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It has been proposed that a core network of brain regions, including the hippocampus, supports both past remembering and future imagining. We investigated the importance of the hippocampus for these functions. Five patients with bilateral hippocampal damage and one patient with large medial temporal lobe lesions were tested for their ability to recount autobiographical episodes from the remote past, the recent past, and to imagine plausible episodes in the near future. The patients with hippocampal damage had intact remote autobiographical memory, modestly impaired recent memory, and an intact ability to imagine the future. The patient with large medial temporal lobe lesions had intact remote memory, markedly impaired recent memory, and also had an intact ability to imagine the future. The findings suggest that the capacity for imagining the future, like the capacity for remembering the remote past, is independent of the hippocampus. episodic memory | semantic memory | medial temporal lobe | remote memory | amnesia doi/ 10.1073/pnas.1014391107

Three emerging strands of evidence are helping to resolve the causes of the anterograde amnesia associated with damage to the diencephalon. First, new anatomical studies have refined our understanding of the links between diencephalic and temporal brain regions associated with amnesia. These studies direct attention to the limited numbers of routes linking the two regions. Second, neuropsychological studies of patients with colloid cysts confirm the importance of at least one of these routes, the fornix, for episodic memory. By combining these anatomical and neuropsychological data strong evidence emerges for the view that damage to hippocampal--mammillary body--anterior thalamic interactions is sufficient to induce amnesia. A third development is the possibility that the retrosplenial cortex provides an integrating link in this functional system. Furthermore, recent evidence indicates that the retrosplenial cortex may suffer 'covert' pathology (i.e., it is functionally lesioned) following damage to the anterior thalamic nuclei or hippocampus. This shared indirect 'lesion' effect on the retrosplenial cortex not only broadens our concept of the neural basis of amnesia but may also help to explain the many similarities between temporal lobe and diencephalic amnesia. Keywords: Temporal lobe; Fornix; Memory; Subiculum; Entorhinal cortex; Hippocampus; Hypothalamus.

Amnesia produced by protein synthesis inhibitors such as anisomycin provides major support for the prevalent view that the formation of long-lasting memories requires de novo protein synthesis. However, inhibition of protein synthesis might disrupt other neural functions to interfere with memory formation. Intraamygdala injections of anisomycin before inhibitory avoidance training impaired memory in rats tested 48 h later. Release of norepinephrine (NE), dopamine (DA), and serotonin, measured at the site of anisomycin infusions, increased quickly by [approximately equal to] 1,000-17,000%, far above the levels seen under normal conditions. NE and DA release later decreased far below baseline for several hours before recovering at 48 h. Intraamygdala injections of a [beta]-adrenergic receptor antagonist or agonist, each timed to blunt effects of increases and decreases in NE release after anisomycin, attenuated anisomycin-induced amnesia. In addition, similar to the effects on memory seen with anisomycin, intraamygdala injections of a high dose of NE before training impaired memory tested at 48 h after training. These findings suggest that altered release of neurotransmitters may mediate amnesia produced by anisomycin and, further, raise important questions about the empirical bases for many molecular theories of memory formation. anisornycin | protein synthesis-dependent memory | norepinephrine

Byline: B. A. Reikhardt (1), O. G. Kulikova (1), G. Yu. Borisova (1), I. Ya. Aleksandrova (1), N. S. Sapronov (1) Keywords: brain; aging; amnesia; gene expression; protein kinase CK2; transcription factors; HMG14 Abstract: The experiments described here demonstrate that disruption of the phosphorylation of transcription factors of the HMG cAMP/Ca-independent protein kinase CK2 class may be the cause of decreased gene expression in age-related cognitive deficits. Amnesia for a conditioned passive avoidance reaction (CPAR) in aged rats (24 months old) was accompanied by decreases in the synthesis of synaptosomal proteins and transcription in nuclei isolated from cortical, hippocampal, and striatal neurons. There was a decrease in chromatin protein kinase CK2 activity and a significant decrease in the phosphorylation of HMG14 by protein kinase CK2. Selective activators of protein kinase CK2 (1-ethyl-4-carbamoyl-5-methylcarbamoylimidazole and 1-ethyl-4,5-dicarbamoylimidazole) increased HMG14 phosphorylation by protein kinase CK2, increased transcription, increased the synthesis of synaptosomal proteins, and decreased amnesia for the CPAR in aged rats. Thus, activation of the 'protein kinase CK2--HMG14' system is accompanied by optimization of synaptic plasticity in aged animals. The results provide evidence for the high therapeutic potential of protein kinase CK2 activators. Author Affiliation: (1) Science Research Institute of Experimental Medicine, Russian Academy of Medical Sciences, 12 Academician Pavlov Street, 197376, St. Petersburg, Russia Article History: Registration Date: 12/10/2004

