The Functional Dissection of Motion Processing Pathways in the Human Visual Cortex: An fMRI-guided TMS Study

The development of modern brain imaging techniques, such as functional magnetic resonance imaging (fMRI), has given neuroscientists unparalleled access to the inner workings of the living human brain. Visual processing in particular has proven to be particularly amenable to study with fMRI. Studies using this technique have revealed the existence of different networks in the brain that are activated by different kinds of visual stimuli, such as motion, colour, faces, objects and so forth.
In this research project we are interested in how the brain analyses information about moving stimuli. The analysis of motion within our visual environment is vitally important to our interaction with the outside world. It provides us with a rich source of information that helps us orientate ourselves within our surroundings, aiding in the avoidance as well as in the recognition of objects as we move around in this environment. The importance of motion perception is reflected by the fact brain imaging experiments reveal that when we look at moving stimuli, this generates neural activity across a large number of visual areas within the brain.
Many of these brain areas contain their own individual representation of the outside world or visual field. But it seems unlikely, not to say inefficient, that each of these brain areas performs exactly the same kind of analysis and contributes in exactly the same way to our perception of motion. Yet precisely what roles these different areas do play in our perception of motion, is far from clear. Whilst fMRI provides us with an excellent means by which we can localise and map different areas across the visual brain, it is less well suited to providing information as to whether neural activity within a particular brain area is crucial for perception or behaviour. However, these kinds of direct or causal links can be made when fMRI is combined with transcranial magnetic stimulation (TMS). TMS is a non-invasive and non-harmful technique which can bring about transient disruption of neural function in small areas of the brain. If this neural activity is important for perception, then its disruption can induce impairments in the ability of human observers to performance specific visual tasks, such a determining the direction motion of stimulus, for example.
Experimental evidence from the monkey brain has shown that different motion areas are responsive to different kinds of moving stimuli such as left-right (translational) motion, optic flow (a kind of radial motion produced on the retina as we physically move through our environment) or boundaries defined by moving stimuli. This work has provided a theoretical framework within which the organisation of motion processing can be studied in the human brain. Using our fMRI-guided TMS approach we aim to establish direct relationships between neural activity within particular brain areas and the ability to perceive different kinds of moving stimuli. In so doing we aim to provide a more complete description as to how each of these brain areas that are responsive to motion contribute to its perception.

Moving visual stimuli elicit neural activity across an extensive network of human brain areas, suggesting that the analysis of motion is dependent upon multiple processing pathways. In this respect, the organisation of human motion processing mirrors that found in the monkey brain, where the existence of separate functional networks for the analysis of different kinds of motion stimuli (e.g. translational motion and optic flow) has been demonstrated.

Using a combination of neuroimaging (fMRI), neurostimulation (TMS) and psychophysical techniques the purpose of this research is to establish casual links between neural activity in human brain areas and specific aspects of motion perception. Our methodology enables us to identify and localise specific visual areas, disrupt neural activity and then measure the behavioural consequences of this disruption. Establishing causal relationships between brain activity and behaviour in this manner is important because at present fMRI can only provide correlative links. We will begin with area V5/MT+ where the existence of functional sub-divisions for the analysis of different types of moving stimuli has yet to be conclusively demonstrated in the human brain. Beyond V5/MT+ we will then go on to map out the processing pathways for different motion stimulus types and elucidate the differential contributions of other brain areas that are responsive to motion.

We will also use multi-variate pattern analysis (MVPA) to examine fMRI motion localiser datasets that we will obtain during the project. MVPA provides a complimentary approach which will be used to test whether we can capture relationships between patterns of fMRI responses generated by different types of motion stimuli and use this information to reliably decode what kind of stimulus was being viewed. This combination of methodologies will provide a clearer understanding as to how and what cortical areas contribute to the perception of moving stimuli in the human brain.

The work to be carried out in this proposal constitutes basic neuroscience relating to human brain function and perception. The major advances of this work will lie in the elucidation of how neural activity in different areas of the brain contributes to the perception of different types of moving stimuli. The outcomes may be of potential interest to a variety of different user groups:
- computational neuroscientists interested in biologically inspired models of motion processing,
- engineers interested in artificial vision and automotive control of steering,
- clinicians who deal with patients with visual deficits caused by brain damage
- the general public who have a general interest in how the human brain works.

Whilst there may not be any obvious and immediate commercially exploitable outcomes of this research we will engage with commercial partners (some of which we have worked with previously) in order to identify any potential avenues for development. In order to reach these groups and ensure that any outcomes of this research are fully exploited the pathways we intend to use

1) Impact Symposia - these will take place at the end of years 2 & 3 of the project and will constitute a forum for discussion with potential academic, commercial and clinical user groups. The purpose of these symposia will be two-fold: firstly, to engage technology industries and researchers in the areas of computational vision and robotics in order identify the commercial and scientifically exploitable aspects of this research. Secondly, the symposia will provide an opportunity to engage with clinical neurologists and neuropsychologists in order to fully explore and exploit the possible clinical benefits of this research.

2) Interactive Public Engagement Activity - The human brain continues to be a subject of fascination and interest to the public. As such, this research provides an opportunity to inform a wider non-scientific audience about the neural processing that underpins visual perception in humans. This will be achieved via public lectures and schools visits and will be a continuation of the applicants' established working practices. Specific to this project we also intend to produce a public facing website which will describe our experiments and provide resources about brain function and motion perception.

In order to facilitate impact outside the immediate research area of the study the applicants will work in conjunction with the University of Bradford's Research and Knowledge Transfer Support Office and the University of York's Research and Enterprise Office. Their expertise will be used to identify any possibilities in this area and develop any possible commercial potential. Alongside clinical, academic and commercial end users of this research members of these offices will be asked to sit on an Impact Advisory Group for this project which will meet at the end of year 2 and 3 (immediately after the impact symposia) to formulate guidance on impact activities. These impact pathways will operate in parallel with the standard methods of engagement with our academic colleagues through publication in peer reviewed journals, depositing data and models in public repositories and by presentation of our work at meetings and in invited talks.