Object Recognition Memory Task Research Articles

Dorsal Hippocampal Kindling Produces a Selective and Enduring Disruption of Hippocampally Mediated Behavior

Kindling produces enduring neural changes that are subsequently manifest in enhanced susceptibility to seizure-evoking stimuli and alterations in some types of behavior. The present study investigated the effects of dorsal hippocampal (dHPC) kindling on a variety of behaviors to clarify the nature of previously reported effects on spatial task performance. Rats were kindled twice daily with dHPC stimulation until three fully generalized seizures were evoked. Beginning 7 d later and on successive days, rats were tested in an elevated plus maze, a large circular open field, an open field object exploration task, and a delayed-match-to-place (DMTP) task in a water maze to assess anxiety-related and activity-related behavior (tasks 1 and 2), object recognition memory (task 3), and spatial cognition (task 4). Kindling disrupted performance on the DMTP task in a manner that was not delay dependent and produced a mild enhancement of activity-related behaviors in the open field task but not the elevated plus maze. All other aspects of testing were spared. These findings indicate that dHPC kindling produces enduring and selective effects on behavior that are consistent with a restricted disruption of hippocampally mediated functions. Possible bases for these effects are changes in local NMDA receptor function and/or changes in local inhibition, which might alter the optimal conditions for experience-dependent induction of intrahippocampal plasticity. This preparation may be useful for studying the mechanisms of mnemonic dysfunction associated with temporal lobe epilepsy and may offer unique insights into the mechanisms underlying normal hippocampal function.

Primate rhinal cortex participates in both visual recognition and working memory tasks: functional mapping with 2-DG.

The rhinal cortex in the medial temporal lobe has been implicated in object recognition memory tasks and indeed is considered to be the critical node in a visual memory network. Previous studies using the 2-deoxyglucose method have shown that thalamic and hippocampal structures thought to be involved in visual recognition memory are also engaged by spatial and object working memory tasks in the nonhuman primate. Networks engaged in memory processing can be recognized by analysis of patterns of activation accompanying performance of specifically designed tasks. In the present study, we compared metabolic activation of the entorhinal and perirhinal cortex during the performance of three working memory tasks [delayed response (DR), delayed alternation (DA), and delayed object alternation (DOA)] to that induced by a standard recognition memory task [delayed match-to-sample (DMS)] and a sensorimotor control task in rhesus monkeys. A region-of-interest analysis revealed elevated local cerebral glucose utilization in the perirhinal cortex in animals performing the DA, DOA, and DMS tasks, and animals performing the DMS task were distinct in showing a strong focus of activation in the lateral perirhinal cortex. No significant differences were evident between groups performing memory and control tasks in the entorhinal cortex. These findings suggest that the perirhinal cortex may play a much broader role in memory processing than has been previously thought, encompassing explicit working memory as well as recognition memory.

The effect of excitotoxic lesions centered on the hippocampus or perirhinal cortex in object recognition and spatial memory tasks.

Rats with bilateral ibotenic acid lesions centered on the hippocampus (HPC) or perirhinal cortex (PRC) and sham-operated controls were tested in a series of object recognition and spatial memory tasks. Both HPC and PRC rats displayed reduced habituation in a novel environment and were impaired in an object-location task. HPC rats were severely impaired in both the reference and working-memory versions of the water maze and radial arm maze tasks. In contrast, although PRC rats displayed mild deficits in the reference memory version of the water maze and radial arm maze tasks, they were markedly impaired in the working-memory version of both the tasks. These findings demonstrate that under certain conditions both the HPC and PRC play a role in the processing of spatial memory. Further investigation of these conditions will provide important new insights into the role of these structures in memory processes.

Excitotoxic lesions of the pre- and parasubiculum disrupt object recognition and spatial memory processes.

Rats with bilateral ibotenic acid lesions centered on the pre- and parasubiculum and control rats were tested in a series of spatial memory and object recognition memory tasks. Lesioned rats were severely impaired relative to controls in both the reference and working memory versions of the water maze task and displayed a delay-dependent deficit in a delayed nonmatch to place procedure conducted in the T-maze. Lesioned rats also displayed reduced exploration in a novel environment, and performance was altered in an object recognition procedure as compared with the control group. These findings indicate that the pre- and parasubiculum plays an important role in the processing of both object recognition and spatial memory.

The effect of excitotoxic lesions centered on the hippocampus or perirhinal cortex in object recognition and spatial memory tasks.

The effect of excitotoxic lesions centered on the hippocampus or perirhinal cortex in object recognition and spatial memory tasks.

Dense amnesia in the monkey after transection of fornix, amygdala and anterior temporal stem

The traditional explanation of dense amnesia after medial temporal lesions is that the amnesia is caused by damage to the hippocampus and related structures. An alternative view is that dense amnesia after medial temporal lesions is caused by the interruption of afferents to the temporal cortex from the basal forebrain. These afferents travel to the temporal cortex through three pathways, namely the anterior temporal stem, the amygdala and the fornix-fimbria, and all these three pathways are damaged in dense medial temporal amnesia. In four experiments using different memory tasks, we tested the effects on memory of sectioning some or all of these three pathways in macaque monkeys. In a test of scene-specific memory for objects, which is analogous in some ways to human episodic memory, section of fornix alone, or section of amygdala and anterior temporal stem sparing the fornix, each produced a significant but mild impairment. When fornix section was added to the section of anterior temporal stem and amygdala in this task, however, a very severe impairment resulted. In an object recognition memory task (delayed matching-to-sample) a severe impairment was seen after section of anterior temporal stem and amygdala alone, with or without the addition of fornix section; this impairment was significantly more severe than that which was seen in the same task after amygdalectomy leaving the temporal stem intact, with or without fornix section. Animals with combined section of anterior temporal stem, amygdala and fornix were also impaired in object–reward association learning. However, the retention of pre-operatively acquired object–reward associations was at a high level. These results show that the pattern of impairments after section of anterior temporal stem, amygdala and fornix in the monkey, leaving hippocampus intact, resembles human dense amnesia and is different from the effects of hippocampal lesions in the monkey.

Spatial learning and memory as a function of age in the dog.

Spatial learning and memory were studied in dogs of varying ages and sources. Compared to young dogs, a significantly higher proportion of aged dogs could not acquire a spatial delayed nonmatching-to-sample task. A regression analysis revealed a significant age effect during acquisition. Spatial memory was studied by comparing performance at delay interval of 20, 70, and 110 s. At short delays aged and young dogs were similar; at longer delays, errors increased to a greater extent in old than in young dogs; however this was not statistically significant. It was possible to identify 2 groups of aged animals, age-impaired and age-unimpaired. Several of the dogs were also tested on an object recognition memory task, which was more difficult to learn than the spatial task. The possibility that these findings are confounded by breed differences is considered. Overall, the present results provide further evidence of the value of a canine model of aging.

Everyday memory impairment, neuroradiological findings and physical disability in multiple sclerosis

Thirty-five multiple sclerosis (MS) patients diagnosed according to the Poser criteria were examined in a variety of cognition and memory tasks. Their performance was compared to age- and gender-matched healthy individuals. While there was no difference in overall intellectual performance and short-term memory between the MS group and control subjects, the patient group showed significant deficits in several everyday memory tasks including story recall, object and face recognition, procedural, topographical and prospective memory tasks. An intra-group comparison in the MS cohort revealed that those patients with a chronic-progressive MS course exhibited the most substantial everyday memory impairments and highest EDSS scores. These findings coincide with the neuroradiological, semiquantitative lesion analysis which was also performed. In this analysis, the latter MS subgroup also had the highest lesion score, as a sign of an overall brain involvement.