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Hippocampal Lesions (hippocampal + lesion)

Distribution by Scientific Domains

Life Sciences	95%

Selected Abstracts

Hippocampal lesions impair spatial memory performance, but not song,A developmental study of independent memory systems in the zebra finch

DEVELOPMENTAL NEUROBIOLOGY, Issue 8 2009
David J. Bailey
Abstract Songbirds demonstrate song- and spatial-learning, forms of memory that appear distinct in formal characteristics and fitting the descriptions and criteria of procedural and episodic-like memory function, respectively. As in other vertebrates, the neural pathways underlying these forms of memory may also be dissociable, and include the corresponding song circuit and hippocampus (HP). Whether (or not) these two memory systems interact is unknown. Interestingly, the HP distinguishes itself as a site of immediate early gene expression in response to song and as a site of estrogen synthesis, a steroid involved in song learning. Thus, an interaction between these memory systems and their anatomical substrates appears reasonable to hypothesize, particularly during development. To test this idea, juvenile male or female zebra finches received chemical lesions of the HP at various points during song learning, as did adults. Song structure, singing behavior, song preference, and spatial memory were tested in adulthood. Although lesions of the HP severely compromised HP-dependent spatial memory function across all ages and in both sexes, we were unable to detect any effects of HP lesions on song learning, singing, or song structure in males. Interestingly, females lesioned as adults, but not as juveniles, did lose the characteristic preference for their father's song. Since compromise of the neural circuits that subserve episodic-like memory does very little (if anything) to affect procedural-like (song learning) memory, we conclude that these memory systems and their anatomical substrates are well dissociated in the developing male zebra finch. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009 [source]

Environmental complexity affects contextual fear conditioning following hippocampal lesions in rats

HIPPOCAMPUS, Issue 5 2007
Sandra N. Moses
Abstract Contextual fear conditioning has become a benchmark measure for hippocampal function, even though several studies report successful acquisition in hippocampal-damaged rodents. The current study examined whether environmental complexity may account for these discrepancies. We directly compared single-session contextual fear conditioning in rats in a simple vs. complex environment. Hippocampal lesions led to reduced fear conditioning in both contexts, as measured by freezing, but the effect was significantly greater in the complex context. As well, lesions led to generalized fear when the complex context was paired with shock, but not when the simple context was paired. We suggest that the representation of the simple context formed by rats with hippocampal lesions was adequate to support associative learning, but the representation of the complex context, which depended to a greater extent on relational learning, was not. The results were interpreted as consistent with theories of hippocampal function that emphasize its role in integrating multiple stimulus elements in a memory trace. © 2007 Wiley-Liss, Inc. [source]

Hippocampal lesions and discrimination performance of mice in the radial maze: Sparing or impairment depending on the representational demands of the task

HIPPOCAMPUS, Issue 2 2003
Nicole Etchamendy
Abstract The effects of ibotenate hippocampal lesions on discrimination performance in an eight-arm radial maze were investigated in mice, using a three-stage paradigm in which the only parameter that varied among stages was the way the arms were presented. In the initial learning phase (stage 1), animals learned the valence or reward contingency associated with six (three positive and three negative) adjacent arms of the maze using a successive (go/no-go) discrimination procedure. In the first test phase (stage 2), the six arms were grouped into three pairs, so that on each trial, the subject was faced with a choice between two adjacent arms of opposite valence (concurrent two-choice discrimination). In the second test phase (stage 3), the subject was faced with all six arms simultaneously (six-choice discrimination). Hippocampal-lesioned mice acquired the initial learning phase at a near-normal rate but behaved as if they had learned nothing when challenged with the two-choice discriminations at stage 2. In contrast, they behaved normally when confronted with the six-choice discrimination at stage 3. Detailed examination of within- and between-stage performance suggests that hippocampal-lesioned mice perform as intact mice when presentation of the discriminanda encourages the storage and use of separate representations (i.e., in initial learning and six-choice discrimination testing), but that they fail in test situations that involve explicit comparisons between such separate representations (two-choice discriminations), hence requiring the use of relational representations. Hippocampus 2003;13:197,211. © 2003 Wiley-Liss, Inc. [source]

