Last year I suggested that mirror neurons are the most hyped concept in neuroscience. Discovered in the 90s by neuroscientists in Italy studying monkeys, these are motor cells in the brain (involved in the control of movement) that are also activated – mirror-like – by the sight of the same movement by others. Thankfully a new open access review has just been published that provides us with a calm update on what we know so far about these fascinating cells.

First, here’s some background on the hype. Neuroscientist V.S. Ramachandran says these cells shaped our civilisation; in fact he says they underlie what it is to be human – being responsible for our powers of empathy, language and the emergence of human culture, including the widespread use of tools and fire. When mirror neurons don’t work properly, Ramachandran believes the result is autism.

For the record, a detailed investigation earlier this year found little evidence to support his theory about autism. Other experts have debunked Ramachandran’s claims linking mirror neurons to the birth of human culture. The activity of mirror neurons can be altered by simple and brief training tasks showing that these cells are just as likely to have been shaped by culture as the shaper of it.

The exaggerated and oversimplified story about mirror neurons has been swallowed whole by the media and much of the public. For a blast of this neuro-bunk try searching for “mirror neurons” on the Daily Mail website. For instance, the paper ran an article earlier this year that claimed the most popular romantic films are distinguished by the fact they activate our mirror neurons. Another claimed that it's thanks to mirror neurons that hospital patients benefit from having visitors. In fact, there is no scientific research that directly backs either of these claims, both of which represent reductionism gone mad.

A brief search on Twitter also shows how far the concept of powerful empathy-giving mirror neurons has spread into popular consciousness. “‘Mirror neurons’ are responsible for us cringing whenever we see someone get seriously hurt,” the @WoWFactz feed announced to its 398,000 followers with misleading confidence earlier this month. “Mirror neurons are so powerful that we are even able to mirror or echo each other’s intentions,” claimed self-help author Dr Caroline Leaf in a tweet sent a few weeks ago.

In fact we do not yet have the research to show that mirror neurons are vital for human empathy, and there are reasons to believe that empathy is possible without them. For starters, we are able to comprehend the intentions behind the actions of other people or animals even if we’ve never performed, or are incapable of performing, their actions ourselves. Many brain damaged patients who can no longer produce speech are still able understand it. There are other patients who have lost the ability to express emotion yet can still understand the emotion of others.

Now 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. This is not to detract from the fascination of mirror neurons. It does show they are not the beginning of a causal path. Rather they are embedded in a complex network of brain activity.

Finally, it’s worth highlighting Kilner and Lemon’s useful summary of where we are at regards identifying mirror neuron function in humans. While Ramachandran and others have been quick to find the roots of humanity in these cells, the reality is that we’re only at the early stages of establishing whether mirror neurons exist in humans. Single-cell recording of the kind used in monkeys is too invasive to be performed in people, other than in exceptional circumstances (such as during required brain surgery). The single study of this kind published to date did find evidence for mirror neurons in the human frontal cortex and temporal lobe.

Brain imaging studies with humans have also reported what looks like mirror neuron activity in many of the same brain regions identified in monkeys. However, many of these papers only looked at the observation of actions, so they can’t determine if the same brain regions are involved in both action and observation. Other brain imaging studies have exploited the principal of adaptation – neurons get less responsive the more they’re activated. If a brain region has mirror properties there should be signs of this fatigue after action performance and observation – in fact the results are mixed with two of five adaptation studies failing to find evidence of mirror-like properties. This could be because mirror neurons don’t show adaptation, but we’ll have to see.

James Kilner and Roger Lemon are to be applauded for providing this much needed overview of the field. No doubt about it – mirror neurons are an exciting, intriguing discovery – but when you see them mentioned in the media, remember that most of the research on these cells has been conducted in monkeys. Remember too that there are many different types of mirror neuron. And that we’re still trying to establish for sure whether they exist in humans, and how they compare with the monkey versions. As for understanding the functional significance of these cells … don’t be fooled: that journey has only just begun.