Reaction time task as unconditional stimulus. Comparing aversive and nonaversive unconditional stimuli

Nonaversive unconditional stimuli (USs) are seldom used in human classic conditioning of autonomic responses. One major objection to their use is that they produce deficits in electrodermal (ED) second- and third-interval response conditioning. However, a nonaversive reaction time (RT) task that includes feedback of success has been shown to be an effective US while avoiding this disadvantage (Lipp and Vaitl 1988). The present study compared this new RT task (RT-new) with a traditional RT task (RT-old) and with a standard aversive US (shock) in differential classic conditioning of ED, heart rate (HR), and digital pulse volume (DPV) responses. Eight-second-delay differential conditioning was applied in three groups of 12 subjects each. Simple geometric features (square, cross) displayed on a television screen served as conditional stimuli (CS+ and CS-). In acquisition, there were no statistically significant differences among the groups; differential conditioning did occur in HR, first- and second-interval ED responses, and first-interval DPV responses. Separate analyses within each group, however, revealed that there was no second-interval ED conditioning in the RT-old group. During extinction, neither DPV nor second-interval ED conditioning could be obtained, whereas HR and first-interval ED conditioning occurred in each group. In third-interval omission ED responses, RT-old and shock groups exhibited extinction, while response differentiation was maintained in the RT-new group throughout extinction. The RT task including feedback proved to be as reliable a US as a standard aversive US, whereas application of a traditional RT task again yielded some weaknesses in second-interval ED conditioning.     

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)     

Ultrasound elicits tonic responses and diminishes the phasic responses to adequate stimuli in thread-hair mechanoreceptors of Acheta domesticus

Single mechanoreceptor cells in filiform hair sensilla on the cercus of Acheta domesticus were stimulated adequately by steplike deflections in their plane of least restraint and inadequately by ultrasound. Ultrasound was fed either into the cercus or into the thread-hair as substrate-borne sound of 110–120 kHz. The receptor responds to deflections of the thread-hair (adequate stimuli) with phasic receptor potentials which can be picked up transepithelially. These responses can be either depolarizing (excitatory responses) or hyperpolarizing (inhibitory responses). Ultrasound applied simultaneously or shortly preceding the adequate stimulus reduces both kinds of responses in a graded way. The receptor can respond to ultrasound alone. At small intensities the responses are predominantly inhibitory; with increasing intensity they may become excitatory. In both cases the responses to ultrasound are tonic and do not reach the peak responses to saturating adequate stimuli. The off-effect, which follows adequate stimuli and leads to inhibitory responses after excitatory stimuli and vice versa, typically does not occur or is exitatory at the end of sonication. The observed effects of sonication are totally reversible. The correlation between transepithelial voltage, spike frequencies and spike amplitudes in the unsonicated and sonicated sensilla allows the responses to be attributed to sonication to the same conductance, which is also modulated by adequate stimuli. A model is discussed, according to which ultrasound exerts its effects by facilitating dissipative relaxation in the dendritic membrane, which is assumed to be involved in stimulus-energy transfer.     

Ultrasound elicits tonic responses and diminishes the phasic responses to adequate stimuli in thread-hair mechanoreceptors of Acheta domesticus

Single mechanoreceptor cells in filiform hair sensilla on the cercus of Acheta domesticus were stimulated adequately by steplike deflections in their plane of least restraint and inadequately by ultrasound. Ultrasound was fed either into the cercus or into the thread-hair as substrate-borne sound of 110-120 kHz. The receptor responds to deflections of the thread-hair (adequate stimuli) with phasic receptor potentials which can be picked up transepithelially . These responses can be either depolarizing (excitatory responses) or hyperpolarizing (inhibitory responses). Ultrasound applied simultaneously or shortly preceding the adequate stimulus reduces both kinds of responses in a graded way. The receptor can respond to ultrasound alone. At small intensities the responses are predominantly inhibitory; with increasing intensity they may become excitatory. In both cases the responses to ultrasound are tonic and do not reach the peak responses to saturating adequate stimuli. The "off-effect", which follows adequate stimuli and leads to inhibitory responses after excitatory stimuli and vice versa, typically does not occur or is excitatory at the end of sonication. The observed effects of sonication are totally reversible. The correlation between transepithelial voltage, spike frequencies and spike amplitudes in the unsonicated and sonicated sensilla allows the responses to be attributed to sonication to the same conductance, which is also modulated by adequate stimuli. A model is discussed, according to which ultrasound exerts its effects by facilitating dissipative relaxation in the dendritic membrane, which is assumed to be involved in stimulus-energy transfer.     