Hippocampal structure and the action of cholinomimetic drugs

DRUG DEVELOPMENT RESEARCH, Issue 3 2002
John G. Csernansky
Abstract Cholinomimetic drugs have become the clinical standard for the treatment of patients with dementia of the Alzheimer type (DAT). However, uncertainty remains as to the proportion of patients that respond to such drugs, and how one might predict the capacity for response before treatment is begun. The thesis of the present review is that the neuroanatomical integrity of the hippocampus determines, at least in part, the capacity of DAT patients to respond to cholinomimetic drugs. Neuroimaging studies suggest that volume losses and other neuroanatomical deformities of the hippocampus are common in patients with even mild DAT. Moreover, more severe neuroanatomical deformities of the hippocampus are associated with more severe dementia symptoms and more rapid clinical decline. Animal research, including studies of cholinergic antagonists, glutamatergic antagonists, hippocampal lesions, and animals with mutant amyloid precursor protein genes, demonstrate that behavioral abnormalities similar to those found in DAT patients, especially those related to memory, are associated with hippocampal pathology. Cholinomimetic drugs, in particular, the cholinesterase inhibitors, have been shown to reverse some but not all of these behavioral abnormalities. More research is needed in DAT patients to determine whether an analysis of hippocampal structure or function can reliably predict the outcome of treatment with cholinomimetic drugs. Further work in animals is also needed to determine the limitations of cholinomimetic drugs for reversing various types of cognitive deficits, and to develop and test other pharmacological strategies for the treatment of DAT. Drug Dev. Res. 56:531,540, 2002. © 2002 Wiley-Liss, Inc. [source]

Distinct contributions of the amygdala and hippocampus to fear expression

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2009
Yogita Chudasama
Abstract The present study attempted to distinguish the independent contributions of the amygdala and hippocampus to fear expression. Rhesus monkeys (Macaca mulatta) with bilateral excitotoxic amygdala lesions (n = 4), bilateral excitotoxic hippocampal lesions (n = 8) and unoperated controls (n = 9) were allowed to reach over a neutral junk object or fear-provoking stimulus (i.e., a rubber snake or a jumping rubber spider) to retrieve a food reward. Monkeys were exposed to each stimulus for 30 s. On each trial we recorded the monkey's latency to retrieve the food reward and scored their whole-body reactions to the object. Confirming previous work we found that, relative to controls, both operated groups showed shorter food-retrieval latencies and exhibited fewer defensive and more approach behaviors when exposed to the fear-provoking stimuli. However, only monkeys with amygdala lesions showed an abnormal, excessive visual interest in the snake and spider. By contrast, monkeys with hippocampal lesions displayed behaviors that were unrelated to the presence of the fear stimuli, thereby indicating a lack of interest in, and emotional reactivity towards, the snake and spider. These data show that the hippocampus and amygdala contribute independently to the overall expression of defensive responses. [source]

Strain differences in the behavioural outcome of neonatal ventral hippocampal lesions are determined by the postnatal environment and not genetic factors

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2001
Graham K. Wood
Abstract It has been demonstrated that not only do rats neonatally lesioned in the ventral hippocampus (VH) develop behavioural hypersensitivity to amphetamine postpubertally, but also that the expression of the sensitivity is strain specific. For example, excitotoxic VH lesions at postnatal day (PD) 7 lead to significant increases in amphetamine-induced locomotion in postpubertal Fischer rats, but not in Lewis rats. However, as it is likely that the effect of strain differences are due to a combination of genetics and environment, we examined the contributions of the environment of the pups in determining the behavioural outcome following neonatal VH lesions. Fisher and Lewis rat pups were cross-fostered at birth, and then at PD7 lesioned bilaterally in the VH with ibotenic acid. anova analysis of postpubertal amphetamine-induced locomotor data revealed a significant effect of the strain of the dams raising the pups but no effect of the strain of the pup. In addition, a post hoc analysis revealed that lesioned Fisher or Lewis rats raised by Fisher, but not those raised by Lewis, dams demonstrated amphetamine-induced hyperlocomotion relative to nonlesioned controls. Observations of the maternal behaviour of Fischer and Lewis dams revealed significant differences in the frequency of arched-back nursing between the two strains. Interestingly, a correlation of the frequency of arched back nursing vs novelty- or amphetamine-induced locomotion revealed that the lesioned rats were significantly more affected by increases in arched-back nursing compared to the controls. The results suggest that the genetic background of the pups does not significantly affect the behavioural outcome following neonatal VH lesions; however, the results do suggest an important role of early environmental variables on the behavioural outcome of neonatal VH lesions. [source]

Hippocampal participation in navigational map learning in young homing pigeons is dependent on training experience

