Combined effects of complex magnetic fields and agmatine for contextual fear learning deficits in rats

Acute post-training exposures to weak intensity theta-burst stimulation (TBS) patterned complex magnetic fields attenuated the magnitude of conditioned fear learning for contextual stimuli. A similar learning impairment was evoked in a linear and dose-dependent manner by pre-conditioning injections of the polyamine agmatine. The present study examined the hypothesis that whole-body applications of the TBS complex magnetic field pattern when co-administered with systemic agmatine treatment may combine to evoke impairments in contextual fear learning. Within minutes of 4 mg/kg agmatine injections, male Wistar rats were fear conditioned to contextual stimuli and immediately exposed for 30 min to the TBS patterned complex magnetic field or to sham conditions. TBS patterned complex magnetic field treatment was found to linearly summate with the contextual fear learning impairment evoked by agmatine treatment alone. Furthermore, we report for sham-treated rats, but not rats exposed to the synthetic magnetic field pattern, that the magnitude of learned fear decreased and the amount of variability in learning increased, as the K-index (a measure of change in intensity of the time-varying ambient geomagnetic field) increased during the 3-hr intervals over which conditioning and testing sessions were conducted.     

Vector representation of associative learning

I. P. Pavlov [12] has shown that conditioned reflexes are selective both with respect to conditioned stimuli and to conditioned reflexes elicited by those conditioned stimuli. At the neuronal level selective aspects of conditioned stimuli are based on detectors selectively tuned to respective stimuli. The selective aspects of conditioned reflexes are due to command neurons representing specific unconditioned reflexes. It can be assumed that conditioned reflexes result from association between selective detectors and specific command neurons. The detectors activated by a conditioned stimulus constitute a combination of excitations--a detector excitation vector. The detector excitation vector acts on a command neuron via a set of plastic synapses--a synaptic weight vector. Plastic synapses are modified in the process of learning making command neuron selectively tuned to a specific conditioned stimulus. The selective tuning of a particular command neuron to a specific excitation vector referred to a conditioned stimulus is a basis of associative learning. The probabilities of conditioned reflexes elicited by conditioned and differential stimuli implicitly contain information concerning excitation vectors that encode respective stimuli. Contribution of the vector code to associative learning was explored combining differential color conditioning with intracellular recording from color-coding neurons. It was shown that colors in carps and monkeys are represented on a hypersphere in the four-dimensional space similar to human color space. The basis of the color space is constituted by red-green, blue-yellow, brightness and darkness neurons.     

Excitability cycles of direct cortical responses during elaboration of conditioned defense reflexes in dogs]

Direct cortical responses (DCRs) to paired stimuli were studied in chronic experiments in dogs during elaboration of classical and instrumental defensive conditioned reflexes. The DCRs were recorded with 20 to 250 ms intervals between stimuli. Paired and single electrical stimulations of the middle suprasylvian gyrus given with a frequency of one per second were used as conditioned stimuli and were reinforced in a similar way. During electrical cutaneous stimulation of the dog's paw and to an even greater extent during isolated action of the conditioned stimulus the initial negativity of the testing DCR became shorter and the degree of its depression diminished. In the case of a following period of facilitation, its degree became greater. It was higher at a distance of 4 to 5 mm from the point of stimulation than at a distance of 2 to 3 mm. During isolated action of the conditioned stimulus, the degree of facilitation was higher than at the period of the possible action of the unconditioned stimulus. The greatest shorterning of the DCR excitability cycle was observed immediately before and during the conditioned lifting of the dog's paw. Excitability cycles of DCR, and possibly of other evoked potentials as well, are a more sensitive indicator of the function state of the cerebral cortex than responses to single stimuli. For this reason it appears promising to use them in studying conditioned reflexes.     

Conditioning analysis of magnetoreception in honeybees

A central problem in the study of magnetic sensitivity in animals has been the lack of behavioral techniques sufficiently powerful for the systematic psychophysical work required for an understanding of magnetosensory capacity and of the transduction mechanism. In recent experiments, free-flying honeybees have been conditioned to discriminate the presence and absence of localized magnetic dipole anomalies superimposed on the uniform background field of the earth. The results obtained thus far suggest that movement is necessary for conditioned responding to magnetic field stimuli and support the hypothesis that magnetic field transduction is based on single-domain particles of magnetite found in the anterodorsal abdomen of honeybees.     

