Memory impairment in monkeys following lesions limited to the hippocampus.

Investigated the degree of memory impairment produced by a lesion limited to the hippocampus in 13 cynomolgus monkeys (Macaca fascicularis) with circumscribed hippocampal lesions who were tested on the delayed-nonmatching-to-sample task, a test of recognition memory that is sensitive to amnesia in humans. Ss were given no preoperative training and were given no postoperative experience prior to training on the task. A marked deficit was observed. The results, taken together with those from previous studies, also provide information about the role of factors that could potentially influence the level of memory impairment following hippocampal lesions. The level of impairment does not appear to be due to any of the following factors: time of testing after surgery, prior postoperative testing, surgical techniques, species differences, or behavioral training methods. However, preoperative training experience does appear to reduce the severity of the impairment, and this factor may account for the observation that the memory impairment associated with hippocampal lesions is sometimes mild. A recent case of human amnesia is discussed in which a bilateral lesion limited to a portion of the hippocampus produced a well-documented memory deficit. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory and the hippocampus in food-storing birds: a comparative approach

Comparative studies provide a unique source of evidence for the role of the hippocampus in learning and memory. Within birds and mammals, the hippocampal volume of scatter-hoarding species that cache food in many different locations is enlarged, relative to the remainder of the telencephalon, when compared with than that of species which cache food in one larder, or do not cache at all. Do food-storing species show enhanced memory function in association with the volumetric enlargement of the hippocampus? Comparative studies within the parids (titmice and chickadees) and corvids (jays, nutcrackers and magpies), two families of birds which show natural variation in food-storing behavior, suggest that there may be two kinds of memory specialization associated with scatter-hoarding. First, in terms of spatial memory, several scatter-hoarding species have a more accurate and enduring spatial memory, and a preference to rely more heavily upon spatial cues, than that of closely related species which store less food, or none at all. Second, some scatter-hoarding parids and corvids are also more resistant to memory interference. While the most critical component about a cache site may be its spatial location, there is mounting evidence that food-storing birds remember additional information about the contents and status of cache sites. What is the underlying neural mechanism by which the hippocampus learns and remembers cache sites? The current mammalian dogma is that the neural mechanisms of learning and memory are achieved primarily by variations in synaptic number and efficacy. Recent work on the concomitant development of food-storing, memory and the avian hippocampus illustrates that the avian hippocampus may swell or shrivel by as much as 30% in response to presence or absence of food-storing experience. Memory for food caches triggers a dramatic increase in the total number of number of neurons within the avian hippocampus by altering the rate at which these cells are born and die.     

Memory for duration: role of hippocampus and medial prefrontal cortex

In this task rats had to learn that a three-dimensional object stimulus (a rectangle) that was visible for 2 s would result in a positive (go) reinforcement for one object (a ball) and no reinforcement (no go) for a different object (a bottle). However, if the rectangle stimulus was visible for 8 s then there would be no reinforcement for the ball (no go), but a reinforcement for the bottle (go). After rats learned this conditional discrimination by responding differentially in terms of latency to approach the object, they received large (dorsal and ventral) lesions of the hippocampus, lesions of the medial prefrontal cortex (anterior cingulate and precentral cortex), lesions of the cortex dorsal to the dorsal hippocampus, or served as sham-operated controls. Following recovery from surgery they were retested. The results indicate that there were major impairments following hippocampal lesions, in contrast to cortical control and medial prefrontal cortex lesions, as indicated by smaller latency differences between positive and negative trials on postsurgery tests. In order to ensure that the deficits observed with hippocampal lesions were not due to a discrimination problem, new rats were trained in an object (gray cylinder) duration discrimination task. In this go/no go procedure, the rats were reinforced for a 2-s exposure (duration) of the gray cylinder, but not a 10-s duration, or vice versa. The results indicate that after hippocampal lesions, there was an initial deficit followed by complete recovery. There were no significant changes for the medial prefrontal, cortical control, or sham-operated animals. It appears that the hippocampus, but not the medial prefrontal cortex, is actively involved in representing in short-term memory temporal attribute information based on the use of markers for the beginning and end of the presence (duration) of a stimulus (object).     

Memory and the hippocampus: A synthesis from findings with rats, monkeys, and humans.

Considers the role of the hippocampus in memory function. A central thesis is that work with rats, monkeys, and humans (which has sometimes seemed to proceed independently in 3 separate literatures) is now largely in agreement about the function of the hippocampus and related structures. A biological perspective is presented that proposes multiple memory systems with different functions and distinct anatomical organizations. The hippocampus (together with anatomically related structures) is essential for a specific kind of memory, here termed declarative memory (similar terms include explicit and relational). Declarative memory is contrasted with a heterogeneous collection of nondeclarative (implicit) memory abilities that do not require the hippocampus (skills and habits, simple conditioning, and the phenomenon of priming). The hippocampus is needed temporarily to bind together distributed sites in neocortex that together represent a whole memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the hippocampus in sex differences in verbal memory: Memory outcome following left anterior temporal lobectomy.

