Our knowledge of the variability of cerebral language lateralization is limited often to the studies of patients with brain lesions, however through these types of studies it is possible to understand organisation of cerebral functions. This is demonstrated through the same primary language capacity in participants with lesions, and through the lack of further developed secondary language processing (Bobe, Deppe, Dräger,Henningsen, Knecht, Lohmann, & Rignelstein 2000, pg. 74).
As such one study by Bobe et al. (2000) attempted to conduct an investigation similar to that known as the ‘Wada Test’ or Intracarotid Amobarbital procedure, in which a barbiturate is introduced to a patient into one hemisphere at a time in order to evaluate which hemisphere is responsible for language and/or memory function by x-ray scans taken during the procedure (Donner, 2010).The study found that healthy, right handed participants appeared to have a natural distribution of language lateralization along the two contrasting structures and was equivalent in both genders. Despite this less than 7.5% of the subjects had right hemisphere dominance in regards to language tasks.
One study mentioned within Bobe et al. (2000) suggests that language is influenced by a large cerebral network, differing in regional involvement and specific language subfunctions. These networks are lateralized to one hemisphere and although it is not yet entirely understood, most people have language lateralisation mainly in their left hemisphere, however the actual variability of language lateralization in the general population is currently unknown. A new brain imaging technique, called functional transcranial Dopple- ultrasonography has allowed for hemisphere differences in activity for different participants to be measured (Hartje, Ringelstein, Kistinger, Fabianek & Willmes, 1994). This technique measures the cerebral perfusion changes by blood flow velocities within the two middle cerebral arteries, which according to Van der Zwan and Hillen (1991) comprises the potential language areas. This can be used in order to provide an operational index of laterality to examine the differences between those with schizophrenia and those without, in order to assist with our understanding of the disorder.
Many of the language abnormalities for those with schizophrenia are believed to be due to the decreased lateralisation of the left cerebral hemisphere, and studies such as that by Nestor, Han, Niznikiewicz, Salisbury, Spencer and Shentom from 2001, indicate the difficulty patients with schizophrenia have in regards to processing the semantic aspects of language and speech accordingly (Rachel, Mitchell, & Crow, 2005). Some other studies which replicate this differentiation, are the neural network simulations studies in regard to abnormal connectivity effect in schizophrenia. This consists of simulating a ‘lesioning’ of a network connection while holding constant the normal network size (Nestor, et al., 2001). Kerns and Berenbaum, Titone and Levy also found patterns in regard to the differences between healthy participants and those with schizophrenia. This method allows for visualisation of neural pathways and the ways they could allow for schizophrenia however, as they are simulations rather than ‘real’ data they do not effectively reflect what is being ascertained within everyday life. Kerns and Berenbaum reviewed studies featuring simulations regarding the process of Formal Thought Disorder (FTD) or disorganised speech as one of the main symptoms of schizophrenia, though other studies focused on individual cases of schizophrenia and how those with the disorder showed reduced ability to comprehend when language was lacking appropriate syntax, revealing that the patients with schizophrenia had overall reduced comprehension accuracy compared to healthy participants.
This trend in literature reflects the hypothesis that those with the disorder schizophrenia have a decreased language ability due to the lack of left hemisphere dominance present in healthy control subjects (Rachel et al. 2005). Given that the left hemisphere is claimed responsible for the majority of language functions, the results of both language lateralisation studies need to be examined in combination with hemispheric differences in order to determine their inter-relationship. This cross examination may allow for bi-hemispheric or uni-hemisperic theories to emerge regarding language, and how the lateralisation of language might be used to identify and diagnose schizophrenia.
Anatomical Asymmetry
Cerebral asymmetry, or torque from the front parietal brain region (right frontal to left occipital) is not only used as an index of speed and neurodevelopment but is also the defining feature of the human brain (Crow, 2004). Broca is said to have originally proposed that language “is a unitary skill, dependent upon a special feature…” known as torque, “… of the human brain anatomy that had evolved especially to support speech” (Donald, 1991, pg. 737). Crow has suggested that schizophrenia is the price that Homo sapiens pay for language and that torque (anatomical asymmetry) and other correlating factors have a significant impact on the liklihood of schizophrenia.Crow’s meta-anaylsis of both post-mortem and anatomical imaging studies suggest that within those with schizophrenia, there was a “reduction in noticeable aspects of asymmetry particulatry in the occipito-temporo-parietal association cortex” (Crow, 2004, pg. 97). The studies also revealed that in some cases, the change in the left temporal lobe progressed with age, and the results appeared to differ for each gender. This in itself introduces further possible variables which could affect the diagnosis and identification of schizophrenia.
