Everyone seeks happiness, but a few individuals succeed in experiencing sustainable happiness. In the enactment of life’s drama, the trichotomy of brain, mind and behavior complicates the scenarios. Many people and even many scientists believe that the human brain is the finest product of the evolutionary process and the subtle script it carries directs the activities of our mind and diversity of our behavior. Essentially every person is like all other humans, though every person is similar to some other humans to some extent and the person is similar to a few person to a small extent.
The brain provides commonality to human behavior. In fact, human brain a combination of three brains: a unicellular brain, a mammalian brain and a human brain. Because of the unicellular brain as possessed by unicellular organisms, we are responsive to simple reflexes, such as moving away from a hot object. Our mammalian brain is helpful in guiding us to do a number of voluntary actions. But the most evolved and most recent brain is the neo-cortex or neo-brain that is distinctively human. If we plan to get up at an unusual hour of 4 am just because we have to catch a bus, we rarely fail. Even if our usual habit is to get up at 6 am in the morning, the auto-suggestion of getting at 4 am works fine with us. The neo-cortex registers the suggestion and we get some sort of signal, such as an unusual dream, to get up. This distinctive property of guiding our behavior is uniquely human.
Although human brain is endowed with unique properties, there are dogmas in the world of brain science. One persistent dogma is that the adult brain is essentially fixed in form and function. The dogma is wrong. Instead, the brain has the property of neuroplasticity, the ability to change the structure and pattern of activity in significant ways not only in childhood, which is not very surprising, but also in adulthood and throughout life. The change can come about as a result of experiences we have as well of purely internal activity – our thoughts.
Experiences may take various forms. The brains of people who have been blind from birth and who learn to read by Braille, the writing system based on tiny raised dots that the finger slide across experience a measurable increase in the size and activity of the motor cortex and somatosensory cortex that control movement and receive tactile sensation from the reading fingers. Even more dramatically, their visual cortex – which is normally hardwired to process signals from the eyes and turn them into visual images – undertakes a career change and takes on the job of processing sensation from the fingers rather than the input from the eyes.
Reading braille is an example of intense, repeated sensory and learning experience of the outside world. But the brain can change in response to messages generated internally (our thoughts and intentions). These changes can increase or decrease the cortical real estate devoted to specific functions. Similarly, thoughts alone can increase or decrease activity in specific brain circuits that underlie psychological illness, as when the therapy quiets the overactivity of the “worry circuit” which causes obsessive–compulsive disorder (OCD). Through mental activity alone, which itself is a produce of the brain, we can intentionally change our brain.
The Cortical Representation
The idea that there is a one-to-one correspondence between structure and function dates back 1862 when French anatomist Paul Broca announced that he had identified the brain region that produces speech. It is an area towards the back of the frontal lobes. He concluded from autopsy of a man who had lost essentially all the powers of speech. The brain’s speech producing area is called the Broca’s area.
With this discovery, other brain scientists joined the race of identifying particular brain area for particular function. A German neurologist Korbinian Brodmann, yielded structure function relationship for fifty-two distinct regions. For example, Brodmann number 1 represents the parts of somatosensory cortex that processes tactile sensation from specific spots in the skin. Brodmann area number 52 represents parainsular region where the temporal lobe and insula meet. The visual cortex is known as Brodmann area number 17. Area number 10 is the front-most part of the prefrontal cortex which has increased most in size over the course of evolution and seems to allow us in multi task.
No region of the brain has been as precisely mapped as the somatosensory cortex. This strip of cortex runs roughly over the top of the brain from ear to ear. The left somatosensory cortex receives signal from the right and vice versa. Each part of the body is assigned a particular spot in the somatosensory cortex for processing. As a result, the somatosensory cortex is essentially a map of the body – one that would give Google mappers a heart attack. In experiments in the 1960s, Canadian neurosurgeon Wilder Penfield stimulated systematically different spots of somatosensory cortex and participants reported sensation in different parts of the body in this way. Penfield was able to “map” the somatosensory cortex assigning each spot a corresponding part of the body.
There is an element of humour in cortical representation. Although the hand is below the arm, the somatosensory hand abuts the region that receives signal from the face. Similarly, the somatosensory representation of the genitals lies directly below the feet. It is observed that with more cortical space, a body part becomes more sensitive. The tip of our tongue, which has a larger representation can feel the ridges of our teeth, whereas the backs of our hands have smaller somatosensory representation.
Because of the past works, the belief was strengthened and carried forward into the idea that particular activity must also be hardwired and if not strictly unchangeable, atleast persistent. According to this view, mental illness such as depression might be caused by underactivity in some area of the prefrontal cortex and overactivity in the amygdala and the underlying biology is as permanent as your finger prints.
