Used in this teardown:
The tactile switch board is connected connected to the main board by a flex connector.
The rest of the circuit is housed inside the molded foam piece, with only the DC charging cable sticking out. The foam piece has holes in the front, perhaps for allowing air circulation around the battery.
There's a debug port for reprogramming, and various firmwares for the mask are available on the NeuroDreamer website! However you do need a ~$30 specialized Zilog programmer (but the software is free).
At the bottom edge of the main board is the analog section for the speakers with capacitors and filter resistors for good quality audio.
Two LED boards are connected via flex connector, with 4 LEDs on each (red, yellow, green, and blue).
At the top edge of the main board is the battery charging circuit with a chip that controls charging so it doesn't overcharge or over-discharge the sensitive lithium polymer battery.