Another study which produced differing results to the meta-analysis by Crow is the investigation by Guerguerian and Lewine. They were attempting to investigate the claim that torque is significantly minimized in men with schizophrenia, reflecting aberrant neurodevelopment (Guerguerian & Lewine, 1998). The study examined both the volumetric and linear asymmetry of a group of 20 individuals with schizophrenia and 20 healthy individuals, all of which where right handed, but the results found that there was no statistically significant difference in torque. Despite this it was noted that “sex difference in torque among those with schizophrenia” (Guerguerian & Lewine, 1998, pg. 178), was greater than that in those without.Torque also appears to be associated with the years of education and age of schizophrenic onset, indicating that “slowed neurodevelopment may be associated with male schizophrenia and may contribute to earlier age of onset and less education” (Guerguerian & Lewine, 1998, pg. 179).
Research literature examined by Coger and Serafetinides all seemed to suggest that people with the disorder may be unable to completely transfer information from the corpus callosum to the two cerebral hemispheres. Brain Imaging Technology has made it possible to take note of the abnormally thickened or thinned corpus callosum within patients with schizophrenia, indicating that this could be another possible anatomical basis for the abnormal organisation of cognitive functions including language processing (Coger & Serafetinides, 1990).
The findings from an investigation by Coger and Serafetinides suggest a connection between the earlier onset of schizophrenia and negative symptom patterns with the thickened corpus callosum. It was also found that positive symptoms and later ofset have been linked with a thinner corpus callosum. The researchers suggest that a “careful analysis of the transfer of infromation…” between the right and left hemispheres of both individuals wih schizophrenia and normal controls can provide important information in regards to “cerebral organization and mechanisms operative in schizophrenia” (Coger & Serafetinides, 1990, pg. 170). This shows how not only language lateralisation but factors such as cerebral asymmetry may relate to schizophrenia. A better understanding of their incidence in those with schizophrenia may improve diagnosis of the disorder.
Handedness
It seems there is convincing evidence that other factors play a role in schizophrenia and handedness is one of the main characteristics believed to impact and be affected by the disorder. Satz and Green (1991) investigated if there was “a leftward shift in the distribution of handedness” in those with the psychosis (Satz & Green, 1991, pg. 77). They found with their research nine positive studies supporting the left handed prevalence in those with schizophrenia, five studies which found no difference in the hand prevalence between those with and without the disorder and two studies which paradoxed the original claim. This suggested that there is infact a slight leftward shift in the distribution, deviating from the “typical J-shaped distrubution long reported in the normal population” (Satz & Green, 1991, pg. 64). This meta-analysis by Satz and Green drew upon the association between schizophrenia and the left or mixed handedness of individuals, while taking into consideration other cognitive, biological and behavioural abnormalities.
Among some of the many studies included within that meta-analysis, it was found that the seemingly leftward shift was due to an increase of mixed handedness compared with normal or patient controls, but only studies by Manoach, Maher and Manschreck (1988) and Gur (1977) reported an increase in left handededness only.
Further research suggests that “In addition left hemisphere pathology is associated with schizophrenia, and this is consistent with the excess non right handedness among those with schizophrenia” (Coren, 1990, pg. 54). Coren also states that left handed people with schizophrenia have a much greater ventricular size and therefore poorer neuropsychological performance, “than that of right handed schizophrenics, suggesting a greater degree of cerebral dysfunction” (Coren, 1990, pg 54). Handedness and the anatomical differences such as that of the ventricular size and hemispheric dominance of schizophrenia patients appear to affect the severity of the disorder, and with further research regarding the prevalence of both anatomical and behavioural differences within those with the disorder it may be possible to identify patterns and thus improve the diagnosis and understanding of schizophrenia in general.
Evaluation
Evaluation of Language Lateralisation
When investigating language lateralisation, many strengths and weaknesses were located in the claim itself and the studies used to support or challenge the claim. As the lateralisation of language is in itself difficult to determine, any research investigating this factor could be regarded as irrelevant as it may not render results appropriate to the investigation as a whole, or in comparison to specific studies mentioned throughout may focus purely on the Broca’s area for instance, whereas the other studies focus on generalised lateralisation and the areas of the brain activated during language related stimuli.
The semantics associated with the term language also make the arguments presented throughout the investigation questionable, as some studies may be found to focus on spoken word, others written text and as such it is deemed necessary to narrow the focus of the investigation in regards to what concept of language will be examined.