Towards the Plasticity Notion
However, more recently there has been change in the structure-function relationship. Edward Taub and his associates initiated a bold series of experiments, known as the Silver Spring Experiments, in the Institute of Behavioural Research Silver Spring (Maryland, USA). The neural centres representing sensory connection to fingers were severed in monkeys. Animals lost all sensation in those limbs. Although the case sparked animal right movement in the USA and Taub had to face criminal investigation, the result of these sensory deprivation studies in 1991 was stunning in the sense it shattered the fixed notion of hardwiring. The region of monkey’s somatosensory cortex which originally processed sensation from the fingers, hands and arms had changed jobs. As a result of receiving no signals from body parts, the region now processed signals from the face instead. The amount of brain now receiving sensations from the face had grown to fourteen square millimeters – a “massive cortical reorganization”.
Around the same time, other studies of monkeys showed that adult primate brain can change in response to something much less extreme than amputation or nerve-cutting strategy. In the seminal study, scientists at the University of California, San Francisco trained owl monkeys to develop an acute sense of touch in their fingers. They were trained to brush a spinning disk. Day in and day out, monkeys underwent this exercise, until they had done it hundreds of times. The region of their brain – specifically in somatosensory cortex – that received signals from the finger had been trained to feel the grooves in the spinning disks. Structure-function relationships are not hardwired. Instead, the physical lay-out of the brain – how much space it assigns to which tasks and body parts – is shaped by how an organism behaves.
Seeing the Thunder, Hearing the Lightening
The place to look into the application of findings obtained from animal research involves the study of sensory experiences from those who are blind or deaf. The brain is capable of bigger reorganization. Studies of blind and deaf examined much bigger chunks of neural real estate: the visual cortex which occupies nearly one-third of the brain’s volume. It is nestled towards the back and the auditory cortex, which stretches across the top of the brain across the ears. We are familiar with a folk wisdom that the blind has especially sharp hearing and the deaf has especially sharp eye sight. But the folk wisdom is not cent percent true. In fact, blind people do not hear softer sounds, and deaf people cannot detect minimal contrasts or see in dimmer light than hearing people can. But compensation works in another way.
In people who are deaf from birth, objects in the peripheral vision are perceived not only in the visual cortex but also in the auditory cortex. The auditory cortex sees. It is as if the auditory cortex, tired of enforced inactivity as a result of receiving no signals from the ears, take upon itself as a regimen of job retraining, so that it now processes visual signals. This has practical consequences. Deaf people are faster and more accurate at detecting the movements of objects in their peripheral vision than are hearing people.
Something comparable happens in people who are blind from birth or an early age. In them, no signals reach the visual cortex. However, the visual cortex does not go waste. In blind people who become proficient in reading, Braille, the visual cortex switches jobs to processing tactile signal from those reading fingers. This discovery was so unexpected that some of neuroscience’s most eminent practitioners refused to believe it. As a consequence, the submission turned down by Science was published by its arch competitor Nature (April 1996).
The brains of the blind change in another way too. When they use their peripheral hearing – to locate the source of a sound, for instance, something they tend to be better at than sighted people – they use their visual cortex. Their brains have gone what we call compensatory reorganization. As a result, the visual cortex hears. Once again, William James proved prescient. A century before these discoveries, in his 1892 book Psychology: The Briefer course, he wondered whether if neurons get crossed inside the brain, “we should hear the lightening and see the thunder” —- a foreshadowing of the profound alternation in the brain’s primary sensory cortices that can result from experience.
In brief, the brain can change assigning a new function to a region that originally did something else. These conclusions were derived from studies conducted on the blind and the deaf. What about normal population?
Pascual-Leone conducted experiments involving “virtual piano players”. It was shown that merely thinking about players’ keyboard exercise expanded the region of motor cortex devoted to moving fingers. In another bold experiment, Pascual-Leone recruited healthy volunteers to spend five days in a safe experiment at Beth Israel Deaconess Medical Center in Boston. The participants were blindfolded. To keep from dying of boredom they were provided with sensorially intense activity learning Braille and fine-tuning their hearing. Prior to experimental intervention, they were subjected to fMRI scans. At the end of the five days of such exercise, they were subjected to scans. When they heard something the activity in their visual cortex increased. The visual cortex is supposed to handle sight. Yet, after a mere five days of an unusual sensory activity, scans indicated a radical change in function.
If the visual cortex, which seems like the most hardwired of all the brain’s hardwired regions, can so quickly alter its function as a result of sensory input and sensory deprivation, surely it is time to question how much the brain is really fixed and unchangeable. In all likelihood the visual cortex did not grow new connections to the ears and fingers, five days wasn’t time enough for that Pascual-Leone suspects that instead “some rudimentary somatosensory and auditory connections to the visual cortex must already be present,” left over from the period of brain development when neurons from the eyes and ears and fingers connect to many regions of the cortex rather than just the ones they’re supposed to. When input from the retina to the visual cortex ceased because of the blind-fold, the other sensory connections were unmasked. Even neural cables that receive no traffic for decades can start carrying signals again.
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