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2000
Paolo Ioalè
Abstract The homing pigeon navigational map is perhaps one of the most striking examples of a naturally occurring spatial representation of the environment used to guide navigation. In a previous study, it was found that hippocampal lesions thoroughly disrupt the ability of young homing pigeons held in an outdoor aviary to learn a navigational map. However, since that study an accumulation of anecdotal data has hinted that hippocampal-lesioned young pigeons allowed to fly during their first summer could learn a navigational map. In the present study, young control and hippocampal-lesioned homing pigeons were either held in an outdoor aviary or allowed to fly during the time of navigational map learning. At the end of their first summer, the birds were experimentally released to test for navigational map learning. Independent of training experience, control pigeons oriented homeward during the experimental releases demonstrating that they learned a navigational map. Surprisingly, while the aviary-held hippocampal-lesioned pigeons failed to learn a navigational map as reported previously, hippocampal-lesioned birds allowed flight experience learned a navigational map indistinguishable from the two control groups. A subsequent experiment revealed that the navigational map learned by the three groups was based on atmospheric odours. The results demonstrate that hippocampal participation in navigational map learning depends on the type of experience a young bird pigeon has, and presumably, the type of navigational map learned. [source]

Does the cingulate cortex contribute to spatial conditional associative learning in the rat?

HIPPOCAMPUS, Issue 7 2009
Marie St-Laurent
Abstract Rats with lesions to the anterior or posterior (retrosplenial) region of the cingulate cortex and rats with lesions that included both the anterior and posterior cingulate cortex were tested on a visual,spatial conditional task in which they had to learn to approach one of the two objects depending on the spatial context within which they were embedded. Lesions restricted to either the anterior or the retrosplenial cingulate region did not impair learning of this task which is known to be very sensitive to the effects of hippocampal lesions. Complete lesions of the cingulate cortex gave rise to only a minor retardation in learning. In contrast, lesions to the retrosplenial cortex impaired performance on a spatial navigation task and the classic radial maze. These results suggest that the retrosplenial portion of the cingulate region forms part of a hippocampal circuit underlying learning about spatial responses. The dissociation between the effects of lesions of the cingulate region on different classes of behavior known to be associated with hippocampal function suggests that, although this neural structure does play a role in an extended hippocampal circuit underlying spatial learning, its role in such learning may be a selective one. © 2009 Wiley-Liss, Inc. [source]

Different behavioral effects of neurotoxic dorsal hippocampal lesions placed under either isoflurane or propofol anesthesia

HIPPOCAMPUS, Issue 3 2008
Mark G. Baxter
Abstract Anesthetic protocols for behavioral neuroscience experiments are evolving as new anesthetics are developed and surgical procedures are refined to improve animal welfare. We tested whether neurotoxic dorsal hippocampal lesions produced under two different anesthetic protocols would have different behavioral and/or histo-pathological effects. Rats were anesthetized with either propofol, an intravenous anesthetic, or isoflurane, a gaseous anesthetic, and multiple injections of an excitotoxin (N -methyl- D -aspartate) were stereotaxically placed in the dorsal hippocampus bilaterally. Intraoperative physiological parameters were similar in the two surgical groups, as were the volumes of the lesions, although the profile of postoperative impairment in a spatial learning task differed between the lesion groups depending on the anesthetic regimen used. These results show that the choice of anesthetic protocol is a critical variable in designing behavioral neuroscience experiments using neurosurgical procedures. This factor should be considered carefully in experimental design and in cross-study comparisons of lesion effects on behavior. © 2007 Wiley-Liss, Inc. [source]

Environmental complexity affects contextual fear conditioning following hippocampal lesions in rats

Effects of hippocampal lesions on the monkey's ability to learn large sets of object-place associations,

HIPPOCAMPUS, Issue 4 2006
Annabelle M. Belcher
Abstract Earlier studies found that recognition memory for object-place associations was impaired in patients with relatively selective hippocampal damage (Vargha-Khadem et al., Science 1997; 277:376,380), but was unaffected after selective hippocampal lesions in monkeys (Malkova and Mishkin, J Neurosci 2003; 23:1956,1965). A potentially important methodological difference between the two studies is that the patients were required to remember a set of 20 object-place associations for several minutes, whereas the monkeys had to remember only two such associations at a time, and only for a few seconds. To approximate more closely the task given to the patients, we trained monkeys on several successive sets of 10 object-place pairs each, with each set requiring learning across days. Despite the increased associative memory demands, monkeys given hippocampal lesions were unimpaired relative to their unoperated controls, suggesting that differences other than set size and memory duration underlie the different outcomes in the human and animal studies. © 2005 Wiley-Liss, Inc. [source]

Context-dependent effects of hippocampal damage on memory in the shock-probe test

