August 19, 2007

Recent Advances in Memory Research

RAM chipsThough how memory is formed, stored or retrieved has not been elucidated yet, things are beginning to unfold as new advances begin to break the frontiers. It was long thought that long term memories (memories such as the persons own name), which remain steadfastly seated in the brain, were etched permanently in the brain. But, recent advances in research has proved to the contrary. Long term memories are not like something as a computer's ROM (Read Only Memory, which once stored can not be erased and it does not need any maintenance current once the data had been entered; EPROM and EEPROM are exceptions), but it resembles a computer's RAM (Random Access Memory, which needs to be continuously fed with electricity in order to retain its memory).

In a classic experiment by Prof. Yadin Dudai, Head of the Department of Neurobiology at Weizmann Institute of Science, Israel, and colleagues had trained rats to learn to avoid certain tastes. This is called conditioned avoidance, a form of operant conditioning (learning that is influenced by environment). This is done by giving an unpleasant stimulus such as electric shock or injecting substances that cause discomfort, along with some foods. Thus the animals 'remember' to avoid these foods which are associated with bad accompaniments. Prof. Yadin Dudai had injected a chemical, an inhibitor of a protein called PKM zeta, into the rats' taste cortex. A single administration was found to erase the long term memories of those rats completely. The rats forgot which tastes they were to avoid.

PKM zeta (or Protein Kinase M zeta) is an isoform of protein kinase C, an enzyme present within the cell membrane. This molecule (PKM zeta) is necessary for an already learned and deep rooted response (long term memory) to remain long term. The constant ferrying activity of PKM zeta in the synapse (junction between two neurones) is needed for the memory to be retained, reminding us of the constant supply of electricity needed in the RAM of computers to retain its memory. Thus the long founded idea that long term memories were etched permanently into the brain is now being challenged and a new dynamically modeled approach such as this is emerging.

A process called long term potentiation (LTP) occurs in the brain which help us to learn. Repeated high frequency stimulation of a synapse strengthens it by LTP. It should be noted in this context that nicotine helps in memory formation since it stimulates the inhibitory inputs to layer V pyramidal cells. These cells exert a negative influence on LTP based learning. Hence suppression of these cells by nicotine helps in memory formation.

Another very useful discovery is the development of a new microscopic technique that has allowed us to 'see' memory traces in the brain. Using restorative deconvolution microscopy, scientists at the university of California at Irvine, has shown how the synapse had expanded after LTP. If you think of the synapse as the space between two balloons, you will realize that by pressing these balloons towards each other, the balloon ends will flatten, leading to a broader synapse with a larger contact area. Just as in Ohmic resistance of electricity, here also the apparent resistance will diminish, leading to a faster and better processing and storing.

Such long giant leaps are needed to achieve better nootropics (memory enhancers), treat and cure Alzheimer's disease and related conditions.
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