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PubMed2003

Recovery effects after extinction in the Morris swimming pool navigation task.

In three experiments in which rats were used as subjects, we developed an extinction procedure using a Morris pool. The animals were trained to find a hidden platform located at a fixed position and were then given extinction trials in which the platform was removed from the pool. When training and extinction were carried out in the same context and time was allowed to elapse between extinction and test, spontaneous recovery of learning was observed. On the other hand, those rats that received extinction in a context different from the one used for training failed to show spontaneous recovery of learning when tested in the extinction context after an interval of 96 h. However, they did show renewal of spatial learning when tested in the training context. These results show that extinction in the spatial domain behaves like extinction in standard conditioning preparations.

Animals↗
PubMed2001

Hippocampal inactivation disrupts contextual retrieval of fear memory after extinction.

Recent studies implicate the hippocampus in contextual memory retrieval. The present experiments explore this possibility by examining the impact of reversible inactivation of the dorsal hippocampus (DH) on the context-specific expression of extinction. In experiment 1, rats were conditioned to fear a tone conditional stimulus (CS) and subsequently extinguished either in the same context as conditioning or in a novel context. A third group of rats underwent fear conditioning but did not receive extinction. After extinction, conditional fear to the tone CS was assessed in the conditioning context by measuring freezing. Rats extinguished in the conditioning context exhibited low levels of freezing, whereas those extinguished in a different context and those that received no extinction showed high levels of freezing. This indicates that the expression of extinction is context-specific. In experiment 2, the context-specific expression of extinction was disrupted by infusion of muscimol, a GABA(A) receptor agonist, into the DH. Rats that received muscimol infusions into the DH showed little freezing to the tone CS, regardless of whether the CS had been extinguished in the testing context or another context. In experiment 3, intrahippocampal muscimol infusions did not disrupt the expression of conditional freezing to the tone CS in rats that did not receive extinction. Thus, muscimol infusion into the DH produced a selective impairment in the context-specific expression of extinction. These results extend findings from other behavioral paradigms and provide additional support for a role for the hippocampus in contextual memory retrieval.

Acoustic Stimulation↗
PubMed2002

Facilitation of conditioned fear extinction by systemic administration or intra-amygdala infusions of D-cycloserine as assessed with fear-potentiated startle in rats.

NMDA receptor antagonists block conditioned fear extinction when injected systemically and also when infused directly into the amygdala. Here we evaluate the ability of D-cycloserine (DCS), a partial agonist at the strychnine-insensitive glycine-recognition site on the NMDA receptor complex, to facilitate conditioned fear extinction after systemic administration or intra-amygdala infusions. Rats received 10 pairings of a 3.7 sec light and a 0.4 mA footshock (fear conditioning). Fear-potentiated startle (increased startle in the presence vs the absence of the light) was subsequently measured before and after 30, 60, or 90 presentations of the light without shock (extinction training). Thirty non-reinforced light presentations produced modest extinction, and 60 or 90 presentations produced nearly complete extinction (experiment 1). DCS injections (3.25, 15, or 30 mg/kg) before 30 non-reinforced light exposures dose-dependently enhanced extinction (experiment 2) but did not influence fear-potentiated startle in rats that did not receive extinction training (experiment 3). These effects were blocked by HA-966, an antagonist at the glycine-recognition site (experiment 4). Neither DCS nor HA-966 altered fear-potentiated startle when injected before testing (experiment 5). The effect of systemic administration was mimicked by intra-amygdala DCS (10 microg/side) infusions (experiment 6). These results indicate that treatments that promote NMDA receptor activity after either systemic or intra-amygdala administration promote the extinction of conditioned fear.

Acoustic Stimulation↗
PubMed2001

[Sensory extinction phenomenon of double simultaneous stimulation: the analysis of consecutive stroke series with acute and unilateral lesions].

