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PubMed1976

Auditory frequency generalization with differing extinction influences in normal and prefrontal dogs trained in instrumental alimentary reflexes.

Following criterion of 90 percent correct responses to a 1,000-Hz tone on a 50 percent reinforcement schedule, 8 of 12 dogs were subjected to lesions of the medial or lateral prefrontal cortex. Three types of auditory frequency generalization tests followed separated by a period of reacquisition of the instrumental response. A sampling procedure of generalization assessment, wherein a block of test trials was contained within 15 partially reinforced trials and repeated over 16 days, revealed complete generalization in the medials and rapid, but discriminative responding in the laterals. The second generalization test was conducted in complete extinction over 5 days. The medials yielded discriminative performance and least overall resistance to extinction, while the laterals showed a higher amount of frequency control and minimal extinction effects. Go-no go differentiation training preceeded the last generalization test [CS(+) = 1,000 Hz; CS(-) = 600 Hz], resulting in retarded acquisition in the laterals and easiest acquisition in the medials. The last generalization test suggested that all groups were comparable, with some trend toward more rapid extinction in the medial dogs. Collectively, the data indicated that performance was determined by the interacting functions between the specific lesions and the density of reinforcement present in the testing procedure.

Animals↗
PubMed1999

Extinction of behavior in infant rats: development of functional coupling between septal, hippocampal, and ventral tegmental regions.

Learning of a behavior at a particular age during the postnatal period presumably occurs when the functional brain circuit mediating the behavior matures. The inability to express a learned behavior, such as inhibition, may be accounted for by the functional dissociation of brain regions comprising the circuit. In this study we tested this hypothesis by measuring brain metabolic activity, as revealed by fluorodeoxyglucose (FDG) autoradiography, during behavioral extinction in 12- and 17-d-old rat pups. Subjects were first trained on a straight alley runway task known as patterned single alternation (PSA), wherein reward and nonreward trials alternate successively. They were then injected with FDG and given 50 trials of continuous nonreward (i.e., extinction). Pups at postnatal day 12 (P12) demonstrated significantly slower extinction rates compared to their P17 counterparts, despite the fact that both reliably demonstrated the PSA effect, i.e., both age groups distinguished between reward and nonreward trials during acquisition. Covariance analysis revealed that the dentate gyrus, hippocampal fields CA1-3, subiculum, and lateral septal area were significantly correlated in P17 but not P12 pups. Significant correlations were also found between the lateral septal area, ventral tegmental area, and the medial septal nucleus in P17 pups. Similar correlative patterns were not found in P12 and P17 handled control animals. Taken together, these results suggest that septal, hippocampal, and mesencephalic regions may be functionally dissociated at P12, and the subsequent maturation of functional connectivity between these regions allows for the more rapid expression of behavioral inhibition during extinction at P17.

Aging↗
PubMed2002

Selective modification of short-term hippocampal synaptic plasticity and impaired memory extinction in mice with a congenitally reduced hippocampal commissure.

The hippocampus is critical for forming new long-term memories, but the contributions of the hippocampal commissure (HC) to memory function and hippocampal synaptic plasticity are unclear. To shed light on this issue, we characterized behavioral memory and hippocampal synaptic plasticity in two inbred mouse strains. BALB/cWah1 mice display a range of corpus callosal defects and an intact HC, whereas 9XCA/Wah mice exhibit a complete absence of corpus callosum and a greatly reduced HC. No differences between strains were found in long-term potentiation (LTP) within two synaptic pathways in hippocampal slices. However, paired-pulse facilitation was deficient in area CA1 of slices from 9XCA/Wah, and it was rescued by decreasing extracellular [Ca2+], suggesting that presynaptic calcium dynamics may be altered in this strain. In addition, contextual fear extinction was impaired in 9XCA/Wah mice, but performance on cued fear extinction and on 24 hr memory tests for cued and contextual fear conditioning were not significantly different between strains. Thus, an intact HC is critical for normal extinction of contextual fear. Intact interhemispheric connectivity is not required for acquisition or expression of cued and contextual fear conditioning. LTP was normal in slices from mice that lacked an intact HC, and this was correlated with normal performance on fear conditioning tests. In contrast, impaired short-term synaptic plasticity was correlated with defective contextual memory extinction in mice lacking an intact HC. Thus, the HC in mice is vital for particular aspects of memory function and for short-term synaptic modification in specific hippocampal circuits.

