Here is the video and a short summary of Professor Joanne Fielding’s presentation at the 2018 Visual Snow Conference event. She talks about how looking at behavioural variables provides insights into Visual Snow.
Visual Snow Conference
In total there are five presentations from the Visual Snow Conference that I have chosen to write about. I recommend that you read about them/watch the videos in this order. The first two are more general, the last three go into more complex detail. If you have already seen some of the videos I recommend that you watch them again anyway, as it is easy to miss certain details.
1. Four Myths About Visual Snow (Peter Goadsby)
2. Visual Snow And Sensory Misperception (Owen White)
3. Behavioural Research Into Visual Snow (Joanne Fielding)
4. The Origins Of Visual Snow (James T. Fulton)
5. Visual Snow And Visual Pathways (Viktoria Pelak)
* These are not necessarily the presentation titles the authors used at the event
Visual Snow And Cognitive Behaviour
Fielding says that they have an interdisciplinary team working on Visual Snow. They are interested in looking at visual and ocular motor systems to work out how the brain works and why it may not work as it should.
At first glance she says we might think that Visual Snow has nothing to do with behaviour – it would seem to involve perception rather than cognition. Indeed as Peter Goadsby was saying she emphasizes that Visual Snow is not a behaviour or something imaginary related to aberrant thinking. Though as Owen White her colleague also mentioned in his presentation: cognition and behaviour are influenced by the functioning of the brain (and vision).
Our senses, experiences, beliefs, and expectations all guide adaptive behaviour and therefore she says network changes can be measured behaviourally provided that the right questions are asked.
Visual Snow And Attentional Networks
Fielding explains that half of the brain is effectively involved in vision. There is the well known visual pathway from the retina to the visual cortices, but many other regions of brain are also involved in vision, and cognitive areas interpret visual information too. Together they form an extensive and integrated network.
The parietal region of brain for example constructs spacial coordinates of world around us. Pre-frontal cortices make sense of visual information and influence top-down visual activity. These two interconnecting subnetworks (parietal and pre-frontal) according to stimulus properties (response driven and bottom up i.e. reflexive) and expectations/goals (cognition driven top down i.e. volitional) integrate information and construct a “priority map”. Stimuli are given attentional priority that is reflected in neural activity. This so called priority map modulates processing in all visual areas.
Attention is a selection process for the brain to focus on what is important she says, it underlies much of what happens within the brain. Relevant information has to be processed, and irrelevant information has to be filtered out. In Visual Snow Syndrome there is the idea of heightened neuronal sensitivity/cortical hyperexcitability. Fielding says that this cortical excitability could also actually also be the result of reduced inhibitory control.
Measuring Network Changes In Visual Snow
Measuring subtle changes to complex and interconnected network function that might be involved in Visual Snow is a challenge. Though it turns out the networks involved in programming attention are the same as those in programming a saccade – a rapid eye movement to change focus of vision. Therefore by looking at eye movements Fielding and her colleagues can measure where attention is directed. They can also with the help of technology manipulate attention using visual stimuli and then measure the response. This (the attentional network) she says is a well defined system and set of processes, it also allows for a sensitive means (saccades) to interrogate and measure those processes in those with Visual Snow.
Hyperexcitable Responses In Those With Visual Snow
Fielding explains the types of saccade experiments that they use and how they work. In “antisaccades” people are told to focus on a cross at centre of screen, then they are told to look away. This is actually quite difficult Fielding says because you need to inhibit a reflexive response and instead facilitate a volitional response. This attentional response supresses activity across the whole visual field. Using brain imaging, they have found that this involves consistent activation of frontal and parietal projections to the brain stem. So, the two areas of interest that Fielding had already mentioned.
Fielding says those with Visual Snow show a higher proportion of directional errors: that is they move the eye towards rather than away from cross. They also display shorter latencies, which means that they made the movement quicker when they did so.
This she says means that the cognitively driven stop process fails to inhibit a stimulus driven response. If the stop process is ok, then the cognitively driven saccade releases more quickly. This implies hyperexcitability or reduced inhibitory control of parts of brain controlling eye movement
“Endogenously cued saccades” require people look at a cross as it pops up on screen. A directional cue (arrow) is presented, and most of the time it correctly predicts the location of the cross. This sets up a degree of expectation, so shorter latencies are to be expected. It increases activity so neurons are ready to fire (i.e. given attentional priority).
In those with Visual Snow there is no change in directional errors or effect of the cue compared to controls. Shorter latencies remain and the missing cue effect in those with Visual Snow shows that expectation is insufficient to modulate a stimulus driven response. Those with Visual Snow seem to display an hyperexcitable stimulus driven response. This she says could be due to top-down fronto-parietal processes that are poorly modulating the stimulus driven responses. Fielding speculates that they could also fail to modulate a virtual visual phenomenon (Visual Snow).
This current work Fielding says doesn’t localise a dysfunction in Visual Snow but demonstrates a capacity to measure change. She says that they will be using more sophisticated paradigms, techniques, and tasks in combination with brain imaging to improve knowledge of Visual Snow:
- Refining the attentional profile and disentangling hyperexcitability from disinhibition
- Characterising and locating dysfunctional mechanisms
- Disassociating performance of those with Visual Snow versus migraine. Fielding says that they have tested those with and without migraine and there is a clear dissascociation.
- Assessing levels of “stop and go” neurotransmitters (e.g. GABA, Glutamate)
This clever research can help greatly towards understanding Visual Snow as well as being able to measure and quantify the condition. If anybody lives locally in Melbourne Australia I would recommend that they get involved in this project.
Although not immediately related to this team’s work – it would be interesting to see research also start to explore how having Visual Snow might as a Syndrome affect behaviour in the sense of anxiety or depersonalisation, or if there is any greater interaction with the other senses.