Modern biomedical research focuses on the brain as the location of memory, in spite of the many signs that this is only part of the story. The reason for the bias is partly historical. It arose from early brain research, some of which was done by the famous Canadian pioneer of neurosurgery, Wilder Penfield, in the 1920s. Penfield discovered that electrical stimulation of particular areas on the brain surface caused patients to re-experience “memories” from the past. These recollections contained vivid details of long-forgotten events that manifest as moving picture like “flashbacks.”
After years of research along these lines, Penfield concluded that electrical brain stimulation could activate sequential records of consciousness laid down during a person’s earlier experience. The detail contained in these recalls was so vivid that Penfield concluded that every experience we ever have is recorded in the brain.
The vividness of memory recall is familiar to massage therapists as well as to practitioners of various other somatic methods, including hypnotic regression, rebirthing, acupuncture, and even music and movement therapies. During sessions employing these and other methods, clients often relive early traumatic experiences. In some cases, experiences that took place at birth, or even in utero, can be recalled in detail, and with observable therapeutic benefit.
Penfield’s discovery that electrical brain stimulation elicits specific recollections led to an obvious, but incorrect, conclusion. Memory traces, which are called “engrams,” seemed to be stored as patterns of neural discharge in specific areas of the brain. This idea was supported by research showing that surgical lesions in certain areas of the cortex can seriously disrupt learning.
Modern researchers have repeated Penfield’s studies and questioned the original interpretations. “Memories” elicited by electrical stimulation of the brain have a dream-like quality, and may not be memories at all. Sometimes stimulation at different sites produces the same recollection, and at other times repeated stimulation at one site evokes different recollections. Even removal of major parts of the temporal lobe, the location of the stimulation points, did not destroy memories of events that had been elicited by electrical stimulation of the lobe before it had been removed.
The brain is part of an intricate system, and the effects of stimulating, damaging, or removing certain parts does not prove that those parts are the locations of memories. Because of the interconnectedness of the nervous system, one cannot be certain that a particular evoked experience is stored near a site of electrical stimulation, or far away from it. Moreover, each region of the cortex refers to a particular part of the body. The brain and distant tissues are connected by motor and sensory nerves and by other communicating channels within the living matrix. Stimulation of a spot on the cortex may activate an intricate system that includes cells and tissues that are very far from the site of stimulation.
The logical problem of confining the search for memory and consciousness to the brain has exacerbated an already difficult problem: study of these phenomena is conducted by narrow disciplines, each with methods to study only a small part of the whole problem.
The brain’s monopoly on memory has been eroding for many decades. Studies done as early as 1940 demonstrated that certain simple reflexes can be conditioned or learned by spinal cord neurons that have been surgically disconnected from the brain (Shurrager and Culler). This fact led to the conclusion that memory may be found in all parts of the nervous system. We now see that this concept, too, may be limited, because of cytoskeletal memory in non-neural cells, and because there are other forms of information storage in soft tissues (ea. as the orientation of connective tissue fibers)
From our point of view, the most significant lines of inquiry arose from studies of neurophysiologists who continued Penfield’s search for the location of the engram. Of these, one of the best known was Karl Lashley, the distinguished Harvard psychologist who spent virtually his entire scientific career, 30 years, in an unsuccessful search for the engram.
Lashley’s basic approach was to train rats to perform tasks such as running in a maze to find food. He would then surgically damage or remove specific parts of the rats’ brains, or cut the connections between them, and test again. His goal was to identify the part of the brain where the maze-running engram was stored. Even removal of large amounts of brain tissue, which impaired the rats’ motor skills, failed to erase memories essential to running through the maze. Lashley concluded that all parts of the functional area where memory is stored are “equipotential.”
Karl Pribram was a student of Lashley, and wanted to continue the search for the engram. After reviewing all of Lashley’s work, Pribram concurred that memory must somehow be distributed throughout the brain as a whole, rather than localized at specific sites. This view was supported by the repeated observation of neurosurgeons that removal of large portions of the brain for medical reasons can dim a person’s memory, but never seems to cause a selective loss of particular memories. The engram is so elusive that some neurophysiologist suspect that it may not exist.
Pribram’s problem was that there was no concept of memory that was consistent with all of the evidence. This fact had a deep impact on the field of experimental psychology, which had great difficulty advancing without a solid understanding of the mechanisms of processes so basic as learning and memory.