Byline: R. Yu. Il'yuchenok (1), N. I. Dubrovina (1), E. V. Popova (1) Abstract: The involvement of presynaptic dopamine receptors in the retention of a conditioned passive avoidance reflex through extinction and amnesia was studied in C57BL/6J mice selected in a 20-day aggressive conflict test for aggressive and submissive behavioral stereotypes. These experiments showed that in aggressive mice, activation of presynaptic receptors with the agonist (+)3-(3-hydroxyphenyl)-N-n-propylpiperidine [(+)3PPP] at a dose of 2 mg/kg degraded learning, significantly decreased the retention time of the acquired conditioned habit in extinction, and increased the effect of an amnesia-inducing treatment. Mice showing submissive behavior in daily confrontations with aggressors responded to administration of (+)3PPP with long-lasting reproduction of the conditioned passive avoidance reaction during extinction and showed no changes in the development of amnesia. These data on the relationship between the effects of activating presynaptic dopamine receptors in reproduction of the memory trace in conditions of trace disruption on the one hand and behavioral status on the other are assessed from the point of view of different basal levels of dopaminergic system operation in aggressive and submissive mice. Author Affiliation: (1) Institute of Physiology, Siberian Division, Russian Academy of Medical Sciences, Novosibirsk Article History: Registration Date: 10/10/2004

INTRODUCTION Memory is not a single faculty but is composed of multiple separate abilities (Schacter, 1987; Squire, 1992; Tulring, 1985; Weiskrantz, 1990). One major distinction contrasts declarative (explicit) memory, which [...], Contrasts between implicit and explicit knowledge in the serial reaction time (SRT) paradigm have been challenged because they have depended on a single dissociation: intact implicit knowledge in the absence of corresponding explicit knowledge. In the SRT task, subjects respond with a corresponding keypress to a cue that appears in one of four locations. The cue follows a repeating sequence of locations, and subjects can exhibit knowledge of the repeating sequence through increasingly rapid performance (an implicit test) or by being able to recognize the sequence (an explicit test). In our study, atonesic patients were given extensive SRT training. Their implicit and explicit test performance was compared to the performance of control subjects who memorized the training sequence. Compared with control subjects, amnesic patients exhibited superior performance on the implicit task and impaired performance on the explicit task. This crossover interaction suggests that implicit and explicit knowledge of the embedded sequence are separate and encapsulated and that they presumably depend on different brain systems.

The relationship between the strength of item memory and the ability to classify new stimulus items was examined in a 73-year-old man with retrograde amnesia. The patient displayed the ability to classify novel stimuli according to whether they belonged to the same category but was unable to recognize a single stimulus after they were presented 40 times in succession. These results suggest that there a highly nonlinear relationship between the strength of item memory and declarative memory.

Research on the memory of amnesic patients, with respect to perceptual priming and control subjects on an auditory identification task in which previously spoken words and new words are presented, reveal that when the encoding task and the speaker's voice are manipulated, amnesic patients exhibit normal priming. By contrast, in tests of recognition memory, they exhibit severely impaired performances, where all subjects show poor explicit memory following nonsemantic study tasks. Results strengthen the idea that auditory priming depends largely on presemantic auditory perceptual representation systems.

