The study of brain lesions (damage to a particular part of the brain) has afforded important insights into the relationship between the brain and behaviour.

From very early observations of the fact that injury to one side of the brain leads to effects in the opposite (contralateral) side of the body, to modern research with MRI, the study of brain lesions has evolved from serendipitous discovery that damage to one part of the brain tends to produce a particular deficit, to a technique where lesions are sought out (or created) to test specific hypotheses about brain function.

However, there are some important limitations to lesion studies, and you will learn about these in the exercises below.

Problems with lesion studies- Example and questions

Example One

The diagram below represents three regions of a rat brain (labelled ‘A’, ‘B’ & ‘C’). A researcher has evidence that region ‘B’ is responsible for some function (let’s say the ability to recognise the smell of cheese

 
In order to test whether ‘B’ really is responsible, she inserts a small electrode into ‘B’ and passes electrical current to destroy ‘B’.

 Our researcher now finds that the rat cannot recognise the smell of cheese and concludes that are ‘B’ is indeed responsible for this ability.

BUT you (being a better researcher) are not so sure. You conduct a more thorough investigation of ‘B’ and discover that there are axons passing through ‘B’ but that do not seem to make any synapses with ‘B’ (see diagram below)

As shown in the diagram above, these axons pass between areas ‘A’ and ‘C’. These are referred to as ‘fibres of passage’ as they are just ‘passing through’ structure ‘B’ without making any functional connections there.

So when the previous researcher used the electrode to lesion area ‘B’ it is possible that she also damaged these fibres of passage.

 Q1.

a.     What is the alternative explanation for the finding that lesioning ‘B’ results in the rat not being able to smell cheese? (2 Marks)  

b.     How could you test your alternative explanation? (1Mark)

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