Phantom limbs are always good value for a news story. The whole concept of people missing limbs still feeling them, and feeling pain in them, is baffling.

A study published this week in the prestigious NEJM examines the even stranger concept of ‘mirror therapy’, where the amputee is shown a mirror image of their existing limb in the position their missing limb once was. This appears to be the amputated limb and some previous studies have suggested this can help with pain relief (Ramachandran 1996 and MacLachlan 2004, for example).

The new study took 22 amputees and assigned them to either mirror therapy, therapy with a covered mirror or mental visualization (ie, no mirror). After four weeks everyone in the first group reported decreased pain, in the other two groups results were mixed. After four weeks everyone was switched to mirror therapy and all groups reported positive results after another four weeks.

“The majority of people got some relief. The range went from some relief to completely gone. We were surprised that the effect was so strongly positive,” Navy neurologist Jack Tsao told Reuters. “It’s certainly my hope that more rehab centers will try this.”

Now someone just needs to work out why it happens. There are some theories. The paper notes it could be to do with mirror neurons being activated in the hemisphere of the brain contralateral to the missing limb. It could also be due to visual input of a supposedly moving limb. However the paper concludes: “the underlying mechanism accounting for the success of this therapy remains to be elucidated”. This is medical speak for “we really don’t know”.

Image: Getty