Approximately ten studies where referred to among the literature review for language lateralisation, and by evaluating these studies, in combination with the flaws and strong sections of the investigation will enable for a less biased outlook on the evidence and hence allow for a valid conclusion to be drawn. Meta analyses are one of the most effective ways of collecting and examining a large number of studies focusing purely on one factor. This allows for a significantly larger number of participants and/or trials in order to support or contradict a hypothesis.
The main danger presented with unsystematic reviews is that they allow for possible bias to occur as the authors may decide only to include a portion of relevant studies, often those which favour the claim made by the author. Despite this, the limitations of meta-analyses fall down onto the quality of the underlying studies and the only way to produce a reliable meta-analysis is to carefully review the separate studies and make an assessment as to their weakness and relevance to the study (Crombie & Davies, 2001). However in the meta-analyses used, such as that by Sommer et al. (2004) were chosen to feature in this investigation as they chose their consisting studies due to dealing with the same definition of “lateralisation in schizophrenia”, published between a specific time period for reasons of sharing the same diagnostic manual (Sommer et al., 2001, pg.128). By doing this it allows for the number of variables within the meta-analysis to be reduced, compared to what it would be if they allowed for studies with differently diagnosed patients. All meta-analyses also eliminated any translation errors by using only English language publications that were featured in international journals and books. One advantage of this investigation is that it allowed for a number of varied brain imaging technology methods to be employed to measure brain activity and the way in which certain areas of the brain are stimulated when the individual is presented with stimuli. This allowed for a large variety of study types to be considered and allow for a more widely generalised claim regarding the link between language lateralisation and schizophrenia, however in doing so illustrates the number of uncontrolled factors that can also contribute. However this can be evaluated through triangulation, and the contribuition of multiple methods.
Evaluation of Anatomical Asymmetry
Many strengths and limitations were identified when examining studies focusing on Anatomical Asymmetry, in particular the broad definition of anatomical asymmetry means that the research regarding it for this investigation needed to have been clearly defined. As such it was determined to focus merely on the overall asymmetry, and in particular, the ‘bridging gap’, corpus callosum that joins both left and right hemispheres. Again with all sections of this analysis it was necessary to determine that the studies had utilized the same method of diagnosis for their participants, however despite this, as the focus of each individual study appeared to be on a different aspect of the brain, the overall investigation may be considered too varied. In one of the studies by Crow (2004), he determined that the occipito-temporo-parietal association cortex appeared to be more symmetrical in those with schizophrenia, compared to the noticeable differences observed among those without. However other studies mentioned within the literature review, such as that by Coger and Seragetinides (1990), focused purely on the corpus callosum, and in particular the thickness of it compared to control subjects without schizophrenia. This variation means that meta-analyses would be the most suitable type of investigation to be featured as they would gather a group of consistent data, focusing on one aspect of anatomical asymmetry.
One major limitation of the meta- analysis type of study is that the introduction of other variables with the varying studies can still impact the findings. In the investigation by Crow, he used both post-mortem and anatomical imaging studies in order to give evidence for the reversal or reduction of asymmetry in the participants with schizophrenia. The combination of both alive and dead imaging could affect the results, as in death it is more difficult to determine whether the occipito-temporo-parietal cortex differs from the control due to the schizophrenia in life.
The differing methods of research in regards to Brain Imaging Technology and the focus of asymmetry within participants means that overall a more specific outlook on the correlation between schizophrenia and brain stucture may be able to be determined. With this taken into consideration, it highlights the way in which it is difficult to determine how certain factors can be relevant to a disorder and it would be necessary to consider all of them, environmental and genetic, in order to develop a better understanding of schizophrenia. However, it is difficult to in fact establish a clear connection between cause and effect, with studies with low ecological validiy, as such in order to develop a more valid interpretation it necessary to combine methods and types of data collected.
Evaluation of Handedness
The concept that an individual’s hand preference is linked to their likelihood of having a form of psychosis, such as schizophrenia is highly debated. The studies mentioned throughout this investigation on handedness and Schizophrenia were often meta-analyses which featured other variables as their main features such as that by Sommer et al. (2001) focusing mainly on language lateralisation and only briefly making reference to the prevalence of schizophrenia in individuals with other characteristics. It is often believed that left handed people are more accident prone, likely to die earlier or more likely to be at risk of disorders, however, much of this folklore has failed to be supported through research. Despite this, upon examining studies on schizophrenia and hand preference, it seemed possible to reach the conclusion that although individuals with left hand preference do not appear to have any stronger link to schizophrenia. Though it was observed from the studies reviewed that ambidextrous people are more prone to psychosis.
