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operant conditioning [keywords]
- Social stress and escalated drug self-administration in mice I. Alcohol and corticosterone. [JOURNAL ARTICLE]
- Psychopharmacology (Berl) 2014 Sep 23.
Stress experiences have been shown to be a risk factor for alcohol abuse in humans; however, a reliable mouse model using episodic social stress has yet to be developed.The current studies investigated the effects of mild and moderate social defeat protocols on plasma corticosterone, voluntary alcohol drinking, and motivation to drink alcohol.Outbred Carworth Farms Webster (CFW) mice were socially defeated for 10 days during which the intruder mouse underwent mild (15 bites: mean = 1.5 min) or moderate (30 bites: mean = 3.8 min) stress. Plasma corticosterone was measured on days 1 and 10 of the defeat. Ethanol drinking during continuous access to alcohol was measured 10 days following the defeat or 10 days prior to, during, and 20 days after the defeat. Motivation to drink was determined using a progressive ratio (PR) operant conditioning schedule during intermittent access to alcohol.Plasma corticosterone was elevated in both stress groups on days 1 and 10. Ethanol consumption and preference following moderate stress were higher (13.3 g/kg/day intake) than both the mild stress group (8.0 g/kg/day) and controls (7.4 g/kg/day). Mice with previously acquired ethanol drinking showed decreased alcohol consumption during the moderate stress followed by an increase 20 days post-defeat. Moderately stressed mice also showed escalated ethanol intake and self-administration during a schedule of intermittent access to alcohol.Social defeat experiences of moderate intensity and duration led to increased ethanol drinking and preference in CFW mice. Ongoing work investigates the interaction between glucocorticoids and dopaminergic systems as neural mechanisms for stress-escalated alcohol consumption.
- Frequency and intensity difference limens in mice. [Journal Article]
- J Acoust Soc Am 2014 Apr; 135(4):2265.
The ability to distinguish between different frequencies and intensities is a fundamental auditory process, yet it has not been explored in CBA/CaJ mice. Previous researchers have used behavioral approaches to examine frequency and intensity discrimination abilities of the NMRI mouse, feral house mice, and other strains of mice with known hearing impairments. The present experiments use operant conditioning procedures to investigate the basic hearing abilities of the normal-hearing CBA/CaJ mouse. Intensity difference limens (IDLs) were obtained for six subjects and frequency difference limens (FDLs) were obtained for three subjects. For both experiments, the Method of Constant Stimuli and a threshold d' of 1.5 were used. IDLs and FDLs were obtained for 12, 16, 24, and 42 kHz tones. FDLs were obtained at 10 dB SL and 30 dB SL whereas the background for the IDL task was only 10 dB SL. At higher frequencies, the calculated FDLs increased. Furthermore, the thresholds were higher when sounds were presented at 30 dB SL compared to 10 dB SL. In the FDL experiment, the mice had a mean just-noticeable-difference of 3.5% Weber fraction across all four frequencies and sound levels. Interestingly, IDLs were similar across all frequencies.
- Comparative perception of temporally overlapping sounds. [Journal Article]
- J Acoust Soc Am 2014 Apr; 135(4):2150.
Parsing the auditory scene is a problem faced by humans and animals alike. Characteristics such as frequency, intensity, and location all help organisms assign concurrent sounds to specific auditory objects. The timing of sounds is also important for object perception. When sounds totally overlap in time, ascribing separate sounds to individual objects is difficult. However, slight temporal separations make this task slightly easier. In humans, synchronous streams of high and low frequency tones are heard as a single auditory stream. When the tones are slightly offset in time from one another, a second stream emerges. Here, we compared the perception of simultaneous, asynchronous, and partially overlapping streams of tones, human speech sounds, and budgerigar (Melopsittacus undulatus) contact calls in budgerigars and humans using operant conditioning methods. Human and bird subjects identified the partially overlapping stimuli differentially. Both species required less temporal separation to identify the sounds as "asynchronous" for the complex stimuli than for the pure tones. Interestingly, the psychometric functions differed between the two species. These results suggest that both humans and nonhumans are capable of using temporal offsets for assigning auditory objects, and that the ability to do this depends on the spectrotemporal characteristics of the sounds.
- Perception of degraded speech sounds differs in chinchilla and human listeners. [Journal Article]
- J Acoust Soc Am 2014 Apr; 135(4):2065.
