These latter findings suggest that Cognitive Disorganization should be regarded separately as a potentially important mediator of thought disorganization and language processing. Additionally, increasing nicotine dependence among smokers predicted a right hemisphere shift of function in both tasks that supports the role of the right hemisphere in compulsive/impulsive behavior.

Performance of younger and older adults in lateralised right and left hemisphere asymmetry tasks supports the HAROLD model

“…Irrespective of participants' age and sex, we replicated previous studies that lexical decisions are more accurate and faster when letter strings are presented to the RVF as compared to the LVF (Dutta & Mandal, 2002;Herzig et al, 2010;Leiber, 1976;Mohr, Krummenacher et al, 2005). We also replicated previous studies on lateralized visual face biases such that information of the left half-face is favoured over the information of the right half-face (Butler & Harvey, 2006;Dutta & Mandal, 2002;Herzig et al, 2010).…”

“…Unfortunately, inconsistencies in the study of hemispheric asymmetry are not new (Efron, 1990). We can only add to this inconsistent literature by here conjecturing that our own results would largely support the HAROLD model, and that these results were obtained from tasks that have shown complementary results before (Herzig et al, 2010). Yet, it remains to be considered to what extent sex and handedness could play a role when contrasting our own results with those of previous studies.…”

“…Thus, the only conclusion we can come up with is that we found evidence for the HAROLD model, at least in men, using a lateralized lexical decision task and a facial sex decision task on composite faces. These tasks have been used before showing complementary results (Herzig et al, 2010). To what extent the current findings will be more reliable than those of other studies remains to be seen.…”

“…Participants were presented with an English version (Herzig et al, 2010) Each word was matched with a non-word of the same length. The remaining non-words were matched to result in an additional set of non-word pairs.…”

“…Important to the present study, performance in both tasks has been assessed in an independent sample with results from the two tasks complementing each other (Herzig, Tracy, Munafò, & Mohr, 2010). One task assessed the left hemisphere's advantage for language using a lateralized lexical decision task (see also Dutta & Mandal, 2002;Mishkin & Forgays, 1952) and the other task assessed the right hemisphere's advantage for visual face processing by assessing sex decisions for chimeric faces (see also Butler & Harvey, 2006;Dutta & Mandal, 2002).…”