To what extent can biological investigations provide evidence to suggest language lateralisation correlates with schizophrenia?

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Candidate Name: Kayla Jackson

Candidate Number: 003562-044

Word count: 3979

School: Queensland Academy for Health Science


Schizophrenia is a form of psychosis featuring cognitive, emotional and behavioural symptoms. The causes of schizophrenia are considered controversial and difficult, if not impossible to determine, however it is considered to be an interaction of genetic and environmental factors. Language lateralisation, however, cannot be specifically defined as to only belonging to one aspect of the brain as many separate sections appear to affect or be affected by the presence of schizophrenia. Within this investigation both the localisation of language functions and the correlation to schizophrenia are visited and evaluated.

This investigation evaluates the evidence of the impact of language lateralisation and other variables on the likelihood of developing schizophrenia. Biological determinates, such as an individual’s hand preference, (left, right or ambidextrous) and their brain structure, in particular asymmetry across both hemispheres, are discussed in order to determine how crucial they are in the development of schizophrenia and how they assist in understanding the disorder.

By evaluating and determining some of the factors which suggest a possible correlation with schizophrenia, it is possible to analyse their contribution. This investigation explores not only the complexity associated with the actual factors, such as the specific lateralisation of schizophrenia, but includes a broader outlook when examining a large variety of brain structures, such as Broca’s area and the corpus callosum.

The investigation allowed for the conclusion to be made that a lack of lateralisation of language does appear to be linked with the presence of schizophrenia. The consideration of biological aspects such as anatomical asymmetry and an individual’s hand preferences allowed for the conclusion to be made that this disorder is not merely relying on language lateralisation but rather a contribution of other variables.

Word count: 280

Table of Contents

Abstract        1

Table of Contents        2

Introduction        3-4

Literature Review        5-8

Language Lateralization        5-6

Anatomical Asymmetry         6-7

Handedness        8

Evaluation        9

Evaluation of Language Lateralization        9-10

Evaluation of Anatomical Asymmetry        10-11

Evaluation of Handedness        11-12

Conclusion        13

References        14-15

Appendix        16


“Schizophrenia is a term first proposed by Eugen Bleuler in 1908 referring to a group of disorders characterised by severe cognitive, emotional and behavioural symptoms” (Brüne, 2004, pg. 41) According to the Diagnostic and Statistical Manual IV-TR, the diagnosis of schizophrenia can be divided into six categories. Section A comprises of characteristic symptoms for which a patient must have:

“Two (or more) of the following, each present for a significant portion of time during a 1 month period. At least one of these should include one to three.

  1. Delusions
  2. Hallucination
  3. Disorganised Speech
  4. Grossly abnormal psychomotor behaviour, such as catatonia.
  5. Negative symptoms i.e. restricted affection or asociality”  (Davison, Kring, Neale, & Johnson, 2007, pg. 351)

The diagnosis of schizophrenia is made largely from clinical observations, often focusing of the patient ability to communicate via their use of language as a way in which to understand their grasp on ‘reality’. Schizophrenia is a complex disorder, in that it has been found to affect most psychological aspects of well being, for instance the patient’s perception, cognition and social interpersonal functions (Titone, 2010).

The causes of schizophrenia are controversial and difficult, if not impossible to determine, however it is believed to consist of a genetic and environmental component. Psychologists such as Heston (1966) and Wendell (1974) have, through research, been able to suggest that schizophrenia runs in families due to the increase in percentage, from 1% to 10% within those who have a first-degree relative with the disorder. “Those with second-degree relatives with the disease also develop schizophrenia more often than the general population…” with the highest risk being that of 40 to 60% for indentical twins  (The National Institute of Mental Health, 2009, para. 1). In regards to situational and environmental factors, many studies have been conducted in order to ascertain which are believed to contribute most signifigantly in the development of schizophrenia. Some of the highest contributing environmental factors according to Sullivan, are that of damage to the Central Nervous System, bereavement during the prenatal stage, and infection such as rubella. These respectively increase the risk of schizophrenia by 7%, 6.25% and 5.25% compared to those lacking these factors (See Figure 1 in Appendix 1).

The prevalence of schizophrenia within Australia is relatively high, with around 3% of adults being severly affected by mental illness and approximately a third of this figure will be affected by schizophrenia at at some point in their life (State Government of Victoria, 2012). A meta-analysis regarding the prevalence of schizophrenia worldwide by Bhugra, found that there was no significant difference in the percentage of men and women affected by the disorder, nor between urban, rural or mixed sites background  (Bhugra, 2005). Despite this claim, other research by Seeman found that the onset for schizophrenia seems to be delayed in the females and they also experience symptoms to a lesser degree, with fewer being hospitalised and with shorter admissions  (Seeman, 2009). As schizophrenia affects a fairly large amount of the population and there is little understanding of the disorder it can be deemed worthy of investigating other possible correlations with schizophrenia and effective methods to assist in diagnosis.

The focus of this essay is on ‘lateralisation and schizophrenia’, and in particular: to what extent does research on the degree of language lateralisation, assist in understanding and diagnosing Schizophrenia? In general, an individual’s handedness, language lateralisation and anatomical brain asymmetry are believed to be linked to schizophrenia, as “cerebral lateralisation appears to be decreased in schizophrenia”  (Sommer, Ramsey, & Mandi, 2004, pg. 344). As such it is necessary to investigate the relevance of language lateralisation and schizophrenia and then compare it to the observable link between the disorder and an individuals hand preference and brain structure.

Literature Review

Language Lateralisation

For this investigation, language lateralisation will refer to the suggested lateralisation found from Electroencephalography (EEG)  studes and dichotic listening studies which make it possible to study the laterality of auditory language processsing by presenting stimuli to each ear, investigating the ability to accurately identify sounds  (Marek, n.d.a). “The most common method used to determine language lateralisation referred to in this investigation is that of dichotic listening studies, in order to illustrate where language processing occurs in the brain. Language lateralisation in itself is difficult to locate, as in addition to being primarily located in the left hemisphere, the right also appears to play “a major role in the connotative and pragmatic aspects of language” (Bradshaw, 1998, pg. 145).

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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 ...

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