The study conducted by Satz and Green (1991) is one of the few studies found that takes into consideration whether the person preference is left, right or ambidextrous. Many of the studies such as that by Coren (1990) group together left and ambidextrous individuals and compare them to the control group (right handed preference). Much of the research used within this essay suggests a link between brain asymmetry and hand preference, indicating that these concepts should be examined in a combined manner rather than separated as this essay originally proposed. In saying this it seems that the linkage of handedness and language lateralisation could also be investigated as the differing anatomical asymmetry between those with different hand preferences allows for the consideration of different lateralisation of the language centre of the brain and therefore could increase likelihood of having schizophrenia.
Though much speculation is made regarding the linkage of hand preference and schizophrenia the articles utilized and referred to present forward the idea that an individual’s dominant or lack of dominant hand preference insinuates that they are more or less likely to have the psychosis. Each article used has its own weaknesses and variables attached, meaning that the results could be somehow interfered with or the result of, say the participant’s characteristics or background, but by including a large number of test subjects and articles it is possible to account for some of these and observe consistent results. This indicates that it is highly likely for a person’s hand preference to be impacted by or impact the likelihood of them having schizophrenia, with ambidextrous people being more prone to the disorder.
Conclusion
The biological factors of language lateralisation, handedness and anatomical brain asymmetry discussed within this investigation provide further understanding of the contributing variables linked to schizophrenia. Although it is impossible to examine every variable that could be linked to schizophrenia, even language lateralisation, by investigating individual studies and comparing them it is possible to suggest the relevance and significance of that factor. The meta-analysis by Sommer et al. (2001) used a large number of studies in order to provide evidence to display how the different factors can be examined in relation to schizophrenia and show the way different results can be analysed revealing the prevalence of each quality in those with schizophrenia. Findings from this study along with other individual studies highlight the inconsistency of data overall but the slight prevalence of the following qualitities, mixed handedness, lack of language lateralisation and reduced anatomical asymmetry within participants with schizophrenia.
Language lateralisation, the focus of this essay is a rather broad subject and it was found necessary to reduce it to being primarily localised within the left hemisphere in order to locate more specific and relavant studies for this investigation. The most common method was that of listening tests which although they limited the scope of language processing they allowed for observing the correlation between an individual’s language lateralisation and their mental health. Other methods are being developed in order to pinpoint the actual localisation of language however most investigations are noted to have observed a change in language function and processing ability within individuals with schizophrenia and those without. When taking into consideration the evaluation, it is possible to take into account the implications of language sections of the brain and schizophrenia in regards to improving diagnosis.
When investigating anatomical brain asymmetry and handedness it was noted that they often correlate with each other. The individuals that were ambidexturous were found to have more ‘symmetrical’ brains in the majority of studies conducted, and within those investigations grouping together left handed and mixed handed participants it was noticed that only some of the results reflected an increased liklihood of schizophrenia. Thus by investigating both factors it is possible to see the interaction between them and schizophrenia allowing for more accurate and specific diagnosis than the current behavioural observations.
This investivation highlighted the way each factor seems to contribute to developming the disorder it suggests that an investigation should be undertaken to see if any correlation between the three factors actually affects the liklihood of having schizophrenia. Thus, even though these factors, mixed handedness, anatomical symmetry and lack of brain lateralisation, appear to have a relatively high correlation with schizophrenia, the only current effective manner of diagnosis of schizophrenia is possible with professional diagnoses using symptoms recorded within statistic manuals such as that of the DSM-IV TR.
List of References
American Psychiatric Association. (2012). B 00 Schizophrenia. Retrieved March 7, 2012, from American Psychiatric Association DSM-5 Development: http://www.dsm5.org/ProposedRevisions/Pages/proposedrevision.aspx?rid=411
Bhugra, D. (2005, May 31). The Global prevalence of Schizophrenia. Public Library of Science .
Bleuler, E. (1911). Dementia paecox order die Gruppe der Schizophrenien. Leipzeig: Deutike .
Bobe, S., Deppe, M., Dräger, Knecht, L., Lohmann, H and Ringelstein, E (2000). Language lateralization in healthy right-handers. Brain , 123 (1), 74-81.
Bradshaw, J. L. (1998). Schizophrenia as failure of hemispheric dominance for language. TINS , 21 (4), 145-146.
Brüne, M. (2004). Schizophrenia-an evolutionary enigma? Neuroscience and Biobehavioural Reviews (28), 41-53.
Coger, R., & Serafetinides, E. (1990). Schizophrenia, corpus callosum, and interhemispheric communication: A review. Elsevier , 34 (2), 163-184.
