Notes on Neuroplasticity, Neurogenesis, and the Divided Brain

Brain reorganizes after sensory loss; unused areas can be repurposed (cross-modal plasticity).
Blindness: Braille reading expands the somatosensory finger area; touch invades the visual cortex.
Deafness: sign language can enhance peripheral and motion-detection vision; temporal lobe awaits stimulation and can adapt to process visual/sign inputs.
Disease/damage: language in the left hemisphere can be taken over by the right hemisphere, which may compensate.
Case example: people born without hands use feet; hand-area somatosensory cortex becomes active for feet.
Phantom limb phenomena (e.g., orgasm perceived in phantom foot) illustrate cortical remapping.
Neurogenesis (birth of new neurons) is debated as a repair mechanism in adults; baby neurons found in various species may form connections and participate in networks.
Stem cells: master stem cells can develop into brain cells; research aims to generate neurons to replace damaged cells and to study development and memory.
Practical impact: promoting neurogenesis via exercise, sleep, and stimulating environments.

Neurogenesis: the formation of new neurons.
Evidence of adult neurogenesis in mice, birds, monkeys, and humans; new neurons may form connections with nearby neurons.
Individual variation in neurogenesis contributes to personal differences in brain plasticity.
Embryonic stem cells can potentially be guided to resemble functioning human neurons for therapy and research.
Natural promoters of neurogenesis include exercise, sleep, and nonstressful but stimulating environments.
Ongoing research seeks to understand how neurogenesis supports memory and brain development.

The brain’s left and right hemispheres have different specializations (lateralization).
Left hemisphere: language, arithmetic, and quick, literal interpretation.
Right hemisphere: inference, emotion recognition, spatial tasks, faces, and holistic processing.
Historically, the right hemisphere was thought less important, but evidence from split-brain studies changed this view.

Corpus callosum: large bundle of fibers connecting the two hemispheres and enabling communication.
Split-brain surgery severs the corpus callosum to stop seizures; patients often recover with surprisingly normal function.
Studying split brains reveals how each hemisphere can operate independently when interhemispheric transfer is disrupted.

Each eye sends information from both visual fields to both hemispheres, but information from the left visual field goes to the right hemisphere and vice versa.
In split-brain patients, information sharing across hemispheres is cut, allowing researchers to test each hemisphere separately.

Experiments show hemispheres can process information independently; the left hemisphere often acts as an interpreter, constructing explanations for actions it cannot fully explain.
Example: when HE-ART is flashed to different visual fields, the left hemisphere may verbally report one word, while the right hemisphere’s actions indicate another.
Left hand (controlled by right hemisphere) can indicate what was seen by the right hemisphere, even if the left hemisphere is unaware of it.
The phrase “two minds” reflects how each hemisphere can drive behavior with limited cross-communication.

In most people, intact brains show lateralization patterns during tasks: right-hemisphere activity for perception, left-hemisphere activity for language and calculation.
Language centers can be mapped by temporarily suppressing the left hemisphere; the right hemisphere’s functions become more prominent (e.g., limb weakness in the opposite arm).
In dogs, left hemisphere tends to process words, right hemisphere processes intonation; language in humans can be spoken or signed, with sign language predominantly processed in the left hemisphere for many individuals.
Deaf signing relies on left-hemisphere language processing similarly to spoken language in hearing individuals.
Right-hemisphere damage can impair inference, emotion, facial recognition, and self-awareness; left-hemisphere damage often disrupts direct language tasks.

Everything psychological is grounded in biology, but mind and brain are distinct levels of explanation.
The mind emerges from the brain’s activity, and there are limits to reductionism: some psychological phenomena are best understood at the level of the mind.
A balance between brain explains and mind-level meanings is needed to understand consciousness, memory, morality, and responsibility.
Quotation highlights: brains enable thoughts, but thoughts can influence brain structure and function; the relationship is bidirectional.