What do I need to do to get a master's degree in neuroscience?
I used to have some interactions in department of neuroscience at my university and I can definitely say that this field is filled with opportunities for people with strong natural science or engineering background but is very forbidding for everybody else. Neuroscience is applied science and to do applied science you need a lot of experience in science in the first place and I am not sure whether architecture has given you the exposure required, perhaps you should tell us why you are interested in neuroscience in the first place and what you are planning to do.

From my observation, to do research in neuroscience you either have to have:


option A) a strong biochemical background or  
option B) a strong engineering background particularly in statistical signal processing, computer science or electronic devices


And this illustrates the research direction of neuroscience departments in general, which is really to understand the brain and its connections from an input-output perspective (hence signal processing, computer graphics, machine learning, devices) and find ways to control it using drug or other stimuli (hence biochemistry background). Of course the type of research being performed varies widely and have many softer areas such as psychology, emotions, learning styles, etc. but these are experiments backed up by theoretical hypothesis and scientific methods which translate into hardcore math and science. Even if it doesn't actually involve that much theoretical calculation, the course work will definitely involved detailed knowledge of mathematics, physics, electronics and biology.

There are many top neuroscience faculties around the world, and in the US, John Hopkins and Duke University comes to mind but these faculties are specialized in the sense that they are sub-disciplines of sub-disciplines i.e. a special branch of psychology, a special branch of electrical engineering. Therefore I am not sure whether GRE subject tests in physics, biology, etc. would impress such a specialized faculty. Most importantly you should show aptitude in doing research in this area by demonstrating the reason behind why you are interested in neuroscience and back it up by some form of outside experience that deals with aspects of neuroscience but again these opportunities are very hard to come by outside of formal university setting. 

Some strategies:


Look at some of the programs offered and their research direction, do you want to go into a biology based stream or engineering based stream? Which appears to be most feasible?
Look at some of the courses in neuroscience (enroll in a college program or find online courses such as Coursera's Bioelectricity course) and see whether you have the prerequisite to engage in this field, if not, work on those preliminaries by enrolling in some form of college program 
If you have the prerequisite and you ace the course with flying colors, then apply what you learned in some special project, look at some of the project involving neuroscience or bioengineering in general such as EEG/EMG/EKG control, etc. and produce a product that is interesting, maybe even marketable
Look at the companies currently doing applied neuroscience related work and see if you have the credential to work for these companies. They maybe related to software for some sort of real time image processing of the brain, psychological tests with fMRI data to backup hypothesis, neuro-interface devices


Architecture to neuroscience is a big leap but then again it all depends on what kind of architecture degree it is, if it is some sort of engineering physics program with architecture specialization you might just have a better shot. While GRE is necessary and good and all, it will not likely to satisfy such a specialized group and reveal your aptitude to produce work in this field