January 18, 2010

Mirror Neurons: Resonant Circuitry in Brain?

Back in the time of the “black and white” motion picture days, when “talkies” weren’t even born, we still could make out the essence of what Charlie Chaplin had to “say”. We understood his unspoken words, courtesy a system of neuronal networking, called the mirror neuron system. Another example: you observe a man kissing ‘his’ girlfriend, ‘your’ neuronal network that would otherwise activate when you ‘actually’ kissed her, would fire! Mirror neurons are at work. Seems to me a bit like ‘mechanical resonance’, where the string of a guitar resonates (vibrates at the fundamental or overtone frequency of its chord's natural frequency of vibration) when a second guitar/chord is strummed nearby.

It all began with the experiment led by Giacomo Rizzolatti, a neuroscientist at the University of Parma. His team wanted to locate regions in the brain which controlled hand and mouth actions in monkeys, such as grasping or licking of an object. So, they had placed electrodes in the ventral premotor cortex, a part of the brain, brain anatomy showing primary motor area, premotor cortex,areas 5 and 7[see fig] of a macaque monkey with the hope that whenever ‘that part’ of the brain were activated, the electrode would activate an electronic circuitry and give an audible beep. But all hell broke loose when a student entered the lab with an ice cream in his hand. Every time he was raising the ice cream to his lips, the system responded with a beep! Thus, although the monkey wasn’t having the ice-cream himself (and not moving his limbs), the mere observation of ‘the act’ fired the neurons that would otherwise be stimulated if the monkey ‘actually’ indulged in ‘the act’. The mirror neuron area, ventral premotor cortex, is also known as ventral premotor area F5.

Mirror neurons are defined as ‘those’ neurons that fire when an animal performs some work and also when the animal observes the ‘same work’ being performed by others. In humans, the activity has been traced down to the ‘premotor cortex’ and ‘inferior parietal cortex’ regions of the brain. When a part of the brain ‘fires’ (discharges), it becomes metabolically active and the areas of this enhanced activity may be mapped by a procedure called fMRI (functional Magnetic Resonance Imaging). In a study bycontext,action,intention clip, testing the mirror neuron system Iacoboni et al, 23 right-handed participants were shown different types of image clips (figure on the left). The pictures consisted of a teapot, a mug, cookie jar and related objects in different contexts, action and intention. At the same time the subjects were shown the pictures, the participants’ brains were also being mapped by fMRI to assess the regions of the brain that lit up during the procedure. The premotor cortex and some other parts of the brain showed a significant signal increase on fMRI scans in the action and intention clips. But the signal increase in the Intention condition was much higher compared to the Action condition, with high activity recorded in visual areas and in the right inferior frontal cortex, they noted. Thus the mirror neuron areas of right inferior frontal cortex were involved in understanding the intentions of others, in addition to action recognition.

This ‘sniffing’ of intention behind action is essential to social animals like humans and a deficit in understanding this is seen in autism, a developmental disorder where there is lack of social smile, aloofness, absent eye to eye contact and marked impairment in interpersonal interaction. Autistic children can see sad or happy faces but they fail to ‘read’ the underlying emotions (sadness or happiness). Normally, children acquire mirror neuron activity by the time they are 1 year old. Exactly how they ‘program’ their neurons into being mirror neurons is not known. Learning by Hebbian association has been proposed. Mirror neurons are also involved in language acquisition, empathy and even possibly mind reading, giving credence to the ‘theory of mind’. Telepathy and clairvoyance now seems plausible (psychologists frequently employ transference and counter-transference, kind of ‘feeling’ a patient by their ‘mirror neuron systems’ and consequently ‘filling’ the patient with his own thoughts to remedy patients, in clinical practice.)

Considering their importance in social communication, our brain would have sufficient number of them. Here, I would like to wonder if pedestrian neurons could spontaneously organize into ‘mirror neuron system’ as a person watched say, an action film. Certainly, this can not happen in real-time, as there will be a delay due to visual processing and synaptic passage within the brain. But, given the plasticity of the brain and the dynamicity of dendritic spines, the idea seems conceivable. Mirror neurons also respond to sound. Breast milk ejection of a mother in response to her baby crying is an example. In cases of postoperative urinary retention, sound of running water has helped the patient to pass urine (1). This may be another example in point. It may also shed light about how ‘suggestion’ works in Hypnosis.

Given the diverse range of inputs, the brain must manage (compress) its database as space within the skull is limited. It certainly can not afford to have different sets of mirror neurons for red oval tea cups or green cylindrical ones and so on. So, what the brain does is pattern matching by some ‘fuzzy logic’ or it may simply analyze the scene; break down the signal by some kind of Fourier analysis into simpler functions and then compare resulting signal with its prior database.

Mirror neurons may explain the elusive LSD Flashback phenomenon. It occurs in LSD abusers who are NOT currently taking the drug, but find themselves in a situation reminiscent of a previous drug spree. The person gets a ‘kick’ even though he may have taken it days ago. Clearly, psychedelic lights may trigger a flashback (and watching violent TV programs has been found to activate mirror neurons in children). We should also ask ourselves if dreams, at least some of them, were the handiwork of some of these neurons.

In her fantastic article ‘Cells That Read Minds’, Sandra Blakeslee ponders and exculpates all men from voyeurism:
“In yet another realm, mirror neurons are powerfully activated by pornography, several scientists said. For example, when a man watches another man have sexual intercourse with a woman, the observer's mirror neurons spring into action. The vicarious thrill of watching sex, it turns out, is not so vicarious after all.”

In a lighter vein it may be said that the search engine Google has developed 'mirror neuron like' properties. Just type, “how can i get my girl” in Google search box and watch: Google would ‘ping’ your intention and come up with some real smart choices.

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Reference: (1) Bailey & Love; A Short Practise of Surgery,18e, page 1230
Mirror neurons and the simulation theory of mind-reading
Cells That Read Minds
Iacoboni M, Molnar-Szakacs I, Gallese V, Buccino G, Mazziotta JC, & Rizzolatti G (2005). Grasping the intentions of others with one's own mirror neuron system. PLoS biology, 3 (3) PMID: 15736981
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