The behavioral responses of chinchillas to noise-vocoded versions of naturally spoken speech sounds were measured using stimulus generalization and operant conditioning. Behavioral performance for speech generalization by chinchillas is compared to recognition by a group of human listeners for the identical speech sounds. The ability of chinchillas to generalize the vocoded versions as tokens of the natural speech sounds is far less than recognition by human listeners. In many cases, responses of chinchillas to noise-vocoded speech sounds were more similar to responses to band limited noise than to the responses to natural speech sounds. Chinchillas were also tested with a middle C musical note as played on a piano. Comparison of the responses of chinchillas for the middle C condition to the responses obtained for the speech conditions suggest that chinchillas may be more influenced by fundamental frequency than by formant structure. The differences between vocoded speech perception in chinchillas and human listeners may reflect differences in their abilities to resolve the formants along the cochlea. It is argued that lengthening of the cochlea during human evolution may have provided one of the auditory mechanisms that influenced the evolution of speech-specific mechanisms.
- Social defeat in adolescent mice increases vulnerability to alcohol consumption. [JOURNAL ARTICLE]
- Addict Biol 2014 Sep 14.
This study employs an oral operant conditioning paradigm to evaluate the effects of repeated social defeat during adolescence on the reinforcing and motivational actions of ethanol in adult OF1 mice. Social interaction, emotional and cognitive behavioral aspects were also analyzed, and real-time polymerase chain reaction (PCR) experiments were performed to study gene expression changes in the mesocorticolimbic and hypothalamus-hypophysis-adrenal (HHA) axis. Social defeat did not alter anxiety-like behavior in the elevated plus maze or cognitive performance in the passive avoidance and Hebb-Williams tests. A social interaction test revealed depression-like symptoms and social subordination behavior in defeated OF1 mice. Interestingly, social defeat in adolescence significantly increased the number of effective responses, ethanol consumption values and motivation to drink. Finally, real-time PCR analyses revealed that social defeat significantly increased tyrosine hydroxylase and corticotropin-releasing hormone in the ventral tegmental area and paraventricular nucleus, respectively. In contrast, mu-opioid receptor gene expression was decreased in the nucleus accumbens of socially defeated mice. In summary, these findings suggest that exposure to social defeat during adolescence increases vulnerability to the rewarding effects of ethanol without affecting emotional or cognitive performance. The gene expression alterations we have observed in the mesocorticolimbic and HHA axis systems of defeated mice could be related with their increased ethanol consumption. These results endorse future research into pharmacological strategies that modulate these systems for the treatment of social stress-related alcohol consumption problems.
- The effect of probability discounting on reward seeking: a three-dimensional perspective. [Journal Article]
- Front Behav Neurosci 2014.:284.
Rats will work for electrical stimulation of the medial forebrain bundle. The rewarding effect arises from the volleys of action potentials fired by the stimulation and subsequent spatio-temporal integration of their post-synpatic impact. The proportion of time allocated to self-stimulation depends on the intensity of the rewarding effect as well as on other key determinants of decision-making, such as subjective opportunity costs and reward probability. We have proposed that a 3D model relating time allocation to the intensity and cost of reward can distinguish manipulations acting prior to the output of the spatio-temporal integrator from those acting at or beyond it. Here, we test this proposition by varying reward probability, a variable that influences the computation of payoff in the 3D model downstream from the output of the integrator. On riskless trials, reward was delivered on every occasion that the rat held down the lever for a cumulative duration called the "price," whereas on risky trials, reward was delivered with probability 0.75 or 0.50. According to the model, the 3D structure relating time allocation to reward intensity and price is shifted leftward along the price axis by reductions in reward probability; the magnitude of the shift estimates the change in subjective probability. The predictions were borne out: reducing reward probability shifted the 3D structure systematically along the price axis while producing only small, inconsistent displacements along the pulse-frequency axis. The results confirm that the model can accurately distinguish manipulations acting at or beyond the spatio-temporal integrator and strengthen the conclusions of previous studies showing similar shifts following dopaminergic manipulations. Subjective and objective reward probabilities appeared indistinguishable over the range of 0.5 ≤ p ≤ 1.0.
- Operant self-administration of ethanol in infant rats. [REVIEW]
- Physiol Behav 2014 Aug 30.
The review focuses on operant self-administration of ethanol in immature, infant rats. Several methods for the analysis of ethanol intake in infants are available, yet only oral self-administration models the typical pattern of ethanol consumption found in humans. The study of ethanol intake in infants is important for our understanding of how early alcohol experiences facilitate subsequent engagement with alcohol. It seems that sensitivity to ethanol-induced operant reinforcement is found very early in life, a few hours after birth, and throughout the first three weeks of life. Most of the studies reviewed complied with most, albeit not all, of the criteria for operant behavior (e.g., greater responding than yoked controls and persistence of this difference after withholding the reinforcer). Operant self-administration of ethanol in infant rats seems to be, at least partially, mediated by endogenous opioid transmission and can be enhanced by prior exposure to ethanol. Furthermore, acquisition of ethanol-mediated operant learning seems to facilitate drug self-administration during adolescence. Relative to older subjects, infants exhibit lower sensitivity to ethanol's sedative, hypnotic and motor impairing effects. On the other hand, they exhibit increased sensitivity to the motor stimulant and rewarding effects of ethanol. We suggest that this pattern of response to ethanol may favor the rapid acquisition of operant self-administration in infant rats.
