The world around us changes all the time, and the brain must adapt to these changes. This process, known as neuroplasticity, peaks during development. Abnormal sensory input early in life can therefore cause lasting changes to the structure of the brain.
One example of this is amblyopia or ‘lazy eye’. Infants who receive insufficient input to one eye – for example, because of cataracts – can lose their sight in that eye, even if the cataracts are later removed. This is because the brain reorganizes itself to ignore messages from the affected eye.
Does the adult visual system also show neuroplasticity? To explore this question, Paola Binda from the University of Pisa, along with Jan W Kurzawski from the University of Florence, and colleagues asked healthy adult volunteers to lie inside a high-resolution brain scanner with a patch covering one eye.
Ventral Visual Stream
At the start of the experiment, roughly half of the brain’s primary visual cortex responded to sensory input from each eye. But when the volunteers removed the patch two hours later, this was no longer the case.
Some areas of the visual cortex that had previously responded to stimuli presented to the non-patched eye now responded to stimuli presented to the patched eye instead. The patched eye had also become more sensitive to visual stimuli.
[caption id="attachment_98125” align="aligncenter” width="680”] Monocular deprivation modulates 7T BOLD responses in early visual cortex.
Credit: Binda, Kurzawski et al. CC-BY[/caption]
Indeed, these changes in visual sensitivity correlated with changes in brain activity in a pathway called the ventral visual stream. This pathway processes the fine details of images.
Groups of neurons within this pathway that responded to stimuli presented to the patched eye were more sensitive to fine details after patching than before.
Visual Perception Abilities
Visual regions of the adult brain thus retain a high degree of neuroplasticity. They adapt rapidly to changes in the environment, in this case by increasing their activity to compensate for a lack of input.
Notably, these changes are in the opposite direction to those that occur as a result of visual deprivation during development. This has important implications because lazy eye syndrome is currently considered untreatable in adulthood.
The data demonstrates that two hours of abnormally unbalanced visual experience is sufficient to induce a functional reorganization of cortical circuits, particularly of the parvocellular pathway, leading to an alteration of basic visual perceptual abilities.
The research was supported by the European Research Council under the European Union’s Seventh Framework Programme and under ERA-NET project ‘Neuro-DREAM’ and by the European Union’s Horizon 2020 Research and Innovation Programme under a Marie Sklodowska-Curie grant, and by the Italian Ministry of University and Research, Fondazione Roma under the Grants for Biomedical Research: Retinitis Pigmentosa (RP)-Call for proposals 2013- ‘Cortical Plasticity in Retinitis Pigmentosa: an Integrated Study from Animal Models to Humans’.
Paola Binda, Jan W Kurzawski, Claudia Lunghi, Laura Biagi, Michela Tosetti, Maria Concetta Morrone Response to short-term deprivation of the human adult visual cortex measured with 7T BOLD eLife 2018;7:e40014 DOI: 10.7554/eLife.40014
Authors: Binda, Kurzawski et al. © 2018, Binda et al. Republished via Creative Commons Attribution License. Top Image: Binda, Kurzawski et al. CC-BY