The truth is both much less interesting, and far more insidious. You don't need nano particles to read the brains of the population. You don't need secret sciences, or nefarious groups controlling the world. All you need is a capitalist political economy, lax regulations on advertisements, no regulations on data collection, basic psychology, and a century of experience influencing the whims of the most propagandized population on earth.

Nowdays, these ads are targeted. There's a bot running on a database right now calculating the last time that you ordered pizza, how this gap correlates with others that they've recorded, and deciding whether it's worth spending a fraction of a cent to buy an ad on the game that you're playing. It's not surprising that a data center designed to figure out when is the optimal moment to tempt you with your favorite treat, manages to send you an advertisement The same time you decide you want that treat. Even less so when they've spent your entire life conditioning you to want that treat.

I Don't doubt for a minute that Google is using its vast data gathering abilities to target advertisements, using microphones and access to email, pooling data together from multiple websites and tracking cookies, but what's terrifying is they don't really need to. They already know my fat ass is going to want pizza sometime soon, they don't need to monitor my microphone for keywords if they know it's just a matter of time. I'm sure they read our emails, but they don't have to read your emails to know that you're single, they don't need to monitor everything you do on your phone, to know people don't like being lonely.