Bilateral visual field maps in a patient with only one hemisphere

Area of Science:

• Neuroscience
• Developmental Biology
• Visual System Research

Background:

• Mammalian visual processing typically involves contralateral mapping of visual fields to cerebral hemispheres.
• Retinotopic maps are established along the visual pathway, including the lateral geniculate nucleus (LGN) and early visual areas (V1-V3).

Observation:

• A patient was studied who was born with only a left cerebral hemisphere due to the termination of right hemisphere development before the seventh embryonic week.
• Despite the absence of the right hemisphere, the patient's left hemisphere developed retinotopic maps for both the contralateral (right) and ipsilateral (left) visual hemifields.

Findings:

• Retinal ganglion cells altered their optic chiasm crossing patterns to innervate the ipsilateral LGN.
• In the visual cortex (V1-V3), ipsilateral visual field representations were found, overlapping or invading cortical areas.
• Specifically, V1 showed continuous overlapping maps of both hemifields, while V2 and V3 displayed distinct patches of ipsilateral quarter-field representations.

Implications:

• This case demonstrates remarkable plasticity in the self-organizing mechanisms of brain development.
• It challenges established principles of visual map formation and hemispheric specialization.
• Suggests that developmental pathways can adapt to extreme structural alterations, leading to unexpected functional organization.