In the context of a threat, real or imagined, our emotional state can rapidly shift into fear or anxiety. This shift in emotional reactivity occurs in emotional related brain regions in the limbic system (or the "emotional brain"). A bottom-up signal is sent to other brain regions to recruit from other brain systems to help regulate via top-down signals specific aspects of emotional reactivity. When this system is working, the regulatory systems initiate changes in attention, thinking, and behavior.
Could I paraphrase the above as follows?
"A bottom-up signal (from the emotional brain) is sent to other brain regions. This is to seek help from other brain regions, because they can help regulate specific aspects of emotional reactivity via top-down signals."
My familiarity with “bottoms-up” and “top-down” have to do with management or planning. Bottoms-up can signify a “grass roots” approach, or a “boots on the ground” approach, or the collection of all the parts of a system. Top-down represents edict/dictation from a central overarching authority.
This is in no way an authoritative answer, just how one AmE speaker hears these phrases.
We are passing through a period of global disruption and fermentation. An age of volatility and risk. The bottoms-up, decentralized and emergent is overtaking the top-down, centralized and directed. - source
No President or Attorney General or Caucus is going to rid the Racism. Belief in ourselves and our ability to achieve and overcome obstacles (on our own) will decrease the effectiveness of those people who see benefit from creating a dependent class. Unfortunately, it’s a “bottoms-up” type of effort as opposed to a “top-down” approach that those who elected Obama had hoped for. - source