A medical team at Frenchay Hospital in Bristol is pioneering a new form of surgery to treat long term depression.

The technique, deep brain stimulation, involves the use of electrodes which are implanted into the brain through holes drilled in the skull.

The electrodes are attached to a battery pack which delivers small amounts of electricity to stimulate or inhibit specific areas in the brain.

A trial is comparing the effects of stimulating two different brain areas.

The first patient to have the electrodes inserted was Sheila Cook, 62, from Torquay who had been suffering from severe depression for nine years.

She says: "I just wanted life to end. It was like being in a dark tunnel, but instead of there being light at the end of it, it was just darkness."

In Sheila's case the deep brain stimulation only had a short term benefit so she went on to have a second operation, called ablative surgery, to further improve her condition.

She says: "I suddenly woke up in the morning and I thought I feel different, I want to get up, I want to do things. And my whole view of life changed."

The research team hopes that deep brain stimulation might one day replace the more destructive ablative surgery that Sheila received.

The results from seven further participants on the trial will be published later in the year.

A programme about the surgery was featured by BBC Inside Out West on Monday 24 January - BBC One at 19:30 - and nationwide on BBC iPlayer.