Changes in the frequency of the hippocampal theta-rhythm in the dog exposed to a conditioned food stimulus

Frequency changes of hippocampal theta-rhythm in the process of elaboration of coinciding or delayed instrumental alimentary reflex was studied in two dogs. Determination of dominating frequency of rhythmical activity was carried out by means of mathematical methods of analysis on a computer. It was found out, that during the action of conditioned alimentary stimulus the frequency of dominating oscillations became enhanced. Animals with a more frequent initial theta-rhythm formed the delayed alimentary reflex more rapidly.     

Parallel reinforcement pathways for conditioned food aversions in the honeybee

Avoiding toxins in food is as important as obtaining nutrition. Conditioned food aversions have been studied in animals as diverse as nematodes and humans [1, 2], but the neural signaling mechanisms underlying this form of learning have been difficult to pinpoint. Honeybees quickly learn to associate floral cues with food [3], a trait that makes them an excellent model organism for studying the neural mechanisms of learning and memory. Here we show that honeybees not only detect toxins but can also learn to associate odors with both the taste of toxins and the postingestive consequences of consuming them. We found that two distinct monoaminergic pathways mediate learned food aversions in the honeybee. As for other insect species conditioned with salt or electric shock reinforcers [4-7], learned avoidances of odors paired with bad-tasting toxins are mediated by dopamine. Our experiments are the first to identify a second, postingestive pathway for learned olfactory aversions that involves serotonin. This second pathway may represent an ancient mechanism for food aversion learning conserved across animal lineages.     

Autoshaping in the rat: conditioned licking response to a stimulus that signals sucrose reinforcement

The present experiments were designed to determine if repeated presentations of an empty sipper tube (the conditioned stimulus or CS) with the response-independent delivery of a sucrose solution (the unconditioned stimulus or US) from a second spout results in the development of Pavlovian conditioned responding. In Experiment 1, rats in the experimental condition received paired CS-US presentations whereas subjects in the control condition were exposed to random presentations of CS and US. In Experiment 2, an additional control condition (CS alone) was included and, to encourage generalized responding between the US and CS, the CS tube was filled with water for all groups. The results of both experiments indicate that the CS-directed responding in the paired CS-US condition was Pavlovian in nature. Thus, the present procedure serves as an autoshaping task in which conditioned licking is generated.     

Effect of the type of reinforcement on conditioned reflex activity in male and female white rats

On 24 males and 26 females of white rats of a mixed line, a study was carried out of the speed of formation and consolidation of instrumental drinking and defensive conditioned reflexes, elaboration of differentiation, changes in conditioned activity by the use of stochastic stereotype and by changing the meanings of the conditioned signals to opposite. Conditioned reflexes were elaborated more rapidly in female rats at drinking reinforcement and in male rats--at the defensive one. Differentiations were elaborated more rapidly and were better expressed in females than in males at both types of reinforcement.     

Thermal dependence of neural activity in the hamster hippocampal slice preparation

1. Neural activity was recorded in an in vitro hamster hippocampal slice preparation while the temperature of the Ringer's solution bathing in the slice was controlled at selected levels. 2. The amplitude of the population spike (action potentials from a group of pyramidal cells) was measured as bath temperature was lowered from 35 degrees C to temperatures where a response could not be evoked. 3. Plots of population spike amplitude versus temperature have bell-shaped curves. The population spikes increased in amplitude as temperature was lowered from 35 degrees C, reached a peak amplitude between 25 and 20 degrees C, and then decreased until a response could not be evoked when temperature was further lowered. 4. These in vitro results obtained in the slice preparation are related to in vivo hippocampal studies. Results are interpreted as consistent with the proposal reviewed here that neural activity in the hippocampus plays a role at specific stages of entrance into and arousal from hibernation.     

The dependence of spatial-motor asymmetry on the nature of the reinforcement]

Spatial-motor asymmetry (SMA) of rats goal-directed running was studied in condition of numerous alternative choices in complex T-maze. In condition of free choices SMA in trained rats depended on reinforcement biological significance, volume and disposition scheme. In condition of non-free choices a change was possible of asymmetry of sequence of goal-directed motor acts adequate to situation, i.e. SMA regulation. Examples of the presence of properties of ego- and allocentric systems in SMA are given. The results of experiments testify to SMA dependence on the motivation of running, to rightfulness of SMA interpretation as behavioural tactics and to non-coming of SMA of goal-directed running to a simple rotation of animals.