November 28 Blog

Eric Kandel does an excellent job of detailing the development of the science of neurobiology in his book In Search of Memory: The Emergence of a New Science of Mind while simultaneously giving an account of his own maturation as a scientist, especially concerning his interest in the science of memory. I was particularly impressed with the earliest steps that were taken to gain an understanding of neural science and was astonished as I read that these scientists were able to hypothesize such complex and detailed mechanisms of nerves, synapses, and impulses with such a limited foundation of knowledge. Though some of the conclusions seemed somewhat logical, such as Cajal’s interpretation of the shape of nerve cells by studying infant animals and using a staining method, other conclusion seemed to be more coincidental. For example, it states further that Cajal inferred that neurons interact through a synapse, in which the axon of one neuron communicates with the dendrites of another. Because it was not detailed in the book, I wonder how Cajal was able to determine this; considering that microscopy was not as well developed, I am curious as to which scientific methods, if any, he used, or if it was merely a “leap of imagination” as Kandel stated on the prior page.

I was also particularly interested in Bourtchouladze’s discussion of the amygdala being involved in emotionally related and emotionally explicit memory. On page 85, he describes a study in which patients with no brain damage, brain damage to the amygdala, brain damage to the hippocampus, and brain damage to both we analyzed in terms of recall and emotional conditioning. Patients with hippocampus damage had no recall but showed normal emotional conditioning, patients with amygdala damage showed accurate recall but no emotional conditioning, and patients with damage to both showed neither. Bourtchouladze comments on the importance of this finding, stating that the results “clearly demonstrate that the amygdala is indispensable for fear condition” and that “they illustrate the double dissociation between emotional and declarative aspects of memory.” While reading this, I thought about reading we had done in previous weeks concerning emotional memories and their higher recall, as compared with non-emotional memories, and I couldn’t help but assume that the amygdala is the key to this. I was also intrigued by the idea of emotional conditioning, which was discussed both in this book and in Kandel’s book, and wondered how a conditioned stimulus is represented within the brain in comparison with an unconditioned stimulus.

After such learning occurs, some sort of memory consolidation must occur to transform it into long-term memory. In Kandel’s discussion of the biological basis of the process, which supported the idea that the transformations necessary for learning and memory occur in the synapses rather than in the variety of cell, he discusses the idea of the number of synaptic terminals and active synapses changes. Specifically, he states that long-term sensitization results in a doubling in the number of synaptic terminals and an increase from 40% to 60% of active synapses, and when the memory fades, the numbers drop again. While this concept makes sense in terms of the words sensitization and habituation, I wondered what role the pruning of neurons and synapses played in the equation.