Spatial memory deficits in a virtual radial arm maze in amnesic participants with hippocampal damage.

Extensive research with laboratory animals indicates that the hippocampus is crucial for the formation and use of spatial memory. Hippocampal lesions in rodents impair spatial memory on radial arm maze tasks. It is unknown whether amnesic patients with hippocampal damage would exhibit similar impairments on a virtual version of a radial arm maze. To evaluate the importance of the hippocampus in spatial learning and memory, we tested amnesic participants with hippocampal damage in a virtual radial arm maze environment. The virtual radial arm maze required participants to learn and remember 4 rewarded arms of 8 total arms. Spatial learning and memory were assessed using the participants' ability to use salient distal cues in the virtual room to remember the 4 rewarded arms. Amnesic participants' latencies were longer and distance traveled was greater to the rewarded arms compared with nonamnesic participants. Amnesic participants made more errors than nonamnesic participants by either entering nonrewarded arms or by revisiting previously entered arms. These data are analogous to previous animal research. Overall, the human hippocampus is necessary for spatial memory and navigation in a virtual radial arm maze task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociating the role of the parietal cortex and dorsal hippocampus for spatial information processing.

Dorsal hippocampus, parietal cortex, and control lesioned rats were tested on both a metric and topological task. The metric task consisted of 2 different objects placed 68 cm apart on a cheese board. After habituation, the objects were moved to a separation of 38 cm on Day 1 and to a separation of 98 cm on Day 2. The topological task consisted of 4 different objects placed in a square orientation. After habituation, the first 2 objects were switched, and after the rats habituated to that change, the back 2 objects were switched. This was repeated on a different day with 4 new objects. The data suggest that the hippocampus is necessary for metric representations, whereas the parietal cortex is necessary for topological representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The interactions and dissociations of the dorsal hippocampus subregions: How the dentate gyrus, CA3, and CA1 process spatial information.

Several studies have demonstrated the significance of a spatial cognitive map and its role for guided and accurate navigation through the environment. Learning and recalling spatial knowledge depends upon proper topological and metric spatial information processing. The present objectives are to better characterize the role of the hippocampus for processing topological and metric spatial information. Rats with dorsal hippocampal subregional lesions (dDG, dCA3, dCA1) were tested on a previously established metric task and topological task. The results of the present study suggest that dCA1, but not dDG or dCA3, mediates topological memory. Furthermore, dDG, dCA3, and dCA1 mediate metric memory. Dorsal DG is required for spatial information processing via pattern separation or orthogonalization of sensory inputs to generate metric representations. Dorsal CA3 and dCA1 then receive these metric representations transmitted from dDG along the trisynaptic loop. The present data add to a growing body of literature suggesting a diversity of function among the hippocampal subregions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Word memory test performance in amnesic patients with hippocampal damage.

Many symptom validity tests (SVTs) assess performance validity via declarative memory paradigms. One widely used SVT, the Word Memory Test (WMT), uses a variety of memory tests to assess performance. It is well known that declarative memory requires the hippocampus and related medial temporal lobe structures. In the present study, WMT performance was examined in nonlitigating amnesic subjects (n = 3) with well-documented focal bilateral hippocampal atrophy who were nondemented and otherwise cognitively unimpaired compared with matched controls. The amnesic subjects had no external incentives. Amnesic subjects performed significantly below the level of matched comparison subjects but above established cutoff scores on the immediate recognition and delay recognition subtests and consistency component. In contrast, the amnesic subjects were impaired relative to our comparison subjects on the multiple-choice, paired associate, free-recall, and long delay free-recall subtests and had extremely low performance on these measures. Thus, there was a differential effect of hippocampal damage on WMT performance where the recognition subtests were performed within the normal range, yet the free recall was profoundly impaired in amnesic subjects. Such an approach where SVT performance is assessed in populations with well-known cognitive impairments adds breadth to SVT clinical interpretations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)