In the Profile settings there are options to adjust BrainHQ's difficulty and the style of training offered by the Personal Trainer.
In the Profile section, there is a Breadth versus Depth slider. By default, the Personal Trainer requires completing 10 levels of an exercise in order to pass it. Moving the slider towards the "Breadth" side changes the Personal Trainer to require completing fewer levels to pass an exercise - for example after 8 or 6 levels must be completed. Once exercises are passed, new exercises are offered, encouraging more variety in training. Conversely, moving the slider towards the "Depth" side sets the Personal Trainer to require the completion of more levels to pass an exercise - for example, after 12 or 14 levels have been completed. Requiring more levels to be completed results in a deeper training experience, exploring more levels from a fewer number of exercises.
Remember that repetition is important, so it's best to spend the most time with a value in the middle or slightly to the right towards depth unless the training is moving too slowly or repeating the same levels over and over again.
The Difficulty preference sets your performance goal, which determines when you have passed an exercise. When you finish a level having earned the number of stars required by your performance goal, the Personal Trainer will consider that level passed and not schedule it again, because you don't need to train any more on it. For example, If you set the Difficulty to "Medium", then once you earn 3 stars during a single level, the Personal Trainer will set aside the level as completed. If you earn only 2 stars at your best, the Personal Trainer will eventually bring the level back for you to train more so you can improve your performance. Setting the Difficulty setting to "Easy" sets the performance goal to 2 stars, "Hard" to 4 stars, and "Expert" sets it to 5 stars.