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Lesion studies (both patients and nonhuman animals) and functional neuroimaging studies of normal, healthy subjects provide complementary, but different types of information. This article suggests that both study types are necessary for deriving inferentially sound conclusions regarding the neural basis of cognition., (Copyright © 2011 by the American Society of Neuroimaging.)

As part of an earlier experiment (Kwok and Buckley, 2009), six macaque monkeys (three with fornix transection and three unoperated controls) were trained postoperatively to discriminate a total of 104 new concurrent visuospatial conditional problems to criterion. Our experiment measured and compared long-term retention of these problems with two separate one-trial postoperative retention tests administered 3 and 15 months, respectively, after acquisition. All animals showed some degree of forgetting of these problems but all remembered above chance levels, even after 15 months. The amount forgotten by each group did not differ significantly at either time point. These results show that long-term retention of visuospatial information is independent of the fornix. Similarities in resistance to forgetting are drawn between fornix-transected macaques and patients with amnesia and the implications for clinical rehabilitation are discussed., (Copyright 2009 Wiley-Liss, Inc.)

As the fornix has previously been implicated in the rapid learning of associations, we hypothesized that fornix transection in macaques would selectively impair the acquisition of rapidly learned conditional visuospatial discrimination problems. Macaque monkeys learned, postoperatively, three sets of concurrent problems of increasing sizes containing 8, 32, and 64 problems, respectively. Each problem consisted of four identical visual stimuli and animals had to learn which stimulus position was rewarded. The lesioned animals made significantly more errors-to-criterion on the smallest set of problems, consistent with the idea that the most rapidly acquired sets would be more vulnerable to fornical damage. Moreover, during the early stages of acquisition across all three sets, fornix transection selectively impeded monkeys' abilities to eliminate nonperseverative errors in correction trials, consistent with an inability to monitor or correct erroneous spatial responses made further back in time than the last trial. Both one-trial learning and an errorless learning (facilitation of performance) were observed in control and fornix lesioned animals but neither were fornix-dependent and overcoming the deleterious effect upon subsequent learning of having made prior errors was also unaffected by fornix transection. The data indicate that the fornix is not important for all forms of new learning; rather it is selectively concerned with the relatively rapid acquisition of spatial and temporal relationships between stimuli and responses.