The effects of combined perirhinal and postrhinal damage on complex discrimination tasks

Abstract

Rats with combined lesions of the perirhinal and postrhinal cortices were trained on a complex discrimination task, the simultaneous feature-positive and feature-negative discrimination task. In this task, a panel light (L) paired with an auditory stimulus determined whether a tone (T) or white noise (N) would be rewarded (+) or not rewarded (−). Thus, the light feature determined whether the target auditory stimuli were rewarded or not. In each session, trial types were LT+, T−, N+, and LN−. We had hypothesized that damage to the target regions would impair performance on this task. Acquisition was altered in the lesioned rats, but not in the predicted direction. Instead, lesioned rats exhibited significantly enhanced acquisition of the discrimination. Manipulation of intertrial intervals indicated that reduction of proactive interference did not explain the enhancement. Lesioned rats were not different from controls on a multiple cued-interval timing task, providing evidence that the enhancement does not extend to all types of discriminations and is not due to a deficit in timing. Other research shows that rats with perirhinal lesions are impaired on similar tasks, thus the enhancement is likely due to the effects of postrhinal damage. Normally in this task, context is thought to accrue inhibitory control over other cues. Without this inhibitory control, animals might be expected to learn the task more efficiently. Our conclusion is that deficits in processing contextual information underlie the enhanced acquisition observed in rats with combined perirhinal and postrhinal damage on this complex discrimination task.

Toward a conceptualization of retrohippocampal contributions to learning and memory

“…Our model would predict that manipulations of POR would not impair the formation of associations between sensory stimuli. Consistent with this, a recent study by Gastelum et al (2012) demonstrated that lesions involving POR did not impair (and in fact enhanced) the formation of associations between stimuli in a feature-positive feature-negative discrimination task. Additional studies such as these are essential in order to fully test the predicted dissociations predicated by a functional model.…”

Hunger-Dependent Enhancement of Food Cue Responses in Mouse Postrhinal Cortex and Lateral Amygdala

“…As such, POR is likely to reflect and integrate aspects of each network. For example, POR likely serves as a relay of visual object information to hippocampus, as lesion studies have implicated POR in object recognition, object learning, and object-directed orienting (Bussey et al, 2003; Davies et al, 2007; Gastelum et al, 2012). The few physiology studies that have recorded from identified POR (Burwell and Hafeman, 2003; Furtak et al, 2012) or nearby lateral cortical areas in rats (Vermaercke et al, 2014) are consistent with this notion.…”

GABAergic inhibition gates excitatory LTP in perirhinal cortex

“…PRh activity is associated with learning and mnemonic processing, and PRh lesions disrupt learned behaviors that involve auditory cues in rodents (Bang & Brown, ; Corodimas & LeDoux, ; Gastelum, Guilhardi, & Burwell, ; Lindquist et al, ; Plakke, Freeman, & Poremba, ; Robinson, Whitt, Horsley, & Jones, ; Sacchetti et al, ). For example, PRh lesions can interfere with learning a task in which visual features determine whether target auditory stimuli are rewarded (Gastelum et al, ). A role for e‐LTP during learning is supported by the observations that PRh neurons become more responsive to an auditory stimulus following conditioning (Furtak, Allen, & Brown, ) or the presentation of a familiar visual stimulus (von Linstow Roloff, Muller, & Brown, ).…”