Agenesis of Corpus Callosum↗
PubMed2005

[Features of a passive avoidance extinction of mice with a different level of anxiety].

The dependence of the passive avoidance extinction from a level of mice initial anxiety is investigated. Mice were classified as high-, medium- and low-anxious by time spent in the open area of the elevated plus-maze. It is revealed that to each from levels of anxiety there corresponds certain dynamics of extinction. The high-anxious mice are characterized absence of the passive avoidance extinction and stability of good retrieval of memory trace for want of testing down to 15 days. At medium-anxious mice the deficit of avoidance habit performance developed since the 7th day of extinction. At low-anxious mice since the 11th day of testing the deterioration of retrieval was observed.

Animals↗
PubMedDate not supplied

[Effects of dehydroepiandrosterone sulfate and dizocilpine on memory trace extinction in aggressive and submissive mice].

It was shown that injections of NMDA receptor antagonist dizocilpine and neurosteroid dehydroepiandrosterone sulfate (DHEAS) and sequential injections of these substances had different effects on learning and extinction of passive avoidance in aggressive and submissive mice. In aggressive mice, dizocilpine impaired and DHEAS did not change learning and retention. However, being injected after dizocilpine, DHEAS blocked the defect of memory trace retrieval induced by dizocilpine. In submissive mice, dizocilpine impaired learning and prolonged extinction of the learned habit. Injection of DHEAS prolonged the extinction in a similar way. Under conditions of sequential injections, DHEAS did not change the suppressive effect of dizocilpine on learning and was not effective in prolongation of extinction.

Aggression↗
PubMed1989

Resistance to extinction following habituation to behaviourally disruptive novel stimuli.

Three experiments tested the prediction, derived from generalized frustration theory (Amsel, 1972), that habituation to behaviourally disruptive stimuli increases resistance to extinction in the runway. In each experiment, rats received initial consistent reinforcement (CRF) training and then either continued CRF (Groups C), partial reinforcement (PRF) training (Groups P), or CRF accompanied by presentations of a novel tactile, tone, or obstacle stimulus (Groups D) in Experiments 1-3, respectively. PRF increased resistance to extinction whether non-reinforcement disrupted behaviour (Experiment 1) or not (Experiments 2 and 3). The tactile and obstacle stimuli very substantially disrupted behaviour, and the tone produced a modest disruption of behaviour. All subjects habituated to the disruptive effects of these stimuli, but Group D was not more resistant to extinction than Group C in any experiment. The results suggest that non-reinforcement has unique stimulus properties, a consequence of which is that habituation to other sources of disruptive stimulation does not promote responding to non-reinforcement in extinction.

Animals↗
PubMedDate not supplied

[Relation between the dynamics of the extinction process and the initial rate of hypothalamic self-stimulation in the rabbit].

In experiments on rabbits with electrodes chronically implanted in the lateral hypothalamus, dynamics was studied of extinction of self-stimulation reaction as a result of cancellation of intracerebral reinforcement. General dynamics of extinction of the unreinforced instrumental actions and behavioural manifestations of orienting-investigating reaction were revealed. It was found, that in 30% of rabbits, the orienting reaction appearing as a result of "discordance" between expected and actual afferentation is attended by a species-specific form of behaviour, expressed in the form of hind paws synergic strokes against the floor. It is suggested that these strokes may be a somatic expression of a negative emotional state of animals during self-stimulation extinction. The comparison of extinction dynamics with the level of self-stimulation background frequency showed a relative independence of the strength of drive towards getting positive emotions on motivational effects created by electric stimulation of the reinforcing brain structures.

