Module 1.4c The Brain: Damage Response and Brain Hemispheres
Responses to Damage
Neuroplasticity refers to the brain's ability to reorganize itself by forming new connections.
Severed neurons in the brain and spinal cord do not regenerate, and brain functions are often localized to specific areas.
Example: A newborn with damage to the temporal lobe for facial recognition may not recognize faces.
Adaptation to Damage
Young children demonstrate greater neuroplasticity, reorganizing functions to compensate for damaged areas.
Blindness/Deafness: Unused brain areas can be reallocated for alternative functions (e.g., touch or smell).
Braille readers may experience expansion of sensory areas in the brain dedicated to touch.
Deaf individuals who learned sign language often have enhanced visual processing abilities.
Reassignment of Functions
When areas of the brain dedicated to certain functions are damaged (e.g., tumor affecting language), other areas may compensate.
Amputation Example: When a finger is amputated, the somatosensory cortex can adapt by becoming more sensitive to adjacent fingers.
Neurogenesis Debate
Researchers are exploring whether the brain can generate new neurons (neurogenesis) in adults, which would aid in recovery from damage.
Studies have shown baby neurons present in various animals and humans, suggesting potential for repair.
Natural promoters of neurogenesis include exercise, sleep, and non-stressful stimulating environments.
The Divided Brain
Research has established lateralization of brain functions, particularly in regard to language and perception.
Left Hemisphere: Dominates verbal functions (reading, writing, speech).
Right Hemisphere: Excels in visual perception, making inferences, and emotional recognition.
Split-Brain Procedures
In the 1960s, surgeons severed the corpus callosum to mitigate severe epilepsy, leading to split-brain conditions.
Results of the Surgery: Patients remained healthy with personalities largely unaffected.
Experimental Findings: By sending information separately to each hemisphere, researchers could explore functions.
Notable Experiments
Gazzaniga and Sperry's studies revealed surprising results with split-brain patients:
If the word "HE•ART" is shown to the right visual field, patients could say “ART,” but when asked to point with the left hand, they pointed to “HE.”
This indicates the right hemisphere's capacity for visual perception, yet inability to verbally express the information.
Independence of Hemispheres
Patients exhibited actions without understanding, often rationalizing actions initiated by the right hemisphere via improvisation from the left hemisphere.
Example: If instructed to walk by the right hemisphere, the left hemisphere might rationalize “I’m going to get a drink.”
Patients could perform tasks requiring different functions simultaneously, revealing independence.
Functional Differences in Intact Brains
Each hemisphere contributes uniquely; tasks like speech center in the left, while visual processing is dominated by the right.
Right hemisphere better at inferring meaning and emotional tone in communication.
Implications and Applications
Results from split-brain patients inform our understanding of psychological functions and how the brain manages tasks collaboratively.
Review and Study Points
Both hemispheres are essential for overall brain function, but each has distinct roles contributing to behavior and cognition.
Key Terms
Neuroplasticity: Brain's ability to reorganize after damage.
Neurogenesis: Generation of new neurons.
Corpus Callosum: Neural fibers connecting the two hemispheres.
Split Brain: Condition resulting from the severing of the corpus callosum.