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Happiness in a bottle? Gary Greenberg's article "The Serotonin Surprise" [July] provided a deeper look into the effects of commonly prescribed antidepressants. The observation that neurogenesis strongly coincides with the effects of antidepressants is far from a comprehensive understanding of these drugs. In brain function, quantitative changes (an increase or decrease in neurons, for instance) contain almost no information without knowledge of the topology, connections, and type of activity. What evokes new neurons into action, where the information is conducted to, whether the neurons are all the same, and whether they keep the same characteristics over time are questions that need to be answered. Neurogenesis may also be the cause of common side effects of antidepressants. Psychiatrist Joseph Glenmullen's concern about the drugs' toxicity over the long term should extend beyond their serotonin-boosting effects. Since no drug is 100 percent selective, long-term effects— especially when high doses are taken— may result from chronic activity at other binding sites.

Gal Levin Dallas, Texas

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Power to the People In Discover Dialogue [July], Christopher Flavin speaks of the future of a "hydrogen infrastructure" for transportation and stationary power sources. To my knowledge, we now have only two industrial sources of hydrogen: electrolysis of water and partial oxidation of fossil fuels. Partial-oxidation power plants are efficient, but they still generate carbon dioxide, which is the big concern in global-warming mitigation. One can make hydrogen from hydropower and solar electricity. But can we divert enough hydropower electricity from present needs or dedicate enough solar panels to generate the hydrogen equivalent of current hydrocarbon transportation fuels? It seems the only practical routes to generating the electricity for hydrolysis— without also generating carbon dioxide— are via nuclear fission or fusion generation.

U. V. Henderson Chesterfield, Virginia

Christopher Flavin responds: The writer is correct that partial oxidation of carbon-based fuels and electrolysis of water are the two most promising ways of deriving large amounts of hydrogen fuel. However, the options for producing hydrogen via electrolysis are far greater than he suggests. Among the renewable energy sources available in abundance are solar energy, wind power, geothermal energy, ocean tidal and current power, and bioenergy. The wind power sweeping across three U.S. states alone— North and South Dakota and Texas— exceeds total U.S. electricity use, and the solar energy striking Earth daily is 6,000 times the energy used by the global economy. The costs of these energy sources have fallen dramatically in the past 10 years and in the case of wind power are already below those of natural gas and nuclear power. Moreover, solar energy and wind power are now the world's fastest-growing energy sources— averaging a growth rate of more than 20 percent per year in the last five years, compared with less than 1 percent for nuclear power. Thus, renewable energy is a far more promising source of energy to produce hydrogen fuel in the coming decades.

Volts Wagon In talking about hybrid electric vehicles ["Go Slower, Get There Faster," June], hardly anyone mentions what happens to these vehicles when they are involved in an accident. The Emergency Response Guide [distributed by Toyota to firefighters and emergency medical service personnel] for the Toyota Prius states: "The Prius carries a high-voltage system (about 300 volts), and its battery contains the highly alkaline electrolyte of the potassium hydroxide solution. Careless handling of the damaged vehicle, therefore, may result in electrocution or severe injury." Among the "necessary items" [response personnel must have] are insulated gloves, goggles, safety shoes, 20 liters of saturated boric acid solution, red litmus paper, and a class D fire extinguisher. As an emergency responder, I worry about the safety of fire and EMS personnel when removing patients from these types of vehicles.

Raymond Poche Prairieville, Louisiana

John Hanson, Toyota national product news manager, responds: The items mentioned in the Prius Emergency Response Guide would apply to handling a chemical spill of any automotive fluids or metal fires. The Prius uses NiMH batteries, which are similar to those used in many consumer products. The battery pack is made up of 38 sealed, nonspillable 7.2-volt modules in a protective metal housing, located in an area rarely damaged in collisions. Unlike the liquid of lead-acid batteries commonly used in automobiles, the electrolyte in the Prius battery is a gel and is fully absorbed into the cell plates. Additionally, an automatic shut-down system isolates the voltage inside the battery housing if the system's computers detect anything unusual.

Truth or Consequences Corey Powell states in "Planet of the Fakes" [Sky Lights, June] that the "face" on Mars "is just an ordinary hill." But as Mr. Powell says himself, "eyes are not always reliable reporters where Mars is concerned." Unless Mr. Powell has visited Mars himself, there is no reason why we should trust his eyes when it comes to the face's origin. There are some interesting ideas about the face on the Web site, which suggests that the face has the earmarks of an artificial structure. The Enterprise Mission has tried to find a natural explanation, but so far it has found nothing that proves this structure is just a hill. The Web site also says the face is old enough to point to the presence of past intelligent life on Mars. It is easy to deny the existence of artificial artifacts on Mars because it goes against everything we've been taught. However, true science should not dismiss a theory out of hand just because it seems silly or impossible. Science should investigate theories fairly by looking at the evidence and proposing ideas.

John True Kansas City, Missouri

Corey S. Powell replies: In science, the burden of proof lies with those making extraordinary claims. Anyone believing the "face" is artificial therefore needs to produce powerful evidence that natural forces could not have produced such a formation; it is not up to researchers to prove a formation that looks like a hill really is a hill. Yet by Mr. True's own admission, the argument in favor of the face's existence rests on little more than some "interesting ideas." If future Mars missions find signs of intelligent life, I will be as excited as anyone by the discovery. But wild speculation based on a heavily processed and altered image is not science.

Click here for more letters on Sky Lights, or letters on the Discover Innovation Awards, Vital Signs and Reviews.

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