We evaluated consecutive stroke patients with an acute, unilateral lesion, in order to elucidate the anatomical correlates and the clinical course of sensory extinction phenomenon as well as its relation with unilateral spatial neglect (USN) and anosognosia for hemiplegia (AHP). Subjects consisted of 76 patients with right cerebral hemispheric lesions (RHL) and 43 with left cerebral hemispheric lesions (LHL). Twelve of 76 patients with RHL and 18 of 43 patients with LHL were excluded from this study, because of consciousness disturbance, aphasia, severe sensory disturbance, hemianopia, or severe dementia. All of the patients included in this study had an ischemic or hemorrhagic stroke, who admitted to our hospital within 24 hours after the onset of stroke. We repeatedly examined the patients to detect the presence of sensory extinction phenomenon, USN, and AHP from their acute to chronic stage. The incidence of extinction phenomenon in RHL was 33% (11/19 with cortical lesions and 10/45 with deep-seated lesions). When we excluded the patients with a lacunar stroke or TIA, 10 of 13 patients with subcortical lesions had sensory extinction phenomenon. Nineteen of 21 patients with RHL who showed sensory extinction phenomenon also accompanied USN, and twelve had associated AHP. The sensory extinction phenomenon disappeared within 20 days in 6 of 10 patients with subcortical lesions and 3 of 11 with cortical lesions. In contrast, three of 25 (12%) patients with LHL showed extinction phenomenon, the incidence being much rarer than the lesion in the right. Of these, two had USN and one had AHP together. All the deficits disappeared within 20 days after the onset of stroke in patients with LHL. Our studies may show that subcortical lesions present with extinction phenomenon more frequently than cortical lesions, although the phenomenon caused by the subcortical lesions of often disappear in a few weeks.

Aged↗
PubMed2003

Metabolic mapping of mouse brain activity after extinction of a conditioned emotional response.

Metabolic mapping with fluorodeoxyglucose (FDG), a radiolabeled glucose analog, was used to assess regional activity changes in the mouse brain that result from extinction of a conditioned emotional response (CER). In the extinction group, Pavlovian tone-foot shock conditioning, followed by repeated tone-alone presentations, resulted in the reduction of the CER (freezing behavior). A second group underwent CER acquisition alone (nonextinction group), and a third group showed no CER after pseudorandom training. Then mice were injected with FDG, and tone-evoked brain activity was mapped. In the auditory system, increased activity resulted from the associative effects of acquisition training. Effects common to extinction and nonextinction groups, presumably reflecting the tone-foot shock association independently of CER expression, were found in the medial geniculate, hippocampus, and subiculum. In the extinction group, a major finding was the elevated activity in prefrontal cortex regions. In addition, brain-behavior correlations between FDG uptake and freezing behavior confirmed that subjects with higher prefrontal activity were more successful at inhibiting the CER. Interregional activity correlations showed extensive functional coupling across large-scale networks in the extinction group. The increased activity of the prefrontal cortex and its negative interactions with other regions within the extinction group suggest a functional network inhibiting the CER composed of prefrontal cortex, medial thalamus, auditory, and hippocampal regions. This is the first time that such a functional network resulting from Pavlovian extinction has been demonstrated, and it supports Pavlov's original hypothesis of extinction as the formation of cortical inhibitory circuits, rather than unlearning or reversal of the acquisition process.

Acoustic Stimulation↗
PubMedDate not supplied

Partial reinforcement and extinction of vasomotor conditioning. A test of cognitive and two-factor theories.

In order to investigate cognitive versus traditional accounts of responding in extinction and the discrimination hypothesis for the partial reinforcement effect, 40 human subjects were randomly divided into two groups and were treated according to thermal vasomotor conditioning procedures using either 25 trials of continuous reinforcement or 100 trials of 25% partial reinforcement. At the onset of extinction, half of each group was given traditional noninformed extinction, while the other (informed) half had the thermal stimulator removed. The usual greater resistance to extinction was obtained after partial reinforcement than after continuous reinforcement in the two noninformed groups, however, immediate extinction of responding was obtained from the first extinction trial in the two informed groups. These results are consistent both with the discrimination hypothesis for the partial reinforcement extinction effect and with cognitive explanations of responding in extinction. Consequences for the behavioral therapies are discussed.

Blood Pressure↗
PubMed1999

Extinction after regular and irregular reward schedules in the infant rat: influence of age and training duration.

Greater persistence in extinction is observed following inconsistent reward compared to that observed following consistent reward, an effect termed the partial reinforcement extinction effect (PREE). We report three experiments in which the extinction rates of random partially reinforced (PRF) or continuously reinforced (CRF) infant rat pups were compared to the extinction rate of pups trained with an alternative and regular schedule of partial reinforcement, known as patterned single alternation (PSA). In PSA, subjects learn to alternate speed of responding in anticipation of the regular alternation of reward and nonreward trials in the straight alley runway. In Experiment 1, 17-day-old PSA subjects showed CRF-like extinction rates; whereas in Experiment 2, in which extinction was initiated early in training prior to the onset of the PSA discrimination, PSA subjects showed prolonged, PRF-like extinction curves. In contrast, 12-day-old pups in Experiment 3 showed no reward-schedule-related differences in extinction, despite differences in behavior during acquisition. These results prompt a modification of Amsel's (1962) model of discrimination learning, and suggest the existence of a dissociation between different types of reward-related expectancies in the younger subjects.

