I’ll see you in my dreams. Why do we dream? Do dreams help us process memories of social interactions? Do we use them to try out possible scenarios in preparation for social encounters in the waking state? Some recent experiments conducted by Patrick McNamara, a MED assistant professor of neurology, and colleagues at Boston University Medical Center, the Veterans Administration Boston Healthcare System, and Harvard Medical School have shed new light on these age-old questions.
The researchers fitted 15 undergraduates with a home-based sleep-wake monitoring system known as Nightcap, which senses eye and head movements to discern between rapid eye movement (REM) sleep, generally characteristic of the first two hours of sleep, and non-REM (NREM) sleep states. The students were awakened several times a night, during both REM and NREM sleep, and recorded detailed descriptions of their dreams on tape. They described where they thought they were, who else was present, and what they were doing, perceiving, feeling, and thinking. Students were also paged four times during the day to record their thoughts just before the page.
The analysis of thought and dream content revealed significant differences in the three states. The researchers found that social interactions were more likely to be reported during either REM or NREM dream states than in waking thoughts. Further, they found that aggressive social interactions were reported almost exclusively during REM sleep and no aggressive interactions were reported during NREM sleep. On the other hand, reports of dreamer-initiated friendliness were much more frequent during NREM sleep, leading the researchers to surmise that there is an active process in NREM sleep that inhibits aggressive social impulses and promotes the emergence of cooperative social impulses.
These results also seem to be in accord with known brain and neurochemical activity patterns that during REM sleep show reduction in serotoninergic activity (related to the neurochemical serotonin, which modulates mood) and activation of brain sites linked to aggression. In contrast, levels of serotonin rise during NREM sleep, and areas of higher functioning are activated in the forebrain.
“This calls into question theories that say dreams are the product of random mental activity,” according to McNamara. “If dreams are simply images that arise without meaning, intention, or cause, then one would not expect them to exhibit the kind of specialization that our results demonstrate.”
This research was published in the February issue of the journal Psychological Science.
Silicon cycles. Silicon, the 14th element on the periodic chart, is the most common element in the Earth’s crust next to oxygen. It is most often found combined with oxygen, forming silicon dioxide, also known as silica. It is the main component of many rocks, minerals, and sand and is used to make glass, bricks, and semiconductors. It also is present in the body: arteries, tendons, skin, connective tissue, the cornea, and the white of the eye contain relatively large amounts of silicon. Weathering of silicon-based minerals buffers soil, preventing it from becoming too acid to support life, and helps regulate the amount of carbon dioxide in the atmosphere.
Andrew Kurtz, a CAS assistant professor of earth sciences, studies the cycles by which elements such as silicon move through ecosystems, from earth to water and through living systems. He and colleagues at Cornell University and the University of California, Santa Barbara, recently completed experiments in Hawaii that challenged conventional thinking about silicon cycles.
Traditionally, earth scientists have believed that the amount of silicon found in water — in streams or in water trapped in soil — depends upon the rate at which rocks weather and release silicon from minerals. In fact, scientists have used measurements of silicon concentration in streams to derive weathering rates for rocks in the vicinity. In the ocean, on the contrary, the evidence points to plants, or plankton, as the dominant players in silicon processing. Silicon levels in the water are low at the surface, where plankton are alive and active, and high at the bottom, where decaying plants release their silicon into the water.
Kurtz and his colleagues found that in the Hawaiian Islands, as in the ocean, silica released to stream water seems to be mediated by biological processes. They hypothesize that silica-containing plants release stored silica to the upper levels of the basaltic soils of Hawaii, which would otherwise be silica-depleted. By maintaining a high concentration of silica in the plants’ rooting zones, they are able to buffer high levels of dissolved aluminum that would otherwise be toxic to the plants. The researchers propose that this process may also be characteristic of other terrestrial ecosystems, such as grasslands.
The silicon research was reported in the February 17 issue of the journal Nature.
Briefs" is written by Joan Schwartz in the Office of the Provost. To read
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