I just returned from the Society for Neuroscience annual conference, where 30,000 neuroscientists swarmed into downtown San Diego to share their latest findings on everything from the teenage brain to the hedonistic synapse. There's never enough time to see everything interesting at this massive meeting, but here's a snapshot of a few things I heard about.

The neurochemistry of trust: Serotonin, that famous chemical messenger of happiness, seems to play a role in trust. Robert Rogers and his colleagues at Oxford University had undergrads play a game known as the Prisoner's dilemma, in which players must choose to cooperate with another player or look out only for themselves. About 75 percent of players chose to cooperate under normal conditions, but when they were given a diet to reduce tryptophan, a precursor of serotonin, students rated other players as less trustworthy, and their cooperation levels dropped significantly. Perhaps that tryptophan-laden Thanksgiving turkey has more significance than we realized.

Alzheimer's disease: If you want to lower your risk of Alzheimer's disease, keep your cholesterol down. Previous studies have suggested a link between Alzheimer's and cholesterol, but a new study presented by Eric Reiman at the University of Arizona found that higher cholesterol levels in middle age were linked to lower activity levels in the brain areas associated with Alzheimer's. The correlation was strongest in people with APOE4, a genetic variation known to boost Alzheimer's risk. Scientists speculate that cholesterol accelerates the molecular processes that boost risk for the disease.

A second study showed that a computer training program, previously shown to boost cognitive function in healthy old people, can also improve symptoms of mild cognitive impairment, a condition that often precedes Alzheimer's. (For more about the computer program, see "Exercising the Brain.")

Spinal cord injury: A new antibody has entered clinical tests for spinal cord injury. The antibody blocks the activity of a chemical released after spinal cord injury that blocks nerve growth. (It's not quite clear why the body releases these inhibitory factors, but they have proved to be a major hurdle in developing treatments for spinal cord injury.) In preliminary tests in monkeys presented by Martin Schwab and his colleagues at the University of Zurich, the antibody was able to restore function to the animal's damaged hand.

Stroke therapy: A simple device under development by BrainPort Technologies could help stroke patients regain their sense of balance. The device hangs around the neck and is attached to a small cord and stimulator placed under the tongue. The neck piece detects the position of the head in space and then transforms that information into electrical impulses on the tongue.