Chapter Three: The Biological Bases of Behavior

E. Right Brain/Left Brain: Cerebral Laterality

Research on laterality has revealed that the two hemispheres may have different abilities. Is it possible we have two separate minds in there?

1. Introduction
2. Bisecting the Brain: Split-Brain Research
3. Hemispheric Specialization in the Intact Brain
4. Handedness and Laterality

Contents

Introduction

Synopsis: Cerebral laterality laterality suggests the two hemispheres have different abilities. The history of how we got the first clue that the hemispheres might be specialized is a history of brain damage.

• Broca's area
  • Production of speech impaired with left hemisphere damage in Broca's area.

  • Figure. of Broca's area (not active -3.23)

  • Picture of Dr. Broca (look if you like "mutton-chops").

• Wernicke's area
  • Comprehension of language impaired with left hemisphere damage in Wernicke's area (see a pattern emerging here? -- damage to areas in the left hemisphere and language is affected)

  • Figure 3.23 (also not active.)

  Historical Update: Early conclusion that there was a dominant/non dominant relationship between the two hemispheres has been changed because of current research.

Bisecting the Brain: Split-Brain Research

Split-brain surgery places the brain in a very unusal state in deed.

Logic of split brain research: This will be a series of links to diagrams and brief video clips demonstrating:

• How the brain is surgically split (severing the corpus callosum), and

• How researchers conduct split brain studies which demonstrate laterality.

For now, split-brain surgery and its effects described in greater detail.

Hemispheric Specialization in the Intact Brain

Not too many college students want to be subjects in split-brain research. Here is a method that allows researchers to study specialization in a normal brain.


Dichotic listening task

• Uses perceptual asymmetries
• Different auditory inputs are simultaneously presented to each ear.
• Differences in the speed and accuracy of identifying different types of stimuli locates specialization areas.

Conclusions about hemispheric specialization:

• Left hemisphere handles verbal processing:
  • language
  • speech
  • reading
  • writing

• Right hemisphere handles non-verbal processing
  • spatial recognition tasks
  • musical recognition tasks
  • visual recognition tasks

• Simplified chart of hemispheric specialization.
  
  
• to discussion of the problem of oversimplification when describing hemispheric specialization.

Handedness and Laterality

Handedness is related to laterality.

Prevalence of handedness

• 90% are right handed.
• 7-8% are left-handed.
• 2-3% are mixed.
• Prevalence is similar across cultures.

Origins of handedness

• Environmental theories
  • Majority of us are right handed because the world around us is set up to promote using our right hand.

  • but, if it handedness were simply a function of social pressure, there would be more cross cultural variation because different cultures have very different attitudes about the appropriateness of being left-handed.
  
  
• Genetic theories
  • Similarity in prevalence of handedness across cultures suggests a genetic factor.

  • but, identical twins are no more similar in handedness than unrelated people.

Correlates of Handedness

Lateralization of language:

• Right handed - language processing in left hemisphere
• Left handed - atypical lateralization (in right hemisphere or both)

Pathologies:

• Autism
• Schizophrenia
• Dyslexia
• Mental retardation
• Alcoholism
• Immune disorders
• EARLY DEATH?- the topic of the Featured Study

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