Hockenbury Discovering Psychology 5th txtbk

The Search for the Biological Basis of Memory261would take up the search for the physical changes associated with learning andmemory. In this section, we look at some of the key discoveries that have been madein trying to understand the biological basis of memory.The Search for the Elusive Memory TraceAn American physiological psychologist named Karl Lashley set out to find evidence forPavlov’s speculations. In the 1920s, Lashley began the search for the memory trace, orengram—the brain changes that were presumed to occur in forming a long-term memory(see photo caption). Guiding Lashley’s research was his belief that memory waslocalized, meaning that a particular memory was stored in a specific brain area.Lashley searched for the specific location of the memory trace that a rat forms forrunning a maze. Lashley (1929) suspected that the specific memory was localizedat a specific site in the cerebral cortex, the outermost covering of the brain that containsthe most sophisticated brain areas. Once a rat had learned to run the maze,Lashley surgically removed tiny portions of the rat’s cortex. After the rat recovered,Lashley tested the rat in the maze again. Obviously, if the rat could still run themaze, then the portion of the brain removed did not contain the memory.Over the course of 30 years, Lashley systematically removed different sections ofthe cortex in trained rats. The result of Lashley’s painstaking research? No matterwhich part of the cortex he removed, the rats were still able to run the maze(Lashley, 1929, 1950). At the end of his professional career, Karl Lashley concludedthat memories are not localized in specific locations but instead are distributed, orstored, throughout the brain.Lashley was wrong, but not completely wrong. Some memories do seem to belocalized at specific spots in the brain. Some 20 years after Lashley’s death, psychologistRichard F. Thompson and his colleagues resumed the search for the locationof the memory trace that would confirm Pavlov’s speculations.Thompson classically conditioned rabbits to perform a very simple behavior—aneye blink. By repeatedly pairing a tone with a puff of air administered to the rabbit’seye, he classically conditioned rabbits to blink reflexively in response to the tonealone (Thompson, 1994, 2005).Thompson discovered that after a rabbit had learned this simple behavior, therewas a change in the brain activity in a small area of the rabbit’s cerebellum, a lowerbrain structure involved in physical movements. When this tiny area of the cerebellumwas removed, the rabbit’s memory of the learned response disappeared. It nolonger blinked at the sound of the tone. However, the puff of air still caused therabbit to blink reflexively, so the reflex itself had not been destroyed.Thompson and his colleagues had confirmed Pavlov’s speculations. The longtermmemory trace of the classically conditioned eye blink was formed and storedin a very localized region of the cerebellum.So why had Karl Lashley failed? Unlike Thompson, Lashleywas working with a relatively complex behavior. Running amaze involves the use of several senses, including vision, smell,and touch. In contrast, Thompson’s rabbits had learned a verysimple reflexive behavior—a classically conditioned eye blink.Thus, part of the reason Lashley failed to find a specific locationfor a rat’s memory of a maze was that the memory wasnot a single memory. Instead, the rat had developed a complexset of interrelated memories involving information from multiplesenses. These interrelated memories were processed andstored in different brain areas. As a result, the rat’s memorieswere distributed and stored across multiple brain locations.Hence, no matter which small brain area Lashley removed, therat could still run the maze. So Lashley was right in suggestingthat some memories are distributed throughout the brain.Karl S. Lashley (1890–1958) Lashley wastrained as a zoologist but turned to psychologyafter he became friends with JohnB. Watson, the founder of behaviorism.Interested in discovering the physical basisof the conditioned reflex, Lashley focusedhis research on how learning and memorywere represented in the brain. After yearsof frustrating research, Lashley (1950)humorously concluded, “This series ofexperiments has yielded a good bit ofinformation about what and where memoryis not. It has discovered nothingdirectly of the real nature of the engram.I sometimes feel in reviewing the evidenceon the localization of the memory trace,that the necessary conclusion is that learningjust is not possible.”Richard F. Thompson (b. 1930)Like Karl Lashley, RichardThompson (1994, 2005), soughtto discover the neurobiologicalbasis for learning and memory.But, unlike Lashley, Thompson(2005) decided to use a verysimple behavior—a classicallyconditioned eye blink—as amodel system to locate amemory trace in the brain. Hesucceeded, identifying thecritical region in the cerebellumwhere the memory of thelearned behavior was stored.