The Smart Gene
The human brain has approximately 100 billion nerve cells, or neurons that are linked in networks to give rise to a variety of mental and cognitive attributes, such as memory, intelligence, and personality. These networks include the nerve cells. At the synapse, information in the form of chemicals called neurotransmitters flows from the so-called presynaptic cell to the postsynaptic cell. These nerve cells become more tightly linked when stimulated by a series of high-frequency electrical pulses. This increase in synaptic strength is know as long-term potentiation (LTP) just as the decrease in strength is known as long-term depression (LTD). LTP is found in the hippocampus, which is a crucial brain structure for memory formation. Research has indicated that "the induction of the major forms of LTP and LTD requires the activation of NMDA (N-methyl-D-asparate) receptors, which sit on the cell membranes of postsynaptic neurons (see Fig 3) (Tsien 2000)." The NMDA receptor, a synaptic coincidence detector, acts as a switch for memory formation, enhancing the signal detection by NMDA receptors should enhance learning and memory. Protein subunits called NR2B are part of the complex of proteins that form the
Using the cues on the laboratory wall the transgenic mice were more likely to swim to it's original location, indicating they had remembered were it should be. " Another experiment to measure emotional learning using fear-extinction was performed. Tsien and his team examined the recombinant NR1-NR2B complex and found that it had a "longer excitatory postsynaptic potential (EPSPs) than the NR1-NR2A complex (Ya-Ping 1999). NR2B expression is downregulated during the transition from juvenile to adult stages, this corresponds with the gradual shortening of the EPSP duration of the NMDA channel. This again confirms better learning and memory in transgenic mice. The conditioned stimulus was an 85dB tone and the unconditioned stimulus was a continuous scrambled foot shock. It is thought that if an animal is repeatedly exposed to the context or conditioned stimulus without the unconditioned stimulus the context or conditioned stimulus will lose its ability to produce fear responses. With Joe Tsien's discovery, Sharon Guynup, author of The Smart Gene, (Guynup 2000) says "it will help researchers better understand the workings of the human brain--and could lead to new treatments for learning disabilities, such as brain damage and Alzheimer's diseases. So, if the NMDA receptor, a synaptic coincidence detector, acts as a switch for memory formation, then enhanced signal detection by NMDA receptors should enhance learning and memory. " In other words, "a synapse between cell A and cell B will be strengthened if the two cells are active at the same time (Gordon 2000). These results indicate the Doogie mice to "have better memory and be faster learners (Tsien 2000). Tsien then set out to prove the theory that overexpression of NR2B in the brains of mice, leads to enhanced activation of NMDA receptors, which in turn leads to superior ability in learning and memory. This analyzed data also showed that the transgenic mice showed again, a much stronger fear response than the wild-type mice. The analysis of these experiments show that there is a significant difference between transgenic and wild-type mice in contextual extinction and in cued extinction.
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