Sunday, June 17, 2007

Remembering Words for where They Were Printed on the Page

Have you ever remembered something you read by recalling and then fanning back in your book to where it was located on the printed page (left page, right page, how far down)? My father and I both do this.

Knowledge of the space around us is central to our behavior, and so we learn to focus our attention in order to remember things and learn our way around. The Greeks had a technique described by Cicero in 55 B.C. of remembering words by picturing the rooms of a house, associating words with each room, and then mentally walking through the rooms in the right order.

Spatial memory is the scientific term concerned with finding one's way around in space. In our hippocampus is something called a spatial map: a cognitive map which internally represents the external environment.

Our brains do not have a sensory organ dedicated to space. So they must combine inputs from several different sensory inputs to generate a complete internal representation. it does this in many areas and many ways, different for men and women.  Brain imaging shows the brains of men and women light up in different areas as they think about space! (In Search Of Memory, pp. 307-316)

Putting Humpty-Dumpty Back Together Again

In relation to my last post, when different aspects of sensual perceptions are reconstructed, where exactly in the brain are they integrated? What strategy does the brain use to read itself out?  For example, if all the visual areas report to a single master cortical area, who or what does that single area report to?  Who is 'looking' at the visual image provided by that master area?" Kandel explains that there is no single cortical area to which all other cortical areas report exclusively, either in the visual or in any other system.   .. This question, which is central to the unitary nature of conscious experience, remains one of the many unresolved mysteries of the new science of mind. 304

The Brains of Birds and Taxi Drivers

In his treatment of spacial memory, Kandel moves into a fascinating discusson of how space is represented in the hippocampus of the brain. "The spatial memory of environments has a prominent internal representation in the hippocampus. This is evident even anatomically. Birds in which spatial memory is particularly important-- those that store food at a large number of sites, for example-- have a larger hippocampus than other birds.... London taxi drivers are another case in point... Functional magnetic resonance imaging revealed that after two years of [rigorous orientation] to the streets of the city, London taxi drivers have a larger hippocampus than other persons the same age." 306

Your Genes and Your Memory


Since my last post on Eric Kandel's In Search of Memory regarding the cellular neurobiology of the brain, I've continued to follow Kandel's discussion as he moves into molecular biology and the role which genes play in memory formation. Kandel draws three fascinating conclusions: 1) Activating long-term memory requires the switching on of genes. 2) To switch on these genes, one kind of protein must be activated and another kind, which suppresses memory-enhancing genes, must be turned off: "The fact that  a gene must be switched on to form long-term memory shows clearly that genes are not simply determinants of behavior but are also responsive to envirnonment stimulation, such as learning." There is a biological constraint on what experiences get stored in memory. (3) The growth and maintenance of new synaptic terminals makes memory persist. "Therefore, to rephrase Kandel, if you remember later anything of this post, it will be because your brain is slightly different after you have finished reading it." 276

The Man Who Mistook His Wife for a Hat

I'm reading this morning again from In Search of Memory, specifically about cognitive psychology and how our perceptions are stored in the brain. "The belief that our perceptions are precise and direct is an illusion-- a perceptual illusion. The brain does not simply take the raw data that it receives through the senses and reproduce it faithfully." Instead, each sensory system analyzes and deconstructs then reconstructs  the raw incoming information according to its own built-in connections and rules. To summarize, "sensation is an abstraction, not a replication, of the real world.  302

When it comes to vision, aspects of visual perception like motion, depth, form, and color are separated and carried along separate neural pathways to the brain, where they are coordinated into a unified perception. In the primary visual are of the cortex, "what" pathways (information about what an object looks like) are separate from "where" pathways (where it is, how the object is moving in space). Unfortunately, some people have defects in their cortexes and aren't able to put Humpty Dumpty back together again. For example, neurologist-neuropsychologist Oliver Sacks shares how  once upon a time he had a a patient who failed to recognize his wife sitting next to him and, thinking she was his hat, tried to pick her up on his head as he was about to leave the doctor's office. 303 Hope you haven't tried to do that!