Effect of response inhibition in cat motor cortex neurons during the expectation of conditioning stimulus

The spike responses of the motor cortex neurons (area 4) associated with forelimb movement were studied in awake cats earlier trained to perform placing motor reactions. Responses produced by the same neurons were compared in two situations: 1) when a sound-click conditioning stimulus (CS) was applied in isolation; 2) when a CS followed a preliminary warning stimulus (WS), a light flash, with a 100–1000 msec delay. During the reflex initiation by combined action of the WS and CS, response components that occurred prior to the placing movement (PM) performance under isolated CS action weakened and arrived 50–150 msec later; yet, response components that appeared in the same situation simultaneously with PM onset or later remained unchanged. PM latent periods were not changed when WS was applied. The temporal interval between WS and CS was characterized by depression of neuronal activity; depression duration was determined by the interstimulus delay. It is conceivable that the described transformations in spike responses of cortical neurons occurred due to changes in the sensory direction of the animal's attention; this direction, in all cases, is a crucial factor in the formation of neuronal activity in the cortex.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 21–27, January–February, 1993.t     

Verbal conditioning of stimulus significance in the orienting response context: an exploration demonstrating a new personality effect

The manipulation of stimulus significance, by instructions from the experimenter, may be taken as an example of verbal conditioning. Consideration of such a mechanism suggested that personality effects previously found in conditioning studies should be apparent in instructional manipulations of significance in a study of the orienting response (OR) to words. Because of recent changes in dimensioning of the personality structure, some of the items originally used to define Eysenck's extraversion (E) dimension are now used to assess the new dimension of psychoticism (P), suggesting that at least some of the established effects of E upon conditioning may be associated now with P. Hence the P scale was focused on in this study. Words differing on the evaluative dimension of the semantic differential were presented in three blocks, the first under indifferent instructions, the second under instructions to rate the words for their affective impact, and the third under indifferent instructions again. These blocks correspond to baseline, conditioning, and extinction conditions respectively. Electrodermal activity indicated enhanced conditioning, together with greater carry-over effects in the extinction phase, for low-P compared with high-P subjects. The results indicate the importance of personality effects in studies of stimulus significance and illustrate the value of the verbal conditioning mechanism in this area of the OR field. They also suggest the need to re-examine previously obtained E-effects in conditioning studies in light of changing personality tests.     

Spike correlation measures that eliminate stimulus effects in response to white noise

When measured in response to non-repeating white noise, standard covariance measures of two neuronal spike trains contain components due simply to a shared stimulus. We argue that, without stimulus repeats, model-free measures cannot in general remove these stimulus-induced components. We present spike correlation measures that eliminate them when the neural response can be approximated by a linear-nonlinear system. One of these measures fully characterizes the correlations in the special case that all remaining correlations are due to small reciprocal connections between the neurons. In addition, we demonstrate that the proposed measures can give accurate results with a more realistic, integrate-and-fire model of neural response, provided that it is driven like a linear-nonlinear system.     

Reaction time task as unconditional stimulus. On conditioning skin conductance responses and heart rate, using a nonaversive unconditional stimulus

The present study was conducted to demonstrate classic conditioning in electrodermal (ED) and heart rate (HR) responses by using a nonaversive reaction time (RT) task as unconditional stimulus (US). Three groups of 12 subjects each were studied to test the efficacy of this US procedure by varying the essential components of the RT task-US between groups. Eight seconds differential delay conditioning was applied in each group. Simple geometric features (square, cross) displayed on a TV screen were used as CS+ and CS-. RT task consisted of a nonaversive tone (72 dBA, 1000 or 1200 Hz) and a motor response (pressing a button with the left index finger). Subjects were asked to respond as soon as the tone stimulus was presented. The three groups received different stimulus sequences during the 16-trial acquisition phase only. In one group (Group C1), CS+ was followed by a tone to which subjects were to respond, whereas CS- was not followed by a tone. Similarly, in a second group (Group H), CS+ was followed by a tone, whereas CS- was not; however, subjects of Group H (habituation group) were not required to respond to the tone. In a third group, (Group C2) CS+ was followed by a tone to which subjects were to respond, while CS- was followed by a different tone requiring no response. According to analysis of Group C1 data, differential conditioning was obtained in each response measure. Group H displayed habituation in each response measure obtained. In Group C2, differential conditioning was obtained in the second latency window of ED responses only.(ABSTRACT TRUNCATED AT 250 WORDS)     

Time-dependency of the response to a single vagal stimulus in the rabbit heart

The time-dependency of vagal effects on P-P cycle was studied in rabbits, chosen because of high heart rate, in order to verify the occurrence of this phenomenon already described for animals with lower heart rate. In five rabbits with different resting cardiac cycles, vagal stimuli were delivered randomly. The results indicate that for heart rates higher than 120 beats/min no occurrence of Brown and Eccles' time-dependency was observed. It is evident, however, the different responsiveness of the pacemaker to vagal stimuli delivered at different times of the cardiac cycle. In particular a stimulus given beyond 40-50% of the cardiac cycle does not affect the same but the next cycle.     

