What does Parelli say about the Left Brain versus Right Brain colt and how does it affect the starting approach?

Pat Parelli's Horsenality system identifies four primary temperament types based on two axes — Left Brain/Right Brain (thinking vs reactive) and Introvert/Extrovert (low energy/high energy) — and the type a young horse falls into significantly affects how its starting should be approached. The Left Brain colt — one that is thinking rather than reactive, that tends toward curiosity rather than fear — is the relatively straightforward colt to start. This horse investigates novel stimuli rather than fleeing them, responds to pressure thoughtfully, and learns quickly because it is comfortable enough in its environment to process information. The challenge with the Left Brain colt is that it may also be dominant — testing boundaries, pushing into the trainer's space, deciding whether it wants to comply — and needs consistent leadership as much as it needs good technique. The Right Brain colt — reactive, emotional, quick to flee — requires a fundamentally different approach that prioritizes creating calm and safety before any training demands are placed on the horse. Parelli teaches that asking a Right Brain horse to perform before its emotional state is regulated is a waste of time at best and actively harmful at worst — the horse cannot learn while its nervous system is in flight mode, and every unsuccessful attempt to train through a reactive state adds more negative emotional experience to the starting process. His approach to Right Brain colts is to spend the time needed — which may be much more than with a Left Brain horse — in the Friendly Game and approach-and-retreat work before any yielding or directional training is introduced. The Right Brain colt needs to experience the human as a source of safety before it can experience the human as a source of direction, and rushing past this stage produces a horse that is compliant under pressure but never genuinely confident. Parelli also notes that Right Brain colts often become the most exceptional horses once their confidence is developed, because the emotional sensitivity that made them difficult to start also makes them extremely responsive and attuned to their riders.