Approximately 70% of people with refractory temporal lobe epilepsy (TLE) - TLE that is unresponsive to antiepileptic drugs - will benefit from a procedure called anterior temporal lobe resection (ATLR) to remove the front part of the affected temporal lobe. However, people often experience emotional disturbances, such as anxiety and depression, as a side-effect of this type of surgery.

The amygdalae of the brain, which are found in the temporal lobes (one on each side), play a large role in the processing of emotions. They are frequently removed as part of ATLRs, or can be damaged in the process, explaining the emotional effects often seen after this operation. These effects are pronounced if the person's brain relied heavily on the affected amygdala for emotional processing prior to surgery.

Clinically it is possible to measure the level of activity in each amygdala, using a special type of imaging called functional magnetic resonance imaging (fMRI).

Researchers at University College London, UK, have been investigating whether fMRI of the amygdalae before ATLR, can be used to predict who will suffer emotional disturbances after surgery.

They recruited 54 patients with TLE (28 with right TLE and 26 with left TLE) and 21 healthy controls. Each person underwent fMRI whilst looking at a series of fearful and neutral faces, intended to stimulate emotion and hence activity in the amygdalae. 21 of the patients with TLE (10 left-sided and 11 right-sided) were assessed for signs of anxiety and depression, using a standard measuring tool. These people then had ATLR surgery on the affected side. Four months after their operations, they were assessed for anxiety and depression again.

The scientists discovered that in healthy controls, the left amygdala became more active when they were shown fearful faces; whereas in right TLE patients, both amygdalae were activated. Interestingly, left TLE patients had reduced activity in both amygdalae, compared to healthy controls and right TLE patients.

These results suggest that people with right TLE are at greater risk of emotional side-effects after ATLR than those with left TLE. This is because in right TLE, the amygdala of the affected temporal lobe plays significant role in emotional processing before surgery, which is not the case in left TLE.

The researchers also found that before surgery in patients with right TLE, the amygdalae became more active upon stimulation if the person was more depressed or anxious. Furthermore, the right TLE patients who had more active amygdalae before their operation generally had even higher anxiety and depression scores four months after surgery. This pattern was not seen in people with left TLE.

Although this study is not conclusive, the results identify people with right TLE who are anxious or depressed, as being most at risk of emotional disturbances after ATLR.

In the future, fMRI could be a very useful clinical tool when deciding whether to refer people for this type of surgery.

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