Inhibitory effects of external stimulation on neuronal spike response in the cat association cortex during conditioning

The effects of external stimulus presentation on neuronal spike response induced in area 7 by conditioned and unconditioned stimuli were investigated in waking cats. Pointing reaction arising in response to the action of external stimuli led to the phasing out of spike response to unconditioned cutaneous stimulation, as well as depression or complete suppression of response in area 7 neurons to conditioned stimulus presentation, despite occurrence of conditioned reflex motion. External stimuli no longer exerted an inhibitory effect on the neuronal spike response induced by protracted use of conditioned and unconditioned stimuli. The fact that the conditioned lever-pressing reflex could occur either following or without neuronal spike response in area 7 would raise the question of whether neurons belonging to this area always participate directly in the triggering and occurrence of conditioned reflex motion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziogiya, Vol. 22, No. 2, pp. 147–155, March–April, 1990.     

Culture media conditioned by heat-shocked osteoblasts enhances the osteogenesis of bone marrow-derived mesenchymal stromal cells

Osteogenic cells differentiated from bone marrow-derived mesenchymal stromal cells (MSC) hold much promise in bone tissue engineering and reconstructive surgery. There is a dire need for well-defined and efficient protocols to promote the osteogenesis of ex vivo cultured MSC. Hence, this study investigated whether a combination of chemical stimuli (ascorbic acid, beta-glycerophosphate and dexamethasone) and culture media conditioned by a human foetal osteoblast cell line (hFOB) had any synergistic effect on the osteogenesis of MSC. Conditioned media with or without prior heat shock treatment (42 degrees C for 1 h) of the hFOB cell line, were collected and tested on rabbit MSC cultures, in the presence and absence of chemical stimuli. Osteogenic differentiation of MSC was assessed on both day 14 and 21 of ex vivo culture. The results showed conclusively that conditioned media promoted osteogenesis of MSC, which was further enhanced by prior heat shock-treatment of the hFOB cells, as well as by the presence of chemical stimuli. Among all experimental groups, the combination of culture medium conditioned by heat shocked hFOB cells together with chemical stimuli, exhibited the highest level of calcium mineralization, as assessed by Von Kossa staining. This provides clear evidence of a synergistic effect of conditioned media, heat shock and chemical stimuli. It is hoped that the data may contribute to the development of a more well-defined and efficient in vitro culture protocol to promote the osteogenesis of MSC for both clinical and non-clinical applications.     

Raised Middle-Finger: Electrocortical Correlates of Social Conditioning with Nonverbal Affective Gestures

Humans form impressions of others by associating persons (faces) with negative or positive social outcomes. This learning process has been referred to as social conditioning. In everyday life, affective nonverbal gestures may constitute important social signals cueing threat or safety, which therefore may support aforementioned learning processes. In conventional aversive conditioning, studies using electroencephalography to investigate visuocortical processing of visual stimuli paired with danger cues such as aversive noise have demonstrated facilitated processing and enhanced sensory gain in visual cortex. The present study aimed at extending this line of research to the field of social conditioning by pairing neutral face stimuli with affective nonverbal gestures. To this end, electro-cortical processing of faces serving as different conditioned stimuli was investigated in a differential social conditioning paradigm. Behavioral ratings and visually evoked steady-state potentials (ssVEP) were recorded in twenty healthy human participants, who underwent a differential conditioning procedure in which three neutral faces were paired with pictures of negative (raised middle finger), neutral (pointing), or positive (thumbs-up) gestures. As expected, faces associated with the aversive hand gesture (raised middle finger) elicited larger ssVEP amplitudes during conditioning. Moreover, theses faces were rated as to be more arousing and unpleasant. These results suggest that cortical engagement in response to faces aversively conditioned with nonverbal gestures is facilitated in order to establish persistent vigilance for social threat-related cues. This form of social conditioning allows to establish a predictive relationship between social stimuli and motivationally relevant outcomes.     