Tonic and phasic receptor neurons in the vertebrate olfactory epithelium

Olfactory receptor neurons (ORNs) respond to odorants with characteristic patterns of action potentials that are relevant for odor coding. Prolonged odorant exposures revealed three populations of dissociated toad ORNs, which were mimicked by depolarizing currents: tonic (TN, displaying sustained firing, 49% of 102 cells), phasic (PN, exhibiting brief action potential trains, 36%) and intermediate neurons (IN, generating trains longer than PN, 15%). We studied the biophysical properties underlying the differences between TNs and PNs, the most extreme cases among ORNs. TNs and PNs possessed similar membrane capacitances (approximately 4 pF), but they differed in resting potential (-82 versus -64 mV), input resistance (4.2 versus 2.9 G(Omega)) and unspecific current, I(u) (TNs: 0 < I(u) 1 pA/pF). Firing behavior did not correlate with differences in voltage-gated conductances. We developed a mathematical model that accurately simulates tonic and phasic patterns. Whole cell recordings from rat ORNs in fragments (approximately 4 mm(2)) of olfactory epithelium showed that such a tissue normally contains tonic and phasic receptor neurons, suggesting that this feature is common across a wide range of vertebrates. Our findings show that the individual passive electrical properties can govern the firing patterns of ORNs.     

Locus of semantic generalization of the galvanic skin response and possible inhibitory influence of conditional stimuli upon unconditional response following conditioning with innocuous and noxious unconditional stimuli

Two different problems were investigated using the GSR index of the orienting reflex (OR): 1) the locus of semantic generalization; and 2) a possible inhibitory influence of the CS upon the UCR. Two experiments were conducted. One experiment employed an innocuous USC, and a second similar experiment used a loud noise as the UCS. Unidirectional word associates were employed in the test of the direction of semantic generalization. Constant and varying CS words were used to test the possible inhibitory influence of the CS upon the UCR. Evidence was obtained of semantic generalization occurring in the training and in the test situation. There was no evidence of the CS developing inhibition over the UCR. Theoretical interpretation of both phenomena were considered. The need for developing theories of conditioning of the OR in humans was emphasized in contrast to current efforts to apply inappropriate cognitive animals learning theories which fail to consider biologic constraints.     

Tonic and phasic guanidinium toxin-block of skeletal muscle Na channels expressed in Mammalian cells

The blockage of skeletal muscle sodium channels by tetrodotoxin (TTX) and saxitoxin (STX) have been studied in CHO cells permanently expressing rat Nav1.4 channels. Tonic and use-dependent blockage were analyzed in the framework of the ion-trapped model. The tonic affinity (26.6 nM) and the maximum affinity (7.7 nM) of TTX, as well as the "on" and "off" rate constants measured in this preparation, are in remarkably good agreement with those measured for Nav1.2 expressed in frog oocytes, indicating that the structure of the toxin receptor of Nav1.4 and Nav1.2 channels are very similar and that the expression method does not have any influence on the pore properties of the sodium channel. The higher affinity of STX for the sodium channels (tonic and maximum affinity of 1.8 nM and 0.74 nM respectively) is explained as an increase on the "on" rate constant (approximately 0.03 s(-1) nM(-1)), compared to that of TTX (approximately 0.003 s(-1) nM(-1)), while the "off" rate constant is the same for both toxins (approximately 0.02 s(-1)). Estimations of the free-energy differences of the toxin-channel interaction indicate that STX is bound in a more external position than TTX. Similarly, the comparison of the toxins free energy of binding to a ion-free, Na(+)- and Ca(2+)-occupied channel, is consistent with a binding site in the selectivity filter for Ca(2+) more external than for Na(+). This data may be useful in further attempts at sodium-channel pore modeling.     

Effects of conditioning history on selective stimulus control by elements of compound discriminative stimuli

Effects of prior discrimination training on stimulus control by color and shape dimensions of compound stimuli were studied with college students. In Phase 1, single-stimulus discrimination training was conducted for two values of color and shape. Phase 2 discrimination training employed two 2-dimensional compound stimuli composed of the color and shape stimuli trained in Phase 1. For conflict-compound stimuli, the stimulus-response-consequence contingency was altered between phases for one stimulus dimension (target dimension), but not for the other, non-target, dimension. Level of congruence (100%, 25%, and 0%) of the contingency for the target dimension between phases was manipulated across groups. When each stimulus value was tested in Phase 3, level of Phase-2-consistent responding to the target dimension varied with level of Phase-1-to-Phase-2 congruence. In Experiment 2, training history for the non-target dimension was altered across three conditions: (a) Correlated with reinforcement, as in Experiment 1, (b) No-Training, or (c) Not-Correlated. Phase-2-consistent responding to the target cue in Phase 3 was lower under the latter conditions than under the Correlated condition, indicating that the non-target dimension modulated control by the target dimension, consistent with stimulus competition. The data suggest elemental, rather than configural processing of the compound stimuli during Phase 2.     

