gazzaniga,1967

The Split Brain in Humans

The human brain consists of two hemispheres, right and left, connected by the corpus callosum.
Surgical division of the cerebrum leads to each hemisphere functioning independently, resembling two separate brains.
Research by Ronald E. Myers and R. W. Sperry revealed independent functions of the hemispheres when the corpus callosum was cut.
Early studies involved animal experiments showing that divided hemispheres could have separate learning experiences.

When tasks were presented to one hemisphere at a time, animals needed to relearn tasks when switching hemispheres.
Questions arose about the role of the corpus callosum in integrating consciousness between hemispheres.
In humans, surgery to divide the brain was used to treat epilepsy, leading to significant reductions in seizures.
Patient behavior showed no major changes in personality or intelligence post-surgery, although some changes in behavior were observed, such as preferential response to right-side stimuli.

Patients displayed a phenomenon known as bisected brain syndrome, where the left side of the body often showed less activity and awareness.
Visual stimuli presented in the left visual field could not be verbally reported by patients due to divison of the speech centers in the left hemisphere while still being recognized in nonverbal tests.
Each hemisphere demonstrated unique abilities and limitations:
- The left hemisphere excelled in verbal processing and fine motor control of the right hand.
- The right hemisphere, despite being unable to verbalize certain tasks, could accurately respond to nonverbal cues and had some understanding of language in a limited capacity.

In tactile tests, objects held in the right hand could be named, while those in the left hand could not be verbally identified but could be matched nonverbally.
Patient responses illustrated that the right hemisphere has the ability to comprehend some language as observable during certain tasks, despite no verbal expression.
Some patients were even able to use their left hand to respond to visual input, suggesting some degree of cross-hemispheric understanding.
A study revealed that right hemispheric engagement could elicit emotional reactions without descriptive capability.

Current research aims to understand the integration processes of the corpus callosum and its role in memory and learning.
Studies indicate that divided hemispheres may work as separate entities capable of high-level mental functions, hinting at dual consciousness.
Observations in split-brain monkeys show they can process almost double the visual information compared to whole-brain animals, suggesting enhanced capacity post-separation
The findings challenge conventional views on consciousness as an indivisible aspect of the brain, opening questions about hemispheric abilities in younger brains and potential for independent mental functions.