Possible Clues:

• Radioactive material initially replaced in hard case
• Skull with key element lacking on top
• A nut-case?
• The skull, major head bone
• The skull, bone enclosing brain
• Board game with the categories "Data Head" and "Word Worm"
• Board game with the categories 'Data Head' and 'Word Worm'
• Skull, bones enclosing brain
• Mental case
• Stuff about even pieces of antique skull