Stable isotope evidence for increasing dietary breadth in the European mid-Upper Paleolithic.
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New carbon and nitrogen stable isotope values for human remains dating to the mid-Upper Paleolithic in Europe indicate significant amounts of aquatic (fish, mollusks, and/or birds) foods in some of their diets. Most of this evidence points to exploitation of inland freshwater aquatic resources in particular. By contrast, European Neandertal collagen carbon and nitrogen stable isotope values do not indicate significant use of inland aquatic foods but instead show that they obtained the majority of their protein from terrestrial herbivores. In agreement with recent zooarcheological analyses, the isotope results indicate shifts toward a more broad-spectrum subsistence economy in inland Europe by the mid-Upper Paleolithic period, probably associated with significant population increases. (+info)
Impaired recognition of the goal location during spatial navigation in rats with hippocampal lesions.
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Converging evidence suggests that the hippocampus is essential for goal-directed spatial navigation. Successful navigation requires not only the ability to compute an appropriate path toward the target but is also guided by recognition of places along the trajectory between start and goal. To determine whether the hippocampus contributes to place recognition, we trained rats with hippocampal lesions in an annular water maze with a remotely controlled escape platform at a constant location in the corridor. The platform remained submerged and unavailable until the rat had swum at least one full lap. Probe trials with the platform unavailable for 60 sec were inserted at regular intervals. In these trials, the rat would swim over the platform several times, regardless of its navigational abilities. After a few training sessions, all sham-operated control animals reduced their swim velocity when they approached the platform, indicating that they recognized the target location. Rats with hippocampal lesions, in contrast, swam at the same velocity as elsewhere in the corridor. Preoperative training or prolonged postoperative training did not alleviate the deficit. Rats with hippocampal lesions were able to learn a cued version of the task, which implies that the failure to slow down was not attributable to motor inflexibility. Thus, hippocampal lesions caused a severe but selective deficit in the identification of a location, suggesting that the hippocampus may be essential for image recognition during spatial navigation. (+info)
Dominant loss of responsiveness to sweet and bitter compounds caused by a single mutation in alpha -gustducin.
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Biochemical and genetic studies have implicated alpha-gustducin as a key component in the transduction of both bitter or sweet taste. Yet, alpha-gustducin-null mice are not completely unresponsive to bitter or sweet compounds. To gain insights into how gustducin mediates responses to bitter and sweet compounds, and to elicit the nature of the gustducin-independent pathways, we generated a dominant-negative form of alpha-gustducin and expressed it as a transgene from the alpha-gustducin promoter in both wild-type and alpha-gustducin-null mice. A single mutation, G352P, introduced into the C-terminal region of alpha-gustducin critical for receptor interaction rendered the mutant protein unresponsive to activation by taste receptor, but left its other functions intact. In control experiments, expression of wild-type alpha-gustducin as a transgene in alpha-gustducin-null mice fully restored responsiveness to bitter and sweet compounds, formally proving that the targeted deletion of the alpha-gustducin gene caused the taste deficits of the null mice. In contrast, transgenic expression of the G352P mutant did not restore responsiveness of the null mice to either bitter or sweet compounds. Furthermore, in the wild-type background, the mutant transgene inhibited endogenous alpha-gustducin's interactions with taste receptors, i.e., it acted as a dominant-negative. That the mutant transgene further diminished the residual bitter and sweet taste responsiveness of the alpha-gustducin-null mice suggests that other guanine nucleotide-binding regulatory proteins expressed in the alpha-gustducin lineage of taste cells mediate these responses. (+info)
Response rate viewed as engagement bouts: effects of relative reinforcement and schedule type.
