Any type of threat can trigger the brain to downshift. A threat is anything that triggers a sense of helplessness in the individual. (Caine, Renate Nummela, and Geoffrey Caine. Making Connections: Teaching and the Human Brain. p 72, 86. VA: ASCD, 1991.)
The concept of downshifting appears to fit with both what is now known about the triune nature of the human brain, and what can continually be seen happening in instructional settings and in daily living. Learning failure results when threat shuts down the brain. The neocortex functions fully only when one feels secure. (Hart, Leslie A. Human Brain and Human Learning. p 108-110. NY:Longman Inc., 1983.)
Refer to Downshifting and the Brain for additional information.