HIPPOCAMPUS, Issue 1 2005
Hugo Lehmann
Abstract We assessed the role of the hippocampus in anterograde memory, using the shock-probe test. Rats with sham or neurotoxic lesions of the hippocampus were given a shock-probe acquisition session during which each time they contacted a probe they received a shock; 24 h later, the rats were given a second shock-probe session to test their retention, but in this instance the probe was not electrified. Rats were tested in either the same context as the one used during acquisition or in a different context. The hippocampal lesions impaired avoidance of the probe and burying on the retention test, suggesting that the lesions induced anterograde amnesia. However, the impairment was context dependent. The hippocampal lesions impaired avoidance only when the rats were tested in the context in which they received the conditioning. The results of the shock-probe test suggest that the anterograde amnesia following hippocampal lesions is due mainly to an inability to associate the context with the shock more than to an inability to associate the probe with shock. © 2004 Wiley-Liss, Inc. [source]

Selective hippocampal damage in rhesus monkeys impairs spatial memory in an open-field test,

HIPPOCAMPUS, Issue 7 2004
Robert R. Hampton
Abstract The hippocampus is critical for remembering locations in a wide variety of species, including humans. However, recent findings from monkeys following selective hippocampal lesions have been equivocal. To approximate more closely the situations in which rodents and birds are tested, we used a spatial memory task in which rhesus monkeys (Macaca mulatta) moved about freely in a large room, on a tether. We used MRI-guided stereotaxic surgery to produce selective hippocampal lesions in five monkeys, and retained five unoperated control monkeys. In the study phase of each trial of the matching-to-location task, monkeys found food in one site in an array of identical foraging sites. During the test, which occurred after a delay, monkeys could return to the site where the food had been found during study to obtain more food. In Experiment 1, normal monkeys showed a small significant tendency to return directly to a site where they had previously found food that day. Operated monkeys showed no such matching tendency. In Experiment 2, further training produced reliable matching-to-location performance in both groups at short delays, but monkeys with selective hippocampal lesions rapidly forgot the location of the food. In Experiment 3, we tested whether monkeys used a "cognitive map" to encode the location of the hidden food, by requiring them to relocate the food from a starting location different from that used during study. As a group, monkeys were more accurate than expected by chance, indicating that they did encode the rewarded location with respect to allocentric landmarks; however, both groups of monkeys were significantly worse at relocating the food when required to approach from a different location. In Experiment 4, probe trials using symmetrical test arrays found no evidence for egocentric coding of the rewarded location. © 2004 Wiley-Liss, Inc. [source]

Hippocampal lesions and discrimination performance of mice in the radial maze: Sparing or impairment depending on the representational demands of the task

Post-training reversible inactivation of hippocampus reveals interference between memory systems

HIPPOCAMPUS, Issue 2 2002
Jason P. Schroeder
Abstract A post-training reversible lesion technique was used to examine the effects of neural inactivation of the dorsal hippocampus on place and response learning. Male Long-Evans rats trained in one of two versions of a water plus-maze task received post-training intra-hippocampal infusions of the local anesthetic drug bupivacaine (0.75% solution, 0.5 ,l), or saline. Post-training intra-hippocampal infusions of bupivacaine attenuated acquisition of the place task and enhanced acquisition of the response task. Delayed (2-h) post-training infusions of bupivacaine did not affect retention in either task. The findings demonstrate (1) enhanced learning after reversible hippocampal lesions that is independent of treatment influences on non-mnemonic factors, and (2) inactivation of the dorsal hippocampus during the post-training memory consolidation period is sufficient to enhance response learning. Hippocampus 2002;12:280,284. © 2002 Wiley-Liss, Inc. [source]

Rats with lesions of the hippocampus are impaired on the delayed nonmatching-to-sample task,

HIPPOCAMPUS, Issue 2 2001
Robert E. Clark
Abstract Rats with ibotenic acid lesions of the hippocampus (H-IBO) were trained on the trial-unique delayed nonmatching-to-sample task (DNMS) using a short delay of 4 s. The H-IBO group learned the nonmatching rule as quickly as control animals. However, performance was impaired on the DNMS task when the delay between the sample and choice phase was increased to 1 or 2 min. The use of 4-s delay (probe) trials indicated that the H-IBO animals retained the nonmatching-to-sample rule throughout testing. In a second experiment, using the same groups of rats, extended training at the 1-min delay did not ameliorate the deficit produced by H-IBO lesions. The finding of impaired recognition memory in rats after hippocampal lesions is consistent with findings from humans and monkeys. Several methodological issues are considered that have complicated the interpretation of earlier studies of recognition memory in rats following hippocampal lesions. The capacity for recognition memory in humans, monkeys, and rodents is discussed as a straightforward example of hippocampus-dependent (declarative) memory. Hippocampus 2001;11:176,186. © 2001 Wiley-Liss, Inc. [source]