ScienceMasterIf it's your job to develop the mind,
shouldn't you know how the brain works?
What Is All This Talk Lately About "Mirror Neurons"?
- Written by Kenneth Wesson Kenneth Wesson
- Published: 28 March 2003 28 March 2003
When a parent sticks his tongue out at a newborn baby, the child will reciprocate. When I yawn, you yawn. While watching a movie or reading a novel, you might find yourself crying. While watching a televised boxing match, football game or mystery, have you ever noticed yourself perspiring? While witnessing someone else’s vaccination, you cringe and sometimes scream, "Ouch!" What mechanisms in the brain cause such outcomes?
A series of "monkey see, monkey do" nerve cells with surprising properties was recently discovered in the cerebral cortex of monkeys. Giaccamo Rizzollati of the University of Parma (Italy) discovered a system of brain cells now known as "mirror cells" in the ventral premotor area (F5) of the frontal lobes. This is a part of the larger premotor cortex, whose activities are linked to planning and initiating movements. Immediately anterior to the motor area is a cortical strip referred to as the Supplementary Motor Area (SMA) or the premotor cortex. Proposed actions are rehearsed there prior to being executed by one’s motor system. The premotor cortex is a functional brain landmark separating the motor input (sensory/detecting) and output (motor/performing) systems.
This cluster of neurons fires a signal when a monkey performs a single highly specific hand action. When pushing, pulling, tugging, grasping, picking up or putting a peanut in its mouth, neurons in the motor cortex are very active. However, the fascinating characteristic about mirror neurons is that many of the very same neurons in the premotor areas also fired when the monkey watched another monkey or the experimenter perform the exact same task! During these experiments, it became easy to predict precisely which neurons would fire based on which activity a monkey was witnessing. When mechanical tools performed the same task, the mirror neurons remained quiet and inactive.
Any time a student watches a teacher or when he watches another student in a cooperative learning setting, mirror neurons must be active in a similar sophisticated observation-execution matching system. When we watch another human being perform a task or even starting to perform that action, mirror neurons fire at an incredible rate. Thus, mirror neurons faithfully assist in "reading" the intentions of others, and they play a critically important, behind-the-scenes, role in empathy, imitation learning, deciphering facial cues, early language development, social skills and cultural rules by allowing us the ability to predict, mimic and understand the actions of others. During verbal discourse, even anticipating another person’s words as they complete a sentence seems to be associated with these newly discovered neurons.
Education and parenting are among some of the human endeavors most reliant on the proper functioning of mirror neurons. Isn’t the goal of teaching and parenting to get exactly the same neuronal systems firing in our students and children that are actively at work within the adult’s neural networks? This is the basis of mentoring programs and the master-apprentice relationship that is effectively used in contemporary educational settings. Mirror cells foster high learning levels, acceptable social behaviors, and basic human understandings concerning one another’s intentions, be they generous or malicious.
There is fairly clear and convincing evidence of what can occur when mirror neurons go awry. Without properly functioning mirror neurons, a child may not understand or empathize with other people and therefore, he will completely withdraw emotionally and socially from the rest of the world. These are the cardinal traits of the autistic child. Antisocial serial killers, interestingly, demonstrate little activity in the F5 region of the brain.
Equally fascinating are the cases in which a patient, who experiences a right hemispheric stroke resulting in complete paralysis on the body’s left side, will predictably complain about it, as would be expected of anyone. However, about 5% of them will vehemently deny experiencing any paralysis at all, known as the "denial" syndrome or anosognosia. These patients will otherwise demonstrate normal mental ability and intelligence. The startling discovery though, was that these patients not only denied their own paralysis, but they also denied any awareness of immobility in other patients whose paralysis was similar to their own. Denying one’s own paralysis was odd enough, but when these patients denied an identical paralysis in other patients, it clearly suggested that there had been some degree of damage to the mirror neurons.
Does nature or nurture play a larger role in brain development?
Every semester, the nature or nurture debate inevitably rears its controversial head in every traditional psychology, neuroanatomy, and teacher’s education course. As the semester quietly ends, so does the still-smoldering discussion pertaining to the dominance of these two developmental factors. There is remarkable news coming out of neuroscience that should excite the debaters on either side of this argument -- they are both correct, since the only accurate answer lies somewhere in the middle. Precisely where that mid-point is may remain a secondary mystery but, in many ways, it is simultaneously irrelevant. The delicate dance of both nature and nurture determines the end result of each human "product."
