Perirhinal and Postrhinal Contributions to Remote Memory for Context

Abstract

The perirhinal (PER) and postrhinal (POR) cortices, two components of the medial temporal lobe memory system, are reciprocally connected with the hippocampus both directly and via the entorhinal cortex. Damage to PER or POR before or shortly after training on a contextual fear conditioning task causes deficits in the subsequent expression of contextual fear, implicating these regions in the acquisition or expression of contextual memory. Here, we examined the contribution of PER and POR to the processing of remotely learned contextual information. Male Long-Evans rats were trained in an unsignaled contextual fear conditioning paradigm. After training, rats received bilateral neurotoxic lesions to PER or POR or sham control surgeries at three different training-to-lesion intervals: 1, 28, or 100 d after training. Two weeks after surgery, lesioned and control rats were returned to the training context to assess contextual fear as measured by freezing. Rats with PER or POR damage froze significantly less in the training context than control rats but were not different from each other. The severity of the deficit did not differ across training-to-lesion intervals for any group. This pattern of deficits differs from that of posttraining hippocampal lesions, for which longer training-to-lesion intervals produce significantly more fear-conditioned contextual freezing than shorter training-to-lesion intervals. In the absence of such a retrograde gradient in the present study, our interpretation is that PER and POR have an ongoing role in the storage or retrieval of representations for context. Alternatively, these regions may be involved in a more extended consolidation process that becomes apparent beyond 100 d after learning.

Functional Dissociation within the Entorhinal Cortex for Memory Retrieval of an Association between Temporally Discontiguous Stimuli

“…In contrast, we found a long-lasting role for the LEC in memory retrieval, as LEC inactivation impaired expression of both recent (1-d-old) and remote (1-month-old) memories in trace eyeblink conditioning. This is consistent with findings of long-lasting retrograde memory impairments when large hippocampal lesions include the rhinal cortices in humans (Bayley et al, 2006) and primates (Suzuki et al, 1993), and with specific lesions to subregions of the rhinal cortices in rodents (Cho and Kesner, 1996;Burwell et al, 2004). Together, these findings suggest that the rhinal cortices play a long-lasting role in memory storage or retrieval.…”

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…Confirmation of these findings come from electrophysiological data which shows that there are different firing patterns observed in the perirhinal cortex during exposure to discontinuous tones compared to continuous tones (Furtak et al, 2007c) and from lesions of the perirhinal cortex where there is impairment of conditioning to ultrasonic vocalisations but not to continuous tones (Lindquist et al, 2004). These results fit with the data generated from recognition and fear conditioning tasks where the perirhinal cortex is required for processing more complex stimuli and contexts (Corodimas and LeDoux, 1995;Sacchetti et al, 1999;Bucci et al, 2000Bucci et al, , 2002Bussey et al, 2000;Eacott et al, 2001;Burwell et al, 2004a).…”

“…Lesions of the rostral perirhinal cortex also lead to an attenuation of olfactory fear conditioning while sparing contextual fear conditioning Otto, 1997, 1998;Otto et al, 2000) and this sparing of contextual fear conditioning following perirhinal lesions has been confirmed by other groups (Phillips and LeDoux, 1995). However, other studies have shown that similar sized lesions in the same location (Corodimas and LeDoux, 1995) and larger ablations of the entire perirhinal cortex disrupt contextual fear conditioning (Sacchetti et al, 1999;Bucci et al, 2000Bucci et al, , 2002Burwell et al, 2004a). More generally temporary inactivation of the rostral perirhinal cortex seems to have an anxiolytic effect in an unconditioned fear task (Schulz-Klaus et al, 2005), this along with many of the above studies singling out the rostral region of the perirhinal cortex as being particularly important when it comes to emotional learning.…”

“…Fear conditioning tasks can be quite varied with different studies using different forms of stimuli across the various sensory modalities to condition subjects and visual, auditory, olfactory, and contextual paradigms have all been explored in the general fear conditioning literature and a number of studies have implicated the perirhinal cortex in visual (Rosen et al, 1992;Campeau et al, 1997;Shi and Davis, 2001), auditory (Campeau et al, 1997;Sacchetti et al, 1999;Kyuhou et al, 2003;Bruchey and GonzalezLima, 2006;Kholodar-Smith et al, 2008a,b;Bang and Brown, 2009a,b), olfactory Otto, 1997, 1998;Otto et al, 2000) and contextual fear conditioning (Sacchetti et al, 1999;Bucci et al, 2000;Burwell et al, 2004a;Kholodar-Smith et al, 2008a,b;SchulzKlaus, 2009). Electrophysiological recordings made in the perirhinal cortex during trace conditioning using auditory stimuli (Furtak et al, 2007c) and immediate early gene imaging shows increased levels of c-Fos in the perirhinal cortex following a fear conditioning task (Campeau et al, 1997).…”

“…Allocentric spatial memory tests like the MWM may exploit a completely different set of neuronal processes compared to tests of spatial memory that do not rely on navigation . Both the perirhinal and postrhinal cortex contribute to contextual associations for long-term memory (Burwell et al, 2004a) but this contextual association does not appear to be necessary for all forms of spatial learning; lesions of the hippocampus and the parahippocampal region suggest allocentric spatial memory can occur without the need for parahippocampal-dependent contextual associative learning (Burwell et al, 2004b) and rats with lesions of the perirhinal cortex are unimpaired in a delayed-matching-to-place task (Glenn and Mumby, 1998). Therefore, in studying the role of the perirhinal cortex in spatial memory, tasks that focus on the contextual properties and not on allocentric properties of spatial memory have been developed.…”