Search

The majority of research regarding contextual learning and memory has focused on the contributions of the hippocampus and related medial temporal lobe structures. However, little is known about other possible cortical contributions to these processes. Our laboratory recently demonstrated that electrolytic lesions of the retrosplenial cortex (RSP), a posterior region of cingulate cortex, impaired contextual but not cue-specific fear conditioning. The present experiments further examined the role of RSP in contextual fear memory using fiber-sparing neurotoxic lesions and both signaled and unsignaled fear conditioning paradigms. Despite comparable acquisition of the conditioned fear response, rats with neurotoxic lesions of RSP exhibited impaired contextual memory relative to control animals in both the signaled and unsignaled paradigms. These results further suggest an important role for RSP in contextual learning and memory. [ABSTRACT FROM AUTHOR]

Lesions of retrosplenial cortex (RSP) disrupt spatial and contextual learning, suggesting that RSP may have a fundamental role in processing overlapping, or simultaneously presented stimuli. If so, then RSP lesions might also be expected to disrupt learning that requires the concurrent processing of phasic conditioned stimuli. In Experiment 1, rats were trained in a compound feature negative discrimination task in which a tone was presented and immediately followed by food on some trials, while on other trials a visual stimulus was simultaneously presented along with the tone and not reinforced. Normal rats learned to discriminate between the trials but RSP-lesioned rats exhibited low levels of conditioning on both types of trials. Experiment 2 demonstrated that this effect was not simply due to a general inability to form associations, since RSP-lesioned rats exhibited normal responding when the visual stimulus was presented alone and paired with food. These findings support the view that RSP has an important role in learning that involves the processing of simultaneously presented stimuli and have implications for understanding the functional relationship between the hippocampus and RSP. [ABSTRACT FROM AUTHOR]

The retrosplenial cortex (RSP) and the posterior parietal cortex (PPC) are the primary sources of cortical sensory input to the postrhinal cortex (POR) in rodents. Together, these areas compose a major corticohippocampal circuit that is involved in processing visuospatial information. The POR has been implicated in contextual learning and memory, consistent with the type of information presumably being processed by this region. By comparison, little is known about the role of the RSP or the PPC in contextual learning. In the present study, rats were trained either before or after surgery in a standard signaled fear conditioning task in which an auditory cue was paired with foot shock. Contextual fear and tone-specific fear were assessed in subsequent test sessions. In Experiment 1, electrolytic damage to the RSP either before or immediately after training impaired the expression of contextual fear but not tone-specific fear. In contrast, electrolytic damage to the PPC had no effect on conditional fear to the context or the tone in Experiment 2. These findings indicate that the RSP, but not the PPC, contributes to the processing of contextual information by the POR corticohippocampal processing stream. [ABSTRACT FROM AUTHOR]

Abstract: Few studies have addressed potential differences in the nature of cognitive impairment observed in males and females with ADHD. In Experiment 1, we examined sex differences in conditioned inhibitory behaviour in spontaneously hypertensive rats (SHR strain), a purported animal model of ADHD. Rats were presented with two types of trials during each of the 15 conditioning sessions. On some trials an auditory stimulus (a tone) was presented and followed immediately by delivery of food reward. On the remaining trials the tone was preceded by presentation of a visual stimulus and on those trials food was not delivered after the tone was presented. As training progressed, conditioned responding during presentation of the tone increased on reinforced trials and decreased during the non-reinforced trials, indicative of successful discrimination and inhibition. Overall, female SHR rats exhibited less conditioned overall food cup behaviour compared to male rats. Female SHR rats also required more training sessions until they responded significantly more during presentation of the tone on reinforced trials versus non-reinforced trials. In addition, the magnitude of the discrimination was smaller in female SHR rats compared to males. In contrast, no sex differences were observed in WKY rats (commonly-used control strain) in Experiment 2. Importantly, there were no significant sex differences in baseline activity or motivation during either experiment, indicating that performance differences could not account for the observed results. These results suggest that male and female SHR rats differ in their ability to form conditioned associations and inhibit behavioural responses and may provide a useful model for sex differences in cognitive dysfunction specific to ADHD. [Copyright &y& Elsevier]