Mirror neurons|snoruen rorriM

For my meeting in Roehampton on Thursday, It would be a large advantage for me to learn a little more about mirror neurons and the big research in that area. Once I've informed myself, I should also check out some articles written by the researchers I will be seeing, and the research aims of their department in general. The purpose of today's blog post is to help me explain my findings to myself, via explaining them to you. A popular adage amongst teachers is "If you can teach other people the material, then you understand it well enough." In favour of that, if you read through this and have any questions, please get back to with them before thursday so I can clarify or study the answers I should give.

This was taken in my old flat, but it gives you an impression of my current work station. This is how research should be done!

Discovery and Basics of Mirror Neurons:

A quick wikipedia examination tells us that mirror neurons were discovered in an experiment in 1992 that was designed to examine what occured in an area of the brain called the premotor cortex (part of the frontal lobe, just to the front of the motor cortex. Apparantly it is very involved in the ability to guide one's movement using one's senses). This study is available as an open and free .pdf so I've had a brief read through.

Pellegrino et al. attached micro-electrodes to individual neurons in the premotor cortex of macaque monkeys, which both recorded neural activity in those neurons and 'microstimulated them'. The researchers carried out a previous study in which they outlined the methods in more detail so I am unaware of the exact procedure for now. Objects of different sizes and shapes were displayed in different positions in the visual field of the macaque. This was repeated until the researchers were certain that the neurons they were recording became active during the macaque's hand movements. Presumably it must be fairly tricky to accurately find a 'hand movement' neuron. I certainly wouldn't know where to look. For the main experiment, Pellegrino et al. presented the monkey with a large box, the front 'door' of which was made up of a one way mirror. There were different shapes inside the box which could not be seen by the monkey. The monkey was directed to press two little plates with thumb and index finger. If the monkey held on for 1.5 secondsish, then the door would open and the monkey could reach the shapes...which very pleasantly had food underneath them.The researchers used a movement recording system called ELITE to compare actual hand movements with the readings coming from the microelectrodes.

As somewhat of a fortunate surprise, the researchers noticed that when they themselves performed actions in front of the monkey, the monkey's recorded neurons would 'fire' (have an action potential, which is essentially a term for a burst of neural activity). The researchers might be presenting food the the monkey, picking it up, moving it, playing with it. Action potentials occured whenever they did any sort of hand movements within the macaque's visual field.

Macaca nemestrina, used in the experiment

The results were pretty astonishing. The microelectrodes picked up very similar readings for when the macaque made certain hand movements, and when it watched the researchers make them. This did not occur for all types of movement. For example moving hands alone would not trigger the neurons, but grasping food with them would. Grasping the same food with tweezers would not. What this suggested was that goal orientated movements which the monkey could physically copy (i.e. use hands to pick up food) were represented in some way inside the premotor cortex. The monkey seemed to be imagining making the same movement. Watch your friend opening a can of coke or punching something, using a needle and thread or picking up a really nice looking burger... at this point it seems like your brain may actually 'code' for the movement even though it isn't you making it. This has many implications in how we are able to learn new physical skills from one another.

In 1996 many of the same researchers from the same group as the previous experiment (primary researcher: Vittorio Gallese) performed a more detailed examination of the mirror neuron phenomenon. They recorded 532 neurons in "area F5" of the brain. I'm not sure of the details of this brain area, but it is referred to as a position where mirror neurons have regularly been found to exist. Research has shown that F5 is related to goal-directed hand movements but there is also some activity when individuals view 3D objects. Of the 532 neurons in each of the two macaques they used, 92 of them were mirror neurons. These neurons were discernable because they fired both when the macaques performed hand actions, and when similar actions were performed by the experimenter. Again, the researchers found that for a mirror neuron to fire, there needed to be an interaction between actor and object. Watching the actor perform an action, or just watching the object, did not produce any firing.  In addition, the mirror neurons were often incredibly precise. Around 30% of them required the macaque view both the basic movement (gripping) and a specific way in which that action was performed (gripping using certain fingers on certain positions). Gallese et al. suggested that the mirror neuron system formed a system which allowed the monkeys to learn physical movements from observation. In other words, allowed them to copy. The argument has been presented that the mirror neurons were really just preparing the monkeys to make the same movement. This was rejected by the finding that the mirror neuron response decreased when the experimenter moved the object within the reach of the monkeys, and only increased again when the monkeys physically grasped the object.

Mirror Neurons and Social Cognition

In a later experiment, Ferrari et al. found strong evidence showing mirror neurons also activated in response to observing mouth movements. Mostly those that were related to eating behaviours. Very relevent to social cognition was the finding that the most reliable way to fire some mirror neurons in the monkey subjects was to have them observe communicative gestures and lip movements. This experiment opened my eyes to the importance of this F5 area in the control of both mouth and hand movements.Rizzolatti et al. pointed out that understanding acitons made by others is essential to social interaction. If mirror neurons exist to aid action understanding, that it may work like this: The observer has a mental representation of what happens when he, say, moves his arm to grab food. He understand that his hand will move from point A to point B. When an observed action matches this mental representation then the observer understands the action.