Excitatory backward conditioning in an appetitive conditioned reinforcement preparation with rats

Four experiments were conducted to examine appetitive backward conditioning in a conditioned reinforcement preparation. In all experiments, off-line classical conditioning was conducted following lever-press training on two levers. Presentations of a sucrose solution by a liquid dipper served as an unconditioned stimulus (US) and two auditory stimuli served as conditioned stimuli (CSs); one was paired with the US in either a forward (Experiment 1a) or a backward (Experiments 1b, 2, and 3) relationship, and the other served as a control CS, which was not paired with the US. In testing, each lever-press response produced a presentation of one of the CSs instead of appetitive reinforcers. The response to a lever was facilitated, compared to the response to another lever, when the response produced the backward CS presentation as well as when it produced the forward CS presentation; that is, the backward CS served as an excitatory conditioned reinforcer.     

Participation of frontal lobe neurons in the organization of successive inhibition and disinhibition of conditioned reflexes in the dog

Neuronal activity in g. proreus was studied during classical secretory conditioning and its differentiation in dogs. Three types of changes in neuronal reaction pattern were identified during differential conditioned stimulus compared to the pattern observed during positive conditioned stimulus. It has been shown that signal significance of the conditioned stimulus may be coded by specific distribution of interspike intervals in response to different conditioned stimuli. In situation of successive inhibition or disinhibition of the differentiation some neurones displayed simultaneous appearance of interspike intervals specific for responses to current and previously presented conditioned stimuli.     

Classical conditioning of ventilatory responses in humans

A classical conditioning experiment, in which an auditory stimulus was paired with a hypoxic stimulus, was carried out on 34 normal subjects assigned to two groups (experimental and control). Each subject took part in one session divided into two phases, acquisition and test. In the acquisition phase, eight hypoxic and eight auditory stimuli were paired in the experimental group and unpaired in the control group. In the test phase, which was identical for the two groups, the hypoxic stimuli were suppressed and three purely auditory stimuli were presented. Significant differences between the two groups in ventilatory response to these auditory stimuli provided evidence for conditioning. In the control group, no significant changes were elicited by the auditory stimuli, whereas a conditioned increase in total cycle duration was observed in the experimental group. The conditioned response closely resembled the first component of the hypoxic response. Analysis of the pattern of the conditioned response, along with postexperimental interviews, strongly suggests that this response was not mediated by volitional factors.     

Fear Conditioning in an Abdominal Pain Model: Neural Responses during Associative Learning and Extinction in Healthy Subjects

Fear conditioning is relevant for elucidating the pathophysiology of anxiety, but may also be useful in the context of chronic pain syndromes which often overlap with anxiety. Thus far, no fear conditioning studies have employed aversive visceral stimuli from the lower gastrointestinal tract. Therefore, we implemented a fear conditioning paradigm to analyze the conditioned response to rectal pain stimuli using fMRI during associative learning, extinction and reinstatement.In N = 21 healthy humans, visual conditioned stimuli (CS⁺) were paired with painful rectal distensions as unconditioned stimuli (US), while different visual stimuli (CS⁻) were presented without US. During extinction, all CSs were presented without US, whereas during reinstatement, a single, unpaired US was presented. In region-of-interest analyses, conditioned anticipatory neural activation was assessed along with perceived CS-US contingency and CS unpleasantness.Fear conditioning resulted in significant contingency awareness and valence change, i.e., learned unpleasantness of a previously neutral stimulus. This was paralleled by anticipatory activation of the anterior cingulate cortex, the somatosensory cortex and precuneus (all during early acquisition) and the amygdala (late acquisition) in response to the CS⁺. During extinction, anticipatory activation of the dorsolateral prefrontal cortex to the CS⁻ was observed. In the reinstatement phase, a tendency for parahippocampal activation was found.Fear conditioning with rectal pain stimuli is feasible and leads to learned unpleasantness of previously neutral stimuli. Within the brain, conditioned anticipatory activations are seen in core areas of the central fear network including the amygdala and the anterior cingulate cortex. During extinction, conditioned responses quickly disappear, and learning of new predictive cue properties is paralleled by prefrontal activation. A tendency for parahippocampal activation during reinstatement could indicate a reactivation of the old memory trace. Together, these findings contribute to our understanding of aversive visceral learning and memory processes relevant to the pathophysiology of chronic abdominal pain.     