Age Factors↗
PubMed2002

Determinants of extinction in the fossil record.

The causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology. It has long been recognized, however, that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity and estimates of taxonomic rates of evolution. This problem has been particularly noted with respect to the principal mass extinctions. Here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth. Many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock. Although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock, it also supports the hypothesis that much of the observed short-term volatility in extinction rates is an artefact of variability in the stratigraphic record.

Animals↗
PubMed2003

Catastrophic extinctions follow deforestation in Singapore.

The looming mass extinction of biodiversity in the humid tropics is a major concern for the future, yet most reports of extinctions in these regions are anecdotal or conjectural, with a scarcity of robust, broad-based empirical data. Here we report on local extinctions among a wide range of terrestrial and freshwater taxa from Singapore (540 km2) in relation to habitat loss exceeding 95% over 183 years. Substantial rates of documented and inferred extinctions were found, especially for forest specialists, with the greatest proportion of extinct taxa (34-87%) in butterflies, fish, birds and mammals. Observed extinctions were generally fewer, but inferred losses often higher, in vascular plants, phasmids, decapods, amphibians and reptiles (5-80%). Forest reserves comprising only 0.25% of Singapore's area now harbour over 50% of the residual native biodiversity. Extrapolations of the observed and inferred local extinction data, using a calibrated species-area model, imply that the current unprecedented rate of habitat destruction in Southeast Asia will result in the loss of 13-42% of regional populations over the next century, at least half of which will represent global species extinctions.

Animals↗
PubMed2004

Food-web interactions govern the resistance of communities after non-random extinctions.

Growing concern about how loss of biodiversity will affect ecosystems has stimulated numerous studies. Although most studies have assumed that species go extinct randomly, species often go extinct in order of their sensitivity to a stress that intensifies through time (such as climate change). Here we show that the consequences of random and ordered extinctions differ. Both depend on food-web interactions that create compensation; that is, the increase of some species when their competitors and/or predators decrease in density due to environmental stress. Compensation makes communities as a whole more resistant to stress by reducing changes in combined species densities. As extinctions progress, the potential for compensation is depleted, and communities become progressively less resistant. For ordered extinctions, however, this depletion is offset and communities retain their resistance, because the surviving species have greater average resistance to the stress. Despite extinctions being ordered, changes in the food web with successive extinctions make it difficult to predict which species will show compensation in the future. This unpredictability argues for 'whole-ecosystem' approaches to biodiversity conservation, as seemingly insignificant species may become important after other species go extinct.

Animals↗
PubMed2002

Survival without recovery after mass extinctions.

Because many survivors of mass extinctions do not participate in postrecovery diversifications, and therefore fall into a pattern that can be termed "Dead Clade Walking" (DCW), the effects of mass extinctions extend beyond the losses observed during the event itself. Analyses at two taxonomic levels provide a first-order test of the prevalence of DCWs by using simple and very conservative operational criteria. For four of the Big Five mass extinctions of the Phanerozoic, the marine genera that survived the extinction suffered approximately 10-20% attrition in the immediately following geologic stage that was significantly greater than the losses sustained in preextinction stages. The stages immediately following the three Paleozoic mass extinctions also account for 17% of all order-level losses in marine invertebrates over that interval, which is, again, significantly greater than that seen for the other stratigraphic stages (no orders are lost immediately after the end-Triassic or end-Cretaceous mass extinctions). DCWs are not evenly distributed among four regional molluscan time-series following the end-Cretaceous extinction, demonstrating the importance of spatial patterns in recovery dynamics. Although biotic interactions have been invoked to explain the differential postextinction success of clades, such hypotheses must be tested against alternatives that include stochastic processes in low-diversity lineages-which is evidently not a general explanation for the ordinal DCW patterns, because postextinction fates are not related to the size of extinction bottlenecks in Paleozoic orders-and ongoing physical environmental changes.

Animals↗
PubMed2000

Ecological basis of extinction risk in birds: habitat loss versus human persecution and introduced predators.

Understanding the ecological mechanisms that underlie extinction is fundamental to conservation. It is well established that not all taxa are equally vulnerable to extinction, but the reasons for these differences are poorly understood. This may be, in part, because different taxa are threatened by different mechanisms. Theoretically, sources of extinction risk that perturb the balance between fecundity and longevity, such as human persecution and introduced predators, should be particularly hazardous for taxa that have slow rates of population growth. In contrast, sources of extinction risk that reduce niche availability, such as habitat loss, should represent a particular threat to taxa that are ecologically specialized. Here we test these predictions by using a phylogenetic comparative method and a database on 95 families of birds. As theory predicts, extinction risk incurred through persecution and introduced predators is associated with large body size and long generation time but is not associated with degree of specialization, whereas extinction risk incurred through habitat loss is associated with habitat specialization and small body size but not with generation time. These results demonstrate the importance of considering separately the multiple mechanisms that underlie contemporary patterns of extinction. They also reveal why it has previously proven so difficult to identify simple ecological correlates of overall extinction risk.

