Bulletin

Issue: September 2005

Research in Action

Uneven pattern of alcohol's effect on the brain

Scientifically, getting a little under the weather is not just a question of our whole brain becoming numbed so that our central nervous system relaxes and makes us feel good.

Research at La Trobe University using eye movements to indicate alcohol's effect on the brain, has produced a surprise result not previously suspected ?| that alcohol taken at relatively low to moderate levels does not appear to depress the whole brain evenly.

Carefully measured doses of alcohol given in a strictly controlled exercise to healthy young male students affected only their posterior cortex – that part located at the rear of the brain which controls reflexive eye movement.

The frontal cortex, the part in the front of their brain which controls voluntary eye movement, was unaffected.

Reflexive movements are those which are used to respond to a stimulus such as the sudden arrival of something into our field of vision while voluntary movement relies on other, less obvious factors.

'The mechanism by which alcohol can affect different parts of the brain is still not fully understood and much more work needs to be done in this area,' says Dr Suzane Vassallo, who carried out the test as part of research for her PhD thesis.

An orthoptist specialising in saccadic eye movement control, Dr Vassallo is an associate lecturer and honours year co-ordinator in La Trobe's Department of Clinical Vision Sciences.

She explained that because our eyes are an extension of our brain, recording eye movements is an effective way to determine brain function. Different types of eye movement reflect activity in different parts of the brain so what happens in these parts of the brain can be gauged by analysing eye movement.

'There is some literature on the effects of alcohol on different eye movements but nothing had previously been done to ascertain the effect of alcohol on different saccadic types in the one population. A saccade is a fast eye movement, like the jerky movement we make as we look from one word to the next while reading,' she said.

With her supervisor, Dr Larry Abel, Dr Vassallo recruited 104 young healthy male student volunteers, most of whom were more than willing to participate. They were divided into four groups.

One acted as the control group and knowingly consumed no alcohol. Members of the second group thought they were drinking alcohol, but were given an effective liquid placebo instead.

Members of the third group drank 1.2 millilitres of alcohol (Vodka) per kilogram of their body weight giving them an average blood alcohol concentration (BAC) of 0.045%. Members of the fourth group drank 2.1 millilitres of alcohol per kilogram of body weight for an average BAC of 0.071%.

Before drinking the alcohol or placebo they were given a battery of eye movement tasks which were recorded using 'infra-red eye movement spectacles' to measures the emission and reception of infra red light. The tests were repeated after consuming the alcohol or placebo.

The device uses two probes – one before each eye – which measures the infra red light absorbed by the coloured part of the eye, the iris and that reflected by the white part, the sclera.

Data thus gained was processed and provided information on the latency – the length of time the brain takes to process the information and tell the eye to move. It also provided information on the speed of the eye movement and its accuracy: whether the eye reached its target or not.

'For the first time in any research of this nature we found that alcohol produced a detrimental effect on the function of the posterior cortex but none we could ascertain on the frontal cortex,' Dr Vassallo said.

'Alcohol is a readily available and widely used recreational drug and our research adds to the pool of knowledge about its effects on the brain. However the mechanism by which it can affect the operation of different parts of the brain differently is not fully understood,' she said.

In using a breathalyser to test the volunteers' blood alcohol concentrations, Dr Vassallo came across an interesting sidelight on the research.

'This was the difference in blood alcohol concentrations recorded among those who had consumed the same amount of alcohol. Those taking the low dose had concentrations between 0.02% and 0.07% BAC and those consuming the higher dose yielded results which ranged from 0.04% to 0.126% BAC. '

'It just went to show that we were at the mercy of our participants' livers', Dr Vassallo said.