Hippocampal place cells acquire location-specific responses to the conditioned stimulus during auditory fear conditioning

We recorded neurons from the hippocampus of freely behaving rats during an auditory fear conditioning task. Rats received either paired or unpaired presentations of an auditory conditioned stimulus (CS) and an electric shock unconditioned stimulus (US). Hippocampal neurons (place and theta cells) acquired responses to the auditory CS in the paired but not in the unpaired group. After CS-US pairing, rhythmic firing of theta cells became synchronized to the onset of the CS. Conditioned responses of place cells were gated by their location-specific firing, so that after CS-US pairing, place cells responded to the CS only when the rat was within the cell's place field. These findings may help to elucidate how the hippocampus contributes to context-specific memory formation during associative learning.     

Response latency of conditioned avoidance responses during generalization experiments in self-stimulated rats

Rats exhibiting steady self-stimulation behavior were trained to avoid a footshock after presentation of a unique brain rewarding stimulation of the postero-lateral part of the hypothalamus. Fifty percent of the animals tested were able to learn this conditioning paradigm. An hypothesis based upon modified internal physiological state elicited by the hypothalamic stimulation is discussed to explain the remaining half of the sample which failed to be conditioned. In the conditioned rats it seems that the time-dependent variable, the latency of response, can be used as a valid index for other experiments in which it is wished to study the internal decision process used to discriminate different hypothalamic stimulations in terms of their rewarding value.     

Varying temporal location of a conditioned stimulus in heart rate conditioning of Macaca mulatta

The several functions that a stimulus can assume were investigated in a Pavlovian conditioning procedure. The subjects were six rhesus monkeys; the response under observation was heart rate. The conditioning began with a temporal separation of zero between a signal and a regularly repeating electric shock; the signal was then moved to a series of earlier locations in the inter-shock interval. After six sessions at each location, two sessions followed in which only the shock was delivered periodically. The findings included: (1) A two-phased conditioned cardiac rate response seen at the first location became more multiphasic and irregular during longer intervals between signal and shock; (2) the location where the conditioned response peaked became increasingly variable as the signal was moved back, but this variability maintained a constant proportion to the signal-shock interval; and (3) heart rate during a presignal period, and during a comparable period in shock only sessions, was generally deceleratory early in training and acceleratory thereafter. Sessions with the signal showed heart rate in the presignal period to have become acceleratory earlier in training than sessions with shock only. The data pertain to stimulus control over heart rate as a function of: (A) the temporal proximity of a signal to an aversive stimulus; and, (B) the presence or absence of the signal. The use of appropriate response units in cardiac conditioning is also discussed.     

Conditioning of active type avoidance in the rat : effect of the interval between conditioned stimulus and unconditioned stimulus

Lengthening the time interval between the conditioned stimulus and the unconditioned stimulus increases the number of active avoidance conditioned responses in subjects that have been trained to a stable level of performance in many previous conditioning sessions. In the present research, rats chosen from a population specially selected for low rates of avoidance conditioning have been used. In addition to this characteristic, subjects were chosen for the exhibition of an apparent absence of retention from one day to another. The dependency of the number of conditioned responses on the time interval between conditioned stimulus and unconditioned stimulus may lead to wrong evaluation of the subjects' conditioning level. In fact, the level of conditioning may be attributed to either learning or memory processes when in many cases it is determined only by the latency time of the conditioned response. The conditioned response has no possibility of manifesting itself when its latency time exceeds in length the time interval between conditioned stimulus and unconditioned stimulus.     

Function of the adrenal cortex during elaboration of the passive avoidance conditioned reflex in immature rats

Plasma 11-hydroxycorticosteroid (11-OHCS) levels were measured in 30-day-old rats by fluorometry during passive avoidance (PA) learning by means of a single electric footshock. In contrast to the data obtained in adult animals, pre-exposure of young rats for 7 days to the experimental environment (over 3 min daily) resulted in elevation of the basal 11-OHCS levels and in the lack of distinct changes in the hormonal background after placing the young rats into a chamber. As in previous experiments on adult rats, one day after PA learning the 11-OHCS levels were significantly lower in young rats displaying PA than in the animals which did not exhibit PA behavior. Five days after PA training these differences in adrenocortical reactivity disappeared, as was the case in adult animals.     

Movement as a signal during classical conditioning

Analysis of the available data and that of the author disclosed the peculiarities of motor reaction when used as a conditioned stimulus. The author's data showed that if signal value is attributed to a motor reaction (passive movement or movement evoked by the direct stimulation of the motor cortex), the changes of excitability in the motor cortex representation of the dog's leg depend on the biological sign of the reinforcing stimulus during classic conditioning. They also remained the same during instrumental conditioning and were opposite in sign, showed increased excitability in the food situation, and decreased excitability in the defense situation. Using the movement as a conditional stimulus, we managed to uncover the commonality between classic and instrumental conditioning. This enabled us to answer questions, discussed by Pavlov and Guthrie, which, it seems to us, had not been convincingly answered during their time.     

Extinction of conditioned opiate withdrawal in rats in a two-chambered place conditioning apparatus

Conditioned opiate withdrawal contributes to relapse in addicts and can be studied in rats by using the opiate withdrawal-induced conditioned place aversion (OW-CPA) paradigm. Attenuation of conditioned withdrawal through extinction may be beneficial in the treatment of addiction. Here we describe a protocol for studying OW-CPA extinction using a two-chambered place conditioning apparatus. Rats are made dependent on morphine through subcutaneous implantation of morphine pellets and then are trained to acquire OW-CPA through pairings of one chamber with naloxone-precipitated withdrawal and the other chamber with saline. Extinction training consists of re-exposures to both chambers in the absence of precipitated withdrawal. Rats tested after the completion of training show a decline in avoidance of the formerly naloxone-paired chamber with increasing numbers of extinction training sessions. The protocol takes a minimum of 7 d; the exact duration varies with the amount of extinction training, which is determined by the goals of the experiment.     

Dissociation of conditioned taste avoidance from conditioned disgust reactions induced by wheel running in rats

It is well established that wheel running in rats produces conditioned taste avoidance; that is, rats that run in wheels after consuming a novel-tasting solution later consume less of that solution than rats that do not run. In experiment 1, we found that wheel running also produces conditioned disgust reactions, indicated by gapes elicited by both the taste and context that were experienced before running. Experiment 2 showed that the conditioned disgust reactions were likely not due to running itself but to a by-product of running, the rocking of the wheel that occurs when the running stops. When rocking was reduced, the disgust reactions were also reduced, but consumption of the taste solution was not changed, showing dissociation of conditioned taste avoidance and disgust. These findings indicate that the taste avoidance induced by wheel running itself is more like the taste avoidance produced by rewarding drugs than that produced by nausea-inducing drugs.