Animals↗
PubMed1984

Assessment and extinction of conditioned withdrawal-like responses in an integrated treatment for opiate dependence.

Recent data have generally been consistent with our pilot findings: a significant proportion--33 to 40%--of opiate-dependent patients show a time-linked decrease in skin-temperature in response to standard drug-related stimuli, suggestive of conditioned withdrawal. Patients' physiological changes are often accompanied by subjective craving and withdrawal, but the correlation among these measures is modest. Though craving seems to diminish with repeated exposure to drug-related stimuli, withdrawal-like symptoms are often persistent and slow to extinguish. Our current design initially assumed that most patients would show conditioned craving and withdrawal to our standard stimuli and that our current procedure would be adequate to produce complete extinction for these "responders.' As it turned out, not all patients respond to our standard stimuli, and our extinction procedure is not completely effective for those who do. Given these two findings, our current design does not permit the best test of the potential clinical benefits of extinction. Our rich experience during the first phase of this project has stimulated several procedural changes which should increase our accuracy in determining the incidence of these conditioned phenomena, our effectiveness in extinguishing them, and permit a better assessment of their potential clinical benefit. These are as follows: Individualize eliciting (drug-related) stimuli--We initially chose to use standard (the same for all patients) stimuli for practical and experimental reasons. However, their use may have resulted in an underestimate of the incidence of conditioned craving and withdrawal, and in less relevant extinction for many patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

[Effect of an alternating magnetic field on development and extinction of conditioned responses in rats].

This paper deals with the problem whether there is an effect of extremely low frequency electromagnetic fields on simple learning processes. The conditioned reaction upon an electromagnetic fields on simple learning processes. The conditioned reaction upon an acoustic stimulus (1000 Hz) reinforced by an electric painful stimulus was used. During the conditioning and extinction process 28 adult albino rats were put in a 10 Hz, 0,3 G magnetic field. Their learning and extinction behaviour was compared with that of a control group of 28 rats trained under normal laboratory conditions. The extinction schedule differs significantly between the experimental and control group: The extinction develops faster in the experimental group (p less than 0.05). In connection with the results of other authors our findings are discussed as a general amount of adaptability by the influence of the 10 Hz field.

Animals↗
PubMed1983

Contextual control of the extinction of conditioned fear: tests for the associative value of the context.

Four conditioned suppression experiments examined the influence of contextual stimuli on the rat's fear of an extinguished conditioned stimulus (CS). When rats received pairings of a CS with shock in one context and then extinction of the CS in another context, fear of the CS was renewed when the CS was returned to and tested in the original context (Experiments 1 and 3). No such renewal was obtained when the CS was tested in a second context after extinction had occurred in the conditioning context (Experiment 4). In Experiment 2, shocks presented following extinction reinstated fear of the CS, but only if they were presented in the context in which the CS was tested. In each experiment, the associative properties of the contexts were independently assessed. Contextual excitation was assessed primarily with context-preference tests in which the rats chose to sit in either the target context or an adjoining side compartment. Contextual inhibition was assessed with summation tests. Although reinstatement was correlated with demonstrable contextual excitation present during testing, the renewal effect was not. Moreover, there was no evidence that contextual inhibition developed during extinction. The results suggest that fear of an extinguished CS can be affected by the excitatory strength of the context but that independently demonstrable contextual excitation or inhibition is not necessary for contexts to control that fear.

Animals↗
PubMed1981

Vagotomy facilitates extinction of conditioned taste aversions in rats.

