// End -->

Uncovering the Complexity of Memory

The true complexity of memory is a recent discovery . Scholars generally agree now that memory is not one but different systems that are not always unified, that function as "modules" independently and in series , and that work both automatically and at will. Memory is limited and perhaps inaccurate. ; , but, in altered states, it is sometimes remarkable reliable and clearly beyond previously accepted limits ; ; ; ; .

The lexicon of modern memory reveals both complexity and confusion: short- and long-term memory, autobiographical memory, semantic memory, affect, perceptual and motor memory, declarative and procedural memory, "habit" memory, recognition and recall, explicit and implicit memory, embryonal imprints, holographic or cellular memory, anniversary memory, out-of-body memory, and past-life recall. Some of these extend completely beyond the "neurological substrate" that is supposed to contain them or make them possible ; .

The immune system, itself newly discovered, seems to have a remarkable memory of its own. This system seems to start identifying and memorizing foreign antigens without waiting for the brain to blossom. Some believe this system deals with an average of seventy viruses at a time and will ultimately accumulate information to deal with perhaps a million different antigens . Fortunately, you and I don’t have to do this consciously!

Another memory, not much studied, is musical memory, displayed, for example, by a virtuoso pianist who can play hours of the most elaborate piano music, all without a page of music… Astounding feats of memory (musical, mathematical, statistical_ are occasionally displayed by "idiot savants", the last persons we would expect to have a fabulous memory .

Research to unravel the mysteries of memory has naturally focused on the brain, especially the brains of live persons with brain injury or disease, or of those who have had radical types of brain surgery such as the split-brain operation that separates the left from the right hemisphere. Very extensive experimental surgery on animals had led to identification of specific circuits and key relay stations for certain kind of memory, fro example, circuits for visual recognition memory, spatial memory, circuits that connect emotions with memories, and senses with memories . Investigators have learned how to inflict memory loss by various combinations of injury and disconnection of the brain components such as the hippocampus and amygdala in the limbic system.

Combining such manipulations with psychological testing has led some neuroscientists to propose contrasting types of memory called declarative memory (knowing that something happened), which is apparently associated with the amygdala, and procedural memory (knowing how to proceed), which is associated with the hippocampus ; . Others find evidence for an entirely different circuit for habit, a memory that may be affiliated with the striatum. Independent of limbic circuits, this part of the forebrain is very ancient in an evolutionary sense and may help to explain how we (and our animal friends) learn things by constant repetition.

But these are not the only brain structures related to memory. Damage to the thalamus and hypothalamus can also hurt memory, as, for example, in Korsakoff’s syndrome where alcohol plays a destructive role.

Knowledge of brain processes is leaping forward with the help of new technology that permits direct observations of the living brain . Computerized tomography (CAT scans) and magnetic resonance imaging (MRI) show brain dimensions in depth and perspective, revealing possible structural abnormalities. Other instruments go beyond structures and can visualize functions of the brain, such as regional cerebral blood flow (RCBF).

Positron emission tomography (PET) can provide a metabolic map of brain activity, including blood flow rate, cell metabolism, and blood volume being delivered to specific areas. Tests done with this elaborate technology have shown electrical and chemical changes in a single neuron as a result of learning. But even with the cyclotron and the team of physicists and chemists required for PET, human memories are still invisible. Powerful as it is, this equipment, when pointed at the brain, does not sow us the expanded boundaries of memory.


or close window