Correlation of the neuronal impulse activity of different areas of the neocortex in rabbits in the switching of positive and inhibitory conditioned reflexes

By cross-correlation method conjugation in impulse activity of pairs of simultaneously recorded units in the visual and sensorimotor areas of the neocortex (representations of the conditioned and unconditioned stimuli) was studied during the switching of defensive positive and inhibitory reflexes in rabbits. 30-second fragments of impulse activity were analyzed in intervals before and after three presentations of positive and inhibitory conditioned stimuli (CS). The activity of single pairs of units in the process of stimuli presentation was characterized by instability. Only in 29% of 51 units' pairs the presence or absence of correlation between their discharges was stable. Analysis of activity of 75 pairs of units showed differences in impulse activity in inhibitory and positive tonic reflexes. The number of pairs of correlated units in about 30 s after inhibitory CS decreased (27%) in comparison with the interval before its action (52%). In the inhibitory tonic conditioned reflex, temporal intervals of discharges of one unit correlated with discharges of the second unit undergo changes. The obtained results testify that such parameter as the number of pairs of units with correlated activity in intersignal time interval is very important for the realization of motor reaction to conditioned stimuli.     

A rift between implicit and explicit conditioned valence in human pain relief learning

Pain is aversive, but does the cessation of pain (‘relief’) have a reward-like effect? Indeed, fruitflies avoid an odour previously presented before a painful event, but approach an odour previously presented after a painful event. Thus, event-timing may turn punishment to reward. However, is event-timing also crucial in humans who can have explicit cognitions about associations? Here, we show that stimuli associated with pain-relief acquire positive implicit valence but are explicitly rated as aversive. Specifically, the startle response, an evolutionarily conserved defence reflex, is attenuated by stimuli that had previously followed a painful event, indicating implicit positive valence of the conditioned stimulus; nevertheless, participants explicitly evaluate these stimuli as ‘emotionally negative’. These results demonstrate a rift between the implicit and explicit conditioned valence induced by pain relief. They might explain why humans in some cases are attracted by conditioned stimuli despite explicitly judging them as negative.     

Significance of the relative position in space of associated stimuli for formation and performance of motor conditioned reflexes

In experiments on cats the rate of formation of conditioned reflexes to sound (running to the feeding trough) depended on the spatial interrelations of the paired stimuli: the closer the source of the conditioned signal to the feeding trough, the sooner the formation of the conditioned reflex. It has been assumed that during formation of a conditioned reflex the closing of connection between conditioned and unconditioned stimuli is also attended with the closing of connection between the spatial parameters of the paired stimuli. Experiments with inactivation through cold of the temporal area (cortical representation of the vestibular system) of one hemisphere have shown that such a connection is formed in central parts of the vestibular analyser. When the conditioned reflex is elaborated to one feeding trough, the connection is duplicated by both hemispheres; in reflexes to two feeding troughs (i.e. spatial choice) such connections are lateralized in each hemisphere.     

Pavlovian conditioning: pigeon nictitating membrane

A new Pavlovian conditioning preparation was developed using the nictitating membrane of the restrained pigeon. Either visual or auditory stimuli served as conditioned stimuli (CSs) with an unconditioned stimulus (US) of a puff of air to the cornea. Movement of the nictitating membrane constituted the conditioned and unconditioned responses (CR and UR). Conditioning was studied with the Kamin blocking procedure. In agreement with findings from other conditioning preparations, responding to the redundant stimulus was attenuated relative to a stimulus that received the same number of CS-US pairings in a compound-conditioning procedure. Although response attenuation occurred, substantial individual variation was observed within the blocking procedure, a finding with some precedent in the experimental literature. Theoretical analysis and neural-network simulations indicate that inter-subject variation in response attenuation may result from differences in the extent to which contextual stimuli contribute to the functional CS.     

Complex perception of stimuli during conditioning

The review concerns the effects of a variety of stimuli on the reproduction of conditioned reflexes. By the literature data, during conditioning of any type, besides the single stimulus intentionally applied by an experimenter as a conditioned one, an animal perceives the whole complex of stimuli (acoustic, visual, olfactory, algesic, and other exteroceptive, proprioceptive, and interoceptive stimuli), including those of the environment and time of the day during training. Many of these stimuli are essential for the reproduction of the acquired habit. The complex of stimuli that act on an animal during the reproduction should in all parameters correspond to that perceived by the animal during training. If the complexes differ at least in one stimulus, the reproduction of the reflex may fail.     

