Fornix transection selectively impairs fast learning of conditional visuospatial discriminations

Abstract

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.

White matter damage and cognitive impairment after traumatic brain injury

“…Previous work has shown the importance of the fornix for memory function (Aggleton, 2008; Tsivilis et al , 2008). In humans, damage to the fornices produces memory deficits (Gaffan and Gaffan, 1991; McMackin et al , 1995; Park et al , 2000; Kesler et al , 2001) and, in the monkey, the fornix has been shown to be critical for the rapid learning of new spatial and non-spatial associations (Brasted et al , 2002, 2003; Kwok and Buckley, 2010). Following traumatic brain injury, the extent of damage to the hippocampi is known to predict memory impairment (Tate and Bigler, 2000), and mean diffusivity within the hippocampal formation has been shown to predict associative memory function (Salmond et al , 2006).…”

High spatial and angular resolution diffusion-weighted imaging reveals forniceal damage related to memory impairment

“…Animal studies of fornix transection have shown deficits in spatial cognition, particularly in the rapid acquisition of spatial relationships [39,40]. DTI measures in the fornix can also discriminate between healthy controls and patients with AD and MCI [34,41].…”

Gene Network Effects on Brain Microstructure and Intellectual Performance Identified in 472 Twins

“…These hub SNPs influenced intellectual performance by modulating the associations between performance IQ and the integrity of the fiber systems that are part of visuospatial circuits (Chiang et al, 2009b; Kravitz et al, 2011), including the optic radiations (Tuch et al, 2005), fornix (Kwok and Buckley, 2010), corpus callosum (Begre et al, 2007), cingulum bundle (Bush et al, 2000), and the superior longitudinal fasciculus, which is associated with spatial working memory performance in children (Vestergaard et al, 2011). Human intelligence is highly heritable; a substantial proportion (40–50%) of variation in IQ is genetically determined (Davies et al, 2011).…”