Results from three experiments indicate that severing the subdiaphragmatic vagus in rats increased the rate of extinction of learned taste aversions. In Experiment 1, although vagotomized rats acquired a saccharin aversion equivalent to that of controls when the illness-inducing agent was the blood-borne toxin apomorphine, vagotomized rats tended to consume more saccharin than controls during repeated extinction tests. In Experiment 2, vagotomy disrupted retention and increased extinction of a preoperatively acquired saccharin aversion. Disruptions were found when the taste aversion was induced by copper sulfate, a local gastric irritant (Experiment 2A), or apomorphine, a systemic toxin (Experiment 2B); in each experiment vagotomized rats consumed more saccharin than controls on the first retention test and extinguished the prior to surgery. Experiment 3 demonstrated that vagotomy did not affect retention or extinction of a shock-induced conditioned emotional response (lick to suppression) to noise. It is concluded that integrity of the vagus is not necessary for acquisition of a learned taste aversion when a blood-borne toxin is used as the ill-inducing agent. However, the vagus apparently mediates an integral portion of the conditioned response following taste-illness acquisition regardless of whether the illness agent is a local gastric irritant or a systemic toxin.

Afferent Pathways↗
PubMedDate not supplied

[Spatial synchronization of brain potentials during extinctive inhibition].

The changes in spatial synchroneity of potentials in the cortex (SSCP) and several subcortical structures (some nuclei of the hypothalamus and non-specific nuclei of the thalamus) were studied in 11 rabbits in the course of extinction of defensive conditioned reflex (CR) to light. In the course of extinction, at the movement of the non-reinforced stimulation, specific increase in SSCP gradually disappears and the synchroneity between the cortex and subcortical structures decreases. In intersignal periods, at the stage of complete extinction, SSCP returns to the values prior to CR elaboration. The obtained data suggest that during CR extinction, a discrepancy of functional states gradually develops both between different cortical areas and between the cortex and the studied subcortical structures.

Animals↗
PubMedDate not supplied

[A spectral-correlational analysis of the electrical activity of the rabbit brain during the extinction of an endogenous food conditioned reflex].

Spectral analysis of electrical activity showed that at the end of extinction of the alimentary conditioned responses, elaborated on the basis of the hunger dominant, the spectral density of electrical activity of the cortical centre of the goal-directed reaction (blinking) of the trained eye and that of the lateral preoptic area, lateral hypothalamus, and ventromedial hypothalamus raised in the delta-band. To the end of the extinction the coherence (Cog) of biopotentials of the cortical centres of blinking of both eyes and electrical activity of the ventro-medial hypothalamus and medial preoptic area was changed in different directions. After the extinction of the goal-directed reaction Cog between biopotentials of the lateral hypothalamus and the electrical activity of the frontal cortex raised in the delta-band and Cog between the activity of the lateral hypothalamus and that of the cortical centres of blinking of both eyes lowered. The level of excitation of the structures included in the dominant constellation was suggested to raise to the end of the extinction of the endogenous conditioned response.

Analog-Digital Conversion↗
PubMed1994

Auditory neglect and the ear extinction effect in dichotic listening: a reply to Beaton and McCarthy (1993).

In our reply to Beaton and McCarthy (1993), we argue that the issue of ear extinction in dichotic listening also should take into account lesion site and lesion extension. When the lesion is primarily affecting the auditory pathways, the resulting dichotic dysfunction may be an ear extinction effect. However, when the lesion is outside of the auditory system, the absence of reports from one ear may be part of a larger cognitive deficit, involving more complex processes, like orientation and attention. Thus, by constraining the definition of an "ear extinction effect" to a perceptual deficit, Beaton and McCarthy confounds the issue of ear extinction with auditory neglect. In our reply we also present some new data from a patient with a left-sided thalamic pulvinar lesion, contrasting his dichotic listening performance with the patient reported in our original 1991 study.

Adult↗
PubMed1998

Extinction times and phase transitions for spatially structured closed epidemics.

