Does the deaf auditory cortex have a role in cognition?

When a sound is made in the environment, neurons fire in the auditory cortex of the brain, giving us the subjective experience of hearing. In congenitally deaf people, following a process known as crossmodal plasticity, this hearing machinery, rather than being redundant, is known to be used for functions such as vision and touch. However, my work suggests that the story may be more complicated. I have shown that the auditory cortex of the deaf is involved in working memory, the cognitive capacity that we use to keep and manipulate information in our mind. This finding suggests that the deaf auditory cortex may not only serve sensory functions, but also reorganise to become part of a cognitive control network.

How is it that activity in the same cortex results in different perceptual experiences in deaf and hearing individuals? Moreover, how does a cortex that evolved to respond to sounds change its function to respond not only to vision and touch, but also to take on higher cognitive functions such as working memory?
Proving these to be true would represent a profound change in our understanding of behaviour, cognition and the brain: namely that, as a consequence of sensory loss and neural reorganisation, parts of the brain that usually have sensory functions can change their role to primarily cognitive functions, and potentially modify our behaviour.

Using functional magnetic resonance imaging (fMRI) to measure neural function in deaf and hearing individuals, and machine learning techniques, I aim to address the following questions: Is the deaf auditory cortex involved in multiple cognitive functions? Can it represent abstract task rules across sensory modalities? Furthermore, can deaf individuals strategically allocate cognitive resources to the auditory cortex?

Over 5% of the world's population has a significant hearing loss, and results from this project will contribute evidence that can guide the development of better (re)habilitation and educational options to these individuals. Moreover, principles derived from this project can be applied to other types of sensory losses, and to the design of electronic devices that can restore missing brain functions (neural prostheses). Thus, this project will not only address a fundamental scientific question, but also has the potential of important benefits for society.

As a consequence of sensory deprivation early in life, affected sensory cortices respond to other senses - a process known as crossmodal plasticity. However, my research in human deafness suggests that typical auditory regions are also recruited for working memory. Can the deaf auditory cortex have a central role in cognitive control? To answer this, I will conduct 3 experiments in deaf (N=20-22) and hearing (N=20-22) individuals:

Experiment 1: Visual tasks that tap into several cognitive functions (working memory, inhibition, planning and task switching) will be conducted using fMRI, showing whether the auditory cortex is recruited during performance of these tasks in deaf individuals.

Experiment 2: fMRI and machine learning algorithms (MVPA) will be used to decode task rules across visual and somatosensory modalities.

Experiment 3: fMRI and MVPA will be used to decode whether the deaf auditory cortex represents sensory information (visual features), and whether the representation is affected by distracting information.

There are two potential outcomes, both of which will provide ground-breaking results:

- Auditory cortex preserves its sensory role - the role of auditory cortex during working memory is specific for the storage of visual information. Thus, perceptual attributes are decoded successfully, but decoding is affected by the presence of distractors.

- Auditory cortex shifts its function towards cognition - all cognitive tasks activate this area, and task rules are decoded successfully from fMRI activity independently of the sensory nature of the stimuli. Based on my previous research, I hypothesise this outcome is more likely.

This research will show whether it is possible to have a functional shift towards cognition in a sensory cortex, not only challenging current assumptions on neural plasticity, but also with the potential to benefit people with sensorimotor deficits, including 800,000 deaf individuals in the UK.

I recognise the challenge in achieving social as well as academic impact, as I have demonstrated throughout my professional career by engaging with deaf individuals, their families, third sector organisations, government and professionals of different disciplines. I am wholly committed to achieving both types of impact, ensuring that the research of this project has an impact on the ways that organisations provide services, and on the experiences of people with sensory loss and those of their families.

The main groups benefiting from this research are:

Deaf and hard of hearing individuals; audiology and related services: Results from this study could be piloted as markers of cochlear implantation success. This will allow deaf and hard of hearing adults to make more informed choices about cochlear implantation, providing a better way of evaluating the odds of implantation success, and how they compare to the benefits they obtain from their current method and modality of communication. In the long term, this could translate into more effective and lower-cost practice in the medical sector.

Deaf children; parents, teachers of the deaf and speech and language therapists: Knowing the function of the auditory cortex in deaf individuals can provide a better understanding of the skills that deaf and hard of hearing children have or will develop. This in turn can be used to design teaching materials and interventions that are aimed at exploiting these skills, potentially improving academic achievement in these groups.

Policy makers and third sector: The project will provide these groups with evidence to inform their recommendations, potentially enhancing the quality of life of deaf individuals and their families, and of the wider community in general.

Private sector: For firms manufacturing auditory prostheses, functional knowledge of the deaf auditory cortex can aid the development of signal processing algorithms to exploit the computations that this cortex can perform.
Sensory substitution prostheses are designed assuming that the sensory cortices of individuals with congenital sensory losses will still be able to either:
- Respond up to a certain extent to the restored sensory modality (i.e. if hearing is restored in a deaf individual, neurons in the auditory cortex will respond to sound stimulation).
- Process sensory information from other modalities (i.e. if neurons in the auditory cortex of deaf individuals do not respond to sounds, they will respond to vision or touch).
This project could lead to a paradigm change, whereby prostheses and interventions will have to be designed taking into account a potential functional shift, in which the lack of early sensory stimulation resulted in these sensory cortices taking on cognitive control functions.
Furthermore, these results could be fundamental for the development of cortical hearing prostheses, which could provide sensory signals for those patients who are not eligible for cochlear implants and for whom brain stem implants are unsuccessful. These same principles can be applied to any other kind of neural prostheses, expanding the reach of this project to all types of sensory substitution and brain-machine interfaces.

Given its potential benefits, this project sits at the junction between scientific discoveries that influence mainstream research and the output of ideas that can produce important social impacts. As a result, the strategy for impact and engagement is specifically designed for the needs and expectations of all of these key stakeholders.