Plasticity in blindness
How is the brain reorganised in the absence of light?
Our group of researchers in the University of Oxford, Holly Bridge, Kate Watkins, Iona Alexander and Gaelle Coullon, have been investigating the brain structure and function in a group of bilaterally anophthalmic individuals. Anophthalmia is a condition where the eyes fail to develop, resulting in complete blindness when both eyes are affected. We are investigating how the brain copes with blindness, particularly what happens to the large part of the brain that typically processes vision.
MRI is a type of brain scan that allows us to see how the brain is organised, processes information and performs skills like vision, speech or memory. This scan is safe and does not involve any needles or injections. Structural imaging is being employed to investigate differences in neural connections and brain structures between anophthalmic and sighted people, with particular interest in changes in areas associated with visual processing. Functional imaging is being used to investigate functional differences in processing in people with anopthalmia, including whether areas usually for visual processing are used for something else.
Structural Imaging in Anophthalmia
We have looked at differences in the size and shape of brain structures due to anophthalmia and how it affects the way brain areas physically connect with each other.
Our results showed that, in fact, the brain of people with anophthalmia were very similar in structure to those of sighted people but there were two striking differences:
- The cortex normally dedicated to visual processing was thicker in anophthalmia
- This 'visual' cortex was also, and unusually, connected differently with other brain areas.
Language Networks in Anophthalmia
To investigate the involvement of 'visual' brain areas in language processing, we asked our participants to perform a language task where they listened to short statements, such as 'Bees make it' and were required to think of a word that matched the description, e.g. 'honey'. We compared brain activity when listening and thinking about words to that when the same people heard the descriptions played backwards (which are impossible to understand). In the anophthalmic volunteers, in addition to the 'language' areas typically activated when listening to speech and thinking about words, some parts of the brain normally processing only visual information were also activated.
- Primary visual cortex was active whenever participants listened, irrespective of whether they heard a speech description they could understand or one played backwards that they could not. We concluded that in bilateral anophthalmia where there is no visual input, primary visual cortex may do early-stage auditory processing instead.
- Lateral occipital cortex (LOC) was activated when the anophthalmic participants heard descriptions they could understand but not when they just listened to backwards speech. In sighted people, LOC is activated when they see recognisable objects and shapes. This area appears to have strong connections with the 'language' areas in anophthalmic people.
Currently, we are aiming to extend the scope of our research beyond people with anophthalmia to include other individuals who are blind since birth.
We are looking for healthy volunteers who lost visual function before the age of 12 months to improve our understanding of how the brain processes information when there is no input to the visual system. In particular we would like to investigate how your brain uses the areas that are normally used for seeing. The study would consist of up to 3 MRI scan sessions of around 1 hour. You would be asked to lie still in a scanner and perform some simple tasks like listening to tones, touching objects or generating words.
Participate in Research
Who are we looking for? Healthy fluent English-speaking men or women who have become blind prior to age 12 months, now aged 18-60, who do not have any metal in their head or body (except fillings), are not pregnant, have not had surgery in the past three months, and do not have any metallic implants (e.g. a pacemaker). If you are interested and would like more information, please contact us at the FMRIB Centre, John Radcliffe Hospital, Oxford on firstname.lastname@example.org.