Fornix--thalamus fibers, motivational states, and contextual retrieval.

The effect of selectively transecting fornix fibers bound for the anterior thalamic nuclei upon the means by which motivational states influence selection of learned responses was assessed. Rats were deprived of food or water on alternate days. During short sessions they had an opportunity to learn to turn one direction to obtain food and the opposite direction to obtain water in the same T-maze. The control group was a combination of animals which had received sham operations and those in which the attempted transection was off target. Experimental animals behaved much less differentially than controls. The performance levels of the experimental animals in obtaining food and water were more negatively correlated than those of controls. During early stages of the learning procedure the experimental animals were more likely to develop strong individual response preferences or biases than controls. Experimental animals also required more trials to reach criterion than controls. The results are interpreted as indicating that after transection of connections between the subiculum and the anterior thalamic nuclei, motivational states no longer act conditionally upon the selection of learned behavior for performance. Rather they are pooled together with other stimuli. Such an interpretation is derived from the theory that the hippocampus is part of a system mediating contextual retrieval of information from memory.