Coren, S. (Ed.). (1990). Left-Handedness: Behavioural Implications and Anomalies. New York: Elseier Science Publishing Company, inc. .
Crombie, I., & Davies, H. (2001). What is meta-analysis. What is..? series , 1-8.
Crow, T. (2004). Cerebral asymmetry and the laterlization of language: core deficits in schizophrenia as pointer to the gene. Current Opinion in Psychiatry , 17 (2), 97-106.
Davison, G., Johnson, S. Kring, A., & Neale, J., (2007). Abrnormal Psychology (10th Edition ed.). (C. Johnson, Ed.) Hoboken, United States of America: John Wiley and Sons Incorporated.
Donald, M. (1991). Origins of the Modern Mind: Three Stages in the Evolution of Culture and Cognition. Harvard University Press.
Donner, E. (2010, April 2). Intracarotid Amobarbital Test (Wada Test). Retrieved April 8, 2012, from aboutkidshealth: http://www.aboutkidshealth.ca/En/ResourceCentres/Epilepsy/TreatmentofEpilepsy/SurgicalTreatmentofEpilepsy/Pre-surgicalEvaluation/Pages/Intracarotid-Amobarbital-Test-Wada-Test.aspx
Guerguerian, R., & Lewine, R. (1998). Brain torque and sex differences in schizophrenia. Schizophrenia Research , 30 (2), 175-181.
Gur, R. (1977). Motoric laterality imbalance in schizophrenia. Archives of General Psychiatry , 34, 33-37.
Hartje, W., Ringelstein, E., Kistinger, B., Fabianek, D., & Willmes, K. (1994). Transcranial Doppler Ultrasonic Assessment of Middle Cerebral-Artery Blood-Flow velocity changes during verbal and visuospatial cognitive tasks. Neuropsychologia , 32 (12), 1443-1452.
Heston. (1980, October 1980). Psychiatric disorders in foster home reared children of schizophrenic mothers. This week's citation classic , 112 (41), pp. 819-825.
Kay, S. R., Fiszbein, A., & Opler, L. A. (1987). The positive and negative syndrome scale (PANSS) for schizophrenia. Schizophrenia Bulletin (13), 261-276.
Manoach, D., Maher, B., & Manschreck, T. (1988). Left-handedness and thought disorder in the schizophrenias. Journal of Abnormal Psychology , 97-99.
Marek, P. (n.d.). Dichotic Listening. Retrieved March 27, 2012, from Online Psychology Laboratory: http://opl.apa.org/Main.aspx
Nestor, P., Han, S., Niznikiewicz, M., Salisbury, D., Spencer, K., Shentom, M., et al. (2001). Semantic disturbance in schizophrenia and its relationship to the cognitive neuroscience of attention. Biological Psychology , 57 (1-3), 23-46.
Rachel, L., Mitchell, C., & Crow, T. (2005). Right hemisphere language functions and schizophrenia: the forgotten hemisphere? Brain , 128 (4), 963-978
Satz, P., & Green, M. (1991). Atypical Handedness in Schizophrenia: Some Methodological and Theoretical Issues. Schizophrenia Bulletin , 25 (1), 63-78.
Seeman, M. V. (2009, May 12). Schizophrenia in women and men. Armenian Medical Network .
Sommer, I., Ramsey, N. F., & Mandi, R. C. (2004). Language activation in monozygotic twins discordant for schizophrenia. (C. J. Van Oel, & R. S. Kahn, Eds.) British Journal of Psychiatry (184), 128-135.
Sommer, I., Ramsey, N., Kahn, R., Aleman, A., & Bouma, A. (2001). Handedness, language lateralisation and anatomical asymmetry in schizophrenia. The British Journal of Psychiatry , 178, 344-351.
State Government of Victoria. (2012, February 20). Mental Illness Prevalence. Retrieved March 11, 2012, from Better Health Channel: www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Mental_illness_prevalence
The National Institute of Mental Health. (2009, September 8). What causes schizophrenia. Retrieved March 11, 2012, from NIMH: http://www.nimh.nih.gov/health/publications/schizophrenia/what-causes-schizophrenia.shtml
Titone, D. (2010, May). Language, Communication and Schizophrenia. Journal of Neurolinguistics , 173-175.
Van der Zwan, A., & Hillen, B. (1991). Review of the variability of the territories of the major cerebral arteries. Stroke , 1078-
Appendix
Figure 1: The odds ratio for risk of having schizophrenia. From “The Genetics of Schizophrenia,” by P. F. Sullivan, 2005, July 26, Public Library of Science, 2(7), retrieved from
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