Showing how readily a newborn macaque will copy the mouth actions of an experimenter. Human babies are also very capable of this from birth, suggesting that there is a ready-built system for copying rather than a simple learned ability. Perhaps mirror neurons are the answer.

35% of mouth motor neurons fired when the macaques in the experiment observed mouth actions. These were thus considered mirror neurons specific to the mouth area. 85% of these fired in response to eating behaviour. 15% to communicative behaviour. The experiment was controlled so that movements made by the macaques during observations were accounted for and so not mistaken for mirror neuron firing. Again, interaction between actor's lips and an object was necessary for mirror neurons to fire, bringing further support of them action as facilitators of action understanding. In humans an fMRI study by Buccino et al. showed evidence for mirror neurons activated in response to watching chewing and biting movements. This activation occurs in area 44 of the human brain, which has been considered the homologue of monkey's area F5 (e.g. petrides and Pandya, 1994).

Communicative mirron neurons were different. They didn't necessitate goal orientated lip movements to fire. Lip-smacking, tongue protrusions etc are not directed towards any object. It is possible that the actions prompted the macaques to imagine the result of that sort of expression when made in the presence of another macaque. These mirron neurons barely fired in response to any ingestive action, suggesting that they are specific to communication to some extent. There is a methodological problem in examining communicative behaviour in an ecologically valid setting, so many questions remain in this area.

An example of the sort of data collected from the macaque experiments. You can see that the strongest mirror neuron response was to interactions between the experimenter and the food. The firing was even stronger when the experimenter used a tool, this will be explained under the last section of this blog entry.

Mirror Neurons in Humans?

fMRI machines are the best friend of researchers looking to examine neural activity in humans. Attaching electrodes to the neurons is a horribly invasive procedure and I still very much dislike the thought of that method being used on macaques, but you know. Science -.-. fMRI scans scan the changes in blood flow throughout the central nervous systems (brain and spinal cord) of anyone in the machine. More blood flow essentially means more activity in the brain. By giving participants tasks or objects to observe whilst they are in the machine, researchers can gain an understanding of what brain areas are involved in what processes.

You've all seen pictures like this before. The coloured areas represent different levels of higher-than-normal blood flow. It clearly displays active areas in the brain.

Lacoboni et al. write that imitation is crucial for human development and practise of communication and social skills. In order to examine the neurological underpinnings of our ability to imitate, the researchers set up an experiment where participants were asked to observe and then copy simple finger movements...whilst in an fMRI machine. Human neonates can copy facial expressions and really basic gestures within a few hours of birth. If you don't believe me, check out this baby of a video!

Direct link: http://www.youtube.com/watch?v=k2YdkQ1G5QI

Remember I spoke about matching an observed action to a mental representation? That is called the "direct matching hypothesis". Lacoboni et al were testing for it. If mirror neurons had a 'matching mechanism' then they should 'fire' more prominently when the participants observed someone actually moving their finger, rather than some symbollic cues. See how that works? If mirror neurons work by activating whenever reality matches imagination, then observing a note saying "Move finger two squares to the right" should not activate mirror neurons.

Indeed, this was the case. Signal intensity was significantly stronger for the direct match observations than for symbols, though there was still some firing in the same brain regions (basically: area 44 or Broca's area. Check it out on wikipedia and you will notice it is described as being primarily linked to speech production. Hence the afflication Broca's Aphasia). Lacoboni et al. saw there being good reason for mirror neurons to be present in that area, seeing as it is the human version of F5 and is known to represent 'distal' movement. Proximal: Area where appendages join the body. Distal: Area furthest from where the appendages join the body. Aren't we learning a lot of terminology today? Additionally, Broca's area is all about speech production, and Lacoboni et al suggests that as imitation is crucial in language acquisition, it makes sense that there would be some neural propensity towards imitation learning there. I'm not too sure about that one after having puzzled out some of Vera Kempe's perspectives on pre-lingual language development, but we'll see. Fourth and last, speech production not only involves learning to words, but learning how to pronounce them physically possibly via direct matching.

