Neuroscientists Reflect on the Nature of Memory

       How do we make memories—and find our way back to them over time?

        In probing the processes of how memory is formed, stored and recalled, brain scientists have made big strides. Recently, a September 2002 issue of Scientific American devoted entirely to the subject of time made me think about updating this site and workshop guide. What convinced me was reading the popular neuroscientist Antonio R. Damasio’s article "Remembering When".  It confirmed intuitions I used to figure out the structure of Power of the Personal Story ^® workshops several years ago, especially the notion of using sensory details to recall experiences.

        In his article, Damasio confirms that the paths back to memories are likely strewn with sensory bread crumbs that show us where the brain has stored them. This is why concentrating on sensory details when going back to "stand in the moment" helps fill out the "picture" of events and enhances our grasp of them.  Damasio’s discoveries, the armature for several well-received books he has written, are a product of deductions from his studies of brain damage;  he seems to use dysfunction to deduce function in showing how the brain operates.

        He believes we operate according to two types of time: circadian, a bio-clock time he calls "body time" and another "mind time"—"how we experience the passage of time and how we organize chronology." It’s still unknown, he declares, how "mind time relates to the biological clock of body time" but he suspects mind time could depend more on information processing than on a time-keeping process and is likely to "be determined by the attention we give events and the emotions we feel when they occur."

       Speaking of how the mind time-stamps events in forming memories, Damasio writes:

       "I was first drawn to the problems of time processing through my work with neurological patients. People who sustain damage to regions of the brain involved in learning and recalling new facts develop major disturbances in their ability to place past events in the correct epoch and sequence.

        "Moreover, these amnesiacs lose the ability to estimate the passage of time accurately…Their biological clock, on the other hand, often remains intact, and so can their ability to sense brief durations lasting a minute or less and to order them properly. At the very least, the experiences of these patients suggest that the processing of time and certain types of memory must share common neurological pathways."

       How do the senses lead us back to key memories?  Continuing from above, Demasio writes:
        "The association between amnesia and time can be seen most dramatically in cases of permanent brain damage to the hippocampus, a region of the brain important to memory, and to the temporal lobe, the regions through which the hippocampus holds a two-way communication with the rest of the cerebral cortex. Damage to the hippocampus prevents the creation of new memories. The ability to form memories is an indispensable part of the construction of a sense of our own chronology. We build our time line event by event, and we connect personal happenings to those that occur around us. When the hippocampus is impaired, patients become unable to hold factual memories for longer than about one minute. Patients so afflicted are said to have anterograde amnesia.

        "Intriguingly, the memories that the hippocampus helps to create are not stored in the hippocampus. They are distributed in neural networks located in parts of the cerebral cortex (including the temporal lobe) related to the material being recorded: areas dedicated to visual impressions, sounds, tactile information and so forth. These networks must be activated to both lay down and recall a memory[my emphasis]; when they are destroyed, patients cannot recover long-term memories, a condition known as retrograde amnesia. The memories most markedly lost in retrograde amnesia are precisely those that bear a time stamp; recollections of unique events that happened in a particular context on a particular occasion."

        This is tantamount to saying, I think, that the brain probably files away memories according to the strongest sensory associations, and—like ants laying down pheromones—lays down a return trail.

        Both physicists and psychologists have their doubts: "Nothing in known physics corresponds to the passage of time," writes Paul Davies, another theoretical physicist, in the September 2002 Scientific American.  "In daily life, we divide time into…past, present and future…In this simple picture, the ‘now’ of our conscious awareness glides steadily forward, transforming events that were once in the unformed future into the concrete but fleeting reality of the present, and thence relegating them to the fixed past."

        This "is seriously at odds with modern physics," declares Davies, citing Albert Einstein’s observation: "The past, present and future are only illusions, even if stubborn ones." His article smoothly wheels readers through a thicket of fascinating notions, concluding with: "After all, we really do not observe the passage of time. What we actually observe is that later states of the world differ from earlier states that we still remember. The fact that we remember the past, rather than the future, is an observation not of the passage of time but of the asymmetry of time."

       Why do women often remember things men usually forget?  Simple:  women are wired to feel and remember more than men.

       We’ve long known that the physical link between brain hemispheres—the corpus callosum—is more heavy-duty in females than in males and likely transmits more sensory-rich, cross-over information.  Now, a recent study of memory finds that “the wiring of emotional experience and the coding of that experience into memory is much more tightly integrated in women than in men.”

        Tested with pictures designed to provoke neutral or strong emotional responses, women recalled 75 percent, men only 60.  Not a whopping difference, though enough to confirm earlier research that women, in general, have superior "autobiographical" powers.

        But is that always good?  Not necessarily.  The study may help determine why women are more prone than men to clinical depression, said lead researcher Turhan Canli, a psychology professor at State University of New York, Stony Brook.  He noted that rumination—chewing over a negative memory—is a risk factor for depression and that the study may spotlight a biological basis for rumination.

        Another reason not to dwell on hurtful memories but to resolve them and bid them goodbye.
 
 

        And finally,

  Déjà vu: Haven’t we met before (or am I dreaming)?

       Though it’s your first visit, you just know you’ve been here before—or already met the person you were just introduced to. We have no definitive answers about why the feeling of déjà vu ("already seen" in French) comes to us but several theories relating to memory give further insight.

        Sigmund Freud thought the process was triggered when someone was reminded of an unconscious fantasy, says James M. Lampinen, professor of psychology at Univ. of Arkansas, in the same special issue of Scientific American . There’s also what psychologists call "global matching models" -–events that share similarities with stored memory. Dutch psychiatrist Herman Sno suggested in 1990 "that memories are stored in a format similar to holograms. Unlike a photograph, each section of a hologram contains all the information needed to reproduce the entire picture. But the smaller the fragment, the fuzzier the resultant image. Déjà vu occurs when "some small detail in one’s current situation closely matches a memory fragment, conjuring up a blurry image of that former experience."

        "Researchers have distinguished between two types of memories," says Lampinen. "Some are based on conscious recollection; for example, most of us can consciously recall our first kiss. Other memories, such as those stimulated when we meet someone we seem to recognize but can't quite place, are based on familiarity."

       Now, about that first kiss…..                                                                      Guide/detail
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