Christian Jarrett in Wired, via Andrew Sullivan:
[A] pair of neuroscientists in London have published a welcome review in the respected journal Current Biology entitled “What we know currently about mirror neurons.” In contrast to the hype that usually surrounds these cells, James Kilner and Roger Lemon at UCL have taken a calm, objective look at the literature.
They acknowledge that it is difficult to interpret mirror neuron activity in humans (using brain imaging) and so they focus on the 25 papers that have involved the direct recording of individual brain cells in monkeys. This research reveals that motor cells with mirror-like properties are found in parts of the front of the brain involved in motor control (so-called premotor regions and in the primary motor cortex) and also in the parietal lobe near the crown of the head.
Reading their paper it soon becomes clear that the term “mirror neurons” conceals a complex mix of cell types. Some motor cells only show mirror-like responses when a monkey sees a live performer in front of them; other cells are also responsive to movements seen on video. Some mirror neurons appear to be fussy – they only respond to a very specific type of action; others are less specific and respond to a far broader range of observed movements. There are even some mirror neurons that are activated by the sound of a particular movement. Others show mirror suppression – that is their activity is reduced during action observation. Another study found evidence in monkeys of touch-sensitive neurons that respond to the sight of another animal being touched in the same location (Ramachandran calls these “Gandhi cells” because he says they dissolve the barriers between human beings).
Importantly, Kilner and Lemon also highlight findings from monkeys showing how the activity of mirror neurons is modulated by such factors as the angle of view, the reward value of the observed movement, and the overall goal of a movement, such as whether it is intended to grasp an object or place it in the mouth. These findings are significant because they show how mirror neurons are not merely activated by incoming sensory information, but also by formulations developed elsewhere in the brain about the meaning of what is being observed.
More here.