Structures in the medial temporal lobe, including the hippocampus and perirhinal cortex, are known to be essential for the formation of long-term memory. Recent animal and human studies have investigated whether perirhinal cortex might also be important for visual perception. In our study, using a simultaneous oddity discrimination task, rats with…

We tested proposals that medial temporal lobe (MTL) structures support not just memory but certain kinds of visual perception as well. Patients with hippocampal lesions or larger MTL lesions attempted to identify the unique object among twin pairs of objects that had a high degree of feature overlap. Patients were markedly impaired under the more…

In four experiments, we explored the capacity for spatial mental imagery in patients with hippocampal lesions, using tasks that minimized the role of learning and memory. On all four tasks, patients with hippocampal lesions performed as well as controls. Nonetheless, in separate tests, the patients were impaired at remembering the materials that…

Early studies of memory-impaired patients with medial temporal lobe (MTL) damage led to the view that the hippocampus and related MTL structures are involved in the formation of long-term memory and that immediate memory and working memory are independent of these structures. This traditional idea has recently been revisited. Impaired performance…

Patients with hippocampal damage are sometimes impaired at remembering information across delays as short as a few seconds. How are these impairments to be understood? One possibility is that retention of some kinds of information is critically dependent on the hippocampus, regardless of the retention interval and regardless of whether the task…

Two recent studies described conditions under which recognition memory performance appeared to be driven by nondeclarative memory. Specifically, participants successfully discriminated old images from highly similar new images even when no conscious memory for the images could be retrieved. Paradoxically, recognition performance was better when…

In rodents, the novel object recognition task (NOR) has become a benchmark task for assessing recognition memory. Yet, despite its widespread use, a consensus has not developed about which brain structures are important for task performance. We assessed both the anterograde and retrograde effects of hippocampal lesions on performance in the NOR…

It has been suggested that the hippocampus selectively supports recollection and that adjacent cortex in the medial temporal lobe can support familiarity. Alternatively, it has been suggested that the hippocampus supports both recollection and familiarity. We tested these suggestions by assessing the performance of patients with hippocampal…

New granule cells are born throughout life in the dentate gyrus of the hippocampal formation. Given the fundamental role of the hippocampus in processes underlying certain forms of learning and memory, it has been speculated that newborn granule cells contribute to cognition. However, previous strategies aiming to causally link newborn neurons…

We explored the circumstances in which rats engage either declarative memory (and the hippocampus) or habit memory (and the dorsal striatum). Rats with damage to the hippocampus or dorsal striatum were given three different two-choice discrimination tasks (odor, object, and pattern). These tasks differed in the number of trials required for…

Conventional lesion methods have shown that damage to the rodent hippocampus can impair previously acquired spatial memory in tasks such as the water maze. In contrast, work with reversible lesion methods using a different spatial task has found remote memory to be spared. To determine whether the finding of spared remote spatial memory depends on…

Studies of memory impairment in humans and experimental animals have been fundamental to learning about the organization of memory and its cellular and molecular substrates. When memory impairment occurs, especially after perturbations of the nervous system, the question inevitably arises whether the impairment reflects impaired information…

We tested recognition memory for items and associations in memory-impaired patients with bilateral lesions thought to be limited to the hippocampal region. In Experiment 1 (Combined memory test), participants studied words and then took a memory test in which studied words, new words, studied word pairs, and recombined word pairs were presented in…

The most useful information about the anatomy of human memory comes from cases where there has been extensive neuropsychological testing followed by detailed post-mortem neurohistological analysis. To our knowledge, only eight such cases have been reported (four with medial temporal lobe damage and four with diencephalic damage). Here we present…

The perirhinal cortex is known to be important for memory, but there has recently been interest in the possibility that it might also be involved in visual perceptual functions. In four experiments, we assessed visual discrimination ability and visual discrimination learning in severely amnesic patients with large medial temporal lobe lesions that…