Behavioral effects of lesions of precommissural and postcommissural fornix.

Lesions which sever different parts of precommissural or postcommissural fornix were compared to the effects of control lesions in several behavioral tasks. Spatial learning and avoidance was impaired by lesions of the descending columns, or by lesions which sever the precommissural communications passing to and from medial septum. Damage to precommissural fibers through lateral septum produced a measurable change only on the avoidance task. This pattern of deficits, considered together with the anatomical relationship of the system, suggests a model in which the medial septum relays kinesthetic information to dorsal hippocampus, which in turn serves as a memory system in the performance of spatial habits. It is less clear what kind of information is relayed by lateral septum, but it may communicate with ventral hippocampus regarding the consequences of punishment, and thus serve as part of a system for defensive suppression of behavior.