Animals↗
PubMed2005

Aphasia and auditory extinction: Preliminary evidence of binding.

Background: McNeil, Odell, and Tseng (1991), and Murray and colleagues (Murray, 2000; Murray, Holland, & Beeson, 1997a, 1997b) have suggested that variability of performance in patients with aphasia may be due to nonlinguistic cognitive variables, such as attention (i.e., resources, capacity, effort), which affect language comprehension and production. Given the research that has supported the relationship between aphasia and attention deficits, it is important to determine what effect this breakdown in attention may have on cognitive processes for individuals with aphasia.Aims: This study aims to determine if auditory extinction is present in individuals with aphasia, and if so, if this is due to a breakdown in binding. If extinction is found for individuals with aphasia, it would further support the notion that auditory attention difficulties are present among individuals with aphasia, since visual and auditory research has attributed extinction to a breakdown in attention (Baylis, Driver, & Rafal, 1993; Deouell, Bentin, & Soroker, 2000; Deouell & Soroker, 2000). If binding is found to be deficient, the fact that individuals with both left and right hemisphere lesions demonstrate this phenomenon would lead to a number of implications regarding the relationship of attention and aphasia.Methods & Procedures: Auditory extinction, in which one stimulus is not perceived during double simultaneous stimulation (DSS) presentation, was examined in six individuals with aphasia (aged 42-74 years) and six age-matched healthy adults. Two different experiments were conducted in which the auditory stimuli, consisting of male and female voices speaking the letters "T" or "O", were systematically varied to investigate whether binding of identification to location contributes to extinction.Outcomes & Results: Participants with aphasia made more omission errors (extinction) than the control group, and extinction was significantly greater for binding versus nonbinding conditions, suggesting that binding may play a role in extinction for individuals with aphasia.Conclusions: These data provide preliminary results that auditory extinction exists in individuals with aphasia and may be due to deficits in binding together identification and localisation information. Research on this phenomenon and how it influences language would be a worthwhile endeavour for future studies. Moreover, little is known about assessment of auditory attention in patients with aphasia. Further research in this area can lead to advancements in theoretical and functional assessment for individuals with aphasia who have auditory attention and/or binding deficits and require speech-language pathology intervention.

Journal Article↗
PubMed2003

Local extinction and the evolution of dispersal rates: causes and correlations.

We present the results of individual-based simulation experiments on the evolution of dispersal rates of organisms living in metapopulations. We find conflicting results regarding the relationship between local extinction rate and evolutionarily stable (ES) dispersal rate depending on which principal mechanism causes extinction: if extinction is caused by environmental catastrophes eradicating local populations, we observe a positive correlation between extinction and ES dispersal rate; if extinction is a consequence of stochastic local dynamics and environmental fluctuations, the correlation becomes ambiguous; and in cases where extinction is caused by dispersal mortality, a negative correlation between local extinction rate and ES dispersal rate emerges. We conclude that extinction rate, which both affects and is affected by dispersal rates, is not an ideal predictor for optimal dispersal rates.

Animals↗
PubMed2000

Time-dependent activation of parieto-frontal networks for directing attention to tactile space. A study with paired transcranial magnetic stimulation pulses in right-brain-damaged patients with extinction.

Tactile extinction has been interpreted as an attentional disorder, closely related to hemineglect, due to hyperactivation of the unaffected hemisphere, resulting in an ipsilesional attentional bias. Paired transcranial magnetic stimulation (TMS) techniques, with a subthreshold conditioning stimulus (CS) followed at various interstimulus intervals (ISIs) by a suprathreshold test stimulus (TS), are useful for investigating intracortical inhibition and facilitation in the human motor cortex. In the present work, we investigated the effects of paired TMS over the posterior parietal and frontal cortex of the unaffected hemisphere in a group of eight right-brain-damaged patients with tactile extinction who were carrying out a bimanual tactile discrimination task. The aim of the study was to verify if paired TMS could induce selective inhibition or facilitation of the unaffected hemisphere depending on the ISI, resulting, respectively, in an improvement and a worsening of contralesional extinction. In addition, we wanted to investigate if the effects of parietal and frontal TMS on contralesional extinction appeared at different intervals, suggesting time-dependent activation in the cortical network for the processing of tactile spatial information. Paired TMS stimuli with a CS and a TS, separated by two ISIs of 1 and 10 ms, were applied over the left parietal and frontal cortex after various intervals from the presentation of bimanual cutaneous stimuli. Single-test parietal TMS stimuli improved the patients' performance, whereas paired TMS had distinct effects depending on the ISI: at ISI = 1 ms the improvement in extinction was greater than that induced by single-pulse TMS; at ISI = 10 ms we observed worsening of extinction, with complete reversal of the effects of single-pulse TMS. Compared with TMS delivered over the frontal cortex, parietal TMS improved the extinction rate in a time window that began earlier. These findings shed further light on the mechanism of tactile extinction, suggesting relative hyperexcitability of the parieto-frontal network in the unaffected hemisphere, which is amenable to study and modulation by paired TMS pulses. In addition, the results show time-dependent processing of tactile spatial information in the parietal and frontal cortices, with a bimodal distribution of activity, at least in the attentional network of the unaffected hemisphere.