Permanent amnesia can be a possible consequence of damage to the inside portion of both temporal lobes of the brain, or to both sides of the thalamus, a large collection of neurons in the middle of the brain. Less is known, however, about the cause of transient global amnesia, in which the patient experiences a dramatic amnesic spell that usually resolves within a few days. A case is now reported in which the patient's brain blood flow was monitored during an actual transient global amnesia attack. The patient was a 55-year-old woman who became bewildered because she did not recall how she came to be at her weekend house with her husband. She recognized her husband and remembered much of her past, but during the neurological examination she kept repeating the same questions and never remembered the explanations of why she was in the hospital. This is called anterograde amnesia, in which events preceding the attack are generally remembered, but new events cannot be recalled. The patient was examined using single-photon emission computed tomography (SPECT), a technique in which a radioactive tracer substance is injected into the blood; gamma rays from this tracer then provide information of the relative flow of blood through different regions of the brain. In the present patient, it was found that there was a significant decrease of blood flow to the left thalamus. The right thalamus was also receiving a decreased flow of blood, but the decrease was not as marked as on the left. The patient's amnesic symptoms improved over the next week and by one month all memory tests were normal. Over this same period, blood flow in the thalamus as measured by SPECT also returned to normal. It is suggested that the decreased blood flow to the thalamus was responsible for the transient amnesia. (Consumer Summary produced by Reliance Medical Information, Inc.)

Objective--To test the hypothesis that visual memory for faces can be dissociated from visual memory for topographical material. Method--A patient who developed a global amnesic syndrome after acute carbon monoxide [...]

Amnesic patients with early and seemingly isolated hippocampal injury show relatively normal recognition memory scores. The cognitive profile of these patients raises the possibility that this recognition performance is maintained mainly by stimulus familiarity in the absence of recollection of contextual information. Here we report electrophysiological data on the status of recognition memory in one of the patients, Jon. Jon's recognition of studied words lacks the event-related potential (ERP) index of recollection, viz., an increase in the late positive component (500-700 ms), under conditions that elicit it reliably in normal subjects. On the other hand, a decrease of the ERP amplitude between 300 and 500 ms, also reliably found in normal subjects, is well preserved. This so-called N400 effect has been linked to stimulus familiarity in previous ERP studies of recognition memory. In Jon, this link is supported by the finding that his recognized and unrecognized studied words evoked topographically distinct ERP effects in the N400 time window. These data suggest that recollection is more dependent on the hippocampal formation than is familiarity, consistent with the view that the hippocampal formation plays a special role in episodic memory, for which recollection is so critical. hippocampus | episodic memory | event-related potentials | amnesia

Background--If they are to be replicable, MRI volume measurements require explicit definitions of structures and of criteria for delineating these structures on MRI. Previously published volumes in healthy subjects show [...]

Background--Cognitive-MRI correlations have often been studied in disorders in which there are multiple cognitive deficits and widespread cortical atrophy, such as Alzheimer's dementia. In such circumstances, the interpretation of any [...]

Background: The relationship between traumatic emotional stress, hippocampal injury, memory loss, and traumatic ('dissociative') amnesia was examined. Method: A survey of the research on emotional trauma, learning, memory loss, glucocosteroid stress hormones, and the hippocampus was conducted, and animal and human studies were reviewed. Results: It is well documented and has been experimentally demonstrated in animals and humans that prolonged and high levels of stress, fear, and arousal commonly induce learning deficits and memory loss ranging from the minimal to the profound. As stress and arousal levels dramatically increase, learning and memory deteriorate in accordance with the classic inverse U-shaped curve. These memory deficits are due to disturbances in hippocampal activation and arousal, and the corticosteroid secretion which can suppress neural activity associated with learning and memory and induce hippocampal atrophy. Risk and predisposing factors include a history of previous emotional trauma or neurological injury involving the temporal lobe and hippocampus, the repetitive and prolonged nature of the trauma, and age and individual differences in baseline arousal and level of cortisol. Conclusions: Although some victims may be unable to forget, amnesia or partial memory loss is not uncommon following severe stress and emotional trauma. Even well publicized national traumas may induce significant forgetting. Memory loss is a consequence of glucocosteroids and stress-induced disturbances involving the hippocampus, a structure which normally plays an important role in the storage of various events in long-term memory. Key Words - Amnesia, Memory, Sex abuse, Hippocampus.

Experiments in artificial grammar learning and implicit memory show that the exemplar-based information is consistent with the conclusion that artificial grammar judgments depend on implicit or nondeclarative knowledge. This interpretation is based on amnesia due to dysfunction in a 'limbic-diencephalic brain system,' important for explicit memory. Sometimes, amnesics perform even better than control subjects on artificial grammar learning. This proves that the small amount of explicit memory available to amnesics may be enough to perform a normal level of classification.