As a cognitive neuroscientist, I think of the stock market as a proxy to the behavior of all people participating. Prices are set by the market, consisting of the aggregate behavior of all those participating. Stock prices can be a way of quantifying sentiment and ideas toward a particular company, sector, or even country. Once information is available to the market and is processed, reaction and behavior quickly follows. Not much different than sensory information entering the brain, being processed, and generating behavior.