Lifetime Blindness and Neurodevelopment

[aj47]

As far as I understand, certain visual areas of the cortex (i.e. sensory and association) develop rapidly from birth through thier constant stimulation.

 

Anyway, if this is true then what would be the result of surgically removing cataracts from a person who has been blinded from birth. Would these areas slowly redevelop or is there an almost cut off point with neurodevelopment, which would result in the person seeing but having no spatial awareness etc?

[Glider]

Rather inhumane animal studies done some time ago showed that if animals (chimpanzees) are raised in a completely dark environment, they remain able to detect light but unable to detect any form of pattern (i.e. they are functionally blind) (see e.g. Riesen, 1947). Studies sisnce then have shown that being raised in the absence of visual stimuli causes neuronal atrpohy in parts of the visual system. These cells, if denied stimulation during the normal development period, remain unresponsive.

 

Further studies showed the specific nature of visual system development. For example, raising kittens in an environment containing only vertical stripes left the animal completely incapable of perciveing horizontal planes. Conversely, animals raised in environments containing only horizontal stimuli were blind to vertical stimuli (Blakemore, & Cooper, 1970).

 

These studies show that there is a critical period for the development of cells in the primary visual cortext and other related areas. Any damage, or failure in this development during this critical period is permanent.

 

In short, removing cataracts from a person who had been blinded by them sisnce birth would not make them see. They would be able to tell light from dark, but nothing else.

 

References:

 

Blakemore, C., and Cooper, G. F. (1970). Development of the brain depends on the visual environment. Nature, 228: 477-478. Cited in: Atkinson, R. L., Atkinson, R. C. Smith, E. E., Bem, D. J. and Hilgard, E. R. (1990). Introduction to Psychology (10th Ed.). USA: Harcourt Brace Jovanovich.

 

Reisen, A. H. (1947). The development of visual perception in man and chimpanzee. Science, 106, 107-108. Cited in: Atkinson, R. L., Atkinson, R. C. Smith, E. E., Bem, D. J. and Hilgard, E. R. (1990). Introduction to Psychology (10th Ed.). USA: Harcourt Brace Jovanovich.

[aj47]

So does this apply to all sensory or even motor areas of the cortex. For example, I remember hearing of cases where children who were raised with out any social contact, could not learn to speak as thier Brocca's and Wernike's areas were so underdeveloped. So in the same way, could lack of a certain stimuli at an early age result in neurological Anosmia or Deafness?

[Glider]

I don't think the same applies to motor function. Sensory systems require more overall integration and the 'output' of sensory systems is arguably more complex than the output of motor systems. I would think that if infants were raised 'swaddled' and unable to move, they could still learn to do so, although the learning would be slower and their motor skills and coordination would suffer. People learn to drive, play instruments, walk on stilts and a whole buch of other motor stuff long after the sensitive period of neurological growth.

 

Audition is not really comparable to vision. Those apes who were raised in the dark and were functionally blind could still see light and dark, they just couldn't percive any kind of patterns. With audition if you can hear sound, you are not deaf.

 

The visual system is a lot more complex. Beyond the promary primary visual cortex, there are cells in the visual system that have evolved to respond to very specific stimuli such as horizontal lines, vertical lines and so-on (i.e. differences in contrast at various angles). There are even individual cells that respond optimally to faces (face detection cells).

 

The auditory systems by contrast is a lot simpler. The coil of the cochlea is lined with detector cells. Each of these projects a hair into the cochlea and they are all the same. Vibration moves the hair and triggers the cell. What determines the frequency of the sound we hear is how far along the cochlea these cells are. Those responding more to low frequency are closer to the wide end (beginning) of the cochlea and those responding to higher frequencies towards the narrow end of the cochlea (where high frequency vibrations can reach). The cell speciallisation in the auditory system is a lot less than in the visual system.

 

I think, like the visual system, these very basic detectors would still function if an infant was raised with ear plugs. However, there may well be impairmant of the areas higher up the system that make sense of the sounds we detect. I suspect it would the higher integrative systems that would suffer.

 

Wernicke's and Broka's areas are more to do with language comprehension and production than plain audition. If they are damaged, the person becomes unable to understand language and their own language becomes garbled; grammar and syntax suffer, but the person can still hear.

[aj47]

Cheers Glider really interesting thanks.

[Glider]

You're welcome.

[michael]

As far as I understand, certain visual areas of the cortex (i.e. sensory and association) develop rapidly from birth through thier constant stimulation.

 

Anyway, if this is true then what would be the result of surgically removing cataracts from a person who has been blinded from birth. Would these areas slowly redevelop or is there an almost cut off point with neurodevelopment, which would result in the person seeing but having no spatial awareness etc?

The psyciatrist Dr Oliver Sacks has a number of case studies of sight being restored to people blind from birth.

They have enourmous difficulty adjusting, some saying they would prefer to stay blind

He suggests that the 'sight' parts of the brain are laid down early in life and if this does not happen in infancy, adults find it very difficult, if not impossible,to adjust to having sight.

 

I recommend all his books to you, very readabale, facinating studies

Sorry I can't remember which of hs many books discuss this .

[aj47]

The psyciatrist Dr Oliver Sacks has a number of case studies of sight being restored to people blind from birth.

They have enourmous difficulty adjusting, some saying they would prefer to stay blind

He suggests that the 'sight' parts of the brain are laid down early in life and if this does not happen in infancy, adults find it very difficult, if not impossible,to adjust to having sight.

 

I recommend all his books to you, very readabale, facinating studies

Sorry I can't remember which of hs many books discuss this .

 

Actually I asked this question on another forum and I was told 'An Anthropoligist on Mars' by Oliver Sacks in parts talks of Visual Agnonsia caused by childhood blindness, so I recently went out and bought it.

 

Although I havn't quite reached the relavant parts I also read 'The Man Who Mistook His Wife For a Hat' where he talks about Visual Agnosia and gives the example of the muscian who had trouble recognising faces after damaging areas of his visual cortex (hence the title of the book). But yea I agree Oliver Sacks books are facisnating.

[Glider]

The inability to recognise familiar faces is prosopagnosia.

[aj47]

Isn't prosopagnosia a just a specific type of Visual Agnosia though?

[Glider]

Yes, it's the inability to recognise familiar faces.

[michael]

But yea I agree Oliver Sacks books are facisnating.

Both those books are great.

I noticed, when I looked up what he has written, that he is very prolific.

 

While he is just telling his stories and not doing "Double Blind Clinical Trials"

He gives you more insight into psychiatric disease than almost anyone I know.