Prof. Dr. Sohan Raj Tater
The brain begins with genes. Genes from both parents combine to design and create the lump of gray flesh in the head, plus the rest of body, which operates and it operated by the brain. The slightest disruption in the physical development of brain can have a devastating effect on future intelligence. A single glitch in the DNA code can limit mental development or cause severe retardation. On the other hand "good" genes make genius possible. There is no single factor more important in an adult's IQ score than genes. However parents also pass along the environment in which the genes are expressed. What we think about, the language we think in, and how we apply our intelligence are all products of the environment; how we will think depends very much on that original set of blue prints from the genes. Just like a person who hopes into a car decides where to go and how to get there, the car sets limit on how fast and how successfully.
Short term memory is similar to the random access memory (RAM) on a computer; it controls the information needed to run at any given moment. Long term memory is like the hard drive, a repository for all the information needed to operate. Just a computer needs both the RAM and a hard drive, so both short term and long term memory are essential for intelligence. For example, adding the numbers 349 and 217 requires long term memory to remember the rules of addition, and short term memory to execute the specific problem. Memory itself is so control to the thinking process that memory is one of the best predictors of human intelligence as measured by IQ tests.
There are two basic types of memory: short term and long term. Short term memory also known as working memory, operates over seconds where as long term memory lasts for minutes to an entire life. If you here a random telephone number 441-9620 you might remember it until the end of sentence, probably not until the end of the paragraph. Your own telephone number, however, is securely stored and easily remembered. The reason is that the random telephone number went into short term memory only, because there was no reason to save it, while your own number is stored in a personal long term vault.
How is information in short-term memory converted into long term memory? It must be a selective process. Otherwise long term memory would soon be swamped with useless information such as restaurant menus, road signs and old TV guides. It would be like the hard drive of a computer that stores every revision of every document, or a radio that records every song. The machinery would soon be filled up with useless, disorganized information, somehow the brain must have a filter to sieve out what needs to be remembered from what can be discarded.
The filter is a physical structure built by genes. It was discovered by studying a simple invertebrate, the sea slug Aplysia. Sea slugs hardly have a brain, and they probably could not pass the bar exam, but they do have a nervous system and are able to 'remember' simple stimuli and respond accordingly, one of the best studied responses is the gill withdrawal reflex. When the gill of a sea slug is touched, the body withdraws into its shell; presumably the touch is a warning that a predator may be nearby. But if the gill is touched repeatedly, the withdrawal response slows down or disappears, as if the sea slug knows that it has nothing to fear. To the extent that intelligence is ability to adopt behaviour to the environment, the sea slug shows a primitive form of intelligence.
Scientist Eric Kandel wanted to know how the sea slug adopts its response. The first step was to recreate the reflex without the sea slug, using isolated nerve cells grown in a petri plate. By recording the electrical signals between nerve cells, kandel found that after a single stimulus there is a strong electrical signals at the synapse between nerve cells, Kandel found that after a single stimulus there is a strong electrical signal at the synapse between nerve cells, but as the stimulus is repeated, the strength of synaptic connection decreases. The nerve cells are "remembering" their past, kandel showed that the nerve cell 'remembers' by synthesizing a burst of proteins and that the key activator of this explosion of gene expression is a protein called CREB. Kandel proved that the nerve cells could be fooled into thinking they had been stimulated simply by adjusting the amount of active CREB protein.
Geneticist Tully established three things: that the flies, just like humans, have two forms of memory, short term and long term; that short term memory is required to learn the difference between odors, where as long term memory is required to remember the difference and behave accordingly: and that converting short term memory into long term memory requires new gene expression. But what genes were turning on? Taking a clue from kandel's work on sea slugs. Tully decided to look at the CREB mechanism. The part of the brain responsible is the hippo campus which makes a mental map in minutes and stores it for weeks. Later, if it is an important map, the information is transferred to the cerebral cortex for long term storage. A damaged hippocampus, as can occur from injury or stoke, would prevent a person from finding his way out of a new room, even though he could remember the layout of a place he had lived long before.
Even though the loss of single gene can prevent a mouse from finding its way, the thought process depends upon more than just genes. A simple experiment showed that experience is important too. Some mice were raised either in a sparse, unfurnished cage with only a water bottle and food tray, while others grew up in a special "play ground" equipped with plastic tubes, a tunnel with multiple openings, and an exercise wheel. After 3 months the mice brought up in the more stimulating environ showed a 15% increase in number of cells in the hippocampus. The more the mice used their brains to remember the complex topography of the play ground, the better their brain becomes. Even for this simple type of intelligence, environment makes a difference.
What do different people, even when they are brought up the same way in the same environment, get different scores on IQ tests? Although there is no single answer to this question, the results of decades worth of study on tens of thousands of subjects have been remarkably consistent in showing that the single most important factor is genes. The "environment" includes many factors that influence intelligence, such as prenatal care, nutrition, child care, schooling etc. Together they are a powerful force, but not one of those environmental factors alone has a great impact that genes.[70]
Doctoral Thesis, JVBU