Every individual is never really quite finished. At any given stage, he or she is still a work in progress. Genes and environment continue to play their respective roles throughout our lifetimes. Recent research has shown that with every experience, a child’s (or adult’s) genetically-constructed brain is subject to physical, chemical and structural alterations based upon any experiences and new stimuli.
During prenatal development, a blossoming fetal brain produces an average of 250,000 new brain cells each minute. There are several points during the process of "neurogenesis" where over 50,000 brain cells are generated every second. By the 20th week of fetal life, over 200 billion neurons have been created, after which a period of pruning back these numbers occurs. Approximately six weeks later, only fifty percent of those cells remain alive. The surviving 100 billion neurons are the healthy cells, which are ready to find a permanent position on an important neural circuit in order to aid the growth and development of a newborn. The overproduction of neurons and synapses (synaptic proliferation) is nature’s way of guaranteeing that a child born anywhere in the world, under nearly any circumstances, has an adequate neural system for survival.
As new learning occurs, neurons respond by reaching out to one another with their dendrites in an elaborate branching process that connects millions of previously unaligned cells and circuits. The result is the creation of "magic trees," as UC Berkeley's Marian Diamond refers to the dense "neural forests" that are the physiological consequences of stimulation and learning. All brain development occurs as a complex interplay between the environment into which a child is born and his/her genes. The genetic blueprints for brain and body construction are cautiously monitored in utero as the developing organs, limbs and operating systems are assembled. Given time, the environment will play an ever-increasing role in the growing young brain.
Similar to a massive piece of wood destined to be transformed into a statue, the brain undergoes a comparable sculpting operation, where environmental circumstances whittle away at the raw material and dictate the eventual outcome. Regardless of a parent’s desires (and later a spouse’s wishes) nurture can only modify that which nature had originally supplied. This universal strategy for growth and adaptation will continue for the next seven or more decades.
The impressive power of the human brain comes, not from the mere number of brain cells, but from the constantly changing, infinite number of connections that the 100 billion surviving neurons make as a consequence of (1) genetic programming, and (2) stimuli encountered in the outside world. These contact points between neurons, "synapses," connect neurons to one another and to the important networks that represent all human functioning.
Peter Huttenlocher (University of Chicago) was the first neuroscientist to successfully conduct a synaptic census in the human brain. He was able to catalog the almost infinite junctures (dendrites and synapses) that enable neurons to communicate. All dendrites, synapses and their respective connections are so minute and abundant that, any pre-Huttenlocher tabulation was based on estimation and speculation, but not grounded in any precise quantification.
Figure 3- Neurons and Neural Connections
Age Neurons and synaptic connections
End of 2nd trimester 200 Billion neurons
At birth (full term) 100 Billion neurons
8 months old 1,000 Trillion connections
By age 10 500 Trillion connections
28-week old fetus 124 million connections (in a pinhead speck of brain
tissue composed of 70K neurons)
Newborn 253 million connections/speck
8-month old infant 572 million connections/speck
By Age 12 (stabilizes) 354 million connections/speck
That a child might have any neural advantage over an adult was never fathomed before. However, the brain of a normal three-year old child has far more neural connections (synapses) with greater density than the adult brain (see figure 3). In addition, it daily consumes 225% more energy than an adult brain. Every time a child learns something new, neurons in the cerebral cortex modify their widespread connections to accommodate the newly acquired information, thereby redefining the operating nature of the developing brain. In addition, the brain also undergoes architectural and structural changes based on new experiences processed by the brain. When any form of learning occurs, a new series of synaptic connections is established among the neurons’ current framework of neural networks. Those same connections will experience additional alterations later, with still newer input. The trillions of linkages make the brain’s capacity to process and store information virtually unlimited. Thus the more we learn, the more we are capable of learning in the future, if that learning is of a similar kind.
All postnatal experiences serve to shape the brain and to re-configure it regularly and faithfully as one’s personal biography continues to carve the three pounds of malleable brain matter into a distinct human being, who functions quite well within the parameters of his specific surroundings. Until death, the brain is never actually finished building and reconstituting itself.