I think this study used an INFUSION method to apply the magnesium. Meaning injection ..probably IV.

The doses therefore would be far in excess of any supplement you may try or use.

Magnesium infusions are sometimes used to also treat migraine.
example:
http://www.ncbi.nlm.nih.gov/pubmed/8984087
1000mg directly into the blood stream.

Compare that to oral use ...which never gives 100% of the dose absorbed. Two SlowMags a day provide 120mg of elemental mag.

So taking a magnesium supplement (not oxide), would deliver about 10% what the study in this link you provided.

When magnesium is taken orally or from a food source there is a slow delay in absorption. This delay sort of buffers its actions.
When you shoot it IV... it floods the body and would have different results. There are studies to show that when used in treating eclampsia of pregnancy, the high IV dose used can sometimes set of myasthenia gravis in some patients. This is not a common event, but is an infusion reaction.

We had a poster on PN who received a magnesium infusion not too long ago, and he reported some side effects from it. This was to treat a severe scalp neuralgia that was thought to be migranous in nature.

So I think this study you provide used very high doses and that is extreme and may be part of the causitive results.

The highest dose I have seen used therapeutically was 6000 mg in 1000ml saline infused over several hours very slowly. This extreme amount is sometimes used to treat patients getting chemotherapy because some chemo drugs deplete magnesium.
But I was rather worried about this dose, and was assured that if the admin rate was very slow, that the body and kidneys can handle it. I think this example is very extreme and monitored by a nurse at all times, so the infusion can be quickly stopped it the patient gets into trouble. The few yearly statistics on magnesium toxicity include IV infusions. In fact they can easily poison an elderly patient or someone with renal failure.

This link shows magnesium infusion dosing... notice it only goes up to 4 grams..
http://www.globalrph.com/magnesium_dilution.htm