Brain Hemispheres, Language, and Neurological Disorders
Brain Hemispheres and Contralateral Control
Each hemisphere, left (L) or right (R), controls the contralateral side of the body. Some movements, like facial expressions or movements of the trunk, are controlled by both hemispheres.
Speech production is controlled in the majority of people by the L hemisphere.
Hemispheric Communication
Hemispheres communicate by means of:
- Corpus Callosum
- Anterior commissure
- Hippocampal commissure
- Other small commissures
Cutting the Corpus Callosum
Cutting the Corpus Callosum avoids communication between R and L hemispheres. It is used for avoiding the spread of severe epilepsy.
Epilepsy
Epilepsy is a condition characterized by repeated episodes of excessive synchronized neural activity. It could be linked to alterations to the GABA neurotransmitter or its receptor.
Split Brain and Hemispheric Dominance
Split Brain patients in the first few weeks after surgery behave like two persons opposing. The L hemisphere tends to suppress the R hemisphere’s interference and manages some situations. In some cases, both hemispheres can cooperate.
Human Language and Animal Communication
Human language differs from other animals because of productivity: It is adaptive, creative, and unlimited.
Language in Nonhuman Species
Nonhuman species can have forms of communication but not language.
- Early attempts to develop language development in chimpanzees, in a form similar to humans, have not prospered. Example of Gua.
- Chimps lack the biological substrate necessary for language.
- Other efforts by means of visual communication have obtained better results.
- Chimps evolved to solve their environmental and proper problems.
- Some critics believe that chimps’ forms of communication are rather the product of a learning process than a real form of communication.
- Response: some chimps are able to generate novel responses (not previously taught).
- These “duck” observations and “words combinations” have been anecdotal and could be a product of imitation of trainers.
- Maybe Bonobos have more language potential compared to other chimpanzees.
- Differences in methods: observation and imitation compared to formal training.
Nonprimates and Language Learning
Alex, an African gray parrot, was trained to learn words in conjunction with specific objects.
- Alex was rewarded if he emitted sounds similar to the words.
- Later, Alex was able to learn spoken answers to spoken questions.
Insights from Non-Human Language Studies
What do these studies in non-humans tell us about language?
- Theory: Human language evolved from precursors in other species.
- Practice: It gives useful knowledge about how to teach language to those who do not learn easily, like autistics and people with brain damage.
Neurological Disorders
Dyslexia
Dyslexia is a specific impairment of reading in someone with intact vision and adequate skills. It is related to difficulty in converting symbols into sounds. It is more common in boys than girls and linked to at least four genes related to deficits in hearing or cognition.
- People with dyslexia have symmetrical cerebral cortexes. Normal individuals have asymmetry in the brain.
- Dyslexic subjects display lower levels of activity in the temporal and parietal cortex.
Types of Dyslexia
Types: Dysphonetic dyslexics and Dyseidetic dyslexics.
- Most dyslexics have auditory problems, a smaller number have deficits in eye movement, and some people have both problems.
Neglect Syndrome
Neglect syndrome: Damage in parts of the right hemisphere, and tendency to ignore the left side of the body.
- Damage to the R parietal cortex tends to cause neglect of the left part of his/her body.
- Damage to the R superior temporal cortex causes neglect of the left side of objects.