Echinacea

The herbal supplement industry is a multi-billion dollar juggernaut. It’s nice to see some of their outlandish claims finally get put to the test. The New England Journal of Medicine today reports that echinacea ( E. angustifolia root) has no effect for curing the common cold. There is a nice story in the New York Times. I’m sure adherents that swear by it (like my parents) will continue to take it but perhaps this study will put a little dent into sales.

The study took 437 volunteers, challenged them with the cold virus and randomly assigned them with pretreatment, treatment or placebo. The result was that there was no evidence that any form of treatment with echinacea had any significant effect in combating the cold or alleviating its symptoms.

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Phosphorus and nitrogen

The six most important elements for life are carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus. The abundances of these elements in biomass approximately mirror what is found in the earth’s crust except for phosphorus which is about 6 times more abundant in biomass. However, the abundance of phosphorus in the ocean is the same as that found in biomass. This is no accident. Oceanographer Alfred Redfield found 70 years ago that the nitrogen to phosphorus ratio was 16:1 in both sea plankton and the ocean. He noted that this was not a coincidence but that the plankton was setting the ratio of the ocean. There is no intrinsic need for this ratio as plankton grown in laboratory conditions can exhibit a wide range.

The phosphorus in the ocean comes from the weathering of rocks on land. It is sequestered by oceanic life forms like plankton and then precipitates to the ocean floor when these organisms die. The availability of phosphorus sets the limit to how much life can be sustained by the ocean. This then sets the balance between oxygen and carbon dioxide in the oceans which in turn affects the balance of carbon dioxide in the atmosphere.

Now, some have argued that the increase of carbon dioxide in the atmosphere will lead to more vegetation which will counter the growth in CO2. However, more vegetation can grow only if it can acquire enough phosphorus and nitrogen. Although the atmosphere is 78% nitrogen, plants, other than legumes, cannot utilize it. They must obtain their nitrogen from the soil which mostly comes from animal waste or decaying biomass. Land animals that eat fish will transfer some nitrogen from the ocean back to the earth. The bottom line is that life on earth is precariously balanced and we really have no idea what will happen when we begin to perturb the system.

Modern Living

The June issue of Smithsonian Magazine has some interesting numbers:

The List: 1970 Price Index

Gasoline $.36/gallon
Median Income $8,734/year
Median Rent $108/month
Median Home $17,000
Bacon $.97/pound
Eggs $.51/dozen
Bread $.24/loaf
Vitamin D Milk $1.14/gallon
First-Class Postage Stamp $.06
Harvard College Tuition $2,600/year

Compared to 2005, the cost of food has changed surprisingly little. The price for eggs and milk have only doubled over the last 35 years while Harvard’s tuition and the cost of housing has gone up by more than a factor of ten. You only have to walk down the streets of any large American city to realize that getting enough food is no longer a major problem. The problem these days is finding affordable housing and putting your kids through college.

According to a February article in Amber Waves (a USDA publication):

Between 1952 and 2003, the ratio of food prices to the price of all other goods has fallen by 12 percent. The drop is even more dramatic if you factor in `quality improvements’—the reduced time cost of acquiring and preparing food (convenience), greater variety, and omnipresent restaurants and vending machines.Foods that once were available only seasonally are now available year-round. Advances in food processing and packaging have introduced a multitude of ready-to-eat foods, available virtually anywhere and at any time.

Harvard University’s David Cutler, Edward Glaser, and Jesse Shapiro have suggested that the increase in food consumption prompted by the falling time cost of food is the major cause behind the surge in obesity since 1980. They note: “Technological innovations—including vacuum packing, improved preservatives, deep freezing, artificial flavors, and microwaves—have enabled food manufacturers to cook food centrally and ship it to consumers for rapid consumption. In 1965, a married woman who didn’t work spent over two hours per day cooking and cleaning up from meals. In 1995, the same tasks took less than half the time.”

Face Cells

The June 23, 2005 issue of Nature reports work by Christof Koch and colleagues on the existence of “face recognition” cells in the hippocampus of the brain. This paper got a lot of play in the popular press because some of the cells only responded to famous people such as Halle Berry. The group found that the cells were highly selective to various views of a given person but not to another person. I think this work confirms some current theories of memory (see for example McClelland et al. Psychological Review, 102:419 (1995)). It’s also more proof that there isn’t much difference between humans and other mammals.

It is known that cells in the hippocampus in the rat code for spatial location in the same way. A given cell will only fire when a rat runs through a given spatial location in a given environment. When the environment changes, that same cell will then code for a completely different location. Location is important to a rat, just as the recognition of people is important to humans.

When the hippocampus is removed, humans can no longer form long term memories. They can remember things as long as they pay attention to it but once they lose their train of thought, the memory is completely gone. It is thus thought that the hippocampus is a form of mid-term memory that stores lots of information that is then slowly uploaded to the cortex for longer term storage.

It’s useful to have different memory systems for different time scales because every time you remember something new you run the risk of erasing something old. One way out of this conundrum is to separate long term memory from short term memory. Simplistically, your hippocampus would store whatever information comes in and indiscriminately overwrite old information. Then slowly over time, the hippocampus would upload information to the temporal cortex (perhaps during dreams) which would update its synapses in a controlled fashion making sure not to erase important old memories.

What this paper shows is completely consistent with this idea. From theoretical work on associative memory, we know that the capacity of any neural network is limited by how correlated the stored patterns are with each other. The more correlated the patterns, the more likely they are to interfere. Thus, one way to make sure you don’t overwrite old memories is to make sure the input patterns are orthogonal. The hippocampus may serve this purpose. A very sparse code, where only a few neurons encode a given concept (like Halle Berry), automatically orthogonalizes the patterns representing given memories presented to the higher cortical areas.

A sparse code is not robust because if you knock out that particular neuron you lose the memory it coded. A more robust code would be a population code where a large group of neurons encodes a given concept. The problem with this type of memory is that it’s hard to train a network. So the way to overcome the trade-off between robustness and speed is to have a fast but fragile system (hippocampus) feed inputs to a slow but robust system (temporal cortex).

It is known that inferotemporal (IT) cortex of monkeys also respond to faces among many other percepts and that a given cell in IT will respond to a wide variety of images. So, if they ever get a chance to implant electrodes in the temporal cortex of humans, I’m sure they’ll find similarly behaving cells.