Normally when humans react to impressions, signals are being sent through different centers in the brain through the chain of: Impression ${\rightarrow}$ Thalamus ${\rightarrow}$ Cerebral Cortex ${\rightarrow}$ Hippocampus ${\rightarrow}$ Amygdala ${\rightarrow}$ Hypothalamus ${\rightarrow}$ Reaction

In some situations, the middle parts are skipped, handling feelings, long-term memory and understanding. The chain in the case consists of: Impression ${\rightarrow}$ Thalamus ${\rightarrow}$ Hypothalamus ${\rightarrow}$ Reaction

Under what circumstances does this alternate path of reacting happen, and what effect does it have on the outcome of the reaction?

  • $\begingroup$ can you add some more detail and background to what you mean by "the signals"? - i.e. some neuroscience language that helps define what you're talking about. Are you speaking specifically about vision in the absence of the other senses. It's unclear what "the middle parts" refers to in your question - can you expand this and be more descriptive? Also, have you been able to look elsewhere for an answer to this question? $\endgroup$ Jan 15, 2017 at 13:54
  • $\begingroup$ The middle parts in this case would be the diff between the first and second scenario which is the cerebral cortex, hippocampus and the amygdala. By "signals" I am referring to just general information, signals or impulses being sent through the brain. The question would be why some impressions are never processed by these three centrum, the cerebral cortex, hippocampus and amygdala. And lastly YES! I really have looked elsewhere :) $\endgroup$ Jan 15, 2017 at 14:35
  • $\begingroup$ Add that information to your question – it will make it a lot better $\endgroup$ Jan 15, 2017 at 15:34
  • $\begingroup$ I think this question is unclear or too broad - there are lots of neural processes that don't follow either of the chains the OP mentions, and the hypothalamus is certainly not the primary output structure that mediates "reactions." I suggest that this question be closed unless the OP is able to modify the question to be more suitable, in its current form the question is unlikely to produce good answers. I don't think this site is meant for playing Jeopardy and guessing "What is fear?" before trying to answer. $\endgroup$
    – Bryan Krause
    Feb 15, 2017 at 22:58

1 Answer 1


As @Pyssling states, it has to do with fear, and how we process situations that are potentially dangerous. There is a distinction between the two concurrent processes that you describe, that go under the title "short route vs long route" or "low road vs high road" (possibly more titles).

The short route (or low road) is the immediate process/reaction/response, which would enable os to avoid death in certain situations - This works on an instinctive level. The long route (or high road) is the process/reaction/response that could be defined as a thorough evaluation of the input/signal that we receive.

This site has descriptions and images that can be read on three "levels of explanation", and I find them highly informative. http://thebrain.mcgill.ca/flash/a/a_04/a_04_cr/a_04_cr_peu/a_04_cr_peu.html

Here is a youtube video on the subject "How fear is wired in the brain" that deals with the same topic. https://www.youtube.com/watch?v=vl_B6nz3UOQ

I am in no way an expert and have stumbled upon these sites based on personal interests, so I do not know if someone may be able to criticize their validity / quality, but I found them excellent.


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