Fornix Lesions Impair Context-Related Cingulothalamic Neuronal Patterns and Concurrent Discrimination Learning in Rabbits (Oryctolagus cuniculus).

Abstract

Cingulothalamic neurons develop topographic patterns of cue-elicited neuronal activity during discrimination learning. These patterns are context-related and are degraded by hippocampal lesions, suggesting that hippocampal modulation of cingulothalamic activity results in the expression of the patterns, which could promote the retrieval of context-appropriate responses and memories. This hypothesis was tested by training rabbits (Oryctolagus cuniculus) with fornix lesions concurrently on two discrimination tasks (approach and avoidance) in different contexts. Because the same conditioned stimuli were used for both tasks, contextual information was critical for overcoming intertask interference during concurrent task acquisition. The lesions degraded the topographic patterns and significantly impaired concurrent learning, suggesting that hippocampal-cingulothalamic interactions and the resulting topographic patterns are critical for processing contextual information needed to defeat interference.

Hippocampal place cells, context, and episodic memory

“…In this way, the hippocampus could bias the behavioral expression systems of the brain . These results support context processing accounts of hippocampal function (Hirsh, 1974;Penick and Solomon, 1991;Kim and Fanselow, 1992;Phillips and LeDoux, 1992;Freeman et al, 1997) and they join a growing body of data that has led to a recent resurgence of interest in the context processing role of the hippocampus (Chun and Phelps, 1999;Rosenbaum et al, 2001;Jeffery et al, 2004;Johnson, 2004;Smith et al, 2004;Weis et al, 2004;LaBar and Phelps, 2005;Shanks et al, 2005).…”

“…The spatial layout of an environment is a critical feature of any context and several authors have used the term ''spatial context'' to denote this relationship (Nadel et al, 1985;Jeffery et al, 2004). It has been suggested that spatial context coding is one example of the general context processing function of the hippocampus (Mizumori et al, in press;Smith et al, 2004;Smith and Mizumori, 2006). Indeed, the spatial representations seen in our studies were clearly dependent on nonspatial features of the context (Fig.…”

“…The hippocampus may contribute contextual information to an extended circuitry, which includes, but is not limited to, the hippocampus. Several authors have suggested that hippocampal memory functions are mediated by circuitry involving the EC, anterior thalamus, prefrontal cortex, and retrosplenial cortex (Aggleton and Brown, 1999;Eichenbaum, 2000;Suzuki and Eichenbaum, 2000;Smith et al, 2004;Wiltgen et al, 2004;Siapas et al, 2005).…”

“…A recent study examined the importance of hippocampal output to cingulate cortical and anterior thalamic brain regions during contextual learning (Smith et al, 2004). This study took advantage of the well-documented role of the cingulate cortex and anterior thalamus in instrumental discrimination learning (Gabriel, 1993) and examined whether hippocampal output modulates functioning in these regions in a context-dependent manner.…”

“…The idea that hippocampal lesions impair context processing is well documented (Penick and Solomon, 1991;Kim and Fanselow, 1992;Phillips and LeDoux, 1992;Freeman et al, 1997;Smith et al, 2004). To determine whether learning the above described context discrimination task depended on the hippocampus, the GABA A agonist muscimol (0.5 lg in 0.5 ll saline in each hemisphere) was used to temporarily inactivate the dorsal hippocampus before the initial two training sessions.…”