4.7 Hemispheric Specialisation

Introduction to Left and Right Brain Myth

• Popular notion: Left-brained individuals are logical, analytical, and scholarly; Right-brained individuals are artistic, creative, and emotional.

• While a kernel of truth exists, both brain hemispheres typically work in unison.

• Key concept: Lateralization, the localization of specific functions in one hemisphere over the other.

Lateralization Explained

• Lateralization: Refers to the tendency for certain brain functions to be more dominant in one hemisphere.

• Split-brain operations often demonstrate these differences, conducted typically to manage severe epilepsy.

• Corpus Callosum: A broad band of myelinated nerve fibers connecting the two hemispheres, crucial for communication between them.

Split-Brain Patients

• In a split-brain surgery, the corpus callosum is severed to limit seizures.

• Post-surgery, each hemisphere can operate independently due to loss of intercommunication.

• Visual Processing: When information is presented visually, the left visual field is processed by the right hemisphere and vice versa, due to the crossover at the optic chiasm.

Roger Sperry's Research

• Roger Sperry received the Nobel Prize in 1981 for groundbreaking work with split-brain patients, studying how each hemisphere processes information differently.

• Experimental setup: Patients fixate centrally while brief stimuli are presented to either visual field, assessing their verbal and non-verbal responses.

• Example Experiment:

  • When the word "face" is shown on the right side, patients can verbally identify it (processed by the left hemisphere).

  • When shown on the left side, patients cannot verbally identify it but can draw it using their left hand (controlled by the right hemisphere).

Insight from Joe's Case Study

• Joe: A split-brain patient whose surgery mitigated his severe epilepsy, providing insights into independent brain functions.

• Behavior Observation: Joe adapts to living with severed hemispheres without feeling different, demonstrating how the mind adjusts.

• Demonstration of Processing: Researchers flash images and words to Joe while observing responses from each hemisphere.

  • Left side input: Joe cannot name items but can draw them.

• Conclusive Insight: The right hemisphere processes information non-verbally despite lacking verbal capabilities.

The Role of Non-Conscious Processes

• Joe's case illustrates significant non-conscious processing capabilities within the brain.

• Independent functions operate outside of conscious awareness, impacting behavior and self-perception.

• The mind comprises several independent "agents”, with the left hemisphere synthesizing this information to create a cohesive understanding or personal theory.

Unified Brain Functionality

• Despite the lateralization of specific functions, the brain normally operates as a cohesive unit.

• Brain imaging shows that both hemispheres communicate extensively during various tasks.

• General consensus: Left hemisphere is stronger in language and verbal skills, while the right is more adept at spatial and pattern recognition tasks.

Conclusion

• Emphasis on the complexity of the brain: While certain tasks may localize in one hemisphere, cooperative functions showcase the necessity of both hemispheres for a unified conscious experience.