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Based on Hubel and Wiesel's research with newborn kittens, sensory deprivation during a critical developmental period can have lasting effects. In their experiment, one of a kitten's eyes was sutured closed. The area of the visual cortex that would normally receive input from that eye was instead taken over by the open eye. This demonstrates that neural connections present at birth can be lost if they do not receive sensory input, leading to functional blindness in the deprived eye.

Visual Deprivation Leads to Blindness

-In binocular deprivation experiments, both eyelids are sutured or frosted contact lenses are provided in order to prevent images from coming in to focus on the retina.

-Depriving animals of sight in both eyes leads to a loss of dendritic spines and a reduction of synapses in visual cortical neurons.

-If binocular deprivation occurs during the sensitive period, which is during the early period of synaptic development in the visual cortex, the animal is never able to recover their eyesight. 

-After the sensitive period, binocular deprivation has little to no effect. 

Binocular Deprivation Experiments 

-monocular deprivation produces structural and functional changes in the visual cortex and thalamus.

-Cortical neurons only respond to input from the nondeprived eye.

-During early development, active synapses in the visual cortex dominate over inactive synapses, thus, when one eye is deprived, synapses from that eye are retracted and the synapses from the nondeprived eye are maintained.

-Sensitive period for cats is the first four months of life and for rhesus monkeys the sensitive period six months.

-Ocular Dominance Histograms show the response of cells in the visual cortex under different conditions 

Monocular Deprivation

The research methods used in visual deprivation studies, such as suturing a kitten's eye closed, raise significant ethical questions. From an animal advocacy perspective, these procedures can be viewed as cruel and abusive. This view is often weighed against the potential for profound medical benefits, such as developing treatments to prevent blindness in human infants and children. This conflict creates a complex ethical dilemma, prompting consideration of different perspectives, such as those of a researcher, an animal welfare advocate, or the parent of a child who could benefit from the research.

Ethical Considerations of Visual Deprivation Experiments

A child is born with a dense cataract in their left eye that completely blocks patterned light from reaching the retina. The right eye is healthy and functions normally. The cataract is not surgically removed until the child is 8 years old. Based on principles of how sensory experience shapes neural connections, what is the most likely long-term outcome for the vision in the child's left eye after the surgery, and why?

Predicting Visual Outcomes Based on Early Development

An infant is born with a dense cataract in their left eye, completely blocking light from reaching the retina. The cataract is surgically removed when the child is 5 years old, restoring a perfectly clear lens. Despite the successful surgery, the child has significant and permanent vision impairment in the left eye. What is the most likely neurological explanation for this outcome?

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