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The rate of a reinforced response is conceptualized as a composite of engagement bouts (visits) and responding during visits. Part I of this paper describes a method for estimating the rate of visit initiations and the average number of responses per visit from log survivor plots: the proportion) of interresponse times (IRTs) longer than some elapsed time (log scale) plotted as a function of elapsed time. In Part 2 the method is applied to IRT distributions from rats that obtained food pellets by nose poking a lighted key under various multiple schedules of reinforcement. As expected, total response rate increased as a function of (a) increasing the rate of reinforcement (i.e., variable-interval [VI] 4 min vs. VI 1 mi), (b) increasing the amount of the reinforcer (one food pellet vs. four pellets), (c) increasing the percentage of reinforcers that were contingent on nose poking (25% vs. 100%), and (d) requiring additional responses after the end of the VI schedule (i.e., adding a tandem variable-ratio [VR] 9 requirement). The first three of these variables (relative reinforcement) increased the visit-initiation rate. The tandem VR, in contrast, increased the number of responses per visit. Thus, variables that have similar effects on total response rate can be differentiated based on their effects on the componemts of response rate. (+info)
Behavioral and pharmacological variables affecting risky choice in rats.
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The effects of manipulations of response requirement, intertrial interval (ITI), and psychoactive drugs (ethanol, phencyclidine, and d-amphetamine) on lever choice under concurrent fixed-ratio schedules were investigated in rats. Responding on the "certain'' lever produced three 45-mg pellets, whereas responding on the "risky" lever produced either 15 pellets (p = .33) or no pellets (p .67). Rats earned all food during the session, which ended after 12 forced trials and 93 choice trials or 90 min, whichever occurred first. When the response requirement was increased from 1 to 16 and the ITI was 20 s, percentage of risky choice was inversely related to fixed-ratio value. When only a single response was required but the ITI was manipulated between 20 and 120 s (with maximum session duration held constant), percentage of risky choice was directly related to length of the ITI. The effects of the drugs were investigated first at an ITI of 20 s, when risky choice was low for most rats, and then at an ITI of 80 s, when risky choice was higher for most rats. Ethanol usually decreased risky choice. Phencyclidine did not usually affect risky choice when the ITI was 20 s but decreased it in half the rats when the ITI was 80 s. For d-amphetamine, the effects appeared to he related to baseline probability of risky choice; that is, low probabilities were increased and high probabilities were decreased. Although increase in risky choice as a function of the ITI is at variance with previous ITI data, it is consistent with foraging data showing that risk aversion decreases as food availability decreases. The pharmacological manipulations showed that drug effects on risky choice may be influenced by the baseline probability of risky choice, just as drug effects can be a function of baseline response rate. (+info)
The general matching law describes choice on concurrent variable-interval schedules of wheel-running reinforcement.
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Six male Wistar rats were exposed to concurrent variable-interval schedules of wheel-running reinforcement. The reinforcer associated with each alternative was the opportunity to run for 15 s, and the duration of the changeover delay was 1 s. Results suggested that time allocation was more sensitive to relative reinforcement rate than was response allocation. For time allocation, the mean slopes and intercepts were 0.82 and 0.008, respectively. In contrast, for response allocation, mean slopes and intercepts were 0.60 and 0.03, respectively. Correction for low response rates and high rates of changing over, however, increased slopes for response allocation to about equal those for time allocation. The results of the present study suggest that the two-operant form of the matching law can be extended to wheel-running reinforcement. 'I'he effects of a low overall response rate, a short Changeover delay, and long postreinforcement pausing on the assessment of matching in the present study are discussed. (+info)
Stimuli inevitably generated by behavior that avoids electric shock are inherently reinforcing.
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A molecular analysis based on the termination of stimuli that are positively correlated with shock and the production of stimuli that are negatively correlated with shock provides a parsimonious count for both traditional discrete-trial avoidance behavior and the data derived from more recent free-operant procedures. The necessary stimuli are provided by the intrinsic feedback generated by the subject's behavior, in addition to those presented by the experimenter. Moreover, all data compatible with the molar principle of shock-frequency reduction as reinforcement are also compatible with a delay-of-shock gradient, but some data compatible with the delay gradient are not compatible with frequency reduction. The delay gradient corresponds to functions relating magnitude of behavioral effect to the time between conditional and unconditional stimuli, the time between conditioned and primary reinforcers, and the time between responses and positive reinforcers. (+info)
Molar versus as a paradigm clash.
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The molar view of behavior arose in response to the demonstrated inadequacy of explanations based on contiguity. Although Dinsmoor's (2001) modifications to two-factor theory render it irrefutable, a more basic criticism arises when we see that the molar and molecular views differ paradigmatically. The molar view has proven more productive. (+info)