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For instance, emotional memories are stored in the amygdala, but words are recorded in the temporal lobe. Meanwhile, colors and other visual information are collected in the occipital lobe, and the sense of touch and movement reside in the parietal lobe. So far, scientists have identified more than twenty categories of memories that are stored in different parts of the brain, including fruits and vegetables, plants, animals, body parts, colors, numbers, letters, nouns, verbs, proper names, faces, facial expressions, and various emotions and sounds. Figure 11. This shows the path taken to create memories. Impulses from the senses pass through the brain stem, to the thalamus, out to the various cortices, and then to the prefrontal cortex. They then pass to the hippocampus to form long-term memories. (illustration credit 5.1) A single memory—for instance, a walk in the park—involves information that is broken down and stored in various regions of the brain, but reliving just one aspect of the memory (e.g., the smell of freshly cut grass) can suddenly send the brain racing to pull the fragments together to form a cohesive recollection. The ultimate goal of memory research is, then, to figure out how these scattered fragments are somehow reassembled when we recall an experience. This is called the “binding problem,” and a solution could potentially explain many puzzling aspects of memory. For instance, Dr. Antonio Damasio has analyzed stroke patients who are incapable of identifying a single category, even though they are able to recall everything else. This is because the stroke has affected just one particular area of the brain, where that certain category was stored. The binding problem is further complicated because all our memories and experiences are highly personal. Memories might be customized for the individual, so that the categories of memories for one person may not correlate with the categories of memories for another. Wine tasters, for example, may have many categories for labeling subtle variations in taste, while physicists may have other categories for certain equations. Categories, after all, are by-products of experience, and different people may therefore have different categories. One novel solution to the binding problem uses the fact that there are electromagnetic vibrations oscillating across the entire brain at roughly forty cycles per second, which can be picked up by EEG scans. One fragment of memory might vibrate at a very precise frequency and stimulate another fragment of memory stored in a distant part of the brain. Previously it was thought that memories might be stored physically close to one another, but this new theory says that memories are not linked spatially but rather temporally, by vibrating in unison. If this theory holds up, it means that there are electromagnetic vibrations constantly flowing through the entire brain, linking up different regions and thereby re-creating entire memories. Hence the constant flow of information between the hippocampus, the prefrontal cortex, the thalamus, and the different cortices might not be entirely neural after all. Some of this flow may be in the form of resonance across different brain structures.
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Michio Kaku (The Future of the Mind: The Scientific Quest to Understand, Enhance, and Empower the Mind)