A new Kiwi study will attempt to reveal what happens to our brains when we take anti-depressants and whether these changes can be easily measured.

Despite the widespread prevalence of depression (one in seven Kiwis experience it before turning 24 years old) accepted treatments fail to work for around one-third of patients.

A lack of understanding around the biological causes of depression has hampered drug development but there's hope advances in brain imaging technology could offer new ways to measure the so-called "bio-markers" of central nervous system disorders.

These natural indicators in the brain could help scientists not only get to grips with what causes disorders such as depression, but how these disorders might be predicted and how treatments can be effectively evaluated.

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A project by a University of Auckland researcher will draw on widely-used brain imaging technology, MRI and electroencephalography (EEG), to measure bio-markers of signs of excitation and inhibition in the cortex.

The study would also hunt for changes in the brain's "neural plasticity"; something Rachael Sumner of the university's School of Psychology, expected to see increase after anti-depressants were taken.

"Neural plasticity is a term we use to describe learning and memory but it means learning and memory at every level of the brain," she said.

It meant the brain itself didn't grow larger but that neural pathways became better connected.

"So it's not simply learning one plus one equals two, but that the brain learns to function more effectively in everything that it does."

Reduced neural plasticity has been implicated in a number of brain-based disorders, including depression.

"Whether it mediates the anti-depressant response, however ... that's something we are still working out," Summers said.

To tease out brain signals, patients in the study would look at patterns and listen to tones that trigger visual or auditory activity.

"We'll be using an anti-depressant that we know works very quickly and should allow us to study the effects in a way that hasn't been done before."

Ultimately, she hoped identified changes in sensory neural plasticity could be used as bio-markers of general brain health in depression.

The study would also be one of the first in the world to search for these changes with the simultaneous use of MRI and EEG.

"A big part of it will be whether we can actually measure it with EEG, which is already in hospitals and clinically available."

Being able to use this technology, much more affordable to use than MRI or magnetoencephalography (MEG), could improve development of new drugs.

The two-year study has been supported with a grant from the Auckland Medical Research Foundation.

Depression in New Zealand

• One in seven Kiwis will experience depression before turning 24 years old. One in eight men will experience it, as will one in five women.

• One in five people with depression or anxiety will experience both at the same time.

• Figures released in 2012 by Pharmac showed one in 10 Kiwis are now prescribed anti-depressants.