This paper considers the time to extinction for a stochastic epidemic model of SEIR form without replacement of susceptibles. It first shows how previous rigorous results can be heuristically explained in terms of the more transparent dynamics of an approximating deterministic system. The model is then extended to include a host population structured into patches, with weak nearest-neighbour mixing of infection. It is shown, by considering the approximating deterministic system, that the expected time to extinction in a population of n + 1 patches each of size N is of the form a log N + bn, provided that N > Nc where Nc is a critical patch size below which transits are unlikely to occur. This corresponds to the simple decomposition of the time of an epidemic into the time it takes to spread through one patch plus the time it takes to transit to each of n successive patches. Expressions for this threshold and the coefficients of the time to extinction are given in terms of the transmission parameters of infection and the coupling strength between patches. These expressions are compared with numerical results using parameters relevant to a study of phocine distemper virus in North Sea seals, and the agreement is found to be good for large and small N. In the region when N approximately Nc, where transits may or may not occur, interesting transitional behaviour is seen, leading to a non-monotonicity of the extinction time as a function of N.

Animals↗
PubMed1998

Optical Sizing of Ultrafine Metallic Particles: Retrieval of Particle Size Distribution from Spectral Extinction Measurements.

The inverse problem of optical sizing of ultrafine metallic particles from the spectral extinction measurements in the visible range is investigated. Solving the inverse problem becomes possible due to the strong size effect which in the framework of classical electrodynamics can be described by the dependence of complex refractive index on the particle size. It is shown that the size effect leads to the considerable increase of information content of spectral extinction data with respect to desired size composition of the particles. This makes it possible to retrieve the size distribution of ultrafine metallic particles with reasonably high accuracy, including the Rayleigh size region. The analysis is performed mainly within the framework of numerical tests by the typical example of ultrafine silver particles in a gelatin matrix. The results in retrieving of size distribution from experimentally measured extinction spectra are also presented. Calculations of spectral extinction coefficient are made by means of Mie theory. In so doing, the dielectric function of particles is modified by using the electron's mean free path limitation model. Copyright 1998 Academic Press.

Journal Article↗
PubMed2002

Resistance to extinction of low fitness virus subjected to plaque-to-plaque transfers: diversification by mutation clustering.

Plaque-to-plaque transfers of RNA viruses lead to accumulation of mutations and fitness decrease. To test whether continuing plaque-to-plaque transfers would lead to viral extinction, we have subjected several low fitness foot-and-mouth disease virus (FMDV) clones to up to 130 successive plaque transfers, and have analyzed the evolution of plaque titers and genomic nucleotide sequences. No case of viral extinction could be documented. Some low fitness clones that posses an internal poly(A) tract evaded extinction by modifying the length or base composition of the poly(A) tract. The comparison of entire genomic sequences of FMDV clones at increasing plaque transfer number revealed that mutations accumulated at a uniform rate, and that they were distributed unevenly along the genome. Clusters of mutations were identified at different genomic sites in two plaque transfer lineages. Mutation clustering appears to occur stochastically and could not be related to fixation of compensatory mutations. The results document resistance of viral clones to extinction, and suggest that mutation clustering may be a mechanism of genetic diversification of low fitness virus.

Animals↗
PubMed2000

Comparing risk factors for population extinction.

Extinction risk of natural populations of animals and plants is enhanced by many different processes, including habitat size reduction and toxic chemical exposure. We develop a method to evaluate different risk factors in terms of the decrease in the mean extinction time. We choose a population model with logistic growth, environmental and demographic stochasticities with three parameters (intrinsic growth rate r, carrying capacity K, and environmental noise sigma(2)(e)). The reduction in the habitat size decreases carrying capacity K only, whilst toxic chemical exposure decreases survivorship (or fertility) and in effect reduces both r and K. We derived a formula for the reduction in habitat size that decrease the mean extinction time by the same magnitude as a given level of toxic chemical exposure. In a large population (large K) or in a slowly growing population (small r), a small decrease in survivorship can cause the extinction risk increase corresponding to a significant reduction in the habitat size. This conclusion depends also on the nonlinearity of dose-effect relationship. To illustrate the method, we analyse a freshwater fish, Japanese crucian carp (Carassius auratus subsp.) in Lake Biwa.

Animals↗