- Dynamic shaping of dopamine signals during probabilistic Pavlovian conditioning. [JOURNAL ARTICLE]
- Neurobiol Learn Mem 2014 Aug 26.
Cue- and reward-evoked phasic dopamine activity during Pavlovian and operant conditioning paradigms is well correlated with reward-prediction errors from formal reinforcement learning models, which feature teaching signals in the form of discrepancies between actual and expected reward outcomes. Additionally, in learning tasks where conditioned cues probabilistically predict rewards, dopamine neurons show sustained cue-evoked responses that are correlated with the variance of reward and are maximal to cues predicting rewards with a probability of 0.5. Therefore, it has been suggested that sustained dopamine activity after cue presentation encodes the uncertainty of impending reward delivery. In the current study we examined the acquisition and maintenance of these neural correlates using fast-scan cyclic voltammetry in rats implanted with carbon fiber electrodes in the nucleus accumbens core during probabilistic Pavlovian conditioning. The advantage of this technique is that we can sample from the same animal and recording location throughout learning with single trial resolution. We report that dopamine release in the nucleus accumbens core contains correlates of both expected value and variance. A quantitative analysis of these signals throughout learning, and during the ongoing updating process after learning in probabilistic conditions, demonstrates that these correlates are dynamically encoded during these phases. Peak CS-evoked responses are correlated with expected value and predominate during early learning while a variance-correlated sustained CS signal develops during the post-asymptotic updating phase.
- Knockdown of CRF1 Receptors in the Ventral Tegmental Area Attenuates Cue- and Acute Food Deprivation Stress-Induced Cocaine Seeking in Mice. [Journal Article]
- J Neurosci 2014 Aug 27; 34(35):11560-70.
Corticotrophin-releasing factor (CRF) modulates the influence of stress on cocaine reward and reward seeking acting at multiple sites, including the ventral tegmental area (VTA). There is controversy, however, concerning the contribution of CRF receptor type 1 (CRFR1) to this effect and whether CRF within the VTA is involved in other aspects of reward seeking independent of acute stress. Here we examine the role of CRFR1 within the VTA in relation to cocaine and natural reward using viral delivery of short hairpin RNAs (lenti-shCRFR1) and investigate the effect on operant self-administration and motivation to self-administer, as well as stress- and cue-induced reward seeking in mice. While knockdown of CRFR1 in the VTA had no effect on self-administration behavior for either cocaine or sucrose, it effectively blocked acute food deprivation stress-induced reinstatement of cocaine seeking. We also observed reduced cue-induced cocaine seeking assessed in a single extinction session after extended abstinence, but cue-induced sucrose seeking was unaffected, suggesting dissociation between the contribution of CRFR1 in the VTA in cocaine reward and sucrose and cocaine seeking. Further, our data indicate a role for VTA CRFR1 signaling in cocaine seeking associated with, and independent of, stress potentially involving conditioning and/or salience attribution of cocaine reward-related cues. CRFR1 signaling in the VTA therefore presents a target for convergent effects of both cue- and stress-induced cocaine-seeking pathways.
- Timbre Influences Chord Discrimination in Black-Capped Chickadees (Poecile atricapillus) but Not Humans (Homo Sapiens). [JOURNAL ARTICLE]
- J Comp Psychol 2014 Aug 25.
Timbre is an important attribute of sound both in music and nature. Previously, using an operant conditioning paradigm, we found that black-capped chickadees and humans show similar response patterns in discriminating triadic chords of the same timbre and transferred this discrimination to a novel key center (novel absolute pitch). The current study examined how varying the timbre of the chords influenced discrimination. Using a similar operant conditioning procedure, we trained humans (Experiment 1) and chickadees (Experiments 2 and 3) to discriminate a major chord from 6 other chord types that had semitone deviations from the major chord. The pattern of errors of the 2 species replicated our previous findings. We then tested participants with novel timbres. We found that humans readily transferred their discrimination to novel timbres, suggesting they were attending to triadic pitch relations. The chickadees failed to transfer to novel timbres, suggesting they were using a different strategy to perform the original chord discrimination. We conducted an acoustic analysis examining frequency ranges that are biologically relevant to chickadees. We found that the relative intensity within each chord of the frequencies used in black-capped chickadee song significantly correlated with chickadees' percent response during probe testing. In Experiment 3, we trained a new set of chickadees by including either expanded pitch or timbre training before testing. Although chickadees showed some transfer to novel chords following this expanded training, we found that neither type of expanded training helped the chickadees when probe tested with novel stimuli. (PsycINFO Database Record (c) 2014 APA, all rights reserved).