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M05.11.01 Hemispheres: left and right
The human brain can be broadly divided into two hemispheres: left and right. While they work together to create a unified experience, each hemisphere tends to specialize in certain functions. Understanding these specializations can be helpful for medical students in various clinical settings.
Lateralization of Function
- Dominance: One hemisphere is typically dominant for certain tasks.
- Left hemisphere: Dominant in language and analytical functions in most individuals.
- Right hemisphere: Dominant for visuospatial tasks and emotional processing.
- Distribution:
- Left dominance:
- 97% of right-handed people.
- 60-70% of left-handed people (due to greater variability in brain lateralization).
- Left dominance:
| Hemisphere | Dominant Function | Examples |
|---|---|---|
| Left | Language and analytical thinking | Speech, reading, writing, math calculations, logic |
| Right | Visuospatial processing and non-verbal communication | Facial recognition, spatial awareness, music perception, artistic expression, emotional processing |
Clinical Corollaries
- Stroke: Damage to a specific hemisphere can lead to characteristic deficits depending on the dominant function.
- Left hemisphere stroke:
- Aphasia (language difficulties).
- Apraxia (impaired motor function despite intact knowledge of how to perform the movement).
- Hemi-neglect (inattention to the left side of the body or environment).
- Increased risk of depression.
- Right hemisphere stroke:
- Spatial neglect (inattention to the left side of the body or environment).
- Visuospatial difficulties (problems with tasks like drawing or navigating).
- Apathy or indifference.
- Left hemisphere stroke:
Important Points to Remember
- Brain lateralization is a spectrum, not an absolute on/off switch. Both hemispheres contribute to most cognitive functions.
- The degree of lateralization can vary between individuals, especially in left-handed people.
- Brain plasticity allows for some reorganization of function after brain injury.
Bibliography
- American Psychological Association. (2020). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: Author.
- Gazzaniga, M. S. (2000). The mind’s past. Berkeley: University of California Press.
- Kolb, B., & Whishaw, I. Q. (2014). Fundamentals of human neuropsychology (8th ed.). New York: Worth Publishers.pen_spark