The adaptation ability of neuronal models subject to a current step stimulus

Three neuronal models of the spike initiating process were investigated with respect to their ability to show adaptation to a current step: (i) the perfect integrator model (PIM), (ii) the leaky integrator model (LIM), and (iii) the Hodgkin-Huxley (HH-) model. It was found that although each neuronal model will generate different response spike trains to a given stimulus, all responses fulfilled the criteria of a deterministic neural response (Awiszus 1988). The results show that both PIM and LIM are unable to show adaptation regardless of the choice of model parameters whereas the HH-model shows a clear rate of discharge adaptation. The reason for this adaptation lies in the fact that there are conditions for the HH-model where a step stimulus is highly effective. These conditions are investigated by means of a phase plane analysis. Consequences of these results for the explanation of neuronal adaptation and the validity of the neuronal models investigated are discussed.     

Chemosensory behavior: the path from stimulus to response

In the past year, candidates have been identified for two long-sought classes of molecules, insect odorant receptors and mammalian taste receptors. In addition, genes directing receptor gene expression and the development of specific chemosensory neurons have been described in Drosophila melanogaster and Caenorhabditis elegans. Finally, recent physiological experiments have provided new insights into the mechanisms by which chemosensory information is processed.     

The milk ejection of the rat,as a stimulus and a response to the litter

A finding that the milk ejection of the rat is stimulated effectively only if at least half the pups are suckled is confirmed. This relationship, however, is found if the mother is anaesthetized but not if the mother is conscious. If the mother is conscious, the milk obtained by individual hungry pups is unaffected by the number of other hungry pups suckled. This is true whether the other pups of the litter are removed, or whether they are present but satiated. After the milk ejection, pups tend to leave the mother's nipple. Milk yield decreases with each milk ejection of a series, but getting less milk does not make the pups more likely to leave the nipple in search of another.     

Glycogen metabolism: the integrated cellular response to a bi-directional metabolic stimulus.

The control exerted by phosphorylase a over the I-conversion of glycogen synthase (1) does not apply to glycogen synthesis, as judged from experiments with intact human leucocytes. 1. In incubated leucocytes conversion of glycogen synthase (GS) (E.C.2.4.1.11) to GS-I is preceeded by inactivation of glycogen phosphorylase a (GPh-a). 2. By the addition of latex particles a flash-activation of GPh-a can be elicited within 10–30 sec. in the intact cells. 3. GPh is inactivated when a glucose load is given. 4. When, in glycogen depleted cells, glucose is given immediately after latex the I-conversion of GS is completely abolished, and GS-I remains low for 20 min although GPh is rapidly inactivated after the glucose is given. 5. However, glycogen synthesis as compared with a control in which only glucose is given, and in which a large I-conversion occurs, is not the least depressed. 6. This apparent contradiction is completely resolved taking into account a newly discovered, intermediate form of GS (2) (GS-R). 7. An important physiological role can be proposed for GS-R.     

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.     

Changes in the phase response curve of the circadian clock to a phase-shifting stimulus.

Experiments were conducted in hamsters to determine whether the phase response curve (PRC) to injections of the short-acting benzodiazepine triazolam is a fixed or a labile property of the circadian clock. The results indicated that (1) both the shape and the amplitude of the PRC to triazolam generated on the first day of transfer from a light-dark cycle (LD 14:10) to constant darkness (DD) (i.e., PRCLD) were different from those of the PRC generated after many days in DD (PRCDD); and (2) the phase-shifting effects of triazolam on the activity rhythms of hamsters transferred from LD 14:10 or 12:12 to DD changed dramatically within the first 8-9 days spent in DD. In an attempt to accelerate the resynchronization of the circadian clock of hamsters subjected to an 8-hr advance in the LD cycle, triazolam was given to the animals at a time selected on the basis of the characteristics of PRCLD. The activity rhythms of five of eight triazolam-treated animals were resynchronized to the new LD cycle within 2-4 days after the shift, whereas those of most of the control animals were resynchronized 21-29 days after the shift. These findings suggest that attempts to use pharmacological or nonpharmacological tools to phase-shift circadian clocks under entrained conditions should take into account information derived from PRCs generated at the time of transition from entrained to free-running conditions.