Would like explanation on Oracle's Automatic Memory Management choices

Hi,
I don't understand why Oracle automatic memory management is giving a huge chunk of memory (50G) to the PGA. I recently started using automated memory management, going from having init parameters:

  sga_target = 32G
  pga_aggregate_target = 400M
  memory_target_max_target = 0
  memory_target = 0

to:

  sga_target = 0
  pga_aggregate_target = 0
  memory_target_max_target = 82G
  memory_target = 82G

After running for about a day I have this:

SQL> select * from V$MEMORY_DYNAMIC_COMPONENTS where current_size != 0;

COMPONENT                                                        CURRENT_SIZE   MIN_SIZE   MAX_SIZE USER_SPECIFIED_SIZE OPER_COUNT LAST_OPER_TYP LAST_OPER LAST_OPER GRANULE_SIZE
---------------------------------------------------------------- ------------ ---------- ---------- ------------------- ---------- ------------- --------- --------- ------------