________________
Knowing, Learning, Memory, Intelligence
55
number) at a time and erases older items as new ones are added. If one wants to retain an item for a longer time, he must rehearse it and transfer it to long-term memory. Are they two independent systems of memory or are they some how interconnected ? We shall see this in the next section. 3. Engrams -Stable Memory Records
Long-term memory records must, surely, involve some physical change, for records of single events can remain for up to 100 years in man. Cyclic activity could not last foreven a fraction of this time without becoming distotred. Moreover, procedures such as shock or anaesthesia do not disrupt such records. Nature of this change remains a matter or speculation and many theories have been advanced including the following three which are worth examining : (1) a change of standing pattern of activity (2) a change of some specific chemical molecules such as those of RNA (3) a change in the pathways, themsleves, between neurons within the
nervous system. (1) In Canadian psychologist Donald Hebb's view, short-term memory is an active or dynamic memory : Sight or sound sets off a pattern of nerve-impulses in the brain. They circle a closed loop of connected neurons, just long enough for the brain to perecive it. This will, them, fade away unless, by some process of consolidation, more permanent structural trace is made. This structural trace, called Engram, would correspond to long-term memory. If the nerve impulses circle their selected pathways long enough, they could leave behind an indelible memory-record and thus convert the short-ierm into long-term memories. (2) The hypothesis that memory has a chemical base is popular with biochemists. According to this theory, memory is coded in proteins or chains of molecules. A new protein called scotophobin was found in laboratory animals by Georges Ungar in 1970. But there have been no convincing experiment to prove that specific chemical molecules are involved in memory.
