In the first installment of this series posted on Dec. 31, 2008, I argued the importance of language for a Theory of Mind. In this installment, I discuss a role for memory.
On Dec. 2, 2008, Henry Gustav Molaison, passed away at the age of 82. H.M., as he became known to scientists around the world, developed seizure activity after an accident at the age of 9 and began to suffer from severe bouts of epilepsy from the age of 16. Since his seizures recurred progressively more frequently and gained in intensity, turning unbearable at the age of 27, the middle temporal lobe of the cerebral cortex was surgically removed from both hemispheres, including parts of the hippocampus and the amygdala.
After surgery, Henry would experience only two other severe seizures in his life, but was a changed man forever. He developed profound amnesia, becoming the subject of intense scientific study for the rest of his life and, since he dedicated his body to science, beyond.
He was well-mannered, could speak eloquently and execute daily routines of hygiene, dress and nourishment. He could mow a lawn and do small household chores. He retained memories of some major historic events before his surgery. He could remember where is family was from. He remembered his name, but he did not know how old he was. He could recall immediate events instantaneously and could judge against internalized references. That is, seeing himself in a mirror he would exclaim: "I am not a boy!" However, he was not able to remember persons or events from the day before and could not make any plans for tomorrow, as if he lived in permanent presence every day anew.
The eminent British psychologist Brenda Milner and her colleagues could demonstrate in elegant series of tests that H.M. was able to learn subconsciously procedural skills involving so-called implicit memory, but could not retrieve declarative explicit memory of episodes in the past. The hippocampus was implicated in the latter type, playing a crucial role in the processing of our conscious thoughts. H.M. retained a sense of self, but could not remember who he was. He had lost a distinct piece of his identity, an essential ingredient of his mind. His neurosurgeon William Beecher Scoville, who strongly opposed this type of surgery after this devastating outcome, and Brenda Milner published their first observations on H.M. in the Journal of Neurology, Neurosurgery and Psychiatry in the late 1950s (Scoville and Milner, 1958).
In 1985, the Swedish neuroscientist David Ingvar published a remarkable essay in the now defunct scientific journal Human Neurobiology on the role of memory and the areas in prefrontal cortex known to be involved in the processing of memory at the time(Ingvar, 1985). About 1970 he, Niels Lassen and others had successfully assembled a scanning device at Bispebjerg Hospital in Copenhagen, Denmark, with which local cerebral blood flow in human cerebral cortex could be mapped non-invasively using radioactive xenon-133 gas as tracer (Lassen, 1985), while the participants were exposed to sensory stimuli or were executing tasks. The Bispebjerg Hospital was set to become the first institution where functional brain imaging would become routine.
In collaboration with Drs. Seymour Kety and Louis Sokoloff at the National Institutes of Health, Drs. Lassen and Ingvar helped pioneer methods used to demonstrate that local cerebral blood flow changes commensurate with metabolic and electric nerve cell activity under normal physiological conditions. Based on this discovery, colleagues at Bispebjerg Hospital would be able to demonstrate later that visual mental imagery, e.g. the navigation of visual scenes in front of the mind's eye, activated many regions of cortex that are ordinarily engaged in the processing of visual input (Roland and Friberg, 1985). They would be able to identify cortical areas activated during the retrieval of memory. One compelling discovery Dr. Ingvar described in his essay in Human Neurobiology was that the same regions in the frontal lobes of cerebral cortex that were activated when people remember episodes in their past were also active when they were asked to make plans for the future. He concluded that there can be no planning of future actions without memory of the past. He called this process forming memories of the future.
Dr. Ingvar's insights inevitably posit that any human invention, any creative process, any idea we form of something unprecedented from mere mental concept to actual implementation hinges on our declarative memory. Indeed, with this wonderful gift we can make dreams come true. Hence, declarative memory must constitute another pillar of a Theory of Mind.
- Prologue to A Theory of Mind
- Theory of Mind I: Feral Children & Language Development
- A Theory of Mind III: Emotions
- On occasion of H.M.'s passing, informative reports appeared in The New York Times on Dec. 4, 2008 (Bendict Carey's article entitled "H. M., an Unforgettable Amnesiac, Dies at 82"), and in the Economist on Dec. 18, 2008 ("Henry Molaison, a man without memories, died on December 2nd, aged 82").
- National Public Radio's Weekend Edition broadcast a segment on H.M. by Brian Newhouse's with the title "H.M.'s Brain and the History of Memory" on Feb. 24, 2007.
- In support of Dr. Ingvar's hypothesis, Hassabis and others (2007) observed that amnesic patients with hippocampal damage were unable to imagine future experiences.
- Joshua Foer tells us about constructing memory palaces in his latest book with the title "Moonwalking with Einstein: The Art and Science of Remembering Everything" just published by Penguin Press, New York. Building memory palaces constitutes an intriguing strategy for retaining excellent memories and may possess profound bearing on a sharper mind. The method was developed in the classical age and rediscovered during the Renaissance. Perhaps, the extraordinary explosion of creativity in the arts and the sciences during that period depended on such strategies to memorize facts in a time when books were still inaccessible to most (03/08/11).
- Ingvar DH (1985) "Memory of the future": an essay on the temporal organization of conscious awareness. Hum Neurobiol 4:127-136.
- Lassen NA (1985) Cerebral blood flow tomography with xenon-133. Semin Nucl Med 15:347-356.
- Roland PE, Friberg L (1985) Localization of cortical areas activated by thinking. J Neurophysiol 53:1219-1243.
- Scoville WB, Milner B (1957) Loss of recent memory after bilateral hippocampal lesions. J Neurol Neurosurg Psychiat 20:11-21.