The authors examined the neural and cognitive bases for sex differences in verbal memory in 57 patients who underwent left anterior temporal lobectomy (ATL) for the treatment of intractable seizures. On the California Verbal Learning Test (D. C. Delis, J. H. Kramer, E. Kaplan, & B. A. Ober, 1987), women recalled more words than men both before and after surgery, regardless of the extent of hippocampal damage. Extent of hippocampal sclerosis was related to memory loss in both men and women. Women's superiority in verbal memory appears to result in part from their use of an efficient encoding strategy. Women were more likely than men to use semantic clustering both before and after ATL, and sex differences in word recall were attenuated after scores were adjusted for semantic clustering. There was no effect of ATL on semantic clustering. Taken together, these results suggest that sex differences in verbal memory are not due to differences in the integrity of the left hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Looking beyond the walls

Once a risk management process limited to hospitals, the practice of practitioner credentialing has expanded to include many other health care organizations, including insurers, health maintenance organizations, preferred provider organizations, management services organizations, medical groups, and independent practice associations. Standards set by recognized accreditation bodies, including the Joint Commission on Accreditation of Healthcare Organizations (Joint Commission), National Committee for Quality Assurance (NCQA), and American Accreditation Health Care Commission/Utilization Review Accreditation Committee mandate a substantial effort to properly evaluate the credentials of health care practitioners. A sector of commerce called the credentials verification organization (CVO) industry has undertaken the mission to make the process of practitioner credentialing more consistent and efficient, faster, and less expensive.     

"Memory and the hippocampus: A synthesis from findings with rats, monkeys, and humans": Correction.

Reports an error in the original article by L. R. Squire (Psychological Review, 1992[Apr], Vol 99[2], 195–231). The caption for Figure 7 was incorrect. The corrected caption is given. (The following abstract of this article originally appeared in record 1992-26428-001.) Considers the role of the hippocampus in memory function. A central thesis involving work with rats, monkeys, and humans (which has sometimes seemed to proceed independently in 3 separate literatures) is now largely in agreement about the function of the hippocampus and related structures. A biological perspective is presented that proposes multiple memory systems with different functions and distinct anatomical organizations. The hippocampus (together with anatomically related structures) is essential for a specific kind of memory, here termed declarative memory (similar terms include explicit and relational). Declarative memory is contrasted with a heterogeneous collection of nondeclarative (implicit) memory abilities that do not require the hippocampus (skills and habits, simple conditioning, and the phenomenon of priming). The hippocampus is needed temporarily to bind together distributed sites in the neocortex that together represent a whole memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Looking beyond the presenting problem

General practitioners tend to manage disease within the context of the patient's total life. They also have to deal with illness in its various forms when no overt 'disease' is evident. Looking at the interplay of these two facets of ill health gives a deeper understanding of what general practice is about and how general practitioners deal with the problems of their practice. Two cases are presented from the author's personal practice which display how general practitioners deal with the whole person rather than isolated problems. Analysis reveals that the ability to listen to the patient and the willingness to take adequate time is crucial to successful general practice.     

Emergency medicine: beyond the basics

Medical emergencies can arise in the dental office. Preparedness for these emergencies is predicated on an ability to rapidly recognize a problem and to effectively institute prompt and proper management. In all emergency situations, management is based on implementation of basic life support, as needed. The author describes the appropriate management of two common emergency situations: allergy and chest pain.     

Lamellar organisation in the rat hippocampus

A series of experiments was conducted in the urethane anaesthetised rat to determine the organisation of some hippocampal pathways in this species, using stimulating and recording microelectrodes to elicit and record pupulation spikes. It was found that the mossy fibres, alvear fibres and perforant path were clearly arranged in a lamellar fashion. Lamellar organisation could not be demonstrated for the afferents in the stratum radiatum which include the Schaffer collaterals. It was concluded that hippocampal organisation in this species essentially resembles that in the rabbit and cat.     

Neurogenesis in the adult human hippocampus

The genesis of new cells, including neurons, in the adult human brain has not yet been demonstrated. This study was undertaken to investigate whether neurogenesis occurs in the adult human brain, in regions previously identified as neurogenic in adult rodents and monkeys. Human brain tissue was obtained postmortem from patients who had been treated with the thymidine analog, bromodeoxyuridine (BrdU), that labels DNA during the S phase. Using immunofluorescent labeling for BrdU and for one of the neuronal markers, NeuN, calbindin or neuron specific enolase (NSE), we demonstrate that new neurons, as defined by these markers, are generated from dividing progenitor cells in the dentate gyrus of adult humans. Our results further indicate that the human hippocampus retains its ability to generate neurons throughout life.