The effects of stimulus type on consistency of responses to conflicting stimuli in Siamese fighting fish

Individuals must often decide among a range of behavioral responses in a given situation and individuals will likely vary from one another in the choices they make. A rarely explored example of this is when both a male and a female are present simultaneously and a male must decide to fight or court. Consistent individual differences have been found in decision-making in Siamese fighting fish; however, dummies were used to explore this question and it is possible that individuals respond differently in this situation when faced with live stimuli as a result of feedback. Therefore, this study investigated whether males behave similarly to dummy and live stimuli by exposing them to male and female conspecifics both simultaneously and separately. Subjects were tested first with dummies and then in the same situations using live conspecifics. It was hypothesized that males would respond in the same manner to both the dummy and live fish. The results indicated that individuals behaved similarly to the dummy fish and the live fish in corresponding conditions. In addition, repeatability levels suggest that individuals behaved similarly across trials of a given treatment type while differing from one another in their responses. This study demonstrates that males are consistent in their responses even when receiving feedback from conspecifics and supports the continued use of dummy stimuli as an effective tool.     

The sympathetic control of blood pressure

Hypertension - the chronic elevation of blood pressure - is a major human health problem. In most cases, the root cause of the disease remains unknown, but there is mounting evidence that many forms of hypertension are initiated and maintained by an elevated sympathetic tone. This review examines how the sympathetic tone to cardiovascular organs is generated, and discusses how elevated sympathetic tone can contribute to hypertension.     

Arachidonic acid metabolites and blood pressure control

The medullary portion of the thick ascending limb of the loop of Henle (TALH) has one of the highest concentrations of Na+-K+-ATPase found in mammalian tissues, reflecting the importance of this nephron segment in the regulation of extracellular fluid volume, as active sodium transport is driven by Na+-K+-ATPase. We have isolated cells derived primarily from the TALH of the outer medulla of rabbit kidney and have identified a cytochrome P450-dependent monooxygenase system which metabolizes arachidonic acid to two biologically active oxygenated peaks, each containing two or more products. One of the peaks potently inhibits cardiac Na+-K+-ATPase and the other relaxes blood vessels. We report that formation of these oxygenated arachidonate metabolites is stimulated by arginine vasopressin and salmon calcitonin. In TALH cells obtained from rabbits made hypertensive by aortic constriction there was a selective increase in P1 and P2 formation compared to other renomedullary cells.     

Basic taste stimuli elicit unique responses in facial skin blood flow

Facial expression changes characteristically with the emotions induced by basic tastes in humans. We tested the hypothesis that the five basic tastes also elicit unique responses in facial skin blood flow. Facial skin blood flow was measured using laser speckle flowgraphy in 16 healthy subjects before and during the application of basic taste stimuli in the oral cavity for 20 s. The skin blood flow in the eyelid increased in response to sweet and umami taste stimuli, while that in the nose decreased in response to a bitter stimulus. There was a significant correlation between the subjective hedonic scores accompanying these taste stimuli and the above changes in skin blood flow. These results demonstrate that sweet, umami, and bitter tastes induce unique changes in facial skin blood flow that reflect subjective hedonic scores.     

Instrumental heterogeneous responses to 2 successive complex stimuli with a common initial stimulus in the dog

Formation and achievement of heterogenous instrumental reflexes to two consecutive complex stimuli was studied in dogs. Under the action of conditioned complex stimulus tone--Pause--tone, the dogs may be trained not to have a motor response to the first tone presentation, but perform alimentary instrumental reaction only to its repeated administration. Introducing into the experiment not only alimentary but also defensive complex stimulus stone-pause--light resulted in a change in animal's reactions in such a sequence: at first alimentary instrumental reaction was disinhibited under the action of the preparatory stimulus and during the pause, then bieffector responses appeared, further on in most of the dogs motor defensive reactions mainly took place. Trigger stimuli evoked the adequate instrumental reaction.     

Graviceptive control of blood pressure in man

The purpose of the study was to demonstrate a rapid 'graviceptive' influence on blood pressure in man. Subjects, sitting in an electrically powered car, made discrete head tilts, some of which were unpredictably accompanied by transient linear accelerations of the car i) with head tilting to align with the direction of the resulting inertial force vector (gravity + car acceleration) so that the graviceptors were not stimulated; ii) with head tilting in the opposite direction 'misaligning' which stimulated the graviceptors but otherwise maintained similarity of other sensory inputs. Stimuli were dispensed in a balanced, cross over, repeated measures design on 8 normal males. Recordings were made of arterial blood pressure in the left radial artery, the electrocardiogram and plethysmographic responses in the right hand first digit. Comparisons of 10s pre-stimulus baseline with 10s post stimulus responses. Misaligned head tilts provoked highly significant peak increases in systolic (7.6-9.4 mm Hg) and diastolic (5-6 mm Hg) BP and average BP over 10s was significantly raised. Head tilts maintaining alignment with the inertial force vector provoked raised systolic BP by 4-6 mm Hg for only one or two heartbeats. Head movements alone caused a slight lowering of BP. Effects were evident within 1-2 heartbeats of the acceleration onset. The results demonstrate that the graviceptors have a direct influence on BP in normal man. They also help to explain the profound vaso-vagal symptoms of patients with vertigo and why patients with autoregulatory impairment may be further compromised by uncontrolled accelerating and braking when they are transported in an ambulance.