Aged↗
PubMed1994

The effects of chronic administration of ceronapril on the partial reinforcement extinction effect and latent inhibition in rats.

Previous experiments showed that acute administration of the angiotensin converting enzyme (ACE) inhibitor, ceronapril, shares with neuroleptic drugs an ability to enhance latent inhibition (LI), which consists of retardation in conditioning to a stimulus as a consequence of its prior non-reinforced pre-exposure. Experiment 1 tested whether ceronapril would produce a neuroleptic-like effect in the partial reinforcement extinction effect (PREE) at one trial a day. The PREE refers to the increased resistance to extinction observed in animals trained on a partial reinforcement (PRF) schedule compared with those trained on a schedule of continuous reinforcement (CRF). Two groups of rats were trained to run in a straight alley. The CRF group received food reward on every trial. The PRF group was rewarded on a quasi-random 50% schedule. All animals were then tested in extinction in which no reward was given. Ceronapril at a dose of 0.05mg/kg was administered in a 2 x 2 design, with drug or no drug in acquisition and drug or no drug in extinction. Rats receiving vehicle in acquisition showed a PREE, regardless of their drug treatment in extinction. In contrast, ceronapril administered in acquisition attenuated the PREE irrespective of drug treatment in extinction, by both increasing resistance to extinction in CRF animals and decreasing resistance to extinction in PRF animals. This pattern of results does not resemble that produced by neuroleptics. The PREE procedure necessitated repeated administration of ceronapril whereas the previous demonstrations of neuroleptic-like enhancement of LI have been obtained with acute administration. Experiment 2 therefore tested the effects of chronic ceronapril administration on LI. Under these conditions, ceronapril abolished LI. The results are discussed in relation to the antipsychotic, anti-anxiety and cognitive-enhancing effects formerly attributed to ACE inhibitors.

Journal Article↗
PubMed2000

Extinction dynamics and the regional persistence of a tree frog metapopulation.

The concept of a metapopulation acknowledges local extinctions as a natural part of the dynamics of a patchily distributed population. However, if extinctions are not balanced by recolonizations or if there is a high degree of spatial synchrony of local extinctions, this poses a threat to and will reduce the metapopulation persistence time. Here we show that, in a metapopulation network of 378 pond patches used by the tree frog (Hyla arborea), even though extinctions are frequent (mean extinction probability p(e) = 0.24) they pose no threat to the metapopulation as they are balanced by recolonizations (p(c) = 0.33). In any one year there was a pattern of large populations tending to persist while small populations became extinct. The total number of individuals belonging to populations that went extinct was small (< 5%) compared with those populations that persisted. A spatial autocorrelation analysis indicated no clustering of local extinctions. The tree frog metapopulation studied consisted of a set of larger, persistent populations mixed with smaller populations characterized by high turnover dynamics.

Animals↗
PubMed2006

Quantifying the extinction vortex.

We developed a database of 10 wild vertebrate populations whose declines to extinction were monitored over at least 12 years. We quantitatively characterized the final declines of these well-monitored populations and tested key theoretical predictions about the process of extinction, obtaining two primary results. First, we found evidence of logarithmic scaling of time-to-extinction as a function of population size for each of the 10 populations. Second, two lines of evidence suggested that these extinction-bound populations collectively exhibited dynamics akin to those theoretically proposed to occur in extinction vortices. Specifically, retrospective analyses suggested that a population size of n individuals within a decade of extinction was somehow less valuable to persistence than the same population size was earlier. Likewise, both year-to-year rates of decline and year-to-year variability increased as the time-to-extinction decreased. Together, these results provide key empirical insights into extinction dynamics, an important topic that has received extensive theoretical attention.

Animals↗