The separation of comprehension and production areas was challenged by Chomskian influence which posited separate components for phonology, syntax and semantics. Lesions in Broca's area were found to affect syntactic processing which, though obvious in production, could be detected in comprehension as well.
The deficit studies were done with natural/accidental lesions as well as with induced ones (for treatment of epilepsy and other brain disorders). Eg. H.M. who after removal of hippocampus developed anteretrograde amnesia - loss of memory for events that happened after the surgery. HM could learn new skills but could not recall new facts or events - could not recognise his daily doctor. His intelligence was unaffected. Showed hippocampus plays a role in storage of new info in memory, but is not the site of memory itself.