17 Mar 2017

Review shines light on eye movement research

Jessica Myles, first author on the study
on eye movement and schizotypy
by Anne Crawford

When 2014 Honours year student Jessica Myles (pictured) started a review of the literature about eye movements and schizotypy in 2014 she had little idea that the project would take her two years and would mean trawling through more than 900 abstracts and articles. “It was a behemoth!” she joked.

Ms Myles’ 22-page paper appeared in the journal ‘Neuroscience and Biobehavioral Reviews’ last month. Overseen by Dr Caroline Gurvich and Adjunct Associate Professor Susan Rossell at the Monash Alfred Psychiatry research centre (MAPrc), the systematic review identified, collated and appraised eye movement studies involving behavioural, neuroimaging and genetic data in individuals with high schizotypy and first-degree relatives of schizophrenia patients, published between 1980 and September 2016.

Schizophrenia is now increasingly viewed in terms of a continuum across the general population rather than as a stand-alone disorder. Schizotypy sits somewhere below a formal diagnosis of schizophrenia but above the average levels of symptoms in the community.  People with high schizotypy are fully functioning individuals who may be creative or spiritual and may have interpersonal issues or issues with cognition.

Impaired eye movements are one of the behavioural hallmarks of schizophrenia, particularly when it comes to what’s called an antisaccade task. In an antisaccade task, the participant is asked to look at a central dot on a screen, then look away when something is flashed in the peripheral area. Failing to inhibit the natural impulse to look at something eye-catching is counted as an error.

Although this had been widely tested on people with schizophrenia, less saccade research had been conducted on the broader schizophrenia continuum, for people with high schizotypy and for first-degree relatives, Ms Myles said.

Research shows that patients with schizophrenia have an error rate on antisaccade tasks of 20–75% compared to a rate of 9–47% in the general population. The literature review  found that those with high schizotypy had an error rate of 6–49% and first degree relatives a rate of 10–68%.

People with schizophrenia also perform less well than the general population on memory- guided saccarade tasks – when they are asked to remember where something flashed on the periphery of the screen after it has gone. Relatives appear to have similar deficits, but no one has investigated memory-guided performance for people with high schizotypy.

“What’s interesting about this, as well as the reason why it’s happening, is that shared areas of brain are affected in both tasks,” Ms Myles said. “So by looking at eye movement we can see what’s happening in certain areas of the brain like the prefrontal cortex,” she said.

The research revealed some valuable aspects of ‘confounds’; variables the researchers had failed to control or eliminate in the past. Rates of nicotine use in participants, for example, could affect results as this improved performance in the tasks. Knowing this meant that researchers could recognise this factor in the future and control for it.

While the examination of eye movements can’t directly be used as a diagnostic tool – antisaccade performance deficits have been identified in other disorders, such as bipolar disorder and major depression – it could help researchers understand the genetic components of schizophrenia and inform areas such as medication, Ms Myles said.

Understanding schizotypy can be used as an analogue to give insights into the symptoms of schizophrenia without the complications of hospitalisation, social isolation and medications associated with the disorder, she said.

Ms Myles, who has continued with MAPrc as a researcher after successfully completing her Honours year, is undertaking her PhD at Latrobe University. She hopes to compare the saccade performance of people with schizophrenia and people with high schizotypy, which hasn’t been done previously.

Myles JB, Rossell SL, Phillipou A, Thomas E, Gurvich C. Insights to the schizophrenia continuum: A systematic review of saccadic eye movements in schizotypy and biological relatives of schizophrenia patients. Neurosci Biobehav Rev. 2017 Jan;72:278-300. doi: 10.1016/j.neubiorev.2016.10.034. Epub 2016 Dec 1.

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