Karana means the cause. Karana is a cause that is invariably an antecedent or a circumstance which precedes another, often having a causal relationship with what follows. Karana shareera is the causal frame of the body, the inner rudiment of the body.
Avyaktha, the unmanifested or invisible state is karana shareera
Sushupthi, the dreamless state is of karana shareera
Karana shareera, the causal body carries the impressions and the tendencies in the seed form. Here, in the deep sleep state, all the senses are merged in the mind; nothing can be seen or imagined. All vasanas are suspended.