Trade 10 brains for a jetpack is a mission in Ratchet & Clank, taking place in the Blarg Research Outpost on planet Gaspar. While Ratchet and Clank searched the planet for an XK-81 Jetpack, they encountered the Brain Scientist, a non-hostile blarg who possessed one, and was willing to give it in exchange for ten telepathopus brains.
This mission requires 10 telepathopus brains to be obtained. Telepathopus brains are contained either in purple egg sacks stuck to the ground with a single brain each (obtained by breaking open the egg sack with the OmniWrench), or in live telepathopi, containing three brains each (obtained by defeating the telepathopus, which is a miniboss). There are 90 brains across the islands out in the lava on Gaspar, though without the Jetpack, you are only able to access a few located in the immediate area.
From where the Brain Scientist is found, head to the left to see the first telepathopus brain contained in an egg sack, obtained by breaking open the egg sack with the OmniWrench to obtain it. From here, rocks and a platform will lead down to another brain on top of a small lava lake island. Kill the sandsharks (or simply summon Mr. Zurkon to kill them for you), obtain the brain, and head left to the ground, containing three brains. Several sandsharks can be found here, along with toxic crabs, a new enemy. Toxic crabs are tough, so use a weapon such as the Predator Launcher or Pixelizer. Obtain the three brains, and then stand on the three red tripod buttons to open a forcefield leading to several rocks upwards. Head up the rocks and obtain the brain here.
There are a set of versa-targets across a pool of lava to the next area. Cross them with a Swingshot to the next area with more toxic crabs and two more brains. Defeat the crabs and obtain the two brains. Nearby, you will find a metallic structure linked to with a versa-target, with the first live telepathopus floating around it. Ignore it for now, and simply head up to an area containing alien swarmers, alien snappers and two brains. Obtain the brains while killing the enemies, which will earn you the 10 brains required to complete the mission. To the left are three versa-targets leading back to the Brain Scientist; cross them with the Swingshot and speak to him to finish this mission.