Supplementation of complex milk lipid concentrate (CMLc) improved the memory of aged rats.

OBJECTIVES: The socio-economic impact from age-related mental decline is escalating. Supplementation of functional foods for sustaining mental health is desirable. We examined the effect of long-term supplementation of complex milk lipid concentrate (CMLc), mixed dairy phospholipids, on memory and associated vascular and neuronal changes in aged rats. METHODS: Fisher/Norway Brown rats were used. Two groups of aged rats (24 months) were fed with either gelatin-formulated CMLc or blank gelatin as the control, for 4 months. To determine age-related changes, a young group (5 months) was also fed with blank gelatin. Morris water maze tests were carried out after the supplementation and brain tissues were collected for biological analysis. RESULTS: The aged control rats learnt to locate the platform slower than the young control rats during acquisition trials (*P < 0.05), and made fewer entries to and more initial heading errors from the platform zone during testing trials (*P < 0.05). The CMLc supplementation improved memory by showing the reduced initial heading errors in a delayed probe trial ((#)P < 0.05). We also found that the aged rats with CMLc supplementation improved vascular density, dopamine output, and neuroplasticity ((#)P < 0.05) in the brain regions involved in memory compared with that of the aged control rats. DISCUSSION: The data suggested that the supplementation of CMLc during the early stage of brain aging may prevent memory decline possibly through improving vascular and neuronal function.

Matching-to-sample performance is better analyzed in terms of a four-term contingency than in terms of a three-term contingency.

Four pigeons performed a simultaneous matching-to-sample (MTS) task involving two samples and two comparisons that differed in their pixel density and luminance. After a long history of reinforcers for correct responses after both samples, 15 conditions arranged either continuous reinforcement of correct responses after Sample 1 and extinction for all responses after Sample 2, or vice versa. The sample after which correct responses were reinforced alternated across successive conditions. The disparity between the samples and the disparity between the comparisons were varied independently across conditions in a quasifactorial design. Contrary to predictions of extant quantitative models, which assume that MTS tasks involve two 3-term contingencies of reinforcement, matching accuracies were not at chance levels in these conditions, comparison-selection ratios differed after the two samples, and effects on matching accuracies of both sample disparity and comparison disparity were observed. These results were, however, consistent with ordinal and sometimes quantitative predictions of Jones' (2003) theory of stimulus and reinforcement effects in MTS tasks. This theory asserts that MTS tasks involve four-term contingencies of reinforcement and that any tendency to select one comparison more often than the other over a set of trials reflects meaningful differences between comparison-discrimination accuracies after the two samples.

New Caledonian crows learn the functional properties of novel tool types.

New Caledonian crows were presented with Bird and Emery's (2009a) Aesop's fable paradigm, which requires stones to be dropped into a water-filled tube to bring floating food within reach. The crows did not spontaneously use stones as tools, but quickly learned to do so, and to choose objects and materials with functional properties. Some crows discarded both inefficient and non-functional objects before observing their effects on the water level. Interestingly, the crows did not learn to discriminate between functional and non-functional objects and materials when there was an arbitrary, rather than causal, link between object and reward. This finding suggests that the crows' performances were not based on associative learning alone. That is, learning was not guided solely by the covariation rate between stimuli and outcomes or the conditioned reinforcement properties acquired by functional objects. Our results, therefore, show that New Caledonian crows can process causal information not only when it is linked to sticks and stick-like tools but also when it concerns the functional properties of novel types of tool.

Contingency discriminability and peak shift in concurrent schedules.

We investigated the effects of discriminative stimuli on choice in a highly variable environment using a procedure in which multiple two-key concurrent VI VI components changed every 10 reinforcers and were signaled by differential flashes of red and yellow keylights. Across conditions, five pigeons were exposed to a number of different combinations of the following component reinforcer ratios: 27:1, 9:1, 3:1, 1:1, 1:3, 1:9, 1:27. Overall, there was clear control by the component signals in that preference, early in components and particularly before any reinforcers had been delivered, was ordinally related to the signaled reinforcer ratios. In conditions in which only two components arranged unequal reinforcer ratios (e.g., 27:1 and 1:27) with the remaining components arranging 1:1 reinforcer ratios, preference before the first reinforcer in a component showed peak shift in that the most extreme preference did not occur in the unequal reinforcer-ratio components, but in 1:1 components further towards the ends of the stimulus dimension. The contingency-discriminability model (Davison & Nevin, 1999) was fitted to the data and provided an excellent description of the interactions between stimulus and reinforcer effects in a highly variable environment.

Local preference in concurrent schedules: the effects of reinforcer sequences.

We investigated the effects that sequences of reinforcers obtained from the same response key have on local preference in concurrent variable-interval schedules with pigeons as subjects. With an overall reinforcer rate of one every 27 s, on average, reinforcers were scheduled dependently, and the probability that a reinforcer would be arranged on the same alternative as the previous reinforcer was manipulated. Throughout the experiment, the overall reinforcer ratio was 1:1, but across conditions we varied the average lengths of same-key reinforcer sequences by varying this conditional probability from 0 to 1. Thus, in some conditions, reinforcer locations changed frequently, whereas in others there tended to be very long sequences of same-key reinforcers. Although there was a general tendency to stay at the just-reinforced alternative, this tendency was considerably decreased in conditions where same-key reinforcer sequences were short. Some effects of reinforcers are at least partly to be accounted for by their signaling subsequent reinforcer locations.