Hockenbury Discovering Psychology 5th txtbk

262 CHAPTER 6 Memorylong-term potentiationA long-lasting increase in synaptic strengthbetween two neurons.Combined, the findings of Lashley and Thompson indicate that memories havethe potential to be both localized and distributed. Very simple memories may belocalized in a specific area, whereas more complex memories are distributedthroughout the brain. A complex memory involves clusters of information, and eachpart of the memory may be stored in the brain area that originally processed theinformation (Greenberg & Rubin, 2003).Adding support to Lashley’s and Thompson’s findings, brain imaging technologyhas confirmed that many kinds of memories are distributed in the humanbrain. When we are performing a relatively complex memory task, multiple brainregions are activated—evidence of the distribution of memories involved in complextasks (Frankland & Bontempi, 2005).The Focus on Neuroscience on page 262 describes a clever study that looked athow memories involving different sensory experiences are assembled when they areretrieved.The Role of Neurons in Long-Term MemoryWhat exactly is it that is localized or distributed? The notion of a memory tracesuggests that some change must occur in the workings of the brain when a newlong-term memory is stored. Logically, two possible changes could occur. First, thefunctioning of the brain’s neurons could change. Second, the structure of theneurons could change.FOCUS ON NEUROSCIENCEAssembling Memories: Echoes and Reflections of PerceptionIf we asked you to remember the theme from Sesame Street, youwould “hear” the song in your head. Conjure up a memory of yourhigh school cafeteria, and you “see” it in your mind. Memories caninclude a great deal of sensory information—sounds, sights, andeven odors, textures, and tastes. How are such rich sensory aspectsof an experience incorporated into a memory that is retrieved?PictureSoundPerception(a)Recall(b)Researchers set out to investigate this question using a simplememory task and fMRI (Wheeler & others, 2000). Participantsstudied names for common objects that were either paired witha picture or a sound associated with the word. For example, theword “dog” was either paired with a picture of a dog or thesound of a dog barking. The researchers then used fMRI tomeasure brain activity when the volunteers were instructed torecall the words they’d memorized.The results? Retrieving the memory activated a subset of thesame brain areas that were involved in perceiving the sensorystimulus. Participants who had memorized the word dog with apicture of a dog showed a high level of activation in the visualcortex when they retrieved the memory. And participants whohad memorized the word dog with the sound of a barking dogshowed a high level of activation in the auditory cortex whenthey retrieved the memory.Of course, many of our memories are highly complex, involvingnot just sensations but also thoughts and emotions. Neuroscientistsassume that such complex memories involve traces that arewidely distributed throughout the brain. However, they still don’tunderstand how all these neural records are bound together andinterrelated to form a single, highly elaborate memory.Retrieving the Memory of a Sensory ExperienceTop row: (a) Perceiving a picture activates areas of the visualcortex. (b) When the memory of the picture is recalled, itreactivates some of the same areas of the visual cortex (arrow)that were involved in the initial perception of the picture. Bottomrow: (c) Perceiving a sound activates areas of the auditorycortex. (d) When the memory of the sound is recalled, it reactivatessome of the same areas of the auditory cortex (arrow)that were involved in the initial perception of the sound.(c)(d)Source: Wheeler & others (2000).