Other areas are involved, according to the researchers, but the reasoning behind them is less well understood. Previous research had used PET scans to observe activity in human brains whilst they watched pantomimes involving complex movements. Participants were asked either to memorise and attempt to copy the movements, or try to work out their purpose. In the first situation the parietal lobe was activated, mainly on the right. The latter sitation saw more activation in the left inferior frontal lobe (same as above). Their interpretation of this research was that a mental representation of the final position and the steps necessary to get to it may have been building in the parietal lobe whilst watching. Broca's area, in contrast, builds a representation of the goal of the body movements but not the actual physical movements needed to arrive there. This hypothesis totally works with F5 areas in Macaques not activating unless there is interaction between actor and object (goal orientated behaviour). A whole wealth of research shows the lesions to these areas causes problems with action understanding, direct matching and other abilities described above. Mirror neurons, although only indirectly observable in humans, seem very clearly to exist in a similar way to macaques.

Scratch that above sentence, humans have more recently been implanted with electordes for direct examination of the existance of mirror neurons. This was in 2010 by Mukamel et al. (I love how many of these articles are free and available to view just with a quick googling! In university so many of the brilliant articles I needed had to be paid for and werent under Abertay's subscription. Also every researcher in this whole area seems to be Italian so far...). They examined 1177 neurons in relevent areas whilst the participants hooked up to the electrodes performed or watched hand graspig and facial expressions. These folks were patients already being treated with invasive surgery so ethically it was cool. That's a relief. Many of these neurons acted as mirror neurons would be expected to act, but some others actually activated during activation but were inhibited during observation so that activation was significantly lower than normal in those neurons. An interesting finding. The rest of the results were consistent with the indirect human research using fMRIs and with the animal research.

How and when do mirror neurons develop in human infants?

So we seem pretty sure that mirror neurons exist, and that they aid in learning how to speak, function in social situations and perform certain types of actions. As we spoke about before, newborn humans have shown the ability to imitate just hours after birth. In an article entitled "Where do mirror neurons come from?" Cecilia Heyes explores possible models of their development. There are no current studies showing mirror neurons existing in newborn infants (you can see why) but many researchers argue that being able to imitate = mirror neurons. A brilliant review of facial expression mimicry in neonates actually finds that the vast majority of reports of this involve just the tongue-poking out action (Anisfeld, 1996). More recently, a very similar finding was discovered for lip-smacking and tongue protrusions in rhesus macaques. If these results are really the trend, then the mimicry of neonates could be put down to more basic copying based on the tongue, not something so complex as mirror neurons.

Some examples of how similar the human and monkey behaviours could be in some of the experiments described in this post. The guy on the right reminds me of a different actor in each photo.

Studies, like one by Ferrari et al. (2005), have shown that mirror neuron responses depend to some extent on life experience. Ferrari et el. gave monkeys opportunities to see human experimenters using tools (a stick / pliers) to pick up or manipulate food. When examined for mirror neuron activity whilst observing these experimenters after several trials, the monkeys exhibited significant firing (as in the figure showing graph output further up the page). This is contrary to the earliest research with macaques that showed no mirror neuron firing when the monkeys observed the experimenter picking up food with tweezers. Experience with tool use had altered the firing responses of the mirror neurons. Haslinger et al. (2005) discovered more mirror neuron activity in human pianists when observing someone playing the piano, then in human non-pianists. Similar results were found in an experiment involving classical ballet dancers (Calvo-Merino et al. 2005). How could mirror neurons be present and functioning at birth if experience in both acting and observing has such a profound effect? Heyes added that certian combinations of sensory input and motor action could actually produce counter-mirroring responses. Catmur et al. (2008) gave various examples of this, including how after specific confusing training, observing movements in the index finger could actually provoke mirror neuron activity in brain areas controlling the pinky finger. The observation of stimuli A had provoked the mental representation of action B in participants who had the experience of the training exercises designed to misdirect.

Heyes concluded that mirror neurons reflect the behaviours and observations we have experienced. This is essential associative learning, which is a well documented phenomenon that has been observed in human and most non human species. As a result, might it be expected that most animal species would have mirror neurons? Heyes goes so far as to suggest that it might be possible to create mirror neurons in animals that wouldn't otherwise have them, by giving them training to associate an interacting behaviour with an itnernal representation. Bizarre thought. Research, it is said in her article, on the effects of mirror neurons is just beginning. If they are produced as a result of associative learning then it does not make sense that they are responsible for prompting humanity to jump forward in its incredible social learning and develop as a species. She believes it is more likely that human sociality boths develops and is developed by mirror neurons. A product and a producer of social interaction. Hmmm. Leaves a lot of questions unanswered. I'm not sure what my perspective is on this yet.

That is enough of an introduction to the topic for now I reckon! I will do more study tomorrow on more specific articles that will or will not be related to mirror neuron research. I also plan to review my work on anxiety (which I mainly directed towards panic disorder) and re-examine the assessments for which I studied Libet and Ramachandran's work. With enough time I will take a quick glance over social brain hypothesis stuff again, and hope that that will be enough work to provide a good impression at this meeting. Good start tonight, I reckon :).