How do you get to the frontier brains in HeartGold?

1. Defeat the Elite Four and Champion Lance.

2. Go to the Pokémon League building in Saffron City and walk on the track behind it.

3. Go to the building located on the right by crossing the bridge.

4. Talk to the man near the reception table and he will tell you to go to Mt. Silver.

5. Go and defeat the 10 trainers near the summit of the mountain.

6. Battle Red at Level 82 and defeat him.

7. Go back to the Pokémon league and talk to the frontier brain.