I've never driven 375s but I did use to sign 465/6s which are similarly configured.
The process that is occurring here is.
1) When the driver applies the brake, the train initially applies the friction (disc) brake at 100% force, ie a step 2 application would give 2 bar brake pressure.
2) Rheostatic or regenerative braking will then be progressively introduced. By changing the excitation field of the AC motors and putting a load across them it is possible to extract energy from them and thereby slow the train down. This is very effective and is usually much better than disc brakes. Engineers tell me that strictly speaking this is not the same as "reconfiguring the motors to become generators", so I have avoided using that expression (I hope !).
3) On DC systems the train will return the energy back into that electrical section ONLY if there is another train taking power out. This is Regen braking.
4) If there isn't anything to absorb the power, the train will revert to Rheostatic braking - whereby the power is dissipated by the train's own resistor bank.
5) Once either of the two dynamic braking techniques is established, the friction (air) braking drops to a holding level (usually about half a bar pressure). This system of mixing dynamic & air braking is called brake blending and the system works to ensure that the required braking force is always maintained.
6) If the train passes over a gap in the third rail or the Traction Current is interrupted for any reason the Brake Blending valve will reintroduce full friction braking. Similarly if the driver puts the controller into Emergency Brake the dynamic brakes are excluded and 100% friction braking is used.
And finally, a little bone of contention with the above mentioned Wiki definition at
http://en.wikipedia.org/wiki/Regenerative_braking
In Europe, Both rheostatic
and regenerative come under the heading of Dynamic Braking, because they only work whilst the train is moving....hence the name dynamic. For the same reason it's important to understand that if the train is at a stand only friction brakes can be used.
I don't know whether the author of the article was confused or maybe it's different in the US. Over there they first had Rheostatic braking on their lovely great diesel locos, and so the name Dynamic came to be associated just with Rheo.
HTH,
Foggy