Schizophrenia and Handedness – Is There a Link?
A Connection Between Schizotypy and Handedness?
Aug 23, 2009
A Definition of Schizophrenia and Schizotypy
Schizophrenia is a mental illness, from which sufferers often show impairments in the perception of the real world. Some schizophrenics experience auditory hallucinations, show disorganized speech and often show little social awareness.
Schizotypy is a concept of personality characteristics that are related to or similar to those found in individuals who have been diagnosed with schizophrenia and psychosis. For example, a person who is found to possess a large degree of schizotypal characteristics might hold stronger beliefs in intangible and supernatural forces in the world, such as fate. However, these individuals will not have the strong, unerring beliefs that would be seen in someone who is diagnosed with schizophrenia. Schizotypy, on the other hand, is not diagnosed as an illness, rather as traits of an individual’s personality.
Although no clear cause or explanation has been found for schizophrenia or schizotypal behaviour, there have been many studies that indicate the handedness of the individual sufferer is related to the presence of schizotypal characteristics.
Evidence Towards a Link Between Schizophrenia and Handedness
A study performed by Annett & Moran in 2006, found much higher rates of schizotypal behaviour in participants who showed a mixed preference towards handedness, (i.e. ambidextrous patients.) This finding was particularly apparent in participants who used their right hand for writing and their left hand for other ‘primary tasks,' such as the use of hammer of kitchen knife.
In 2007 a study by Preti, Sardu & Piga investigated the potential link using a sample of 527 (87.3%) right-handers, 53 (8.8%) ambidextrous, and 24 (4.0%) left-handers. The study found that mixed handed participants scored statistically higher than right-handers or left-handers on a scale of belief in delusions. Both studies therefore suggest that there is a significant correlation between mixed handedness and the development of schizotypy.
In 1996 Crow, Done & Sacker performed a study was performed using data on 16,980 children from the UK National Child Development Study. It investigated admission to psychiatric care by the age of 28. This study found that children described as ‘pre-schizophrenic’ were much more likely to be rated as mixed handed by their parents at age 7. At age 11, they were much more likely to be rated as ‘less strongly right handed’ in comparison to a control sample. This adds further fuel to the argument that the trait of showing mixed handed selection has a significant link influence on the development of schizophrenia.
Evidence Against a Link Between Schizophrenia and Handedness
However, not all evidence falls the same way.
A study in 2007, performed by Fonseca-Pedrero et al., investigated a sample of 296 participants with the ‘Thinking and Perceptual Style Questionnaire,’ ‘The Multidimensional Schizotypal Traits Questionnaire,’ ‘Edinburgh Handedness Inventory’ and the ‘Youth Self Report’ to measure and compare the two variables of handedness and schizoptypy. These accurate measurements ensure there is no misinterpretation of data, as exact measures have to be met in order to classify a participant in a category, this therefore greatly increases the reliability of the findings. This study found no significant correlation between the two variables.
Also in 2005, a study by Manoach et al. compared hemispheric specialisation in the brain, which would lead to specialisation in hand preference, in 16 schizophrenic patients and 12 ‘healthy’ control participants. No difference in specialisation of either brain hemisphere was found between the two groups. This suggests the development of the structure and lateralisations of the brains, and therefore the development of handedness, may not have a great impact on the acquisition of schizophrenia.
A Connection Between Hand Usage and Schizotypy
Like so many supposed and hypothesized psychological links, there is evidence that suggests a link exists between handedness and schizophrenia and schizotypy, however there is also evidence against this conclusion. However, the wealth of literature and evidence pointing towards a link certainly cannot be dismissed. Perhaps the link is not as simple as was first suggested. As seems the case in most scientific conclusions, the debate can go either way and the research must continue onwards.
Sources:
- Annett M, Moran P. (2006). Schizotypy is increased in mixed-handers, especially right-handed writers who use the left hand for primary actions. Schizophrenia Research 81, 239-246.
- Crow TJ, Done DJ, Sacker A. (1996). Cerebral lateralization is delayed in children who later develop schizophrenia, Schizophrenia Research 22, 181-185.
- Fonseca-Pedrero E, Muniz J, Giraldez S, Garcia-Cueto E, Campillo-Alvarez A. (2007). Handedness, emotional problems, and schizotypy. Psicothema 19, 467-472.
- Manoach DS, White N, Lindgren KA, Heckers S, Coleman MJ, Dubal S, Goff DC, Holzman PS. (2005). Intact hemispheric specialization for spatial and shape working memory in schizophrenia. Schizophrenia Research 78, 1-12.
- Preti A, Sardu C, Piga A. (2007). Mixed-handedness is associated with the reporting of psychotic-like beliefs in a non-clinical Italian sample, Schizophrenia Research 92, 15-23.
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