Characteristics of higher nervous activity in the suslik Citellus fulvus during its active period

In experiments on active ground squirrels, it was possible to form motor defensive conditioned reflexes and to re-arrange the conditioned reflexes from visual and auditory analysers. It was originally demonstrated that repetitive alteration of the informational content of the conditioned stimuli results in neurotic disturbances in animals.     

A model of ventilatory instability induced in the unrestrained rat.

A classic conditioning paradigm was used to examine the hypothesis that perturbations during sleep in the neonate rat can have a lasting impact on breathing. During the first 4 wk of life, stimuli were presented to rats during behaviorally defined sleep. In a conditioned hypoxic (CH) group, brief periods of hypoxic gas were used as the unconditioned stimulus. Tactile and auditory stimuli were used as the conditioned stimuli. In a conditioned control (CC) group, air was used as the unconditioned stimulus. A third group of unconditioned control (UC) rats was not exposed to the conditioning paradigm. Animals were provided routine care for 3.5 mo; ventilation was then assessed using plethysmography. Conditioning during neonatal life produced increased ventilatory irregularities and apnea during behaviorally defined sleep in adult rats. Both CH and CC rats showed a significantly greater number of apneic events compared with UC rats. Over a 2-h sleep period, CH rats exhibited a total of 105.1 +/- 9.4 (SE) apneic events, CC rats 69.4 +/- 4.2 events, and UC rats 42.1 +/- 3.1 events [F(2,18) = 25.568; P < 0.0001]. These findings suggest that experiences in the first few weeks of life will alter ventilatory patterning in the adult animal.     

Effect of a cyclic enkephalin analog on the protein content in the hippocampal neurons of rats during the acquisition of a 2-way avoidance conditioned reflex

The protein content has been determined by means of cytointerferometry in neurons of fields CA-1 and CA-3 of the dorsal hippocampus in rats, which were trained in a conditioned reflex of two-way avoidance (CRTA) with the action of subcutaneously injected enkephalin cyclic analogue (ECA) in a dose 10 mkg. It has been found that after ECA injection the protein content in the neuronal nuclei of the hippocampal CA-3 field reduces. The acceleration of the CRTA elaboration occurring during the action of ECA is accompanied by a drastic increase of the protein content in the neuronal nuclei of the CA-3 field. The ECA administration to the rats of the active control groups to which were presented the same number of unpaired conditioned and unconditioned stimuli as during the CRTA elaboration also enhances the protein content in the neurons of the CA-3 field. The rats of all investigated groups in the neurons of the CA-1 field display no such significant shifts. The conclusion has been drawn that ECA produces a regulating influence on protein metabolism in hippocampal neurons depending on their functional state.     

Adult Learning and Mate Choice: Possibilities and Experimental Evidence

A critical issue in the study of mate choice is the analysisof the stimuli that elicit and regulate sexual behavior. Studieswith Japanese quail, several mammalian species, and a fish species(the blue gourami) indicate that the stimulus control of sexualbehavior is determined in part by what animals learn as a resultof sexual interactions in adulthood.Species specific stimuliprovided by a sexual partner can become conditioned by sexualreinforcement and thereby come to elicit more vigorous socialbehavior. Discrete localized stimuli as well as spatial contextualcues of the environment in which social interactions occur canalso become conditioned. Sexually conditioned localized stimulimay elicit approach and?/or courtship conditioned responsesand may increase responding to species specific eliciting stimuliprovided by a sexual partner. Sexually conditioned contextualstimuli also may increase responding to species specific stimulusfeatures of a sexual partner. These findings indicate that thefeatures of a conspecific to which an animal responds sometimesmay be determined by what that animal has learned as a resultof sexual experience. The findings also suggest that a completeaccount of the stimulus control of sexual behavior requiresconsideration of not only stimulus aspects of conspecifics thatelicit sexual responses but also discrete and contextual environmentalstimuli that may become associated with sexual experience.